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The origins, 1925 to 1930. When Barnack was busy constructing and refining his camera around 1907 to 1911 , and decided to use a format of 24x36mm on cine-film, no suitable lens was available on the market. As any lens projects a circular image, you need a angular coverage equal to the length of the diagonal of the image format .
The diagonal of the 24x36mm format has a length of 43,27mm, which gives a maximum image height of 21.6mm from the centre of the image. Barnack therefore needed a lens with a angular view of 46o to cover the format. A lens with a focal length of anything between 40mm and 60mm would do. Barnack, working at the Leitz factory, a well-known microscope manufacturer, found a series of lenses, made by Leitz and named Mikro-Summar and Milar with several focal lengths to choose from.
Figure 1: 2.1 A Mikro Summar
He chose the Mikro-Summar 1:4.5/42mm, which he fitted in at least one of his three prototypes. The Ur-Leica, residing in the museum in Solms, has been equipped with this lens. Some researchers have identified the lens as a Milar or a Summar. There is no inscription on the lens, so there is room for some interpretation. The exact focal length however can be measured and recently the optical engineers at Solms just did this and established a focal length of 42mm. The only lens in the Leitz microscope catalogue around 1910 is the Mikro-Summar, a six element symmetrical lens. So we may now reveal with certainty the identity of the mysterious lens in the Ur-Leica. It is a Mikro-Summar with 6 elements, symmetrically arranged.
Why did Barnack settle on the 24x36 format? Previous and contemporary designers of cameras, based on the 35mm perforated cine-film ('Kino-film') had used 24x24, 32x44, 18x24, 30x42 formats. Barnack himself tells us that he wanted to use the 'Kino-film' and that he decided to go for maximum area to ensure good image quality. The dimensions of 24x36mm have a 1:1.5 relation, just as the 6x9cm negative of the then ubiquitously available Roll film camera, the 'point and shoot camera' of the early part of the previous century. The Leica camera had to face a very strong competition from this format, as the most used print format was also 6x9cm and this could be produced from a 6x9cm negative as a direct copy, without any enlarging and subsequent losses in image quality. And the next steps in print format (9x12cm and 13x18cm) have relations 1:1.35, so quite close to the 1:1,5 (with a slight safety margin). It was one of Barnack's primary concerns that his compact camera and its small negative could deliver image quality as good as, if not better than the 6x9cm contact-print. His device would be unacceptable to most prospective users if the image was inferior to the roll-film competitor. Here we see already the interaction between the demands from the practical user and the capabilities and ambitions of the optical designer that will characterize the development of optical design.
Figure 2: 2.1.1A Barnack sketch.
Note similarity to Berek drawing The next step, after having established the dimensions of the image area, was to define the requirements for the recording capabilities of the lens.
Most photographic prints in the early decades of the 20th century had dimensions between 6x9cm and 13x18cm. A comfortable viewing distance for these pictures is around 25cm. It so happens that we are able to see the whole 9x12cm print at this distance without moving our eyes. The resolution of the eye (that is the finest detail we can distinguish when viewing an object) is of course the limiting factor for the optical requirements. It has been established by research that the best resolution of the eye will be found when the eye is focused at a distance of 1.2meter to 1.5meter.
But for photographic purposes we have to stick to the normal viewing distance of 25cm. This distance has been used as the reference distance for the definition of the circle of confusion. Assuming an enlarging factor of the negative of 3 to 5 times for a print of 9x12cm (in fact 7.2x10.8cm) the smallest point on the negative should be at least 0.1mm/3. That is 1/30mm or 0.0333mm. This value is used by Leitz as the criterion for the calculation of depth of field tables or engraving depth scales on the lens mount. The optical calculations however are not based on this value. It is clear that the designer will try to concentrate all light rays on as small an area as possible.
The value of 0.03mm then constitutes the limiting case, the minimum value so to speak, that is a point should have at least the diameter of 0.03mm or 30 micrometer (mu). When reflecting on these topics Berek and Barnack settled for 0.03mm. They could not know at what distances the Leica pictures would be viewed by the user, nor what enlargements they would choose. The value of 0.03mm is the standard circle of confusion at the film, used as a reference. It should not be considered the target value. See the chapter 1.2 for more details on this topic.
The first lens, specifically designed for the Leica format was the Leica Anastigmat , later renamed Elmax (presumably the combination from Ernst Leitz and Max Berek). This lens had five elements, where the Zeiss Tessar had four. Berek designed the Anastigmat with the last group composed of three cemented elements. This lens then has the unique distinction as being the first lens, designed with the specific requirements for the 35mm Leica format in mind. Max Berek designed the lens around 1922 (As the date on the original drawings at Solms tells us).
Figure 3: 2.1.3 A (Computation page: already at Hove)
Figure 4: 2.1.3 B Anastigmat
As the Elmax was a bit complicated to build (as a cemented triple) Berek changed the design to a triplet with the last element as a cemented doublet.
Figure 5: 2.1.3 C Elmax.
The Elmar was born. The design date on the documents tell us that the first design of the Elmar was completed in 1925. This lens had improved imagery when compared to the Elmax. The Elmar design is similar to a Tessar design, with one important exception, the location of the stop. In optical design the location of the stop is part of the tools for aberration correction. Depending on the design this location can be more or less influential. In the case of the Elmar, the stop is located between the first and second element. This forward location cuts off some of the rays at the edge of the lens and while producing some additional vignetting, also improves the central definition. As the lens is now unsymmetrical around the stop, we see some astigmatism and coma in the outer zones of the field.
Figure 6: 2.1.3 D: Elmar diagram
The Elmar 1:3.5/50mm established the fame of the Leica camera, by providing image quality of a high order for its day. Analysis by modern computer based design programs of the original Elmar configuration show that the basic design is difficult to improve upon. A tribute to the old masters no doubt! A designer would cement two glass elements together ( or split one element into two separate lenses) to create a glass type that is not available in the glass catalogues. Basically the Elmar is a triplet, where the last lens element is cemented to generate a new type of glass, that was needed for the computation.
If advances are to be made, the only route is the glass selection. And we may be sure that the Elmar lens in its long history of 1925 to 1961 underwent changes of this kind. Inevitably older glass types were removed from the catalogues and so the designers were forced to adapt to these circumstances. But modern optimization analysis also shows that the gains are relatively modest and so it may come as no surprise that the image quality of this lens is quite stable over the years. Of course newer glasses and specifically the coating of surfaces might give a modest gain under adverse conditions. The design of the Elmar allowed for the correction of the basic aberrations with minimal means. This makes the computation especially labourious and when done with only a slide rule and logarithmic tables is very demanding on the insight and creativity of the designer. Any four-element lens has limited possibilities for the correction of the important aberrations. A compromise is always needed.
Broadly speaking the four-element triplet has a typical character like good central sharpness and weaker performance in the field. A designer can and will adopt a specific solution, that gives every version of this type a different fingerprint. The Elmar at full aperture gives a low to medium contrast image, with good recording of coarse detail over an image circle of about 12mm radius. One of the advantages of the Leica, when compared to larger format cameras is the extended depth of field when using the lens wide open. Max Berek rightly placed emphasis on the axis (centre) performance and also on a good colour correction over the whole spectrum, including the red part of it. Stopped down to about 1:5.6 the contrast improves markedly, crispening the rendition of fine detail. Berek again assumed that the lens would be stopped down in order to increase depth of field to maximize the comparative advantages with the roll film cameras.
Figure 7: 2.1.3 E-Late type Elmar
We may regard the Elmar as a classical example of an excellent design that stretched to the limits the inherent possibilities of the type. The three element Cooke triplet has comparable performance on axis as the classical four-element Elmar type.
Computer analysis show that the relative differences in performance are zonal astigmatism and oblique spherical aberration, both of which are better corrected in the Elmar. The differences are small, but quite noticeable and could make the success or failure in the marketplace. So it was a wise choice from Berek and Leitz to opt for the 4-element Elmar to compete with the Cooke type triplets employed in most roll-film cameras. The performance edge indeed is important and outweighs the higher production costs, due to the more elaborate construction.
Around 1925 most films were of the orthochromatic type and had sensibilities of ISO20 to ISO30. Panchromatic films were also available, but with reduced speeds (ISO10 to ISO15). Even with a 3.5 lens, these speeds limited the possibilities of the Leica user to shoot pictures in low light situations. But the Leica was the camera to record all aspects of human life in its various surroundings. Today, when we look at early Leica pictures made in 'available light' we should marvel at the expertise of the average Leica user to use this modest equipment. Ask any modern counterpart to capture indoor scenes at an aperture of 3.5 with an ISO25 film and you will hear all kinds of protests. Using current Kodachrome 25 and the Tri-Elmar 4/28-50mm or the Vario-Elmar-R 1:4/35-70mm at 1:4 would simulate these conditions quite well.
Results would be superior, evidently, but we should reflect for a moment on the role of the Elmar in its historical and technical context. For many scenes, the aperture of 3.5 is still an excellent choice as it combines depth of field, needed for most solid subjects with a slightly safety margin for inaccuracy of focus and a good image quality. Using the f/16 rule, we can estimate the shutter speeds to be useable with an ISO20 film as 1/20 sec at f16 or 1/500 at 1:4 in the sun or 1/10 at 1:4 for a cloudy, dull scene with side lighting. The latter conditions are at the limit, but within the grasp of an able photographer.
It is not clear if Barnack did envisage the use of interchangeable lenses, when he laid out the basic principles of his design. At first no additional lens has been offered and later they had to be matched individually to the body. A sure sign that Leitz was still in the beginning of the learning curve of becoming a manufacturer of high precision camera systems. This is remarkable as Leitz were well acquainted with the production of microscopes. These instruments were designed to be individually calibrated, which could not be done in the photography department. The concept of manufacturing interchangeable lenses to match with great accuracy to any body was really a challenge to the factory. But the availability of lenses with different focal lengths and apertures was the raison-d'-etre for the Leica. From 1930 the Elmar design is stretched in two directions: wide angle: 35mm and narrow angle: 90mm, with a short excursion into the 105mm focal length, and the 135mm. In fact we have only two major configurations in the Leica lens line-up from 1925 on. The triplet basic form uses a configuration of three singlet elements (positive, negative, positive). If we replace the third element by a cemented triplet, we get the Elmax. Replace the rear element by a doublet and we have the Elmar lenses 1:3.5/35, 1:3.5/50, 1:4/90, 1:6.3/105 and 1:4.5/135mm. Exchange all three singlets by doublets and we get the Hektor 1:2.5/50 and 1:1.9/73mm. Replace the front and rear singlets by a doublet and we get the Hektor 1:6.3/28mm. Replace only the centre element by a doublet and we have the Hektor 1:2.5/125 and Hektor 1:4.5/135 and Thambar 1:2.2/90mm.
Figure 8: 2.2.2 A: basic lens types
The second basic form is the symmetrical doublet or double-Gauss type. This lens had been expanded to a six element version by Lee and the basic configuration has a grouping of singlet, cemented double and cemented double, singlet in a slightly asymmetrical sequence. This is also the design of the Summar. Split the first singlet into two separate lenses and we get the Summitar and first Summicron versions. Split the rear singlet into two air spaced elements and we have the Xenon/ Summarit versions. Use this configuration, add a Merté surface and we get the Summarex 1:1.5/85mm. When adding the long focus designs of the Telyt 1:4.5/200 and the 1:5/400mm, the complete lens line is covered by three basic designs. There are several reasons for this economy of design types. First of all, there was not enough time and theoretical knowledge to explore more exotic designs. Several studies done by Leitz designers in the early period, generated some very promising and exciting designs, but lack of suitable glass types, the required mechanical tolerances and careful assembly made such designs not feasible in those days. So the designer had to use his ingenuity to stretch existing lenses to cover the requirements. Secondly it made sense in those early days to concentrate on a few designs and glass types and try to manufacture as many lenses as possible. One should remember that the cost of designing a new lens was often prohibitively high and success was not guaranteed.
The designer calculated the lens on paper and had a good idea of the performance that it could deliver. In those days the designer had limited means for the calculation of aberrations. Tracing rays through the optical system is quite labourious. And sometimes, in the case of skew rays, the mathematics are quite complex. So a designer could not trace enough rays to get a full picture of the design. The physical prototype was needed for a practical evaluation of the design. The design on paper was a close approximation to the desired correction, but the designer could not predict fully its state of aberration correction. Some mysteries remained, that could be detected after the prototype had been built. A proven design then was often the only or more practical way to proceed.
188.8.131.52 The Summar type.
In those days then every additional speed gain would be welcomed. The Hektor 1:2.5/50mm was the first answer by Leitz to the request for more speed. Its design in 3 groups of 2 cemented elements each, classifies it as a triplet variant. It had only six air-to-glass surfaces and was intended by Berek as the answer of Leitz to the Sonnar designs with 6 air-to-glass surfaces too. Definition of finer detail on axis could be preserved, but at maximum aperture overall contrast was on the low side. Films in those days had thick emulsions and low resolution, which gave the muted sharpness impression of many older photographs with the 35mm format. The modest wide open performance would have been in line with what was the accepted norm then.
High speed lenses for the 35mm format were quite difficult to compute, as the relatively wide aperture introduced a high level of coma and astigmatism, which softens the outer zones considerably. Furthermore the absence of anti-reflection coatings produced additional sensitivity to flare and reduced contrast. And last but not least, the requirements of Leica users for enhanced recording capabilities, triggered by improved emulsions, necessitated the search for new optical designs. To reduce unwanted flare and reflections, one had to reduce the number of air-to-glass surfaces and one could use one of several types of the triplet (like the Hektor). This triplet type (consisting of two positive singlet elements (crown type) at front and rear and one inner negative singlet element (flint type) is the base configuration. We can then play with this design and use one or more cemented doublets to replace a singlet element or we can split a singlet into two or more elements. The second major type is an expansion of the original Gauss doublet (two air-spaced meniscus elements). When we place two Gauss doublets back-to-back symmetrically around an aperture stop we get the double-Gauss type and playing again with the design we can add a cemented element to each negative meniscus. The classical and justly famous Double-Gauss six element lens is born. This design type has excellent possibilities for aberration reduction. So Berek was quite right in his decision to base the Leica high speed 50mm lenses on the Double-Gauss design and neglect the triplet derivatives (as the Zeiss Sonnar and Ernostar), even if these had a short-time practical advantage. Without anti-reflex-coating, the many glass to air transitions of the Summar lowered the overall image quality. The cross section of the Summar looks remarkably similar to that of the later Summicron family. The Summar 1:2/50mm exhibited a low contrast image at full aperture, with a strong presence of astigmatism in the outer zones and a fair amount of veiling glare. The edges of the fine detail outlines are fuzzy, which give the impression of a slight unsharpness.
Figure 9: 2.2.1 A Summar lens rigid
The Summar had not the crisp recording of coarse detail that the contemporary splittriplet- type of lenses could offer, and its image quality lacked punch. Leitz however, kept on studying and improving the design and so gained valuable experience, which could be used to good effect when Leitz introduced the Summitar 1:2/50mm in 1939. This lens has somewhat higher contrast and noticeably less vignetting, partly due to a bigger front lens . Its general characteristics wide open closely follow the Summar specs. Its central area of good definition is larger as is the reduction of astigmatism. Most importantly the Summitar improves rapidly on stopping down The improved colour correction (longitudinal) and better definition of finer details were needed to support the new generation of emulsions. The first Kodachrome from 1935 offered a staggering ISO value of 6, but the monochrome emulsions, especially the Agfa Isopan Super Special already had a speed value of ISO100, which is as sensitive as current standard B&W films. So in a few years time effective film speed increased two- to fourfold with finer grain than before and demands for better corrected high speed lenses became louder and louder. The colour negative and transparency films hovered around 20ISO for a long period and in 1950 reached ISO40. The first ISO100 colour film was the Super Anscochrome from 1957. It is also of interest to note that the granularity and resolving power values were in a really different category than what we expect today. The 1930 generation of films had RMS values that were four times higher than today's films of comparable speed and offered a resolving power of around 20 to 30 lp/mm in standard lightning conditions. This value, low as it may seem today, still presented a challenge to the lens designers. While the performance of the Summitar on axis exceeded the capabilities of the film with great ease, the image quality in the field (zonal areas) showed a low contrast at 10lp/mm already. The value of 30lp/mm (an indication of the recording capabilities for finer textural details) was reached but with very fuzzy edges and low contrast. The wider the aperture and/or the larger the image field, the more difficult it will be for a designer to control the aberrations. The low sensitivity of the filmemulsions and the wish of photographers to record events in very dim light encouraged the designers to compute lenses with an aperture of 1:1.5 was busy with a 1.5 design and finished one in 1938. But in 1932 the Contax offered already a 1.5 lens of Sonnar (triplet) design and Leitz needed a lens with similar specifications urgently. So the company licensed the Schneider design, the Xenon 1:1.5/50mm.
From a historical perspective we may regret this decision, as it would have very interesting to see which design of the two contemporary giants in optical design (Bertele and Berek) would be the better one. The Leitz Xenon allowed the user to expand his practical picture taking opportunities into hitherto uncharted realms. The performance of the lens at full aperture is however only acceptable for reportage type of pictures. A strong presence of coma introduces patches of flare around specular highlights. The quite dreamy and romantic atmosphere of pictures taken with high speed lenses at wider apertures in those days can be witnessed in many picture examples.
184.108.40.206 The Elmar type.
The Elmar family expanded quickly from 1930 in a few years to a range of lenses, covering 35, 90, 105 and 135mm focal lengths. Apertures were a modest 1:3.5 to 1:4.5. The Elmar 1:4/90 at full aperture has low to medium overall contrast and renders coarse detail with good clarity over an extended area (image height about 12mm). The 90mm lens started its life not as a portrait lens as they have been baptized later. In the '30's film emulsions were coarse-grained and even at moderate enlargements, details in the subject could get lost in the grain clumping. So the first use of the 90mm was the ability to record details sufficiently large on film that the grain could handle the finer image details. The so-called Berg-Elmar 1:4/105mm is a compact and very light-weight lens of only 240grams. This lens shows the concern of the Leitz company to produce lenses that are compact and light-weight. These characteristics match the Leica body as the camera for dynamic photography and the camera as travel companion. The Elmar 1:4.5/135mm again has the typical Elmar fingerprint of good central sharpness, but showed also chromatic errors, which are unavoidable in a long focus design. Leitz replaced this lens with the better Hektor 1:4.5/135mm. The Elmar 1:3.5/35mm at full aperture has some vignetting and the family character of lower contrast, good central definition of details and soft outer zones. It is a very compact lens, as were most of the lenses for the Leica in those days. Leitz even announced an Elmar 1:4.5/35mm in 1935. It had fix focus click stops for ease of use. This one and the Berg-Elmar are indications that Leitz made every effort to provide the user of the Leica with a system of lenses that covered a wide range of applications. Every type of photography (from travel to commercial illustration) could be covered with the Leica system. 220.127.116.11The Hektor type. The Hektor 1:1,9/73mm was the first attempt of .i.; to design a high speed lens with a moderate angle of field. The triplet design however could not be stretched too much.
The Hektor 2.5/50mm and the Hektor 1.9/73mm allow the same amount of energy flow to pass through the lens. The wider aperture of 1.9 (2/3 of a stop more than the 1:2.5) is offset by a 50% smaller angle of field. (30oversus 45o). clearly was aware of the limits of the generic Hektor design. The 1:1.9/73mm short telephoto lens at the wider apertures has that typical softness at the edges of outlines and the very smooth transition of the sharpness plane into the unsharpness blur of fore-and background, that became the defining characteristic of the portrait lens for generations of photographers. The Thambar 1:2.2/90mm is a so-called soft-focus lens that allowed the photographer to make portraits with the soft effects that were very popular in those days. The extent of softness can be regulated by the iris diaphragm and a special opaque disc, that can be placed in front of the lens and cuts off the central rays. As now only the outer rays will be available for image formation, we see a strong degradation of quality as these outer rays are generally less well corrected than he central rays, that are blocked now. Longer focal lengths have a smaller angle of field and the correction of aberrations is somewhat simpler as long as apertures are moderate. The wide angle have a larger angle of field and now vignetting and zonal aberrations are becoming a problem for the designer. The first 28mm lens, the Hektor 1:6.3/28mm, was introduced in 1935. When the angle widens the vignetting and distortion ask for all attention. The large front and rear lenses help reduce vignetting which indeed is gone by 1:8. The diameter of the front lens is +10mm, twice as large as is needed from geometry only. The overall image quality is a bit dull and fine detail is softly rendered without the clarity and bite we do note in current lenses. 18.104.22.168 The Telyt type. The coupling accuracy of the Leitz rangefinder/body combination is limited to the 135mm focal length and when a longer focal length is required, a new device, the mirror reflex housing (Visoflex or the as it has been designated in the early period PLOOT), had to be used. This device, ingenious and a marvel of mechanical engineering, transforms the Barnack camera into a mostly stationary photographic instrument. For some assignments however the longer focal lengths are indispensable. The Olympic games in 1936 were a strong incentive to produce new telephoto-lenses and the Telyt 1:4.5/200mm and 1:5/400mm were designed with this deployment in mind. Both Telyt lenses were true long focus lenses, and performance is good for the 200mm version, but weak for the 400mm.
During the war Leitz managed to keep the production lines going, but production increasingly shifted to military, medical and projection purposes. The only new lens to appear for the presumably civilian market was the Summarex. This lens is described in the beautiful and colourful Leitz brochure from 1943: 'auswechselbaren Leica-Objektive'. The state of the economy would not have encouraged anyone to buy this lens, even if it were available, which is highly unlikely. The price in 1936 for the Hektor 1:1.9/7.3 cm was RM 260.00, way beyond normal purchasing power. The Summarex 85mm had modest image quality at full aperture but improved remarkably on stopping down to 1:5.6 and 1:8.
Figure 10: 2.3A- lens overview 1943
The last lens-series has been registered on March 15, 1944. It was a batch of about 10 lenses of exotic specifications: 1:0.85/150mm, the last lens having the serial number #594852. The list of specialized designs is quite long. Examples are the Elkinor 1:1.5/300 and 1:1.5/400mm, IRSummar 1:0.85/75mm and 1:0.85/150mm, URSummar 1:1/90mm and 1:1/150mm. Coating was also introduced on the military versions of the lenses in 1941. The civilian production however did not receive this treatment until after the war. The topic of the use of coating has not found its final treatment. Rogliatti notes that coating had been applied to lenses from #587601 (Summitar) from 11 November 1945. The factory lists indicate that at 6 November 1945 the serial numbers 600000 to 601000 have been allocated for a batch of Hektor 13.5cm lenses. The first Summitar series begins with 603000 in early 1946. The #number 587601 is part of a batch of Summitars from #586001 to 590000, allocated in 1942! The factory archives in the optical department note that coating was applied from October 1941 (from serial# 580000) and I quote:' from October 1941 all Leica lenses receive anti-reflexion coatings. These lenses are not available for amateurs, but only for war photographers (Kriegsberichterstatter)'. A report by the US Naval Research Labaratory, dated 3 October 1946, on German coating methods during the wartime does indeed note that Zeiss, Leitz and Schott all used several methods of coating during that period. The report remarks that Dr. Männchen from Leitz demonstrated an (experimental) method of centrifugal coating (as compared with the Zeiss method of thermal evaporation coating), which however produced a very soft coating.
Production was resumed already in June 1945 with serial number 595000: a batch of 1001 Elmar 1:3.5/50mm lenses. Between October 1941 and June 1945 Leitz manufactured about 15000 lenses, and some larger batches were reserved for the specialist lenses for military applications, some of which were very rare, like the IRTessar 5/5000mm. It is reasonable to assume that most of these 15000 lenses went to the government. As it is also very likely that not all lenses, produced before October 1941 were sold out at that date and Leitz would be able to provide amateurs with the non-coated version of their lenses.
The Leitz factory emerged after the war almost intact. The buildings however were in a desolate state and the American Occupation had copied and transferred all the valuable Leitz documentation to the USA. It is typical of the wisdom and vision of Ernst Leitz that he was not bothered at all by this transfer and he remarked to a close aid that as long as the Americans allowed the workforce in the factory to continue with their work he was not worried about it at all. He knew what is still valid today.
The real power of the factory is the creativity, brains and motivation of the people.
Already in the spring of 1945 Leitz-Werke resumed production with the same core product line as was available in 1939. The first new design was the Summaron 1:3.5/35mm, introduced in 1949. Like the Hektor 28mm, the diameter of the front and rear lenses were quite large for the same reason (reduction of vignetting). This six element Gauss design had more potential for aberration correction than the Elmar of the same specifications, and its introduction so soon after resuming civilian production, showed the determination of Leitz to improve the image quality of the Leica lens line. During the war Leitz introduced single layer coating (around 1941) and after the war new glasses became available, many of them specifically researched in the Leitz glass lab, founded in 1949. In the past the optical designers had stated too often that they could get better correction of aberrations if they could use a glass with specific properties. These glasses however did not exist and the idea to have to wait and see if and when Schott or other manufacturers produced the glass so eagerly awaited for, was not in the interest of Leitz. In 1950 the Summarex 1:1.5/85mm was relaunched in a chrome version and with coated glasses. Its inherent characteristics were not changed and, while having an impressive appearance and a heavy weight , image quality became quite good only after stopping down to 2.8. At full aperture the lens gave modest performance, and its weight must have been a heavy burden for the Leica bodies of the day. Indeed, the structural weakness of the screw mount Leica bodies when the heavier lenses were mounted, was one of the arguments to develop the M-series. The Summaron 1:5.6/28mm (1955) improved upon its predecessor. Its design is symmetrical which gives better performance when taking pictures at closer range. Also distortion and coma are slightly reduced by this design. Overall it is medium contrast lens with a commendable definition of fine detail over a larger image circle of about 12mm. The outer zones are soft to very soft. The wide angle of field gave the designers a lot of trouble and an even coverage including the edges was still a pipe-dream. When considering the introduction of a new lens, Leitz had to weigh two factors. The high cost of the design process and the number of units sold.
But sometimes the Leitz designers had no suitable design available. The 21mm lens is an example. The optical solution for the design of an ultra wide angle lens had been found by Zeiss and Schneider. Leitz offered the Schneider Super-Angulon 1:4/21mm from 1958. This is a symmetrical design that covers a wide angular field.
Its construction incorporates negative outer elements and a wide spacing between the elements. This type of construction helps flatten the field, which is very important for a wide angle. Coma and distortion are also reduced. The Super- Angulon has indeed very low distortion and slight curvature of field. It also exhibits the low to medium contrast typical of the period and the rendition of fine detail is on the soft side.
Figure 11: 2.4 A-early Summicron
The collapsible version of the new Summicron 1:2/50mm (1953) is a lens that marks the transition to the next period. While the lens itself belongs in the first period, I will discuss it in relation with the newer rigid version, that is specifically designed with the new M-mount in mind.
Theoretical knowledge of the optical aberrations and how to correct them is based on the work of some eminent scientists of the period around 1900. Schröder, Moser and Miethe studied the equations needed for the complex calculations for photographic lenses, Abbe experimented with new glass types, and people like Rudolph, Merté and Lee explored unknown territory to get the best imagery possible.
The designs they used, (triplets, Petzval versions, double-gauss derivatives) were all based on constructs from the 19th century and it is in fact remarkable to note that most of the early efforts were concentrated on improving old designs and specifically to get rid of astigmatism. It is also interesting to remark that in the period form 1900 to 1940 the demand for photographic lenses was so high that most designers at first had to generate designs that could satisfy that tremendous demand. Room for fundamental research hardly existed. Commercial arguments prevailed in this expanding industry and the manufacturers exploited the available experience to the utmost. The widespread use of the Leica and its 35mm format and the expansion of focal lengths into the wide angle area, put heavy demands on optical performance and so did the surprising introduction of colour film around 1935. It became clear to some designers that the traditional methods and formulae for the calculation of aberrations did not suffice and that even the theoretical knowledge of the aberrations themselves deserved a reworking of basic principles. The geometrical (trigonometric) approach to lens design was insufficient to study and correct the higher level of aberrations that needed to be controlled for better image quality. The direction to follow was a study of the energy balances in the optical system, Berek understood this very well and he even devoted a full chapter to this topic in his book 'Grundlagen der praktischen Optik' (1930). This chapter 10 ('Energiebilanzen') is part of the Leitz philosophy of lens design. The staggering amount of numerical results, needed to analyze lenses in this new theoretical approach, could not be handled with the classical log-tables and numerical methods. Indeed the full use of these insights had to wait until the computer became available early in the '50s. Max was not the only one to run against the limits of the traditional methods of computation. Albrecht Tronnier of Nokton fame was also acutely aware of the vanishing possibilities of the old approach. War however changed the course of humanity for a long period. Behind closely guarded doors the research continued, and the foundations for this new approach were intensively studied. Also new evaluation methods for the appraisal of optical performance were introduced as the mirror image of this research. The first studies into the importance of contrast for image quality were laid down by a Zeiss employee, Hansen in 1943. The period from 1925 to 1957 can be characterized as the search to adapt the known optical principles to the exacting demands of the Leica format and of colour photography. A few proven designs were selected as the platform on which to construct and manufacture the lenses that were commercially and conceptually required by the quickly expanding user base for the Leica camera.
Figure 12: 2.5 A :the Leica system Study of the production
Figures over the period 1930 to 1940 indicates that a total of 414.000 lenses left the factory, of which 169.000 were of the type Elmar 1:3.5/50mm and 123.000 of the type Summar 1:2/50mm. The Elmar 1:4/90mm and the Elmar 1:3,5/35mm had a production of 28.000 and 26.000. More than 70% of all lenses that were produced by the 'Leitzianer' in the Wetzlar 'Hochhaus' were of the 50mm focal length. The 35 and 90mm lenses added another 13%. These figures are a clear indication of the commercial viability of new designs, and when we add the worldwide recession after 1929 into the equation, it is sound business practice of Ernst Leitz to stick to the well-proven designs.
Figure 13: 2.5B: the Leica image
In the late thirties the Leica user could choose focal lengths from 28 to 400mm and apertures from 1:1.5, including some special lenses like the Berg-Elmar 1:6.3/105mm and the Thambar 1:2.2/90mm and (hypothetically) the Summarex 1:1,5/85. While it is true that some of the Leica lenses overstretched the optical limits a bit, designing and producing the lenses was of paramount importance for the next period. Leitz tried to expand the system concept of the Leica as quickly as possible as he understood quite well, that the success of the Leica depended on a comprehensive line of lenses, that provided most users with every option they could imagine. When evaluating the optical performance of a lens, designed and produced in those days, one should take into account that the lenses then were not checked and tested as we do today. The British report states that the Summitar was checked for image quality at the factory at the aperture of 1:3.2. Presumably the lens testers used some numerical rules to relate the quality available at 1:3.2 to the one at full aperture. The success of the 'Leica'-camera was in part based on the large depth of field of the lenses, coupled to the 35mm format. The depth of field is greater when one stops down to middle apertures, and this technique was used in most circumstances. The full aperture setting was primarily reserved for the really difficult low light situations, where slow shutter speeds and high speed, grainy film-emulsions would not record fine detail at all. It was a fact of life that the image quality available at full aperture would be less that what could be delivered at smaller apertures.
The Leica company had to face several challenges during these decades, some of which were optical in nature and others were related to the course of the photographic industry. The German 'Wirtschaftswunder' generated unprecedented economical wealth, photography became the prime hobby for large segments of the population in the industrialized western part of the world. In 1955 the Leitz company, now located in three different factories in and around Wetzlar, produced 40.000 camera bodies a year and close to 100.000 lenses.
Figure 14: 2.3 A: lens # 2.000.000
In 1964 the production of lens# 2.000.000 was proudly announced, 12 years after #1.000.000 in 1952. In those days Leitz manufactured a thousand different products, which were assembled from 300.000 discrete components. Every month millions of parts had to be shop tested for tolerances, often less than 0.01mm. Such a diversified range of products, most of which were of high precision optical-mechanical nature, put a strain on the production and engineering divisions and of course on the design department too. Manufacturing technology was in essence the same as before the war, improved and modernized of course, but manual labour constituted the bulk of the workflow. Around 1965 the economy slowed down and the photographic industry became dominated by the Japanese and one main camera type, the single lens reflex. The high quality compact rangefinder camera was the second strategic product for the market. Leitz was squeezed by both product types, for which they did not have an immediate answer. The Leicaflex (1964) and the Leica CL (1972) were too late and of too modest specifications to have any impact on the market.
The optical challenges were large too. Japanese designs covered an ever growing range of lenses of improved optical performance. The Leitz philosophy of design and manufacture of lenses made them less flexible in the area of extended specifications. The universal adoption of computer aided optical design gave lens designers equivalent opportunities and in the seventies one might note a plateau in lens performance. The leading marques produced lenses that delivered image quality on a level that satisfied most professionals and amateurs alike. It became increasingly difficult for Leitz to distinguish themselves and create optical systems of cutting edge performance. The amounts of money for the required research and development to stay ahead were simply not available, as the falling production of the Leica cameras reduced the profits of the company and asked for investment money too. The challenges seemed indeed insurmountable. On the organizational and management level, Leitz worked within the constraints of a traditional method of manufacture and decision making and the famous feeling of Leitz for the trends in photography was fading away too. On the marketing level, Leitz had to cope at the same time with the problem of a smaller production volume and the need to expand the range of products. On the level of design and innovation one has to note that the Leitz designers were quite innovative within their chosen domain of excellence, the high speed lens of fixed focal length, and were very advanced in the research for new solutions (glass, aspherics, even vario lens designs and even auto focus). Leitz focused all attention and development on one goal only and that was the development of lenses with very high image quality, which could only be delivered when the mechanical mounts were of very high quality too. . The true dilemma is simple: the high optical performance necessitates an expensive production process and a mechanically elaborate mount , which in turn defines the physical dimensions of the lens and as these dimensions cannot grow beyond manageable proportions, the specifications are fixed too. Leitz started the period in great prosperity, with an enviable product line, that sold very well, and a fine tradition of design and manufacture. The allowed themselves the luxury of two different and sometimes competing design departments in Wetzlar and Midland and a glass research lab. Later Leitz even added a very elaborate and costly technical lab for testing lenses and designing new methods for image evaluation. The big changes in the photographic world and in the photographic industry were only reluctantly acknowledged and Leitz tried with cooperation, and the adoption of lenses made by several manufacturers to expand the product line, while staying faithful to the traditional values of optical quality and superb mechanical craftsmanship.
Figure 15: 2.3B: telyt 3.4/180
Figure 16: 2.3C Macro Elmarit
Figure 17; 2.3D Noctilux 1/50
In 1972 the Leitz family stepped back from the management and in 1974 Wild Heerbrugg was in complete control. Not much changed however and the next period from 1974 to 1988 is characterized by a painful process of global marginalization.
Some outstanding products were created in this period, like the M6 and R6, the Noctilux and the Apo-Telyt 3.4/180 and the Apo-Macro-Elmarit-2.8/100mm, but the impact of Leica on the market had been lost.
During this period the photographic division of the Leitz company did indeed change dramatically. With the M3 and its range of lenses, Leitz established itself as the premium manufacturer of precision miniature rangefinder cameras and was without doubt the photographic company with the highest esteem in the world. The M3 with the Noctilux 1:1.2/50mm (1966) confirmed the position of Leitz as a world leader in advanced optics and the role of the M3 as the available light/reportage camera.
Figure 18: 2.3.1 A M3
While Leitz concentrated a substantial part of its resources on the rangefinder concept, the photographic world at large gradually shifted to the SLR-concept. This change occurred in a few years and must have been a surprise to Leitz. They were the only company in the world that expressed faith in the rangefinder concept for a professional camera system. The factory however could not overlook the drop in sales figures for the M-series. Leitz reluctantly followed the trend with the Leicaflex in 1964. The birth-pangs of this camera have been noted in the contemporary press and the announcement of a reflex Leica were rumoured since 1958. The design and development of the reflex line is not part of this story. Suffice it to say, that the Leicaflex and its successor models were less successful than Leitz anticipated. The development of a comprehensive lens-line to compete with the professional Japanese and German models of those days was no easy task. At the same time the sales of the rangefinder camera dropped significantly. In 1960 the sales of the M2/M3 were around 30000, and a few years earlier were above the 35 thousand level. But in 1970 the M4 sales were around 12.000, and the Leicaflex SL had a designated production run of 10.000. Leitz was in a difficult position as its market share shrank, while the investment for research and development had to increase to compete with the ever more innovative Japanese companies.
Figure 19: 2.3.1 B M System
Being alone in the rangefinder market, Leitz tried to break out of the M3/4 mould, with bold new designs. The M5 was clearly targeted at the professional photographer who was accustomed to features like the through the lens exposure metering. The CL, on the other hand incorporated modern features that tried to open up the new vast market of the dedicated amateur photographer. These models, with their quite innovative engineering, did not capture the mood of the market however and were withdrawn after only a few years. In fact the fate of these models dealt a heavy blow to the confidence of Leitz in the RF-future. Is was decided in Wetzlar to end the RFproduction and to concentrate on the SLR as the main product line. The dedication and enthusiasm of a few persons, saved the M-system: the production of the camera was transferred to Midland (the M4-2).
Figure 20: 2.3.1 C: Leicaflex
The Leicaflex SL2, the last of the 'true' Wetzlar reflex bodies, had run out of steam already at its introduction and Leitz, following the maxim 'if you cannot beat them, join them', teamed up with Japanese suppliers to produce the next generation SLR, the Leica R3. The history of the R-development is not part of our story. Suffice it to note that the Leica R3 and the successor model R4 sold well, but did not inspire that confidence in the solid engineering Leitz were famous for. The R5 and especially the R6 and R7 restored the reputation, but now we already entering the nineties and that is the Solms-era. The cooperation with Minolta did extend into the optical area, and Leitz used several Minolta designs to fill in the gaps of the lens line for the R-system.
In the mid-seventies the photographic industry reached a performance plateau: the SLR development had virtually stopped after the incorporation of Auto-Exposure techniques. The lenses too, helped by computer assisted design programs, had evolved to a state where it was becoming difficult for the casual and critical observer alike to see big differences in image quality between the leading marques. The independent suppliers of lenses, improved their optical quality to a level that started to challenge the leaders, at least optically. And with a very favourable priceperformance ratio, coupled to innovative designs, these makers made substantial inroads in the traditional markets. On the optical front, the Leitz designs, while still first class, ran into stiff competition from several Japanese and German companies, whose design teams, aided by computer programs and a large selection of commercially available glass types, produced lenses that were sometimes uncomfortably close to the Leitz designs in image quality. The domains where the Leitz performance could show its advantages (slide projection and large format B&W prints) were shrinking. The increasing use of the colour-negative print also diminished perceivable differences in mage quality. Leitz had one very important advantage, that is often overlooked: the mechanical quality and engineering precision of the lens mounts is second to none. The longevity and durability of Leitz lenses can be seen in any older lens that is in use today. Leica lenses also stay within tolerances, even after prolonged and heavy-duty use.
Figure 21: 2.3.1D: Lens mount
The Leitz company started the 35mm boom in photography in 1925. The company was sold to Wild in December 1986 and the production facilities transferred to Solms in June 1988. It is a strange quirk of history that Leitz always went against the current mood: in the twenties when against all odds and advice the Leica Standard was produced, in the fifties when the decision was made to continue the development of the RF system and in the eighties when they decided to stick to the manual focus SLR. The Leitz management then had to accomplish a true mission impossible. They felt pressed to offer a comprehensive range of lenses for two different systems, they had to improve the optical quality and at the same time contain the cost of production to adjust to a lower sales volume of the R- and Msystems.
These decisions had important consequences for the development and characteristics of the Leitz lens families. For the rangefinder and reflex systems the company wanted state of the art performance for their lenses. Where 'state-of-theart' was to be defined within the limits of the Leitz philosophy of lens design. The designers had set themselves a certain minimum level of image quality. When you have designed a lens (focal length, aperture, volume, number of lens elements etc.) you can calculate the (theoretical) performance of a lens with a technique called 'ray intercept curves'. These curves can be graphically displayed and their shape is very important as they give the designer a full insight into the quality of the lens. Now you can define that the bundle of curves should be within certain upper and lower limits.
Any lens that has curves that extend beyond these limits, delivers less image quality than a lens that has graphs within these boundaries. Leitz did design several prototypes for the R-system, but performance at full aperture could not be fitted within these optical limits (and the production constraints). They might have been very good lenses by most standards and would certainly have drawn attention to the Leica R, but Leitz, bound by their own strict performance levels could not be persuaded to manufacture this lens.
2.3.2 An Herculean task From 1957 to 1988
Leitz introduced more than 40 new or redesigned lens types for the M-system and more than 50 lens types for the R-system, on average three lens types per year. The Leicaflex has been introduced on the market in 1964, but the design of lenses for this system started around 1960. At first the designs for the R-system were optically completely different from the M-equivalents. In 1964 the Leicaflex was accompanied by four lenses: 1:2.8/35mm, 1:2/50, 1:2.8/90 and 1:2.8/135, the classical quartet. All four were new optical designs, and of Canadian origin with the exception of the 35mm lens, which was created in Wetzlar. The larger throat diameter of the R-body and the bigger distance from lens flange to film plane (27.8mm for M and 47mm for R) force the designer to create retro-focus designs for lenses with focal length below 50mm, which are more difficult to design. The retro focus principle also requires larger front elements. There is a 'hard' rule in optical design that states that a physically larger lens is easier to correct for aberrations than a smaller lens. And the type of correction could be different too. Leitz then needed two distinctive design philosophies so to speak, one to optimize the smaller M-lenses and one to optimize the larger R-lenses. How did Leitz cope with these incompatible challenges? In the beginning the factory followed two different design strategies, one for M and one for R. In the M-domain, they pursued to improve the image quality of existing designs and to develop lenses with daring specifications, like the Noctilux. These new lenses were made possible by the advances in optical knowledge, partly by theoretical study, creative inspiration and the assistance of the computer and partly by the research into new types of glass. In the R-domain, Leitz started quite conservatively with lenses of moderate specifications and forged ahead later with longer focus lenses with apochromatic correction. Of course there was a sharing of insights between the developers of the M and R lenses and this can be seen quite clearly in the development of the 50mm lens.
Figure 22: 2.3.2 A reliance on manual labour.
One of the first strategies to be used by Leitz is the pooling of resources by designing lenses that could be used in the M- and R-systems. One example was to use the long lenses, developed for the Visoflex, in a different mount for the Rsystem.
The later Summicron 1:2/50mm lenses, the Summilux 75/80 lenses and the Elmarit 1:2.8/135mm lenses are examples of this trend too. We should note however that the two design-departments (ELW and ELC) were thousands of kilometres apart, and pursued their own design philosophy under two independent management teams and so the potential for competition was as much part of life as the potential for synergy. Another strategy is to cooperate with other lens manufacturers. The range of lenses that Leitz could develop themselves was limited, so for a number of lens designs , notably zoom lenses and very wide angle lenses, the factory used lenses from third parties, like Schneider, Zeiss and Minolta. Behind these strategies, the true battle of that period is between the drive to improve the image quality and the possibility to translate this improvement into the production of the lens, while holding down the cost of manufacture. The use of the computer, new research into optical glass, better grasp of the optical theory and more insights into the design process all helped to improve designs significantly. There is a hint of a true Greek drama here, that Leitz succeeded in advancing the theory of optical design, but could not find the right way to produce these exciting designs. First of all: the method of producing, assembling and mounting lenses did not change over the years and had much in common with the way lenses were manufactured in Berek's days. But the improved designs needed tighter production tolerances, that were not possible without a higher cost. And that was the economic constraint as the lower sales volume could not bear this.
The development of the lens systems for R and M has to be described and interpreted against this background. We can illustrate these developments with a few significant acts. From 1954 to 1971 (the period of the M2/3/4) Leitz expanded the M-line into a full blown system concept, with lenses from 15 to 800mm. At the same time the factory redesigned many of the lenses, for improved performance, and/or easier handling. In several instances the drive for enhanced optical quality collided with the limits of production technology and/or production costs. After 1971 (introduction of the M5 and CL) the rangefinder concept was developed more selectively with lenses in the 21 to 135mm bandwidth. But the reduced sales forced the design-department to economize on the introduction of new designs and find ways to control the production costs of existing designs. Between 1975 and 1980 Leitz introduced a number of very high speed lenses for the resurrected M4-2 (and M4P), that could be seen as the state-of-the-art profile for the rangefinder concept.
From 19080 to 1990 no new lenses for the M-system have been constructed.
Figure 23: 2.3.3 A CL
Figure 24: 2.3.3 B M Lenses
For a long time Leitz maintained and expanded the M-system as the dedicated tool in the great tradition of the documentary photography. Many lenses were redesigned for improved optical quality and/or better handling. (smaller volume, less weight).
Some exciting designs like the Noctilux 1:1.2/50mm indicated the dedication of Leitz to deliver the best possible optical quality to its demanding customers. But the system-concept of the M was not abandoned after the introduction in 1964 of the Leicaflex and for a longer period Leitz had to develop two lens lines which at the long focus end were competing with each other. This also blurred the distinction between the two systems. With the Telyt lenses (400mm to 800mm) Leitz used the same optical cells in different mounts, which reduced cost of development, but hardly of production, one may assume.
Figure 25: 2.3.3 C Noct 1.2/50
The evolution of the R-system can also be sketched in some clearly defined stages.
After 1964, the year of the introduction of the Leicaflex, the development of the lenses for the R-system proceeded slowly. For the R-system Leitz concentrated on these focal lengths they had most experience with, that is the lenses that were also the backbone for the M-system: 28mm to 135mm. The maximum apertures however were quite modest (even for those days). The 35mm, 90mm, 100mm, 135mm and 180mm all had apertures of 1:2.8. The first 1:1.4 design was the 50mm Summilux in 1969, ten years after the M-version.
Figure 26: 2.3.3 D R-1.4/35
The aperture of 1.4 for the 35mm had to wait till 1984, before Leitz felt confident enough to produce he Summilux 1:1.4/35mm. The 1:2/35mm lens arrived in 1972, more than a decade later than the M-version. One may only guess why Leitz has been so conservative in the specifications for the R lenses. The obvious commercial argument might be that they did not want to have competition between the Leitz camera-systems. Leitz obviously had defined the SLR-system as a complement to the M-system, not as a competitor. More philosophically one might argue that the focusing screen and the mirror box with its time lag, typical of the SLR-system, dedicated the Leicaflex to a different type of photography and Leitz designed lenses exactly for that goal. Leitz, with its rangefinder expertise, may have had the opinion that the inaccuracy of focus with the split-image rangefinder of the SLR precluded the use of very high speed lenses. And on a more mundane level, one should be aware that Leitz had hardly any experience with the design of lenses for a SLR system.
Figure 27: 2.3.3 E R19
Around 1975, more than 10 years after the Leicaflex appeared, the first wavelet of innovations for the R-system was announced: the 19mm and the Apo-Telyt 3.4/180mm, the first apochromatically corrected lens, developed by Leitz Canada. It is interesting to note that the Wetzlar designers were more concerned with the technique of aspherics and Midland with the apo-correction, at least in those days.
The M5 and the R-body however required many lenses in the wide angle and standard focal lengths to be redesigned as retro-focus lenses. Leitz however had at first hardly any experience with retro-focus lenses for Slr-systems. That learning curve is visible in the many redesigns of the 28mm lenses for the M-system and the 35mm lenses for R-system. The first original Leitz designs in the very wide angle domain are the Elmarit-R 1:2.8/19mm and the Elmarit-M 1:2.8/21mm in 1975 and 1980, an indication of the long gestation period that Leitz needed to feel confident to design these types of lenses. After 1980, when the development for the M-system stopped, the R-system expanded rapidly with landmark designs like the Summilux-R 1.4/35mm design (1984) with floating elements and the Apo-Elmarit-R 2.8/100mm (1987). At the same time, Leitz adopted many designs from Minolta and others. It is evident that Leitz had not the capacity nor the money to undertake a massive development program for two different systems and we see a relocation of forces over time, and a switch of main focus from Rangefinder to SLR after around 1978.
Figure 28: 2.3.3 F: expanding system
As suitable glass types seemed to be the biggest obstacle for the advancement of new designs, Leitz set up its own glass laboratory and around 1953 the first fruit of that effort was the introduction of the Summicron 1:2/50mm (collapsible). Its design was completed in 1949 and a slightly different computation became necessary in 1952 when Schott glass had to be incorporated. After the introduction of the Summitar, the 'Leitz Rechenbüro' continued to explore this design as it was clear that the competition would not sleep and a high quality 2/50 lens was of utmost importance for the critical Leica user. In those days the limits of the diameter of the lens mount of the current models became painfully clear. When wider apertures were needed or a higher level of correction, the diameter simply was too small. The patent literature of the four-tap bayonet mount for the later M-models, specifically mentions the reduced vignetting as one of the prime characteristics. The first Summicron version closely followed the design parameters of the Summitar and the increase in image quality was slight. It too is a low contrast lens, and shares the optical 'fingerprint' with its predecessor. The rigid version of the Summicron 1:2/50mm arrived on the market in 1957, but was on the drawing board several years earlier. It utilized the optical improvements that were made available with the wider throat for the M-body.
The seven-element Summicron split the front element in two separate lens elements and used the air space between the two elements as an additional lens (an air lens or Luftlinse). Leitz also separated the front doublet and used the same technique for enhanced correction, specifically for a reduction of spherical aberration and of the secondary spectrum (the chromatic aberrations). The Leitz designers also incorporated in the new design the new Lanthanum glass types, developed by the research lab. The air-lenses are a mixed blessing though as they allow for a better control of aberrations, but also introduce more flare and they are very sensitive to small deviations in tolerances. After 1957 Leitz introduced in quick succession several lenses for the M-system, that can be regarded as the first series of lenses with markedly improved imagery, when compared to the predecessors. The image quality of these lenses was a true testimony to the progress in the optical and mechanical fields, that the Leitz engineers had been able to make since the war ended. In the late thirties Leitz had noted that the traditional methods of design, the knowledge about aberrations, the commercially available glass types and the methods of production would seriously handicap the search for new optical solutions. In 1949, the year that Max Berek died, the company had inherited a large body of knowledge and had accumulated a vast pool of experience. One should remember that much of optical theory originated in the microscope division, which was very valuable but needed some fundamental transformation before it could be used with good result in the photographic department. The microscope lens has a much smaller field than the standard photographic lens and aberrations which are very troublesome in photographic applications are less so than in the microscope. The converse is true too, of course. As example I may remark that apochromatic correction of microscope lenses was standard practice, long before this approach was applied in photographic lenses. A major part of the research and design efforts of Leitz in the period from 1950 to 1980 was devoted to the exploration of the double-Gauss highspeed lens. As I mentioned before, this lens type is very flexible and can be adapted to several classes of demands. A lower speed wide angle lens as the Summaron 1:2.8/35mm and the high speed Summilux 1:1.4/50mm or the Summicron 1:2/90mm ask for a different type of aberration correction. The difficulties in finetuning the several sets of requirements can be seen quite clearly in the long list of lens versions for the M- and R-systems. Some designs were replaced very soon by improved versions: witness the Summicron 1:2/90 (1959) and the Summilux 1:1.4/50mm (1961). Here we see a trait that is most characteristic of Leitz lens development. The optical department in the Wetzlar 'Hochhaus' tried to refine and improve the existing lenses continuously, and they committed a fair share of their resources to that end. Leitz would never be content with the idea that a certain lens is good enough. His drive was to provide the photographer with the optimum optical performance. The many redesigns of classical focal lengths in the 28mm-135mm range do show this intention. Sometimes a lens is not changed for decades. The Summilux 1:1.4/35mm is an example. At full aperture it has low contrast and it suffers from coma. Its overall characteristics would indicate it to be a Summicron 1:2/35mm, opened up one stop. Given the constraints (optical and mechanical) of a high speed wide angle lens, the definition of this lens could not be improved upon. It is perhaps more accurate to say that the Leitz designers could, within certain limits, create a (theoretical) lens that could deliver better performance, but it would be very difficult to produce such a lens. We do not often realize that suitable glass must be available, that the production tolerances must be realistic and that the amount of manual adjustments during assembly should be low. The designer might calculate a very fine lens, but if the glass needed has a thermal expansion that is not in line with the other glasses, or has properties that make it difficult to manipulate (grind, polish), he cannot use it. It took almost 30 years before the technique of aspherical lenses could break this Gordian knot for this type of lens. The first Noctilux 1:1.2/50mm with two aspherical lens-surfaces (1966) does indicate the relationship between the several variables. This lens was optically a breakthrough, but the amount of manual labour, the exactitude of the tolerances and the overall optical/mechanical sensitivity denied the lens the commercial success, Leitz had hoped for. In the category of very high speed lenses (1.4 and wider) Leitz redesigned the 1:1.4/50 in 1961 and introduced the R-version in 1970. The R- lens stayed in production until 1998 when a much improved version with 8 elements appeared. The M-lens is still in production, but begins to show its age. It is however not that easy to design a version that delivers improved image quality while staying competitive in price and physical dimensions. The long production period of the Summilux 35 mm (M and R-version) is a clear indication how difficult it is to improve on a well designed lens when the parameters are really difficult (1.4 aperture and an angle of 64o are heavy obstacles for a designer.). The Summilux -R for the 35mm focal length was a Wetzlar design and they needed a vast array of optical means to improve upon the M-version from 1961. The M-version had to be designed within the limits of a compact lens and it may represent what was possible with conventional means. The R-version could be designed with more liberty concerning the size and so a ten element optical system with floating elements emerged from the drawing board.
During and after the mid-seventies, Leitz tried to rationalize their lens systems, sharing mounts and lens elements wherever possible. As example we may look at the Summicron 1:2/50mm standard lens. This lens family is an example of the double goal for more image quality (and cost containment at the same time). The Summicron (type I) was the collapsible one from 1953 or 1954. The Summicron (II) for M was introduced in 1957. For the new R-system (1964) Leitz Canada designed a different lens, now with six elements and higher level of symmetry and different glass types. A few years (1969) later ELC introduced the Summicron (III) for the M-line, a design that differed from the predecessors and generally offered higher image quality.
In 1969 the Summicron for M had the same overall construction as the Summicron for R, introduced in 1964 and the reduction from 7 to 6 lens elements improved the imagery and at the same time reduced the assembly and production costs. There was evidently one element less to grind, check and mount and the performance was improved at the same time. The next stage of the design for the R arrived in 1976 with the Summicron-R (II). This lens is a highly evolved design that delivers high image quality, better than the predecessor, especially in its behaviour at full aperture.
It gave a high contrast image with quite even performance over most of the image area. An almost identical version for the M-system was introduced in 1979 with the Summicron-M (IV). Both versions are remarkable as they have 5 plane surfaces, instead of the curved surfaces of the other types of Summicron lens. A plane surface is easier to manufacture and handle, so its use will lower the production cost. In addition a plane surface does not generate unwanted reflections, and it is sufficient to use a single-layer coating.
Figure 29: 2.3.5.A M50
Figure 30: 2.3.5B R50
On the other hand a plane surface has less potential for aberration control. The key for explaining this apparent contradiction (simpler design and higher image quality) is the improved optimization capability of modern optical design programs. The Tele- Elmarit 1:2.8/90mm is a very interesting example. This lens has been introduced in 1973, as a parallel development of the Elmar-C 1:4/90mm for the Leica CL. It shared no components with the 1964-version for the Leicaflex. In 1980 a completely different and improved 90mm for the R-system appeared, but this lens was not adapted for the M-system until 1990. There is an interesting story behind the Tele- Elmarit for M. The 135mm lens was not selling well and disregarding its outstanding imagery, was to be axed from the catalogues. But the focal length of 135mm had to be taken care of. In the Leitz archives we find the key for the strange role of this lens. The Leitz designers had in mind a teleconverter 1.4x for the M-system and the compact Tele-Elmarit. This combination would deliver a very small and lightweight 135mm lens of acceptable aperture (1:4.0). This idea however has been shelved, because of lacklustre performance. It does indicate that creative solutions were actively searched for.
Figure 31: 2.3.5.C Novoflex
A third example is the Novoflex system, which used the optical cell of the Telyt lenses, made for Visoflex and R-bodies too.
Here we can identify one of several strategies that Leitz choose to use: cooperation with several lens manufacturers. In hindsight it is easy to comment upon the decision of Leitz to neglect the zoom lenses for the R-system. The official position of Leitz regarding this type of lenses was the statement that the optical quality of Leitz lenses with fixed focal length could not be attained by the zoom-lens. I would regard this as a marketing act. Technically Leitz were not equipped to design zoom-lenses that lived up to their standard of optical quality at those days. On a more philosophical level, I would venture to remark that the zoom lens with its physical bulk, its many lens elements and complicated engineering and indeed its lower quality, did not fit in with the Leitz philosophy of lens design. Leitz tried to use the least possible lens elements to get optimum results by studying the character of a lens system in depth first. The basics of a complex zoom lens are very difficult to study as there are so many variables involved. A zoom lens can be designed with optical compensation or a mechanical compensation as a tool for correcting aberrations. When the first zoom lenses arrived on the market, both methods were used, but none of them gave the results Leitz was looking for. The optical compensation did not give exciting results, but the mechanical one was an engineering nightmare, at least in the Leitz tradition of mechanical precision.
Figure 32: 2.3.6
A Angenieux Whatever Leitz' view on the zoom lens, the market demanded a range of zoom lenses and so Leitz had to offer them in order to broaden the appeal of the R-system. The first supplier of zoom lenses was the French company Angenieux.
This company offered three versions:1:2.8/45-90mm, 1:2.5/35-70mm and 1:3.5/70- 210mm. The cooperation was quite limited. Leitz allowed Angenieux to use the bayonet-mount of the Leicaflex, and promoted the sales of these lenses. The relationship with Minolta was much tighter. There was in fact a technology transfer deal, and we may remark that in optical matters Minolta learned more from Leitz than the other way around. The Japanese contacts however established a base on which Leitz and later Leica could expand their contacts with Japanese suppliers. The Minolta zoom lenses were delivered as Leitz lenses and they were 'adopted' as Leitz products. The optical performance of these lenses was for many intents and purposes good enough for a broad range of users. Branded as Leica lenses, they did not perform with the characteristic Leica fingerprint. And critical users might question the choice of the Leica system if the backbone of that system consisted of third party lenses.
Figure 33: 2.3.6 B Minolta
Figure 34: 2.3.6.C Schneider
Figure 35: 2.3.6.D Zeiss
Leitz clearly lacked knowledge and possibly resources to expand the Leicaflex and Leica R system with only Leitz designed lenses. The Mirror lens, the Fisheye lens and the 15 to 24 wide angle lenses came from various sources (Zeiss, Schneider and Minolta). The same strategy was followed with the zoom lens. Angenieux, Minolta and were the suppliers. There is some discussion if the third-party lenses were just rebranded designs or if Leitz added some value to these lenses. The Angenieux 1:2.8/45-90mm was the first in 1969, in 1974 followed by the 1:4.5/80-200 from Minolta. The next was the 1:4.5/75-200, again by Minolta and the redesign in 1984 while the 4/70-210 had additional Leitz input? The 3.5/35-70 had two versions, one in 1982 and the second in 1988. (both Minolta design). (The 3.5-4.5/28-70mm in 1990 was a Sigma product.) We have to wait till the next period to see what Leica designers can do with a zoom lens after they had acquainted themselves with the technicalities and optical properties. The very wide angle lenses for both M and R were supplied by Schneider (21mm) and Leitz also used Schneider designs for the wide angle lenses with perspective control. Leitz did not design their own zoom lenses, and at first used Angenieux designs. This strategy of cooperation and adoption of lenses from third party suppliers continued and expanded during the seventies and early eighties with several Minolta designs, (fisheye lens, wide angle lenses, mirror lens and zoom lenses) and a Zeiss super wide angle (15mm).
In 1949 Max Berek died and Dr. Zimmermann took over. Some years later a second optical design department was established in Canada under the direction of Dr.
Walter Mandler. The fifties presented several challenges to the Wetzlar company.
The introduction of faster means of computation (desk calculator and electronic computer) allowed the exploration of better designs and as a result deepened the theoretical understanding of aberration theory. This research could be transformed into commercially viable designs if new glass-types were available and if the small engineering tolerances that were required could be held in manufacture and assembly. And last but not least, the demands of the Leica users for ever better imagery intensified the exploration into the realm of image assessment. The arguments for the establishment of the Midland branch have been the bleak cold war prospects in Europe and the prominence of the American market for Leitz. The choice of Midland as a town has been a decision of Leitz himself as he had some private relations with the town. Midland was set up as a design and production facility and many lenses have left the factory since the first days. The first lens to be manufactured was the Summarit in early 1952 with serial number 987101. After about 1955 some fundamental changes occurred. One of the most far-reaching is the gradual shift of balance of camera lens design to the Canadian factory. Many of the lenses for the M-system and a fair proportion of the lenses for the R-system originated from ELC (Ernst Leitz Canada). Mr. Mandler, who already worked in the Wetzlar factory when Max Berek headed the department, went to Midland, Canada in the mid fifties to organize and manage the optical department there. Both Wetzlar and Midland used electronic calculators and later computers for faster and more elaborate computations. At first the speed of the computer was employed as a convenient replacement of the older logarithmic tables and to speed up ray tracing.
Later algorithms were programmed to compute and analyze the aberrations themselves and in a third stage additional computer programs were written to optimize (automatically correct) optical designs. In Wetzlar the foundation of aberration theory and its corrections originated from the design and construction of microscopes and its lenses. The specific concerns and characteristics of 35mm photography were added to this body of knowledge and experience in proprietary programs. In the mid seventies prof. H. Marx almost single-handedly designed the computer programs that are still used by Solms designers, all be it in much improved format. The COMO program is the heart of the computer programs in use now in Solms. Correction, Optimization, Minimization, Orthogonalisation are the keywords in the name.
Figure 36: 2.3.7: Marx pictures on CD!!!
Research into exotic designs continued in both departments. Looking at the list of prototypes, it seems as if the Wetzlar people were deeper into the fundamental research. In Wetzlar we find lenses with three aspherical surfaces, and specially designed glass composites. The prototype 1.2/50mm lens with aspherics and segmented glass is a fine example of this drive to the limits of design and manufacturing technology.
Figure 37: 2.3.7.A lens picture
Figure 38: 2.3.7.B drawing
Meanwhile in Canada, the designers adopted the optimization programs at an earlier stage and so were often able to design lenses faster than their Wetzlar counterparts.
ELC designed lenses were also optimized for economical manufacture. More so than the Wetzlar designs. In a period that Leitz became more and more vulnerable to the prevailing market forces, this was an important consideration. Recall that around 1970 the M-system was far beyond its zenith and the R-system faced stiff competition. The M5 and CL bodies needed new designs (resp. more retro focus lenses and more compact ones) and the Leitz philosophy to stick to high quality fixed focal lengths and thus neglecting the trend of the zoom lenses, put a heavy load on the design teams at both sides of the Atlantic. Commercial considerations however forced Leitz to include zoom-lenses in the catalogue and just as a decade earlier with the Schneider cooperation, Leitz added some Minolta zoom-lenses to fill the gaps.
The glass lab existed from 1948 to 1990. The Leitz glass lab is the focus of many stories. The glass lab, by its very dimensions was not equipped to handle or melt large blocks of glass in any quantity. The true role of the glass lab was the research into the composition of new glass types, with properties that could be used by the optical designers to help them with the computation of new lenses. This role was an important one and many of the glass types now in the catalogues of large manufacturers like Schott or Corning have been first explored in the Leitz glass lab.
One may say that without the glass lab the Leitz designers would not have been able to acquire the tools and the knowledge to improve the Leitz lenses. The original building is still to be seen on the old Leitz Wetzlar Industry Park (Werksgelände), tucked away between the imposing main ten-storey buildings. It has an area of about 10x20 meters and these dimensions indicate its role. There were four small melting pots, that could handle 5 to 10 kilograms of glass at a time. The dilemma for the optical designer is that he needs special glass to optimize his designs, but only in small quantities. The direction of research for Leitz was in the exploration of high refractive glass with very good colour transmission. That proved to be a problem and only when one started to use lanthanum oxide and (radio-active) thorium oxide, both characteristics could be combined. The use of rare earth additives (lanthanum) is an invention of Kodak in 1938 and later widely used by other manufacturers.
Figure 39: 2.3.8 A glass map of Schott two versions!
Figure 40: 2.3.8.B Leitz additions
The glass lab did introduce many new formulations of special glasses that could be more easily machined. Often glass with exotic specifications can not be handled in the manufacturing process, due to specific problems: glass too brittle, glass starts to discolour, etc. As the lab had no production capacity, they had to make an arrangement with a glass manufacturer, like Schott or Sofirel or Corning who would then produce the glass under several types of agreement. The true significance of the glass lab is for the optical development that it helped to support and even foster and for the microscopy department where one needs glass of more demanding specifications and tolerances than is needed for photography. Only very few glass has been melted there for production purposes. The well-known Noctilux glass (900403) has been produced for some time in the glass lab, as Schott could not comply with the specifications. Later the glass has been replaced by one that could be obtained from regular sources.
The design department needed about two years and sometimes longer to complete a new design. Often the designers had to address other topics and could not work continuously at the project. Sometimes optical problems proved to be difficult to tackle. And sometimes one had to make a fresh start At least a year was needed for testing and adjusting the production cycle to this design and then another period was required to stabilize the production to the manufacturing quality that was expected.
Figure 41: 2.3.9.A Centering of lenses.
The manufacture of the lenses was separated, physically and as organizations, from the design department. The optical designers were primarily focused on the goal of optimum image quality and left it to the production engineers to find a way to hold the necessary tolerances for machining and assembling the mechanical and optical parts to the required specification. It is clear that some professional tension existed between both departments. The optical people might specify a certain glass, because it had the required optical properties. During the processing stage, one could discover that the glass would discolour a bit, and the transmission properties were altered. In such a case, an alternative glass had to be searched for. Or the rim of the glass was too thin and would give problems when fitting the lens in its mount. For a classical Double-Gauss design, the optical department would specify the thickness tolerance of the cemented doublet (the middle part) as 0.1mm and the sum of both doublets as 0.02mm. Such a matching scheme is only possible as lenses are manufactured with tolerances on both sides and this matching may be labourious and error prone. The mechanical department then would ask for a different set of tolerances.
Figure 42: 2.3.9.B Checking mounts
Thicknesses of lens elements and spacing are very critical and the natural tolerances within a production process need to be taken into consideration. A thickness tolerance of 0.1mm is acceptable for larger scale grinding of lenses, but to keep a tight tolerance of 0.01mm in even a small production run, is a hell of a job and a very expensive one too. The optical designer has the goal to find the best optical performance, but also to create an optical system that can be manufactured economically. The division of labour asked for an elaborate interaction between the departments. After the lens is computed on paper a few prototypes are manually assembled, which includes the grinding of lenses. When prototypes are assembled, elaborate testing in the laboratories (to check the residual aberration, but also to test the quality of manufacture) and in practical photo shootings (to check the visible image quality) is required. If the visible image quality is not as expected (compared to predecessors and other lenses) the defects are noted and the optical department has to change some of its parameters. Or the lens may be optically on target, but it is too difficult to produce. There are no clear-cut solutions in this interplay of mathematical and engineering parameters. Sometimes an optical redesign would take a long time to accomplish and might not deliver the required improvement. In such a case it would be cheaper to make educated guesses and make new prototypes on the basis of these proposed changes.
Figure 43: 2.3.9.C Interferometric testing of surfaces. Interferometric
To understand the magnitude of this task you may reflect on the fact that the optical designers are looking at the sub-micron level when they discuss tolerances and changes (much less than 1/1000 of a mm). The mechanical engineer however will consider tolerances of 1/100 of a mm as quite exacting. This 'engineering' gap of a factor of 10 to 20 in requirements, presented a challenge to the Leica engineers working in the optical and mechanical departments. A challenge by the way that still exists today. As Leitz took very great care that the lens at the end of the assembly line was indeed within the specified tolerances, the process of cost cutting had its 'natural' limits. Lens assembly at Leitz was and is a labour intensive process, that only a qualified and experienced workforce can handle. Any new lens design requires that the workforce has to be retrained to produce and assemble the lens. A designer can easily create an exciting design that is impossible or very difficult to construct. Lens elements are polished on a single block and the more elements can be polished in a single run, the cheaper it will be. But then the curvature of the elements should be as flat as possible. That limits the designer's freedom. Any lens element or steel or brass or aluminium component has some deviation from the zero-tolerance norm, however careful the production process. A clever designer has to allow for some tolerance and make sure that image quality does not drop beyond a certain specified level, as some manufacturing deviations are to be expected. This is part of the optical design itself. But many components will have different values within the tolerance bandwidth. Throwing away is no option, so the technique of matching and compensation is required. This matching and checking and correcting takes time and the design should allow for this technique. A common method at Leitz was to assemble lens elements in sub-units that could be individually and manually adjusted to the required specifications. Leica lenses are solidly build with finely machined components. These characteristics are the result of the design and production methods used then and exemplify the level of quality Leitz did build into any lens.
There is a persistent view that the Leica lenses till the sixties are better built than later series, with a 'cost is inconsequential ' consideration. That would be economical suicide of course. But is there a grain of truth is this view. As with many Leica topics, a clear-cut answer is not easy. Brass and aluminium and a layer of chrome give an impressive appearance and feeling. Part of the truth is this: older designs were assembled form subassemblies, that housed some of the lens groups. This was done to be able to adjust the lens elements and lens groups to the required tolerances as specified by the optical department. Manufacturing technology of mechanical parts, in those days, could not hold the very fine tolerances needed. The same applies to the individual lens elements. The assembly workers used parts that were classified into tolerance groups, finely graded in plus and minus tolerances so as to combine a suitable pair to match the numerical demands. As so many lens elements have to on stock to help the matching process, costs will be higher too. It is true that Leitz built their lenses with high quality materials and with great precision, but the manufacturing cost of the lens governed the production process.
The level of performance of the lenses for the R and M systems had improved over the years to an enviable level and it is quite easy to understand that any further improvement in image quality required more and more study in the optical department. It is one task to design a new or improved version with a lower level of aberrations as calculated. It is quite another task to transfer this improvement into production, given the much tighter tolerances and it is a third task to make these optical improvements clearly visible for the user in practical shooting assignments. It is the same story as with an athlete. To cut the time for the 100 meters from 13 to 11 seconds takes a short training period.
To go from there to the sound-barrier of 10 seconds takes years of intense training.
So it is with a lens. To control the classical third order aberrations is relatively easy, once you have understood the principles. To get a grip on the next level of aberrations is much more complicated. When we take a closer look at the Leica lens history we note a slightly different pattern of evolution for the M-system. Here we see four trends: the change to retro focus designs in the wide angle group of lenses, the simplification of optical systems for many lenses in the 35 to 90mm category with some improvements, a markedly higher performance in the 135mm group and a special effort in the 50mm group of lenses to advance the higher speed lenses to a class of its own. For the R-system we see some similar and some specific trends.
Again we see a simplification of designs with the additional aim to provide enhanced performance. Then we note the adoption of third party lenses to close gaps in the proprietary lens-line to provide a comprehensive system of lenses and a specific strategy to enhance performance of the longer focus lenses markedly by apochromatic correction. The complete strategic neglect of the zoom-lenses may seem strange at first, but can be explained if not excused by the concentration on the core strength of the company: fixed focal length systems. Still Leitz had a special team of people that studied the theory and possibilities of the zoom lens. It seems as if Leitz were reluctant to explore new worlds. The invention of the Correfot is another example of a Leitz innovation, that was not developed further. When the M5/CL pair failed in the marketplace and the R3 succeeded the Leicaflex line, the spirit of the Leitz company faltered. With the M5 and the Leicaflex SL, Leitz tried to redefine the classic rangefinder concept and define the SLR-camera within Leitz parameters and in both cases had to admit that the Leitz approach failed to capture the market. Designs like the Noctilux 1:1/50mm and the Apo-Telyt -R 1:3.4/180mm were true to the optical mission of the company. The exploration of the ultra high speed lenses for M and R too (a 1.2/50 design for R has been contemplated) and the design of the best possible image quality by using special glasses and apochromatic corrections continued. Quietly however, a new level of possibilities for optical correction gave rise to designs of less spectacular specifications. The Elmarit-R 1:2.8/90mm (1983) and the Apo-Macro-Elmarit-R 1:2.8/100mm (1987) were of much humbler specifications, but they were signposts of the direction to follow. The Apo-Macro-Elmarit-R 1:2.8/100mm is the last lens that, supervised by Mr. Vollrath, left the Wetzlar design department. It became the standard by which all other Leica lenses were measured. At full aperture it delivers outstanding image quality over the whole image field with very high overall contrast. The outlines of larger subject details are recorded with almost 100% contrast transfer. And finer detail still is delineated with a rarely seen 95% contrast transfer. This high edge contrast is supplemented by a very crisp recording of the finest possible textural details that are rendered with very good clarity The last lens to leave the Wetzlar factory was a Summicron-M 1:2/50mm with serial number 3451920 at the end of 1987. The new owners separated the camera manufacture and optical design department from the Wetzlar microscope and instruments division and set up a new and independent factory in an existing building at the outskirts of Solms, about 7 kilometres from Wetzlar.
From 1980 to 1990, no new lenses for the M-system have been produced. If we look closely at the M-lenses, we note that the last lenses specifically designed for this system have been the Noctilux 1:1/50mm from 1975 and the Elmarit-M 1:2.8/21mm from 1980. The 2/50mm, the 2.8/90mm, the 2/90mm, the 2.8/135mm and the 1.4/75 were all developed in parallel to the R-system. The Summilux 1.4/75mm is the last lens that left the drawing boards of ELC. ELC became a manufacturing division and a design department for non-photographic lenses.
During this decade the introductions of new lenses for the R-system were quite few too. The 1.4/35mm (1984), the 2.8/280mm, the 2.8/100mm, (1987) and the 2.8/19mm were designed during this decade. The centre of optical excellence shifted back to Leitz Wetzlar, but the much reduced resources for R&D and the precarious state of the photographic department discouraged the pursuit of new optical designs and techniques of manufacture. In hindsight one has to make some critical remarks about the decision to split the optical design department over two continents. The official argument by Leitz for this division of labour is the threat of the Cold War and the possibility of a nuclear clash between the super powers. Leitz wanted to preserve the optical expertise of the factory and thought it wise to duplicate the design department. A more practical argument might have been the growing demand for military optical equipment by the American army. The Canadian optical department developed, only partially influenced by the Wetzlar department their own design philosophy, and used different tools to compute the lenses. The fact that many lenses were designed in Midland and manufactured in Wetzlar, certainly induced some tension into the production cycle. It was however accepted practice to split the design and production departments into two groups with different and separate responsibilities. The dominant position of ELC during the period 1955 to 1975 gave the Leica lenses a specific flavour and character. It also helped the Wetzlar team to pursue fundamental research into optical design and aberration theory. This work laid the foundations for the next generation. No doubt the practical dominance of the ELC designs, frustrated the Wetzlar engineers and designers. In practical testing the ELW designs were often better than the ELC counterparts. Still the Midland proposals were selected as the production versions as they could be produced more quickly or efficiently. And that was an important consideration in those days. The theoretical studies in the Wetzlar department became, in a certain way, a goal in itself and the famous optical lab was the result. It did not live up to its promises however and it was finally closed. The head of the lab, Mr Thomas, noted in LFI (7/1982) that the role of the lab had been reduced to the testing of lenses of the competition.
Lothar Kölsch became the new Head of the Optical department at Leica, Solms. The first lens to be produced by the new team, working in the Solms factory, was the Summilux-M 1:1.4/35mm aspherical. The patent is filed in 1991, and its inventor is identified as Walter Watz, one of several unknown masters of optical design. As an important aside I would like to draw attention to the many anonymous individuals, who worked in Wetzlar and who now work in Solms, outside of publicity. Their tireless research into the foundations of aberrations and their creativity in transforming that knowledge into an optical system, consisting of glass and metal, that will satisfy the demands of exceedingly critical users, has to be mentioned and acknowledged.
Figure 44: 2.4.1.A Summilux aspherical
This first Summilux with two aspherical lens surfaces is evidently the direct descendent of the original Noctilux 1:1.2/50mm from 1966. During the design stage of the 1.4/35mm lens, it became clear that the use of aspherics alone would not bring the desired improvements. A high speed lens with a focal length of 35mm is more difficult to correct than a 50mm lens, because of the increased influence of zonal aberrations. One can identify these zonal errors when one takes a look at the performance of the original 1.4/35mm lens for the M-system. The new design performs very well already at the wider apertures, with a high contrast image at full aperture and a clear, crisp definition of finer detail in the zonal areas. The revolution of the aspherical design is not so much the use of the aspherical surfaces, but the radical departure from the classical and time honored Double-Gauss principle. The system comprises nine lens elements in five groups, with the first surface of the first element and the last surface of the last element of a concave shape. The design is more symmetrical too, which helps reduce some aberrations. The path of the light rays, passing through this system, is more 'relaxed' than in a traditional Double- Gauss system, a characteristic, that is not obvious and of a more philosophical nature. It does signify a new aspect of lens design at Leica. That is the study of and reflection on the fundamentals of a design. The current approach to lens design in Solms is characterized by several interlocking aspects. The most important trait is the search for the most simple solution for the required lens parameters, as maximum aperture, focal length and physical size. To find such a solution, the designer needs to study the intrinsic behavior and possibilities of the optical system. Supported by quite sophisticated and indigenous computer programs, the designer will then search for an optimum solution, that can be manufactured within the required tolerances.
New insights into the character and potential of the glass types available on the market bring additional advantages for aberration correction. If I had to single out the most important characteristic in the current design approach, it would be the tight cooperation between the optical designers and mechanical engineers. The second factor which helps explain the performance and the cost of a new Leica design is the principle of manufacture, where the fabrication process is adapted to the requirements of the selected glass and of the tolerances needed. This is a large step forward when compared to the previous method of manufacture that was the same, irrespective of the specifics of lens design and glass manipulations.
Figure 45: 2.4.1.B grinding the aspherical
The two aspheric surfaces were grinded and polished mechanically on a spherical glass surface. This method was an improvement on the original manually grinded aspherics, but still quite labourious, with a high rejection rate. The second version, recomputed in 1994, employed a new press-molding technique, in combination with Hoya glass. Leica has been heavily involved in the invention and development of this technique.
Figure 46: 2.4.1.C 2/180
From 1993 to 1996 the designers gave all attention to the renewal of a number of lenses for the R-system. A new series of high speed telephoto lenses with exceptional apochromatic correction and high speed were developed. The Apo-Telyt-R 1:4/280mm is probably the best corrected lens in the whole R-stable. This one is indeed diffraction limited. The Apo-Summicron-R 1:2/180mm (1994) and the Apo- Elmarit-R 1:2.8/180mm (1998) offer performance that is truly a quantum leap ahead of the predecessors and do indicate the mastery of the optical designers. These lenses also embody new techniques, like internal focusing that is in addition employed for further aberration correction and macro-functions. New mounting techniques deliver a very smooth, fast and accurate focusing operation.
Figure 47: 2.4.1.D 2.8/180 apo
In the field of zoom lenses, Leica has made impressive progress and reduced their dependence on third party suppliers. And one might add, with a vengeance as the new variableness, including the first one, the Vario-Apo-Elmarit-R 1:2.8/70-180mm, equal and often surpass the image quality of the equivalent fixed focal lengths. In quick succession the family is expanded with a 4/80-200 and a 4.2/105-280mm version. It does show that as soon as the designer has studied and understood the basics of a design, it is relatively easy to develop several versions. This same technique of spin-off we see in the Summicron-M 2/35mm ASPH, which is a variant of the 1.4/35mm ASPH. The Elmarit-M 1:2.8/21mm ASPH and 1:2.8/24mm ASPH share family characteristics and especially the 24mm lens delivers outstanding imagery and is a landmark design.
Figure 48: 2.4.1.E Vario 70-180
Figure 49: 2.4.1.F vario 80-200
The first combination of apochromatic correction, which is primarily a glass selection technique and the use of aspherical surfaces which can be used for several purposes (see chapter 1.2) we find in the Apo-Summicron-M 1:2/90mm ASPH. This lens is arguably one of the very best lenses Leica has ever designed, as of this moment of writing. Already at full aperture it delivers outstanding quality that even surpasses the performance of the Summicron-M 1:2/50mm at 1:2. In the same league we can place the Apo-Telyt-M 1:3.4/135mm, a compact and light weight telephoto lens, that approaches the old dream of a lens that does not improve on stopping down. At apertures from 1:5.6, the Apo-Telyt is only slightly better than the previous Tele-Elmar-M 1:4/135mm (thanks to the apochromatic correction, which brings a small but visible improvement, even at smaller apertures). For most purposes these differences are not that important. The exceptional performance of Leica lenses is best appreciated at the wider apertures. To deliver this quality, the manufacturing tolerances, the production technique and the quality checks must all match. The lens that in my view exemplifies this marriage of mechanical and optical expertise and production technology is the new Tri-Elmar-M 1:4/28-50mm. Its image quality is better than most Leica-M lenses of comparable fixed focal length.
But its mechanical layout is the true measure of excellence in this case. This lens can be used on all Leica M bodies, even the earliest ones, like the M3. The rotating ring that selects the different focal lengths has to accommodate different spring tensions and cam curvatures. The solution is mechanically very complex, but it brings zoom convenience in a rangefinder model and so defies obsolescence. The engineers however have designed an even better solution, which will be introduced at Photokina 2000 and sports improved ergonomics and redesigned internal mechanics.
Figure 50: 2.4.1.G Tri-Elmar
Many observers of the Leica world would select the two Noctilux versions as the defining icons of the optical excellence in the rangefinder domain. I would beg to differ. The Noctilux lenses are optically quite good and do radiate exquisite mechanical engineering and optical expertise. The Tri-Elmar, Elmarit 24mm and Apo-Summicron 90 and Telyt 135mm point to an exciting future direction and are more versatile and effective in everyday use. The position of the R-system is not so easy to sketch. The current Solms-designed vario-lenses are outstanding products, but physically at the limit. Now Leica will tell you that this volume is needed to deliver the optical quality and I do not question this statement. Still the challenge is twofold: to design fixed focal lengths with even better performance than the current vario-lenses is not easy and the efforts and cost must be offset by a sizeable sales volume. The demands for designs of variableness are threefold: a wider zoom range; ergonomically convenient to use in handheld situations; small physical dimensions and comparable, if not improved performance versus the fixed focal length lenses.
These requirements are very difficult to combine in one set. The current range of Rlenses is composed of three groups. In the first group, the vario lenses, we find new lenses, designed by Leica itself and some lenses supplied by third party manufacturers. In the second group, the fixed focal length, we have a number of recent developments, like the 2.8/28mm and the 1.4/50mm, both of outstanding quality and a family of telephoto-lenses in the 180mm to 280mm class of really superior performance. A number of the older fixed focal lengths lenses, however, begins to show their age, like the 35mm lenses, the 60mm and the 80mm. As with the vario group, , there are a number of lenses from third parties, like the 15, 16 and 24mm and the PC 28mm. The third group consists of the module system from 280mm to 800mm, which is specifically designed for economy of cost and flexibility of use. This system has added value if the user needs more than one focal length and so the target group of users is limited.
The improvements in image quality in current Leica lenses are visible for anyone with an experienced eye. Some Leica users might defend the idea that the older lenses are as good as, or even better than the current ones. Image characteristics, like 3-dimensional representation, plasticity and smooth unsharpness gradients, cited as being instrumental for the unique fingerprint of older Leica lenses, are supposed to have disappeared. Some observers have tried to discern two different schools of design theory, the German and the Japanese philosophy, the latter putting all emphasis on image contrast and the former school going for a smoother image quality. In all fairness, these two schools do not and have never existed in this extreme juxtaposition. Of course designers differ in their balancing of aberrations and the rigor of aberration corrections. It may be the case that Japanese designers follow a different route to design a lens. But generally any designer everywhere has the same type of tools and uses the same aberration theory. Why and how are the current Leica lenses improvements on the older designs and how do they differ from others? Modern optical design is a creative activity, based on experience, insight, a very thorough knowledge of optical theory and even a sprinkling of luck. We know that optical systems for photographic purposes are not completely aberration free.
(There are exceptions. Some R-lenses, and many microscope and telescope lenses, are indeed diffracted limited (which amounts to stating they are aberration free).
Most photographic lenses will exhibit, after correction and optimization, some residual aberrations. These residuals have to be carefully controlled and balanced.
The optimization techniques will help of course, but no computer program can improve on a design that is not promising from the start. Leica lens designs will start a design with the absolute minimum of lens elements. Having less elements one can study the aberration content and the contribution of every lens element to the aberrations more carefully and more effectively. Current computer programs are very powerful and can make the best of any design by a kind of brute force method. By using more and more lens elements to counter the aberration content, a lens can be made to perform quite satisfactorily. It will not show the finesse and elegance of design of the Leica lenses and it most certainly will not perform on the same level.
22.214.171.124 Progress in design methodology.
The art of designing optical systems is a most fascinating subject. The lens designer today still uses methods, concepts and terminology that have been developed in the previous century. The employment of high speed computers and very sophisticated software has freed the designer from the drudgery of the past, when slogging through labourious computations to trace the light rays, using tables of logarithms or mathematical approximations was the only way to design a lens. The current practice of optical design then is a fine example of a successful amalgamation of a century-old (time honored) science and a very potent modern technology (the high-speed computer). The genius of Gauss, Clark, Rudolph, Lee, Berek and others should be acknowledged with great admiration, as they combined quite crude computational methods with a most profound insight into the fundamentals of aberration theory.
The computer, as we all know, is a very sophisticated device for number crunching with phenomenal computational speed. It took Rudolph and Lee and later Berek at least five years of dedicated attention to trace enough rays with the required precision to get a good grasp on the aberrations in the optical system. Nowadays a potent personal computer can trace 600.000 skew ray surfaces per second. In 's time this amount of skew rays would take a big part of the lifetime of one designer. Before the advent of the computer a lens would be designed and evaluated by tracing real (trigonometrical) geometrical rays from lens surface to lens surface. In the past, every calculation of a surface took a few minutes. You need to trace a few hundred rays through all surfaces, often more than 10 or 12 surfaces and do that again and again after you find that the image points you calculated so diligently are still distorted by aberrations. All the points calculated with this method are meridional rays, that is rays that lay in the same plane (are coplanar with) as the optical axis. When we trace a ray on a flat piece of paper, as we all do, the paper plane is the meridional plane. This a two-dimensional plane. But we also have skew rays, that is rays that go into the lens from an oblique angle. Now we need three-dimensional ray tracing, which is almost impossible to do by hand or even pocket calculator. So in the past these rays were not traced at all, or all kinds of 'tricks' or approximations were used to study the skew rays. Many of the troublesome aberrations (coma, astigmatism as examples) are caused by these skew rays. So in the not so distant past ,designers had to accept they could not all the information they needed to fully correct a lens. So working with imperfect knowledge, the designs could not be as fully corrected as was theoretically feasible. If we look at the older designs with modern expectations, their image quality may be a bit disappointing. The designers of those days (1930 till 1960) compensated their approximation strategy with admirable creativity and let us call it gut feeling to select basic designs that work and serve the photographer well. Leitz was one of the first to implement a computer in order to support the designers, The Zuse Z5 was introduced in 1953 and helped the designers to compute the oblique pencils of rays.
Before the introduction of the computer Leitz designers used the Seidel-Theory to circumvent part of the complex computations of oblique rays. This knowledge and experience proved to be of great value after the Z5 became the preferred tool for ray-tracing. It is fascinating to know how this work was organized at Leitz. The romantic idea of one designer working for years on his design is of course a myth. In reality, the chief designer supervised a group of workers, mostly women, who carried out a good part of the calculations. The chief designer gave instructions and got the partial results of every ray tracing equation from them at the end of the day and then decided to proceed or adjust his design. The resulting design is invariably a compromise, composed of both known and unknown factors. The development of lens design methodology interacted with the development of aberration theory and both allowed lenses to be designed with a much higher image quality. Now we have two new areas to give close attention to. The first area is hardly ever mentioned, but in fact it might be designated as the true revolution in lens design. The manufacturing processes (grinding, polishing, coating, centering) and the mounting procedures are of paramount importance for the image quality . Studying fabrication tolerancing to ensure that the image quality as defined by the designer, is a major part of the design process. Here the art of optical design and a superior grasp of the manufacturing process and the limits of tolerancing join to create the results we see and expect (if not demand) from current Leica lenses. The Leica aspherical lenses may only be serviced in the factory itself. An indication that the mounting procedure is quite demanding. In this case we see clearly the value and necessity of the manufacturing processes in boosting or supporting the higher level of image quality possible.
126.96.36.199 Progress in manufacturing processing and mounting techniques.
I have remarked several times and documented in the lens reports, that Leica lenses are designed for higher contrast at much higher frequencies than in the past. A design that is can record higher frequencies with high contrast needs very small tolerances. Contrast of very fine detail is very sensitive to focus and alignment errors.
Figure 51: 188.8.131.52.X precision grinding
Decentring is very bad for the ultimate image quality. In the past, when manufacturing tolerances were not so tight, groups of lens elements were mounted in their own subassemblies. At the final mounting stage these subassemblies could be adjusted a bit to compensate for decentring and other errors. An optical surface has two related qualities: accuracy and quality. Accuracy refers to the dimensional characteristics: is the surface uniform in its radius value?. Quality refers to the finish of the surface: is the polish incomplete (rough spots), does it have pits?
Figure 52: 184.108.40.206.A Interference patterns check
Figure 53: 220.127.116.11.B Checks for centring etc
If the surface quality is not immaculate the following process of thin film coating with its thinness of several microns will also be irregular. Relatively speaking of course: we are dealing with wavelength dimensions where a micron is a big distance.
Some requirements at Leica demand that a polished lens must be coated within hours after the polishing as the surface can deteriorate when not protected immediately. A Leica lens is now designed by a team of optical and mechanical engineers who work together from the start. The production engineer has the last word: if the tolerances are unrealistic, the optical designer has to start all over. In the past the departments were more divided. Then the optical designer designed the lens as he deemed necessary according to its state of aberration correction. Then he almost literally would hand over the design prescriptions to the production department. Sensitive glasses with strong radius and thin ends that were very difficult to mount without stress gave the designers of the mounts headaches. And sometimes the designed lens could not be built within required tolerances. One had to accept a slightly lower image quality or a production with a much higher rejection rate. At the beginning of this section I mentioned that physical ray tracing is still the approach used by designers to study and correct aberrations. Physically we should not look at individual rays but at the total energy that flows through the lens at one single instant in time. When we take a picture all energy reflected from the subject enters the lens in one instance (1/250 sec as example) and the total light energy flows through the optical system in one flash. Leica designers take care that this flow is eased from lens element to lens element. Abrupt changes in the path of a ray that occur when glasses of highly different refractive indices or greatly varying curvatures are employed are avoided. One might see a Zen approach here.
Figure 54: 18.104.22.168.C complex mount
Can modern Leica lenses be improved? Yes they can and Leica is constantly searching for economical means to produce improved versions of existing lenses and to expand research into exciting new designs. Just as with the Olympics the levels of achievement are set higher every time, so these new generation Leica lenses also set the quality level a few notches higher.
22.214.171.124 Procedures for testing a lens.
When a lens is designed, it is obvious that you calculate with the exact figures, that is you assume a zero-tolerance. After the ideal design, you have to allow for fabrication errors and tolerances. It is also obvious that if you optimize the design to the utmost level, any manufactured lens will be below tolerance and these errors will degrade performance. So the assumption of fabrication errors must be part of the design process. A small list of fabrication errors would comprise: surface curvature errors, index and dispersion errors, thickness errors of the lens elements or air spaces, axial displacement errors, surface tilt errors (decentring). All of these errors occur and have to accounted for in the design and manufacture. The nature of fabrication errors implies that errors occur at both sides of the target figure. If a tolerance of 5% is specified, then in reality the values will be + 5% around the target. Some of these errors cancel out, and sometimes you have a lens that is above the target value and sometimes below this norm. You may however not assume that the spread around the target is normally distributed, with the same number of lenses above and below he target. Leica specifies the target line very high and so most of the lenses will be a bit below the norm, but well within the tolerance band.
Figure 55: 126.96.36.199.A Testing MTF
There is however a second method to handle production errors. That is the use of compensators in the lens. One could designate one lens-element or group of lenses as a mechanical compensator and use the possibility to shift this element a little or one can shift the whole lens s bit, which is identical to a focus shift, which can improve the optical performance significantly. (see the chapter 1.2). Leica uses all these methods of testing a lens and adjusting the parameters. Every lens that leaves the assembly department is tested. For lenses that have a stable performance pattern and are relatively easy to assemble, the projection test is used. A complicated test pattern (of Leica design) is projected through the lens on a wall and studied at close distance to check for errors. If the reproduction of the pattern is within specifications the lens is passed. Some types of lenses are individually tested and adjusted with an MTF device. Here the method of focus shift adjustment is employed. The optical cell (that part of the lens that comprises the glass) has its own effective focal length and the mount of the lens has a mechanical flange focal distance. The lens is adjusted for best focal position (optimum focus plane) with the help of very thin shims (0.01mm) that can be inserted between the bayonet flange and the lens mount. The target value is the contrast value. These measurements are done for 8 circular positions on the lens in steps of 45o. After the lens is adjusted for optimal focus, a new series of contrast measurements is conducted to check for decentring and other errors. This procedure ensures that every lens meets the specifications, stipulated at the design stage.© Erwin Puts
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