The Polaroid SX-70 1972 and the Alpha edition was released 5 years later in 1977. Like the SX-70 the Alpha is an Instant film camera that is compact when folded and a SLR. It uses the same 4-element glass, 116 mm, and f/8 lens. It also has a focus dial and a split screen range finder circle for the through the lens setup. The lens ring is graduated in feet from 1 foot to infinity but has a 10.4-inch (26 cm) minimum focusing distance. There is also a Lighten / darken control wheel setting but is best to keep in the center for the first picture. All SX-70 models feature an electronically controlled 'flash-bar' socket across the top front of the camera over the lens, for insertion of a 10-times use flashbulb unit. Polaroid - as well as other companies - made external flash units that plugged into this socket. Polaroid film is no longer feasible but they work with “Impossible” SX-70 type film.