The Yunon Optical Company Limited was established in Pei Tou a suburb of Taipei in 1974. The Trademark YUNON for cameras and photographic equipment was registered in the USA in 1984. By 1984 there were at least four major players in the US ultra-cheap 35mm camera market. They were Formosa Plastics Corporation (FPC), Yunon Optical Company, the New Taiwan Photographic Corporation (Ouyama 1982) and A..V. Lavec, (1978) which was a trademark initially associated with the manufacture of cooking equipment and cooking utensils.
The earliest date quoted for the Yunon YN 500 is 1984, and we know that production continued in 1985 and 6 because Yunon thoughtfully incorporated the year in its 'Quality Passed' stickers. There were three variations on the Yunon 500; this one, an all-black model, and one with an American Eagle and a 'Yunon Optical Glass Lens'. The clones include the Lynx PPL-500XL 'Color Optical Glass Lens' 1985 and 'Optical Color Lens' (plastic?) 1986, The Sceptre YN500 with eagle and a 'Sceptre Optical Color Lens' 1986, the Photoflex MX-35 with an 'Optical Color Lens' (Photoflex was founded 1985), the Impac with an 'Impac Optical Color Lens', the MVP with an 'Optical Color Lens' 1986 (this was a promotion of the Ford Motor Company), the Quartz and the Limp. All of these have the same series number 742677 on the lens ring which is not found on cameras branded by the other companies or their clones. The maximum aperture for the Yunon YN 500 is probably about F8 and the minimum about F22; the lens is about 42-45mm not 50mm; the viewfinder window is not in the correct ratio for a 35mm frame. As noted elsewhere, these cameras were built to be cheap and quality was low, so low that they are often dismissed as toys, but in competent hands they could produce results similar to those from a cheap Kodak Instamatic.