1980: 50mm f/2 aF Rikenon
Made by Ricoh in Japan, this was the first autofocus lens made to work with any manual-focus 35mm SLR that used the popular K mount. Using what the manufacturer called solid-state triangulation, it worked much like a traditional rangefinder, but with a sensor taking the place of the human eye. On to this sensor were projected twin images from two rangefinder-like windows. As the lens was activated, one mirror swung so that one image on the sensor moved in relation to the other. The sensor recognised when the two coincided as a point where maximum contrast was detected and information was passed to a motor that rotated the lens for correct focus.