The XA, introduced in 1979 was the benchmark of the series containing a true rangefinder focusing mechanism and an aperture priority exposure system within its tiny case. It had a six element Zuiko 35mm f:2.8 lens, a CdS exposure meter and a shutter to 1/500. The aperture is changed thanks to a small lever. It is also possible to compensate the exposure by two ways : a lever at the bottom plate of the camera ensures a + 1.5 EV back light ; the ISO sensitivity lever, at the bottom of the lens, allows to change the value easily to under or to overexpose the frame. A self-timer is also available. Accurate focusing in a pocketable design, combined with convenient autoexposure, made this a very successful model. - camera-wiki.org