Classic Pentax KX with K-series 35mm F3.5 lens. The following year came the M series which offered the same manual focus, manual aperture functionality with smaller and lighter designs. In 1983 came the "A" setting on the aperture ring, offering shutter priority and program operation. The camera could now automatically set the aperture if desired. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.