Brand
Pentax cameras came from Asahi Optical, founded in November 1919 by Kumao Kajiwara. Its first camera, the 1952 Asahiflex, was the first Japanese SLR to use 35mm film. The Pentax name started as an East German Zeiss Ikon trademark, a blend of pentaprism and Contax, and Asahi bought it in 1957. The Spotmatic of 1964 metered through the lens on the M42 screw mount. In 1975 Pentax switched to the K bayonet with the K2, KM and KX, and the K1000 joined in 1976. For years photography courses recommended or required the K1000, because its manual controls make you learn exposure. Pentax also built the 6×7 from 1969 and the 645 from 1984. Hoya absorbed Pentax in 2008, and Ricoh bought it in 2011.
7 cameras we cover.

Pentax · 35mm SLR
Meter onlyPentax K mount · 1976–1997
$150–$250 typical ask
224 on eBay

Pentax · 35mm SLR
Meter onlyM42 screw mount · 1964 to the mid 1970s
$80–$200 typical ask
173 on eBay

Pentax · 35mm SLR
Backup speedsPentax K mount · About 1980 to the mid 1980s
$80–$130 typical ask
140 on eBay

Pentax · 35mm SLR
Meter onlyPentax K mount · 1976 to the mid 1980s
$230–$350 typical ask
171 on eBay
Pentax · 35mm SLR
Battery neededPentax K mount · From 1985
$55–$140 typical ask
197 on eBay
Pentax · Medium-format SLR
Battery neededPentax 645 mount · From 1984
$400–$800 typical ask
127 on eBay

Pentax · Medium-format SLR
Battery neededPentax 67 mount · 1969–2009
$625–$1,225 typical ask
217 on eBay