Originally posted by Baard-Einar Cool, a "AP"? That would be the first SLR modell from Pentax. How did you obtain that?
The 1957 AP was not the first SLR from Asahi. It was the first to bear the name Pentax. At that time, Pentax was a model name, not a brand name. It was so successful that Asahi chose to call all their subsequent cameras "Pentax". I believe that the AP was also the first Asahi camera to use the M42 "universal" screw mount. The AP was the first Asahi camera to have a pentaprism viewfinder, hence the name.
The company name remained Asahi Optical Company until the late nineties, when they finally changed the name to the Pentax Corporation. Now, the Pentax Corporation no longer exists. It is merely a brand name, owned by the Hoya Corporation.
In 1952, Asahi introduced the Asahiflex I, which had a waist-level finder, non-instant return mirror, and used the M39 screw mount. In the years between 1952 and 1957, there were several more iterations, including the Asahiflex II, the IIa. These were also sold by Sears in the US, under the Tower name.
BTW, the story I have heard is that Contax invented the pentaprism viewfinder and came up with two names; Contaflex and Pentax. They chose to use the first name for their own cameras and sold the rights to the name Pentax to Asahi. The rest, as they say, is history.