Quote Originally Posted by Les Sarile View Post
According to Pentax history, Pentax came from Pentacon and Contax and was the source of their pentaprism design and not Edixa.

The original Asahi Pentax did in fact incorporate all those features + rewind crank and the more important instant return mirror first. All these features were incorporated into all successful cameras thereafter.

Other Pentax Milestones
Yes the 1957 Pentax used the layout introduced on the 1954 Edixa. There's no getting around the fact that the Edixa was introduced in 1954, and the Pentax came out in 1957. You will not find a 35mm SLR with right handed lever advance, pentaprism, bottom rewind button, and ASA reminder dial around the rewind made before 1954. The Pentax is often presented a big leap forward in SLR design "setting the pattern", but really all they did was bring something they had already invented in the Asahiflex II to a design layout that had already been proven by the earlier Edixa SLR.

If you take a good look at the original Pentax, you'll see something interesting about the styling of the pentaprism cover:

Pentax AP by Aaron Raisey, on Flickr

Compare the shape of that prism to those used by Exakta, Miranda, Topcon, Pentacon/Contax in the 1950s, and you'll see little resemblance. It does however bear a rather interesting resemblance to the prism of one particular German SLR dating back to 1954.

Quote Originally Posted by Les Sarile View Post
History has already shown no SLR's met with success without instant return mirror. Can you imagine SLRs today without instant return mirrors? However, we see even today's users adopt manual lenses on their auto everything cameras and are using these old lenses in stop down mode.
Modern SLRs do have automatic diaphragm operation though. It is not the manufacturers who are selling people lenses which are incompatible with the diaphragm mechanism in their cameras. Most of the people adapting lenses seem to be photographing flowers, cats, and other inanimate or lethargic subjects. Otherwise they are using cameras which are not constrained by mirror/focus screen/prism technology. In any event I don't think Canon will say their next line of lenses will be preset only.

The only 35mm SLR I can think of which survived the 1960s without an automatic aperture would be the Zenits. And only because they had to be the cheapest of the cheap. Even the lowly Exa recieved internal diaphragm operation (although never an instant return mirror, and it survived into the 1980s).