Originally posted by raphtze just mounted my smc pentax-m 1:2 50mm on my pz-1p to check, and in A mode, if i turn the collar, the camera will set a shutter speed accordingly for correct exposure, so i can see where BETLOG is going with this. -raph
That's because film cameras all had a stop-down coupler that could receive the current aperture
difference from the lens. The body did not know what aperture was used, just that it was (for example) 2-1/2 stops down from the wide open value...
This coupler was removed since the last film bodies (low-end MZ and the *ist, I think), so our DSLRs cannot know what aperture is actually selected on the lens...
But even so, I don't think there was a Tv mode (thus a P mode also) available with PK-m lenses, as the camera had no way to know the smallest aperture available on the lens...
So, apart from a complex (and hard to implement) solution involving manually entering max aperture, then the body mapping the aperture lever effect on exposure, and recording the results under a custom name, which frankly I don't see Pentax doing, there is no way for the body to control aperture on PK-m lenses (and even those old film camera had not this feature).
Like I said, my proposal is the simplest and easiest solution about this, and maybe the only one that has a chance to be included in future releases due to its small footprint on firmwares.