I have a k10d and also have a large swag of old Pentax glass. It must be noted that the optical design is different for digital lenses compared to film. Film does not care what angle the light emerges from the lens and hits the film, but digital does not fare well with non parrallel light rays. Digital lenses have the rear nodal point further from the film plane. Also the problem with wide angles being much less wide angle as well as the wide angles having the rear nodal point closer to the film plane(ideally the focal length away.) My beloved 20mm f/2.8 internal focus is very ho hum on digital
as is the 17mmf/4 full frame Takumar fisheye
. Telephotos become more telephoto though, which is
. Old lenses will not have the image stabilization effect-it is coupled to compatible lenses only.