Originally posted by Trickortreat Wait! Aperture ring can be used to change aperture settings on Pentax DSLRs?
Sure thing. I do it all the time. The only requirement is that you use M, B, or X modes.
Originally posted by grispie Changing aperture of M lenses on pentax dslrs require pushing the green button... assume something similar on nikon z6.
I am not sure what steve meant with the below "automatic actuation".
The green button is one of three metering strategies and has nothing to do with changing the aperture setting. The other two are using the DOF preview lever or an external meter. Some might also include "sunny 16".
As for automatic aperture actuation, most modern lenses support it and it is the feature, probably more than anything else, that makes SLR photography practical. In simplest terms, it frees the user from having to manually stop the lens down before making an exposure. On most K-mount lenses, it is done through the actuator lever on the back of lens. Adapted lenses on mirrorless cameras always require the intermediate manual step to stop down, similar to adapted M42 lenses on a K-mount camera.
Cheaper mirrorless adapters provide full manual as the only option and are incompatible with lenses that lack an aperture ring. With such, one must either count clicks or adjust the aperture ring visually if a specific f-stop is desired. More expensive adapters have a stop-down ring that allows a the adapter/lens combo to act as pre-set lens when an aperture ring is present and as a stepless aperture ring emulation for lenses lacking an aperture ring.
As noted above, so-called "auto" aperture was an amazing feature at one time and was called out for marketing purposes through much of the 1960s and early 1970s when many lenses did not support the required coupling and stop-down mechanism. By the late 1960s most M42 lenses featured the silver actuator pin on the back as well as the auto/manual switch on the side that allowed backward compatibility to older bodies as well as being adapted to non-M42 bodies.
Moving to using K-mount lenses on a mirrorless body is a lot like using M42 lenses on a Pentax SLR.
Steve