Originally posted by paulh You need an A - type manual lens for this. It has the electrical contacts that communicate with the body, so you can use all modes (Av, Tv, etc) automatically. You still have to manually focus. The M & K series lenses have no communication with the body, so you can only use M-mode, and must use stop-down (green button) metering for the camera to make a calculation.
Correct. You do need and A lens for this with Pentax's current implementation. But I do not understand why it has to be this way.
With just a bit of extra code, I think that Pentax could have had the user input the aperture of the lens (the lens and body are not communicating, but the body knows the aperture because you dialed it into the body). This would make m-lenses a lot more functional. It seems like the camera could ask you to enter the wide open aperture of the lens (just like it asks you for the focal length for manual lenses), and then allow you to dial in the aperture you are using. From this information, figuring out the metering is a piece of cake. You could make an menu option to turn off the feature for those who do not want it.
Anyway, just a feature I wish Pentax had implemented to increase the functionality of manual lenses. I am unsure if they did not think of it, thought it would be too complicated for users, or wanted to protect new lens sales. Or, it is possible I am missing something.