Originally posted by vonBaloney Well, it should work on M mode if the lens is stopped down manually -- hit green button to set shutter. But apparently that is not happening on K30/K50. But Av mode is much easier I think, and some have said it is less accurate, I haven't seen that happen either. (Seems to be somewhat lens dependent.)
Well, I guess I didn't really understand the original question. Let me see if I am getting to the point. There are 2 kinds of m42 lens, one with A/M switch and one without. So, the m42 lens without A/M switch operates like only in Auto mode; which relies on the operation of the PIN to stop down. Alternatively, people, myself included, alter the lens mechanism to make it like full time M switch mode (no need to press the PIN to stop down). Therefore, with m42 lens, one can set the aperture by turning the aperture ring for the camera to meter, hence we can use Av mode instead of Manual mode.
Although with m42 lens (assuming you have M switch on) you could still use M mode on the camera, but why would you? With Av mode, one can set the front dial to ISO and the green button for auto-ISO, then essentially you are shooting a m42 lens in TAv mode. Why use M mode for m42 lens for k-01, k-30/k-50. I have the k-01 and use Av mode with no problem at all.