Originally posted by Shaloot! I noticed that the previous owner had it on manual, so have it switched to auto after reading up on it. I took a look the photos on in takumar thread and now I need to go ahead and order that adapter!
Thanks for the tip about keeping it on manual for the k10d, though why is that?
The terms "manual" and "automatic" in the days the lenses were made referred to the aperture opening/closing mechanism. In "automatic" the aperture stayed open until the moment of shooting (just as K-mount lenses do these days) and an aperture activation rod pushed the pin on the back of the lens to close it when you press the shutter. The aperture then opened up again automatically. In "manual" the aperture blades open and close as you move the aperture ring. That worked as the DOF preview on M42 cameras (or in cameras with meter switches turning the meter on/off did the same thing with the lens set to "automatic").
Both film and digital cameras made after the switch the K-mount have no means of operating the aperture mechanism on the M42 lenses. That means that when you shoot, nothing happens to the aperture; it just sits there. There is no physical connection between body and lens. So in order to shoot at any aperture other than wide open you have to put the lens in "manual" and stop down the aperture to your desired setting immediately prior to shooting. I usually leave my lenses at about f4 for focusing, stop down to shoot (counting clicks), and then open back to f4 again immediately after shooting.