Originally posted by séamuis ... all Takumars from super through SMC have this auto/manual switch. all m42 lenses still being made (such as the new Zeiss ZS series) still use this method.
Some exceptions to that are Russian-made lenses like the M42-mount Zenitars, which don't have an auto-manual switch. They are always "auto".
Another exception is a lens like this:
It's labeled "Auto-Takumar" but used like a Super-Takumar.
For use on a K-mount camera, these "auto" features are mostly irrelevant. With the typical M42 adapter, in "auto" mode the lens will always be wide open. You need to shoot in "manual" (on the lens, not the camera), so the aperture will stop down. So the lens needs "manual" mode to take photos. The "auto" modes are sometimes useful for focusing wide open. You can use the auto/manual switch in auto for focusing, then move it to manual for metering and taking the photo.
Written down, it sounds very complex. Using the lenses is not that tricky.