Originally posted by bluestringer I really don't want auto focus, which I find useless for macro and I use catch in focus exclusively when shooting macro which requires a manual focus lens, I think?
Its a little more complicated than that. It needs a lens that is in MF mode. This means you can either use a manual focus lens (with a conductive K-mount!)
or switch the lens from AF to MF (problem here is that most DA and DFA lenses do not have AF/MF button at all! This is a trend with modern lenses in general, unfortunately).
There are some workarounds, like tweaking an AF lens to make it MF, but those are generally not recommended.
So, yes, for CiF you would have best bet to use an older lens, or use a new DA/DFA lens with non-AF extension tube (but this can cause another problem - most DA/DFA lenses don't have aperture ring, so you can get stuck at f22 or worse). That said, I hardly ever use any kind of focusing on the lens when doing macro. And the focus confirm hexagon in the viewfinder still appears, or you can use live view with Focus peaking if your camera has it. Just giving you some alternatives to think about.
Pentax A 100mm f2.8 would be a good choice, though. It is MF, but it has A-mode and aperture ring. Very versatile. Note that there are two versions of A 100mm macro, and the better one is a little expensive. Honestly, the Samyang 100mm might be your best bet overall