Replacing a lens af/mf switch

SOURCE: K100D AF/MF SWITCH STUCK IN

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1) If it is a manual focus lens, you need to turn off Autofocus on the body of your K10D. On my K100D, there is a switch on the side of the lens mount that says [-MF or -AF]. "-MF" is manual focus mode & "-AF" is autofocus mode. Since your lens doesn't have autofocus capability, turn it to the "-MF" mode.

Also . . . When I press "Menu" and go to "Custom Setting", I change two settings . . .

1) I change "Using aperture ring" to "Permitted". This allows you to use manual lenses (M lenses) that do not have an auto(exposure) setting, and also lets you use Auto lenses (A, KA, KA2, FA, etc.) in either the Auto or manual aperture setting modes.

2) I change "Fl with S lens used" so that even with a manual focus lens, although I don't have autofocus capability, my K100D beeps and shows a little red square in the viewfinder when I have successfully focused manually!

The K10D should have the same options.

This should get you up and running!

I have had a load of fun with my old lens on my new digital Pentax!

SOURCE: Auto focus suddenly stopped working

This may not be the same as your issue, but our AF stopped working as well. I tried all the recommended fixes - removing the card and battery, recharging the latter, removing the lens and cleaning the contacts, etc. None of those things worked. However, I then switched to MF, requiring me to turn the barrel, and I realized it was stuck and just needed a little force to get unstuck. Might have been the humidity. Anyway, our problem was solved - AF was back to normal after that.

SOURCE: I just got the Canon XSI with the 18-55m lens.

Try cleaning the metal contacts on the lens and body.