Originally posted by RioRico The R/K designation means it's meant for Ricoh and Pentax cameras.
Just below the 3-o'clock position is a screw, and under that, just above the blue shadow, is the position for a Ricoh pin. Funny, I didn't know that existed on non-A-type lenses -- A-types have a row of contacts between the 12- and 3-o'clock positions. Anyway, I have a few KR|RK lenses with Ricoh 'buttons' not 'pins', that don't get stuck in Pentax mounts. The Ricoh button is no more intrusive than an A-type lens' contacts. Do you have an A, F, FA, or DA lens to compare with? If that Ricoh-whatever protrudes more than a contact button, then it is probably the infamous pin and should be removed.
I took it apart and ground the pin down with a dremel tool until it was smooth to the surface. I then took off the black part and cut it down to the size of the regular size so it would fit in the slot.
and here is the result of my effort
just a try out shot, 200mm wide open. yes I needed to put in some contrast with and sharpening in photoshop, but seems great for 10 dollars and 1/2 hours work. not bad for wide open
cheers and thanks for the help
PS I ground down the pin on my other ricoh lens just in case