see http://forums.dpreview.com/forums/read.asp?forum=1036&message=19214685
for eg images of problem lens



from http://www.markcassino.com/b2evolution/index.php?title=subjective_impressions_of...
Note about Ricoh lens compatability:

Ricoh program lenses are not compatible with Pentax Auto-Focus bodies. You can identify these lenses by a “P” on the aperture ring – when the ring is rotated into the “P” (Program) position, it locks in place and you have to depress a small button to get the aperture ring to move again.

The Ricoh program lenses have a small ball bearing contact on the rear flange of the lens that will pop right into the hole that holds the AF cam on Pentax autofocus bodies. The result will be that the lens gets locked tight on the body, only halfway mounted. I learned this the hard way trying to mount a Ricoh lens on my Pz-1p! It took a trip to the repair shop to get the lens off the camera.

The Ricoh program lenses will work fine on manual focus Pentax bodies – no AF cam or hole to get stuck on. With my Ricoh 50mm f 1.7 I just removed the back flange from the lens and took out the ball bearing contact. With the modification it no longer works as a program lens on Ricoh bodies (not that I have any Ricoh program bodies) but it is now compatible with Pentax AF bodies.

Older, non program Ricoh lenses do not have the contact or this problem These lenses are basically like SMC-M or K lenses in their aperture operation.

With the exception of the 50mm f1.7 mentioned above, all of the Ricoh lenses reviewed here are the older, non-program models, that fit without problem on all Pentax bodies, both manual and auto focus.

Hi Gtis

I've got a vivitar 105mm macro that says its pk-a pk-r that fits fine.
As I recall the issue is a ball bearing on only some ricoh fittings that pops into an indent on the pentax DSLR mount and is then a right pain to release!
I'll dig through my bookmarks to find links to the sites with pictures of what to look out for
Cheers
Overthere

Noticed amazon have DA 12- 24 for £450 ie £400 with cash back which looks v tempting

Best codes I could see at the minute are JESSOPS5 for 5% off then throw in something extra to getit just over £50 for free delivery to kick in