The Rikenon, XR and P

The notorious Rikenon's have a bad name in the market only because of one little pin on these babies. The 'P' labelled Rikenons sometimes get jammed on Pentax cameras and are painful to dismount. Does that mean these optical gems cannot be used on any other camera?
The answer is that not all Rikenons have the evil pin, it's only the 'P' labelled ones. And optically all of them work wonderfully on other cameras and their quality is sometimes even compared to the Pentax Taks and Super Taks except the flare control is not as good as the Taks. With the prices of CZJ Flektogon and Super Taks so inflated, Rikenons are the underdogs at the moment for manual focus enthusiasts.

There are a few versions of these:

• normal Rikenon
• XR Rikenon
• XR Rikenon L 
• XR Rikenon S
• Rikenon P

The XR versions are the ones with better optical quality. The XR and the P labelled models are essentially of the same optical grade and image quality the only difference being the pin appears on the P model for use in AV mode on Pentax cameras. The 'XR L' is a plastic body variant of XR. While I am yet to find much information about the 'S' variant.

The XR Rikenon 50mm f2.0 (and hence the Rikenon P 50mm f2.0) is said to be the sharpest lens in this range of any brand!