I have the original f/2 135. I always use the metal lens hood to protect the glass. The front element is big (72mm filter size!) and is protected only by a small rim, so it can be easily damaged. The lens itself is big and very heavy- I mean, seriously heavy, heavier than most Contax bodies - but worth every gram/ounce. It produces wonderful images - this is a lens you definitly want to use wide open. Because it's so fast, you get an incredibly bright image in the viewfinder, and it's very easy to use the microprisms and split image when focusing. It's a pleasure to use.
Something to be aware of: this lens cannot be used on a tripod with all Contax cameras. The lens barrel is so thick that it extends below the camera's baseplate on some bodies. Mounted on a tripod, the aperture ring would be mashed against the tripod mounting plate. Not only would this jam the aperture ring, you could potentially damage the lens or camara if you tightened the tripod screw.
The bodies that I know have this problem are the RTS, RTS II, 139 Q, and S2. I've never used the 159, but it looks like its baseplate is also too short. The 137 MA and 137 MD might be OK; can someone else confirm this?
If you add a motor or winder to the RTS, RTS II or 139 Q, then these bodies will work fine. With their tall bodies and fat battery compartments, the RTS III and AX have no problem. From pictures, it looks like the RX is OK because of its fat baseplate.
The f/2 135mm is not the only lens that is too thick for tripod mounting on some bodies; others that I own are the f/1.4 35mm, f/1.4 85mm, and the f/3.5 200mm.
My 139Q came with a white plastic spacer that you could put between the camera and tripod to address this problem, but my S2 did not come with this. It would be easy to rig something up; simply find a piece of wood, plastic, rubber or other material that's thick enough, drill a hole in it for the tripod screw, and put it between the camera and mounting plate.
- Paul