I collect cameras, all of which I use. A little while ago I got a Rikenon P 50mm f1.7 lens to replace my 50mm f2.0. When I tried it the view finder dimed but the shutter did not fire. I replaced the f2.0 and same thing. Camera works fine with my 2X extender in KAR mt for Ricoh and Pentax, and my 80-200 zoom in Kar mount. My Tokina in Kar mount acts like my Primes. If I slowly remove the lens, the mirror goes all the way up, the view finder goes dark and the shutter fires, but the mirror does not drop down until I completely remove the lens. FWIW the levers on the Tokina more closely match the Rikenon mounts than the other KAR mounts. Any ideas? Suggestions?