We were discussing the possibility of permanently mounting an M42 to K-Bayonet adaptor to a screw mount lens some time ago. On the surface, it is quite an easy modification to make, with some caveats. The biggie is that some screw mount lenses don't have a wide enough base to catch the locking pin on the K-mount camera. The 17mm fisheye Tak that I wanted to modify has a large enough base. The mod is incredibly simple. You need to remove the spring clip from an M42 adaptor. This is done simply by removing the screw that holds it on. The adaptor I used had the spring removed already, so I had to find a replacement screw to fit. Fortunately, I had dismantled a Nikon FG-20 some years ago, and had kept a film tin with all the little screws, so I was able to find a screw fairly easily. On the adaptor that I used, the screw hole for the spring clip was not quite drilled all the way through. I just forced a screw through, enlarging the hole in the process. I then burnished the metal bits off the inside of the adaptor. After that, I mounted the adaptor to the lens, and torqued it on fairly tightly. I just put the whole assembly onto a camera body and turned it quite tight. After that, I put the screw into the adaptor, and tightened it until it locked the lens onto the adaptor. I had to thin down the screw head a wee bit with the Dremel and a small cutting wheel.
The next part is to figure out just where to put the notch in the lens mount for the pin. I decided the best way was to put a bit of ink onto the locking pin of a dead camera body, and mount the lens while holding the pin in, then releasing the pin when the lens was mounted. Depress the lens release and hold it until the lens was off, and I had a nice little round outline in the lens mount where the pin wanted to be. After that, it was a simple task to cut a small slot into the mount with a Dremel and a small rotary file that came with the tool. The Dremel does tend to try to dance around a bit, and I scored the mount in a couple of places, and I seem to have gone a tad deeper than I needed to, It ain't the prettiest, but it worked, and my 17mm Fisheye Tak can be mounted just like a K-mount lens. William Robb
