The LTM to M-mount world is a little more complicated than it used to be. Since 2006, when Leica implemented 6-bit coding, you don’t have to use the code, but your LTM adapter should cover the optical sensor anyway. If you’ve got an older Leica M-mount camera, this won’t be an issue for you.
It started with the search for a wide angle lens for my M10-P. To me, 28mm is about normal but on occasion a wider look is nice. The key is “on occasion.” That signals that the cost of Leica lenses isn’t warrented for this application. After noodling around the web, I came across the Voigtlander 21 f/4 Color Skopar as a really nice option. It’s super compact, just a little larger than the Leica 28 Summaron, which means it can go along easily without taking up a lot of space. Perhaps the perfect lens to provide the occasional wide angle perspective.
Taking the economics of this matter even further, while the M-mount Voigtlander is pretty economical (~$400) the LTM version used is about a hundred bucks cheaper. All you have to do is come up with a Leica thread mount to M-mount adapter. A used LTM version Color Skopar was located in Japan and ordered.
Next, get the LTM to M-mount adapter. After searching around Amazon and Ebay I found a couple of LTM adapter options. The M10 has 6-bit coding for the lenses, although it’s not required to use 6-bit coded lenses. You can manually input the lens from a menu in the M10. The first choice, a Kipon adapter which includes the machined pockets for filling in the appropriate lens code will take awhile to arrive. I ordered it and am willing to wait a little bit for it. At the same time though, my newly Ebay acquired Color Skopar didn’t want to wait. I ordered another, non-6-bit coded LTM adapter, this one by Beschoi.
When assembled onto the Voigtlander, the Bechoi adapter fit fine and everything seemed okay until the camera seemed to get confused thinking no lens was mounted when I operated the focusing ring on the lens. Fiddling around with the lens the realization struck that the optical sensor which is used to read the 6-bit coding on Leica lenses was exposed rather than covered by the lens mount. Every time I moved the focus ring the sensor would “see” my finger and think something had changed with the lens. The M10-P would display “no lens mounted” in the live view mode. If not using live view, it didn’t seem to be an issue; the fact that the camera doesn’t know what kind of lens is mounted aside.
For this particular lens, I want to used the M10 built-in lens corrections for 21mm, so it’s an issue for me.
For the time being I installed a piece of gaffer tape to cover the sensor. That prevents the sensor from believing that the lens was swapped because the shadow of my finger crossed it while focusing.