For whatever reason, there seems to be a serious dearth of information regarding lens modification on the C-mount Computar 12.5mm f/1.3 lens. I am going to share my experience modifying this lens, in the hope that it will prevent other people from having the same issues which I have encountered.
As a quick disclaimer, you really should not blame me if you break your lens, or if it eats your children or animals. This either will or will not work for you. You have been warned.
You will need:
- File or dremel
- Very small screwdriver (flathead)
- C-mount to M4/3 adapter (I used the Fotoasy one)
File down the edges of the back mount a little. I do not think that I can stress “a little” enough. If you file this down too much, you will run into the same issue I ran into, and will break the back metal piece of your lens. I used a triangular file and edged it down to a nice smooth surface.
Unscrew the three screws at the base. This will remove the metal back of the lens.
Loosen the center column of the lens. You will see a small lens assembly protruding from the back of the rest of the lens. Loosen it a few turns. This is a trial-and-error thing, so be patient.
Reattach the backing with the screws. The lens assembly should be protruding further from the back of the C-mount to M4/3 adapter, when attached.
Attempt infinity focus. Attach to the camera, attempt focus.
If infinity focus is not attainable by step 5, repeat steps 2-5 until it is.
If you end up breaking or cracking the rear C-mount, you can permanently attach the lens to your C-mount to M4/3 adapter using some solder or hot-glue.