correcting IIIc back focus

[mh2000]

I have tested and confirmed that my IIIc has a backfocus problem. Infinity and lens scale match RF, so it isn't just a simple adjustment. I guess it is just a matter of shimming the lens mount.

Who can do this realiably for a reasonable cost? Or do I just have to find the time to do it myself?

(I know the expensive recommendations always given, but I just don't think a simple Barnack camera should be that hard to work on... an M, yes, but not a totally basic camera)

 

[john neal]

Depends where you are - in the US - Youxin Ye, in the UK - CRR. I can't help elsewhere, sorry.

 

[colyn]

I've never seen a IIIc that needed the lens mount shimmed. The crate and lens ring (mount) is made to exact standard. Maybe it has had the lens mount replaced at some time with a non-Leica mount...

 

[mh2000]

it is certainly not a FED or Zorki mount and the camera is very clean. I tested with 4 different lenses and they are all consistent. Infinity on the RF is spot on.

I guess I should check my film focus by scale and tape measure to see if it is camera or RF.

thanks.

 

[colyn]

it is certainly not a FED or Zorki mount and the camera is very clean. I tested with 4 different lenses and they are all consistent. Infinity on the RF is spot on.

I guess I should check my film focus by scale and tape measure to see if it is camera or RF.

thanks.

Many of the Japanese Leica copies had identical looking mounts but varied in actual thickness. I had a couple of these models which had shimmed mounts..

 

[Sonnar Brian]

If the mount was thicker, the RF cam of the lens would also be displaced relative to the RF pickup of the body. The RF and the lens scale would not match. Someone could have adjusted the RF to match the lens scale after replacing the part, but then never tested it with film.

Strange.

 

[John Shriver]

You can collimate it with an SLR with a telephoto lens known to be properly collimated to focus at infinity.

Take some film, and make marks on the emulsion with a Sharpie market. Load it in the camera. Remove one screw from the bottom of the shutter crate so you can illuminate the film with a lens in place. (Or drop in a tiny coin-cell LED flashlight.) Focus LTM lens at infinity. Point SLR into lens. See if marks in film are in focus. If not, see how far you have to focus LTM lens to focus marks on film. Measure that change in distance, and that's the required shim thickness.

If the shims are lost, perhaps it's better to measure the amount needed with a depth gauge. The shims were also used to get the mount parallel to the film, so they may vary by quadrant.

 

[ZorkiKat]

You can also do a plain groundglass test. The IIIc allows the mechanism to be taken out of its body shell with the lens mount attached. Check the focus on the image.

Using a groundglass, properly attached to the rails, will also allow you to use a depth caliper easier than using it on the pressure plate. The glass won't be pushed out by the caliper's probe and measurements can be done easily.

Once you set the lens mount flange to focal distance properly, recalibrate the RF. With Leica IIIc, it's just a matter of lining the images up at infinity.

 

[colyn]

You can also do a plain groundglass test. The IIIc allows the mechanism to be taken out of its body shell with the lens mount attached. Check the focus on the image.

Be sure to place the gg so the smooth side is facing out.