How do the techs repair a backfocussing lens?

[surfer dude]

Just wondering if any of you know how they go about repairing a lens that is slightly back focussing. I recently acquired a 135mm Elmar and it seems to be focussing just a bit beyond where the rangefinder indicates it is in focus.

I assume they will adress the issue on the lens and not on the camera body as the body works perfectly with my other lenes.

Any ideas? Thank you in advance.

 

[Sonnar Brian]

Easiest way to correct for back-focus is to either shim the optics module in the focus mount to move it out.

A DIY fix is to build of the RF Cam of the lens, I use a layer of copper tape.

 

[pphuang]

Along the same lines, if all of your lenses consistently front focus on a particular camera (in my case, an M3), is the problem commonly with the rangefinder, the mount, or both? I'm somewhat suspicious of the mount, since none of my lenses can be turned all the way to the infinity mark when mounted on the camera - so something must not be right with the mount. Is there a simple way to check/test?

 

[surfer dude]

Thanks a lot, Brian and Paul. I think that the problem must be in the lens itself - it is a little inaccurate now that I look at it in telling me where infinity is it stops 1mm or so before getting to the centre of the symbol). Much as you suggest Paul. I could try a layer of copper tape as you suggest Brian - does this provide a consistent and permanent fix or would I have to replace it from time to time?

Not being too technically inclined, or wishing to do harm to the lens (which used to belong to a famous photographer) I might take it up to the experts tomorrow to have a look.

So long as they don't alter the M6ttl body...

 

[Sonnar Brian]

Small Faces? I have Itchykoo Park on 45 or 33... Have not played it in years.

Keep them away from the M6! The optics module unscrews from the focus mount, that is the best way to have a shop fix the problem.

When a lens front-focuses, it is too far out. I had a 9cm F4 Elmar do that. I had to grind the mount down so the optics module would screw in properly. A shop can do that as well.

 

[surfer dude]

Hi Brian,

Great song - I have a story about why I like it so much. I also have an old EP with that and "Tin Soldier" on it - great stuff!

I'll request the shop to NOT touch the ttl. They are Leica trained, and the official Leica agents downunder, so they should know what they're doing.

Thanks again for your reply.