Canon 50mm 1.4 LTM doesn't focus correctly. How to fix?

[Redseele]

Hi all,

Just today I got a 50mm 1.4 ltm from someone for relatively cheap. I will use it with my Leica M3. The lens seems to be in perfect shape, but I noticed that the Leica RF doesn't match the lens focus when focused to infinity.

I am using this lens with a Metabones 50mm adapter. I've heard it is supposed to be on par with the Voigtlander and Leitz adapters.

I have been reading that I could add a shim (pieces of paper?) between the adapter and the bottom of the lens. But I've also read that, for a more elegant solution, I could disasemble the lens and calibrate it for using it with my M3.

My question: does anyone know how to do this? I've seen there used to be pictures of a disassembled 1.4 canon ltm lens a long time ago but those pictures are gone now.

Thank you.

 

[Brian Legge]

I'd try it with another adapter you know is in spec (or a LTM body that focuses correctly). It's possible someone tried to repair the lens and messed it up or that your adapter is not perfect. Difficult to know whic without others to compare it against.

 

[ottluuk]

Are you simply looking at the lens markings or checking actual focus? Before proceeding towards any surgery, you should check focus using a piece of ground glass placed at the film gate (translucent tape can also work in a pinch). That way you can get a better idea what is really going on and how bad is it.

There are three possible points of error here - lens, adapter and camera body (you don't mention other lenses). To me, the adapter is the most likely suspect. Adapters that are intended for use on SLR or live-view digital cameras are often made to overshoot infinity by design - this way you can get proper infinity focus despite small variations between lenses and adapter thicknesses - but this is unacceptable with RF cameras. For critical RF use (fast/long lenses), I would only trust manufacturers who have in-house experience with rangefinder cameras - i.e. Leica and Cosina/Voigtländer.

 

[mdarnton]

Later (black) Canon lenses often this type of problem. I've had two 135s and an 85 that didn't focus right.

Which reaches infinity first, the scale (RF won't get to infinity before focus ring stops) or the rangefinder (lens turns past where the RF indicates infinity)? The solution would be different in either case.

Is the scale off, or the RFcoupling (when you focus normally with the RF, are the resulting pictures out of focus or not)? If shots are in focus (use real film, not a ground glass, and certainly not a piece of floppy tape) but the scale reads wrong, that's a third, different problem, and you're probably best just leaving it alone. This is the very first check to run.

It's probably not the adapter. It's really not that hard to make a proper adapter. I have measured quite a few with a micrometer, different brands, Leica, Voigtlander, and $8 Chinese, and not found a single bad one in regard to thickness. Usually adapter problems express themselves other, more complex places, like they cut you, or you can't get them on or off the camera.

Unless you have a digital Leica, one that you KNOW is right, you are in for a world of hurt zeroing in on a fix for this with just an M3, in some of the above cases.

Regardless, this isn't a simple problem to solve; if you have to ask, you shouldn't be trying to "repair" it. If you do try something, please do us all a favor by scratching your Social Security number all over the mount so that none of us will buy a lens you have messed up doing in-the-dark DIY.

My experience with one well-respected lens guru getting this fixed wasn't successful, as the problem was too much for him, conceptually. In desperation, I did finally hash it through on my own, but I did a whole lot more thinking than tooling. Part of the process was asking and reading on various forums and getting what I already knew were wrong answers from every single person who responded. So, because I don't own that lens, and haven't worked on it, I'm not going to post as an expert here about what you should do, either, except to say that your chances of messing up are vey high, especially using advice from the internet.

 

[Robert Lai]

By any chance does it have the Canon A rear cap?

My 50 1.4 came with that cap. What happens is that the cap is TOO SHORT for the rangefinder cam with the lens at infinity. If you screw down that rear cap, then put the lens focus on infinity, something has to give. What gives is that your infinity focus goes to H*LL.

Clarence Gass fixed the lens for me, and at the same time adjusted the RF on my Canon 7. Now they focus so accurately at f/1.4 that it never fails to amaze me.

Anyway, throw away that Canon vintage rear cap. Though beautifully made of thick plastic, it's a remarkable bit of poor engineering on Canon's part.