Canon 50mm 1.4 LTM Focus Issue

[Kumachrome]

Hi, I can't seem to find anything specific on how to fix this issue. So, I've decided to just go ahead and ask. If this has already been addressed, please excuse my noobness at using Google.

I've recently acquired a Canon 50mm 1.4 ltm lens for my Leica M2. I am using a Voigtlander 50mm adapter for it. The main issue is that there seems to be some back focusing on it. It's off by the slightest amount. This seems apparent at all apertures. Let's say I shoot it at f1.4 and am focusing on my subject's eyes. The lens will tend to focus on their hair that is behind them slightly. Or, for street photography, subjects just look out of focus except for behind them. Basically, the focus isn't spot on.
I'm quite sure it's not my camera or adapter, as I was previously using the Canon 50mm 1.8 ltm and the focus was spot on at all apertures.

Any tips on what to fix inside it, if need be? I saw on one disassembly video that showed within the lens, when the focusing knob is taken off to expose the elements, there is a brass type ring (a washer?) that can be removed if focusing is off. Anyone have any idea or more information about this? All help will be appreciated!
Thanks.

 

[Kumachrome]

https://imgur.com/a/jKOHY

Here are some images I took on a test roll to demonstrate what is happening. I have circled what I was attempting to get in focus

 

[rfaspen]

I feel for you. That brass ring you reference is in fact a shim to adjust focusing.

The Canon 50/1.4 is known to be slightly off when used on digital RF cameras. On film, it usually doesn't show up. And when it does, only at wide apertures (e.g., 1.4 and 2).

You might have a missing shim. You might have a copy of the lens that's just not quite in spec. Or, you might have a lens that was "serviced" at some point and not reassembled correctly (for example, without a necessary shim).

I have this lens, and mine is off slightly at wide open on digital RF's. I plan to disassemble it and bring it into spec at the same time I deal with the stiff focus and stiff aperture ring. We'll see if I have a shim, or need to make one. You too. Welcome to the finicky world of rangefinder lenses. You're not alone.

How are your results at f/2.8 and above? The Canon 50/1.4 has the potential to be a stunning performer. A lot of people with the focus discrepancy just memorize how far off the plane of focus is from the rangefinder focus, and move the camera forward or backward by the appropriate amount. That's what I'm doing now. My lens focuses about 2cm beyond my RF focus point. So I move my head back about 2cm before pressing the shutter.

Ask ANYONE with a 1.5 Sonnar, and you'll see this is a common technique.

 

[rfaspen]

Oooh😕 That link you provided. Is that how your lens performs?

Bad. Something is not right. Not seeing the lens or knowing its history, I can only guess it has been mistreated, or taken apart and reassembled incorrectly. Sorry I can't be of more help than that. Regardless, that sample image is not at all what I expect from the 50/1.4. Here's a random image from my lens:

 

[Kumachrome]

Thanks for your response. Is there supposed to be two shims inside? I noticed there was only one in mine. I took it out and the focus actually got worse. Above f2.8 the lens is eh. Earlier I was out and about in the street shooting at around f5.6 to f16. Only like 2 were really in focus where I wanted it to be, even on shots of still subjects.

 

[jonmanjiro]

That's WAAAAY more than a little back focus. Something is not right.

First of all, is the problem with the camera or the lens? Have you tried another lens on your M2?

If the problem is with the lens (and it certainly appears to be the case, but lets not rule out the camera just yet), is the problem caused by the focus cam being off (does the RF line up correctly at infinity?) or incorrect positioning of optics in the lens barrel (some shimming or reassembly would be required)???.

If the M2 is fine and the RF lines up at infinity, adding a shim to the existing shim may fix the problem.

Is there supposed to be two shims inside? I noticed there was only one in mine. I took it out and the focus actually got worse.

Usually only one, but not always. Taking the shim out means the optical block sits closer to the film plane > increased back focus. To fix back focus, you need to move the optical block forward away from the film plane > extra shim of the right thickness.

 

[Kumachrome]

Ah I see. Yes, the rangefinder is accurate. I brought it into a tech recently and said nothing really needed to be done since everything was accurate. I've also tried the camera with my Canon 50mm 1.8 ltm and the focus was spot on. How would I go about adding another shim? I mean, aside from spending 60 or so on a broken lens just to get the little metal ring.
Oh, forgot to add. Those photos are what turned out after I took out the shim. I've put it back now. Here is a photo from earlier today with the lens fully assembled:

http://imgur.com/a/o2czM

In the first two, you can see the focus is off. In the last one with the 2 men conversing, I tried going for the one guy's face (in blue). But, the lens ended up focusing on a plant behind him. He was standing pretty still and I took my time focusing that shot. This was a consistent result on pretty much the entire roll. 🙁

 

[jonmanjiro]

Oh, forgot to add. Those photos are what turned out after I took out the shim. I've put it back now. Here is a photo from earlier today with the lens fully assembled:

http://imgur.com/a/o2czM

Ahhhhh ok.

You're going to have to experiment by adding thickness to your existing shim until you find the right thickness.

It doesn't really matter what you use - cellophane tape, aluminum foil, copper tape etc. Whatever works basically.

 

[Kumachrome]

Call me crazy, or maybe I fixed my lens somehow by taking it apart and putting it back, but during my reshimming process, I encountered something. So, I looked up how to do it. Seemed easy enough to add shims. Of course, first I had to see how much it was off by. So, I reassemble the lens, mount it on the camera, take the back plate off and I put an old focusing screen from a broken Nikon F right behind the shutter curtain. Secured it with tape. Set the camera to Bulb mode. I focused on a calendar on my fridge using the viewfinder. Fired the shutter and looked through the screen. It appears to be accurate. The focusing screen split image that I'm using looks spot on. Perhaps I am doing it wrong? Or maybe I somehow fixed it?

 

[Mjd-djm]

Important question... when you focus the lens to infinity does the rangefinder patch line up at infinity too? It should line up perfectly. If the rangefinder goes beyond infinity then the lens will front focus. If it doesn't get to infinity then it will back focus. IMO it is more likely to be rangefinder alignment than the lens, although both are possible. I have owned several of these and used on m2 and m6. All of them focussed ok.

 

[Kumachrome]

I'm not sure what exactly I did, but after fiddling around a bit with the lens...somehow it's fixed! I tested out a roll here:
https://imgur.com/a/H8j2n