Leica rangefinder coupling distance and lens infinity focus adjustment

Couldn't find this info anywhere. I was trying to adjust my cameras rangefinder, however I also wasn't sure whether the lens is set up correctly for rangefinder coupling (I also had the lens disassembled). So finally I just measured the distance at which the rear ring, that presses the rangefinder lever, protrudes backwards at infinity (measured from flenge plate). So I tested several lenses with Leica M mount and Leica LTM (L39) mount using a micrometer with a 0,01mm precision. I got to 7.50mm for LTM lenses and accordingly 6.50mm for Leica M-Mount. I got around +- 0.01-0.02mm tolerance (similar I guess to the Leica flenge distance tolerance).
Does anyone know the true numbers? Do these look right?

I need to adjust the infinity on a Summicron M 90mm F2 lens made in Canada. I tried disassembling it, but I cannot find any shims or anything that would allow that. How do I adjust it? I think I would need to move the optical assembly like 0.1mm closer to the camera at infinity.

Moderator note: I've merged these two questions into a single thread because of the functional relation between both aspects.

If you're working on an M camera you can check focus with a ground glass. I'LL claim too many years and too few Summicrons to be of any help(?) beyond that.

Not having any self-control though I believe it's more likely to have had a shim installed if it was needed from the factory.

I have a 1960ish and a 1998ish Ernst Leitz Canada 90mm Summicron both work great. I purchased a used Apo Summicron (Germany) 90mm (and returned) from a reputable (Roberts) dealer, it was screwy.

On the basis that you should never adjust a rangefinder lens to the body, or adjust the body to the lens (which would mean either the body or lens wouldn't work with other bodies or lenses) it may be that somebody in the past has done exactly what you shouldn't do and maybe removed a shim? Unless there is massive wear it's unlikely to have gone out of adjustment on it's own but the camera can more easily go out of adjustment. The thing to do is confirm the body is accurately set up by testing with other lenses and then go back to the 90mm, or take them both to a camera tech who'll have the equipment to adjust both independently of each other and get them back in tolerance again.

The body is even less likely to go out of specs (film to flange distance) than the lens. The rangefinder could easily go out of alignment, though.

It's not quite clear why OP would want to use a lens that was disassembled to calibrate the rangefinder (are the rest of the lenses in even less known state?)... If I were OP and wanted to do this without a help of a good technician, I would check the lenses I have at hand set at infinity on film. I'd use the lens that seems to have the best infinity sharpness to adjust the camera's rangefinder at infinity. If rangefinder then works properly for that lens also at mid and short distances it would be a good sign that rangefinder is properly adjusted. Check the rest of the lenses. If only one lens doesn't agree with the rangefinder, adjust that lens.

The topic was merged by the moderator, which made it less clear. These are actually two separate unrelated questions.
1. I would like to have an absolute calibration of the camera rangefinder based on a specific protrusion distance of the rear of the lens towards onto the rangefinder lever. I assume it is defined somewhere what the exact distance is at which the rangefinder should be at infinity (similar to how a flenge distance is defined as 27.8mm+- (presumable) 0.02mm. For this purpose I measured this distance with a 0.01mm precision depth gauge and found it to be somewhere in the range of 6.5mm for Leica M Mount. What I am asking is if anyone knows the actual Leica specification or where it can be found?

2. Adjusting the summicron 90mm f2. This lens is not correctly adjusted for infinity (I tested it on a digital camera). The Optical group needs to be moved a bit closer to the film plane, this would mean removing some shims if there were any. But I cannot find any shims. There is an element (I think made of brass) which the optical assembly screws on to (you can simply unscrew this lens about the middle of the lens body so the front comes off). I was thinking maybe that element was not adjusted correctly in assembly and maybe you'd need to grind off like 0.1mm?
I can actually also well imagine that at the time when the lens was made such offset in focal plan was actually tolerated? Now with the mirrorless digital camera at 10x magnification you can really see the slightest offset in focus that you maybe weren't able before? Anyways does anyone know how I could adjust the lens assembly closer to the body? (just to clarify has nothing to do with rangefinder coupling, the coupling mechanism is tested and gives infinity where the lens marking is at infinity)

stan_1 said:

The topic was merged by the moderator, which made it less clear.

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I think you're missing the implications of what @250swb and @brbo have said, but this is the reason why your separate threads were merged. It appears you've set out on an adventure to adjust flange focal distances, and you're running into the observation that apparently, that's not the usual (and likely, proper) way to do things. The main question that arises from here is how come you find yourself with both a Leica body and a lens that are seemingly significantly out of spec. The first question I would start asking is whether your conclusion that both are out of spec is justified. For instance, you mention having tested the lens on a mirrorless camera and found it was out of alignment - did you verify this with a Leica camera, or a camera with an adapter that allows mounting a Leica lens? In case of the latter, have you determined with absolute certainty that the spacing problem is in the lens and not the adapter?

So the reason why your threads are merged is because we could suggest things like "machine the barrel of the lens down by x mm and see what happens", but as far as we know now, we may be suggesting you commit to performing irreversible work on either the camera or the lens while in hindsight it turns out that it wasn't necessary.

koraks said:

I think you're missing the implications of what @250swb and @brbo have said, but this is the reason why your separate threads were merged. It appears you've set out on an adventure to adjust flange focal distances, and you're running into the observation that apparently, that's not the usual (and likely, proper) way to do things. The main question that arises from here is how come you find yourself with both a Leica body and a lens that are seemingly significantly out of spec. The first question I would start asking is whether your conclusion that both are out of spec is justified. For instance, you mention having tested the lens on a mirrorless camera and found it was out of alignment - did you verify this with a Leica camera, or a camera with an adapter that allows mounting a Leica lens? In case of the latter, have you determined with absolute certainty that the spacing problem is in the lens and not the adapter?

So the reason why your threads are merged is because we could suggest things like "machine the barrel of the lens down by x mm and see what happens", but as far as we know now, we may be suggesting you commit to performing irreversible work on either the camera or the lens while in hindsight it turns out that it wasn't necessary.

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Thank you for your reply @koraks. I completely understood those implications and that's why it was important to me to underline that these are two separate points. They just came up at the same time. I tested the lens with a serviced M-Mount camera and it is consistently off in the same way as with the digital one (focuses slightly before the object). For the sake of this thread please safely assume that my assumptions are correct. It is completely clear to me that anything I do is at my own risk Grinding the barrel is the last resort is also clear to me, that's why I am asking if someone has actually some experience with adjusting this Leica lens.

250swb said:

On the basis that you should never adjust a rangefinder lens to the body, or adjust the body to the lens (which would mean either the body or lens wouldn't work with other bodies or lenses) it may be that somebody in the past has done exactly what you shouldn't do and maybe removed a shim? Unless there is massive wear it's unlikely to have gone out of adjustment on it's own but the camera can more easily go out of adjustment. The thing to do is confirm the body is accurately set up by testing with other lenses and then go back to the 90mm, or take them both to a camera tech who'll have the equipment to adjust both independently of each other and get them back in tolerance again.

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The camera tech you are talking about is most likely Leica itself in the 'holy' city of Wetzlar. I wouldn't trust anybody else with this!