Leica M flange distance and shapness

[zwieback]

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Hallo,

recently I was not very happy with the quality of the negatives that I was getting in respect to sharpness. Thought it might be linked to development and the film that I just experimented with to obtain the best results. I excluded the range finder adjustment by capturing object at infinity at F5.6/8. Also this did not quite satisfy me. Then some days ago I looked at some older negatives and saw what of a difference there was to the current negatives. I remember that I used a different body but same lens, which triggered the idea of checking the flange distance between a few Ms I own. To measure it accurately I layed the camera with removed door on top of a precision ground prism. The prism made contact to the inner film guides of the camera. I zeroed a digital height gauge to the top of the prism and this would allow me to now measure the flange distance quite precisely with a digital height gauge.

I checked three M6 and a M4 for the start. On average, without exactly calculating it, the average distance was 27.75mm, with 27.80 being the nominal dimension claimed for Leica Ms. The camera I was using in the past had all four 90> positions being equal and a 27.75 (left, right, top, bottom). on one of the other M6 I found a difference of 0.1mm at the bottom and on the M4 I saw the biggest diversion of 0.2mm! at the top of the bajonet. It has to be said, that on all cameras the seal on the bajonet mounting screws was not broken, so nobody messed around with it. The 0.2mm on the M4 would tilt the lens and the defocusing would roughly correspond to and offset like between infinity and a bit over 10m focusing distance on A 50 summicron.

My conclusion is that if you are getting pictures that are slightly out of focus it does not necessarily have to be the range finder adjustment but might be an inaccurate flange distance setting on the camera. Only looking at those four cameras the differences always occurred at either top or bottom of the bajonet but never left or right. It also was only one of the four positions that I repeatably found to be out, so no general inclination of the flange. On the M4 I checked the flange for flatness and as expected from the measurements it was distorted.

The problem I see now is that, in order to get it right, I would need to modify the camera, which requires breaking the seal and adjusting the entire flane or to no touch the seal but to remachinve it to what's possible. Regardless which way, camera would lose value. Could of corse also send it to Leica and hope they get it right (which seems not to have happened in the first go).

I guess I will decide one camera to be my workhorse and do whatever is required to get it right regardless of resale value. In the end it has to work for me. I don't see any sense in spending 1000s of euro for lenses and not being able to use their qualities.

Anybody facing the same issue?

 

Edited December 23, 2021 by zwieback

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[a.noctilux]

Many thanks for your measurements and conclusion.

Many years ago, as user of more than one Leica M on film which was more tolerant, I had same conclusion as yours now.

I understand better why Leica added the bottom screw on M-A and MP,

comparing to my older M4, here

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This didn't prevent me from taking thousands of Kodachrome.

I did from time to time the "depth-measurement" then used some Leica repair men/women to adjust/repair what I've found.

Good for a while 😉

 

By then it was far easier than by now.

Edited December 23, 2021 by a.noctilux

[zwieback]

thanks for the explanation of the bottom screw. Did not think of it. So I am not the only one and Leica's super precision craftsmanship can also sometimes be off 🙂 

[a.noctilux]

In my use, I think that maybe the heavy lens in use can destroy the original precision craftmanship.

 

I remember that one repair man told me not to stress the mount of my M4/M5 when I used the Elmarit 2.8/135mm (730g comparing to 150g of 35mm lenses that most M users mounted on their M those days).

He told me whenever possible holding the lens ( why it has the tripod mount built-in) and not holding only the camera.

 

As I remember also that the 'soft metal' (bronze or brass ? ) eyelets turned before detaching from M4 (M5 is better in this respect), so they needed to be replaced from time to time.

 

In newer M-A and MP,  these eyelets are steel made attached to the body with two screws.

Edited December 23, 2021 by a.noctilux

[zwieback]

the reccomendation would fit my observations because only top- or bottom of the flange were affected. The top on the M4 was "extended" by 0.2mm and the bottom of another M6 was "squashed" by 0.1mm, so the weight stress you mentioned might serve as an explaination.  find this still a bit odd though but it at least seems to have been adressed with the additional screw on the newer film Ms. It accordingly also seems like the flange would be the week spot and not the housing. I will monitor this.

[zwieback]

the point to make is that if you are not getting a very good quality from your negatives, there is a reason for it and it is worth tracing where the origin can be found. The cameras at least are very capable and known to be since decades.

[250swb]

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I'm not sure why you'd jump to the conclusion you need to modify the camera. Have you actually tried tightening the screws? As always the best thing is to loosen them all and then gradually tighten them again opposite to opposite, just like centreing the flange on a lens or tightening a cylinder head on a car. Screws can stretch over time, or become lose, or both. 

[zwieback]

undoing the screws and breaking the seals is what I menat be "modifying the camera".

The alternative was to machine the flange to be at least flat but depending on the offset you need to compensate, you cannot add material by machining, so the possibilities are limited.

Ideally I wanted to avoid any of the two...

[250swb]

10 hours ago, zwieback said:

undoing the screws and breaking the seals is what I menat be "modifying the camera".

The alternative was to machine the flange to be at least flat but depending on the offset you need to compensate, you cannot add material by machining, so the possibilities are limited.

Ideally I wanted to avoid any of the two...

A/ a qualified technician, or Leica themselves, won't be machining anything to true up the flange. They may also check your measurements before starting work. It's absurd to think the flange can be machined without compromising the lens that is attached to it, the locking mechanism isn't going to be adjusted as well is it? 

B/ either way the seal needs to be removed, no big deal, any old camera with an intact Leica seal suggests it has never been serviced, so avoid unless an avid collector.

Edited December 24, 2021 by 250swb