Odd distance measuring behaviour between Leica rangefinders

[Oxygalacteus]

Hello everyone! Long time reader, first-time poster here, so I'd like to say thank you for all the effort in creating and maintaining this excellent forum as a resource for information and discussion.

I have experienced some odd rangefinder behaviour after recently adding a used Leica MP to my camera collection.
The "problem" involves the following equipment:

-Leica M5 (serviced by independent technician)
-Leica MP (rangefinder recently adjusted by Leitz)

-Zeiss 35mm f/2 Biogon ZM (adjusted to factory specs)
-Leitz Summicron 50mm f2 type 3 according to Ken Rockwell's nomenclature (serviced by same technician as M5)


And I am experiencing this:
-Both lenses work fine with the M5 rangefinder, I am able to achieve infinity focus.
-The Zeiss 35mm works fine with the MP, I am able to achieve infinity focus.
-The Summicron 50mm does NOT work fine with the MP, infinity is not quite achieved and I would have to turn the focus ring maybe 5-10 degrees more in order to do so.
-Intermediate distances ranging from 1-5 metres are exactly the same on both lenses (50mm on M5, 35mm on MP)

What is going on? I am aware that this sounds somewhat like one of those old-timey riddles, but I'm seriously at a loss as far as the solution goes.

The M5 has a wider rangefinder baselength than the MP and should therefore be more exact.
The Summicron 50mm has by far a wider focus throw than the Zeiss 35mm and should therefore be more exact.

The MPs rangefinder adjustment is perfectly in synch with the previous owner's collection of a total of 9 M-mount lenses from different manufacturers and with varying focus throw lengths (I confirmed this personally with a Zeiss 50mm they brought to our meeting and my Zeiss 35mm). They weren't totally happy with the factory settings and therefore had the rangefinder re-adjusted by Leitz, which is documented.

My first thought was that my Summicron 50mm was "out" at infinity, but why would it work with the M5 then?
Or is the opposite true and the long focus throw of the Summicron unvcovers sloppy adjustment work made by yours truly, Leitz?

Please let me know about your ideas and if you know what the likely cause of my experience is.
Thank you very much for your time and effort in advance!

Sincerely yours,
David


PS: I am aware that "perfect infinity" is not necessary for taking in-focus pictures. As long as the short distances are spot-on, I'm not overly concerned. This is just something that makes me scratch my head in confusion.

 

[Pieter12]

How do the photos turn out? In focus at infinity?

 

[Oxygalacteus]

Hello Pieter12,

the M5 has always delivered solid in-focus infinity photos. I yet have to put a film through the MP, but the previous owner was happy with it after Leitz did a re-adjust and reportedly didn't have any problems ever since. It's a somewhat recent build from 2017 and has obviously been very well cared for, so no drops or knocks or any other adverse events.
I'll put a roll through it and report back with results!

 

[NB23]

Mp and m5 have the same baselength.

 

[NB23]

It is simply a difference between both cameras, obviously.

I’d say that the MP is out of sync. And if it’s out of sync by 5-10 degrees at infinity, it will also be out by that amount at minimum distance.

test with a tripod at minimum distance and the difference shall be clear.

 

[Oxygalacteus]

Mp and m5 have the same baselength.

Thanks for the correction! I really don't know how I came up with the information that they were different...

 

[etn]

Welcome to Photrio!
Where are you located in Germany? There are several (i don’t want to say German, as not all of them are) members spread around the country.

 

[Oxygalacteus]

Welcome to Photrio!
Where are you located in Germany? There are several (i don’t want to say German, as not all of them are) members spread around the country.

Thank you! I'm located in the Stuttgart area, so not too far off from Munich.

 

[Oxygalacteus]

I currently have a "sloppy" (just stuff on the horizon and some minimum distance around the house with widest aperture possible) test roll drying, shot on the MP, split between 35 and 50 mm.

For anyone who could be interested in this, here's an odd update:
I built a small impromptu minimum distance test range using a miniature porta potty I brought back from Japan a while ago. It has male/female pictograms on the front which make for a great focus target, so that's that.

The Summicron 50 does not have a hard stop at 0.7m but rather goes on to roughly .68, which is a fair bit, due to the long overall focus throw that extends as the focus distance diminishes. Therefore, I used the Zeiss Biogon 35 for it has said hard stop.
As it turns out, the MPs film plane (sadly not indicated on the body, unless I missed something here) hits 0.7m spot-on together with the range indicator on the lens. Since I only bought the latter this January, adjustments from the factory should still be viable (If you're interested in modern Zeiss ZM lenses you'll have read that they appear to require readjustment faster than other lenses do).
So I switched the 35mm lens over to the M5 body...and oh my....0.7m on the lens clocked in at a real distance of roughly 0.68, which could prooobably but unlikely become an issue at f2. I check my rangefinder regularly and this was not the case last time I did. Not only this, but my Summicron 50 exhibits a very slight but noticeable wobble upon further inspection when grabbed all the way at the back and the front, which is not where I hold my lenses ususally at the same time.

My working theory for now is that the loose lens and the ever so slightly out-of-adjustment rangefinder of the M5 somehow even out and create the experience I am currently not-so-enjoying.
Is my theory too wild?

 

[NB23]

If the 50 is wobbly, does it move its cam as well? Try this: while it’s mounted on a camera push the front part of the lens. While pushed, if it moves the camera’s focus patch, then it’s the lens’ problem

Also, for a proper camera test, it is very simple. Forget the minimum distance. Install a tripod with the M5 and the 50mm lens. Focus on any object within a 1-3 meter range and mark the focus point on the lens (or better, tape the whole focusing ring so it stays in this exact focus posotion. Then, carefuly unmount the 50mm lens and mount it on the MP.
Now mount the MP on the tripod (the tripod hasn’t moved abd it’s in the exact position as it was woith the M5). Now when you look through the MP’s viewfinder, is it in focus? Probably not. In theory, you should now refocus the 50mm lens of about 5-10 degrees (as you oreviously noted) in order to achieve correct overlapping focus patches. This indicated that one camera is off by that amount.

This is an easy diy fix, but you must determine which camera needs to have its infinity focus calibrated.

as a sidenote; i did have a few lenses that were wobbly and which were messing with the camera’s focusing arm as I played with the wobble.

 

[Oxygalacteus]

Dear NB23,
thank you for your time and effort of writing this up for me!

The cam does indeed move with the wobble, so everything aside from the bayonet mount does.
I just tried pushing on the front of the 50mm as you proposed and, alas, I noticed the focusing patch shifting to the left, towards infinity, ever so slightly.
Edit: Although it's barely noticeable at infinity, the double image movement becomes significantly more pronounced if I conduct the test at close distance and the more the lens is extended from its base.

New theory: the lens wobble was probably less pronounced and went unnoticed when I had the 50mm and M5 serviced last. Therefore, the M5s rangefinder got adjusted for the slighlty wobbly lens which is why I never really noticed. Additionally, the M5s rangefinder arm could provide less tension than the MPs, which is why the problem is more pronounced with the latter pushing against the focussing cam with more resistance. Does this sound realistic?