Focus problem with M-Elmarit 90/2.8 (M39)

[pegelli]

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I have an Elmarit 90/2.9 from 1959. It's a M39 version and has a genuine Leitz M39 to M-mount adapter for mounting on an M camera.

On my M246M the focus at infinity is flawless but when I start focussing closer the live view and rangefinder start to deviate from each other.

For instance a subject at ~5 meter is sharp in live view with the lens set around 5 meter, while the double image in the rangefinder overlaps with a lens setting of ~3,5 meter and obviously the photo is then out of focus. When focussing at an object ~1meter I need to move the camera ~10 cm between sharp live view and the rangefinder overlapping.

All my other M-lenses are spot on, no significant difference between live view and the rangefinder (35/2.8, 50/2.8, 50/3.5, 90/4 and 135/4 all Leica). I tested all my lenses this way at infinity, a distance of ~5 meter and at the minimum focus distance. All came out perfectly OK, so it seems the rangefinder of the camera body is not causing the problem.

The lens has been CLA'd and checked inside/out by Will van Manen twice and he can't find anything wrong on his measurement tools, but he can only adjust infinity (which is perfect) and after that the lens internal helicoil should move the notch that pushes the rangefinder lever in the body the right amount, but obviously there goes something wrong with that. But according to Will there's nothing he can adjust on that.

I've also checked that the rangefinder notch in the lens mount is straight in front of the roller on the rangefinder lever in the body and all that looks perfectly normal. And even if the roller would not be aligned and moves on the tapered side of this notch the problem should be reverse, i.e. the rangefinder showing a bigger distance then when the lens is sharp and it now indicates a smaller distance vs. the correct one. Somehow the lens notch doesn't move enough when the lens is focussing resulting in this problem.

On sunday I can test the lens on the M10 of a friend to see if we can shed some more light on the problem.

But in case anybody experienced this problem before, or can shed some light on what's causing it, or even better how to remedy it I would be very grateful.

[a.noctilux]

Can you check if the numberings are same on the mount and optical cell ?

When you unscrew the optical cell, you can see the "real" focal length as xx in 1/10 mm to compare to the number on the mount,

near infinity mark or under "GERMANY".

[pegelli]

Hi Arnaud, the lens (optical cell) has serial number 1657596 but I can't find a (serial) number on the mount/helicoid part. There's something "scratched" in there that looks like 508 and a little further W11 (all "handwritten"). When the parts are screwed together these scratched marks are not visible. There's 00 engraved below "Germany" which I think means thet the exact focal lenth of this unit is measured as 90,0 mm, but that's on the mount/helicoid and not on the optical cell.

My father bought this lens new in 1959 for his IIIf so as far as I know this optical cell and mount/helicoid have always been together and didn't give problems (as far as I can tell) on his M2 or my M2, but looking back at my shots with this lens most are larger distances and around f8, so there the problem isn't as big as at shorter distances and larger apertures.

[a.noctilux]

I checked on my two Elmarit-M 90mm,

the "real" focal lengths are scratched at the border of the optical cell, very hard to see.

One has "90,0" + on the lens mount with "00".

Another one has "90,5" + on the lens mount with "05".

I can not swap the mount/optical cell without discrepencies in RF.

Maybe something wrong in the optical cell or whatever.

With your M246 liveview, why not take time to note if the RF/LV discrepencies are in same way or "random" over distances.

Sorry I can not help you more.

[lct]

20 minutes ago, pegelli said:

Hi Arnaud, the lens (optical cell) has serial number 1657596 but I can't find a (serial) number on the mount/helicoid part. There's something "scratched" in there that looks like 508 and a little further W11 (all "handwritten"). When the parts are screwed together these scratched marks are not visible. There's 00 engraved below "Germany" which I think means thet the exact focal lenth of this unit is measured as 90,0 mm, but that's on the mount/helicoid and not on the optical cell.

If there is "00" engraved on the focusing mount it means that the focal length is exactly 90mm as you say bu you should see "90,0" hand written on the optical cell in my experience. @a.noctilux knows better than me though as my Elmarit is an M version from 1968.

[pegelli]

Many thanks for the help @a.noctilux and @lct.

Closer inspection of the optical cell indeed revealed an engraving "05" and also an engraving of the last three digits of the serial number. This means the exact focallength of the optical cell is 90,5 mm and should be mounted on a base with 05 engraved below Germany

How this came together with a mount/helicoid that's engraved 00 I have no idea, but I have an old photo from 2008 (a few years after my father sold most of his Leica stuff and gave this lens to me) that shows the 00 on the mount/helicoid and has the identical serial number on the optical cell so if it was ever accidentally exchanged it happened much longer ago. Sometimes my father sent stuff to ODIN in Arnhem to be cleaned/adjusted/repaired, maybe it was exchanged during one of those trips, who knows.

@a.noctilux, good idea to make a little table for the times I don't want to use live view and adjust manually, however this will not be quick 🙄

Do you happen to know how much you need to move the camera when focussing at something ~1 meter distance between "live view sharp" and "rangefinder sharp" when you screw your 05 optical cell in the 00 mount? Is it anywhere close to the ~10 cm I found when I tested this with my lens? I might dig into some optical formulas but it seems a big discrepancy for such a small change in focal length but obviously my hunch may be totally off.

[adan]

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3 hours ago, pegelli said:

The lens has been CLA'd and checked inside/out by Will van Manen twice and he can't find anything wrong on his measurement tools, but he can only adjust infinity (which is perfect) and after that the lens internal helicoil should move the notch that pushes the rangefinder lever in the body the right amount, but obviously there goes something wrong with that. But according to Will there's nothing he can adjust on that.

SINCE YOU SEEM TO HAVE FOUND THE PROBLEM (mismatched focus tube and lens head - congratulations, I guess!!), I LEAVE THIS POST JUST FOR OTHERS WHO MAY HAVE A 90 ELMARIT FOCUS PROBLEM IN THE FUTURE.

I would test the operation of that push-rod or "notch."

That connection between the internal helicoid and the camera roller moves towards the camera under the force of your fingers turning the lens and pushing it backwards - but it moves outwards (from infinity to closer distances, following the helicoid) under the force of a return spring.

camera ////[---()(()) lens front

camera /  /  /  /[---()(()) lens front

If that push-rod or rail encounters resistance, from dried grease, or dirt/dust, and/or the spring itself is worn out, it can fail to "follow" the internal helical reliably.

Test (1): off the camera, set the lens to infinity by the scale. Then focus down to minimum focus while watching the tip of the pushrod \_/. Does it move continuously and smoothly all the way to minimum focus? Or does it stick somewhere?

Test (2): set the lens to minumun focus (full extention) and use a fingernail to push and pull on the notch/push-rod tip (the underside should be ridged). Your finger can apply more force than the spring.

Does it feel sticky or skippy, or suddenly "break loose," or does it move over its full range smoothly?

I've never owned an original 1950s-60s 90 Elmarit - mostly because the ones I've run across often have focus problems, and often because of a sticky focus push-rod.

If the lens passes those tests, then the problem may be a mismatch between lens head (true focal length) and the focusing mount, due to someone swapping them at some point. Or a damaged or incorrect inner helicoid.

[a.noctilux]

4 hours ago, pegelli said:

Do you happen to know how much you need to move the camera when focussing at something ~1 meter distance between "live view sharp" and "rangefinder sharp" when you screw your 05 optical cell in the 00 mount? Is it anywhere close to the ~10 cm I found when I tested this with my lens? I might dig into some optical formulas but it seems a big discrepancy for such a small change in focal length but obviously my hunch may be totally off.

I don't know exactly, but out of curiosity I took some distances with "00" mount + "05" optical cell and my M246 at f/2.8.

results : RF focus reading on the focus ring   then  LV reading when "sharpest" on LCD

1.  RF 1.1m .... LV 1.0m
2.   2m      .... 1.7m
3.    2.5m   .... 2.2m

 

my conclusion is "not usable" as such too much discrepencies.

 

[pegelli]

Thanks for doing these measurements @a.noctilux, it's very close to my own experience with my "unit".

@adan, good point about the push rod spring, fortunately on my lens this was sliding flawlessly after the CLA by Kamera-Service (Will van Manen).

I also have an Elmar 135/4 from 1960 with a similar mechanism and there it also slides without any problem/resistance.

Btw, I quickly checked this 135/4 which has a 55 engravement below Germany on the mount/helicoid and removing the optical cell I could see a vague engravement 135,5, which means that for that lens (which I bought off the internet 2 years ago) the two parts are a perfect match, as indicated by corrosponding LV and RF readings at all distances.

My 1956 Elmar 90/4 doesn't have these engravings, but is also perfect focus wise.

So my Elmarit 90/2.8 will be doomed to be used with LV or the EVF2 until I find a matching mount/helicoid with a 05 engraving. But I don't think these things are offered for sale very often 😞

How my unit ended up with a mis-match will always remain a mistery, it's been bought new by my father in 1959 and always remained in the family. So it was either delivered as such (and never noticed on the film bodies) or somewhere during a CLA/repair the mount/helicoid was replaced by a wrong one. The serial number on the optical cell matches the number in my father's notes about the lens.

Edited August 6, 2022 by pegelli