Leica Summicron 90mm E55 (pre-asph) with massive front focus - DIY calibration?!

[lukx]

Hi all,

I recently found a deal for a 90mm Leitz Canada Summicron from the 80s. Got the lens, focus was smooth, rangefinder seemed (!) to align correctly, what could go wrong?! So I took it on a trip immediately, shot a couple rolls with it.

Well, turns out the lens’ focus is off by a LOT. At a three meter (10ft) distance, it front focuses by about 1.5m (5ft). To focus correctly on a target 3m away, I have to turn the focus all the way until the scale says 7m. I doubt the lens is capable of reaching infinity at all. This is tested with a well calibrated Leica adapter on my Fuji digital and a recently serviced, well working Leica M3. Incorrect focus scale aside, the images look fine on digital.

So the next question is: what can I do about it. I am a capable lens repairer, but I find little info on how to work with the Summicron. No guides seem available. It doesn’t seem too easily serviceable.

So I am turning to you nice people in hope that some of you have serviced this lens, successfully dealt with similar issues.
The issue is definitely the lens not the camera body. What could cause this? The lens helicoid and the camera seem fine. It must be the shimming of the optical block relative to the helicoid, or the spacing of the lens elements (rear group too far out would lead to a longer focal length, which could explain the effect I see…)

Any hints are welcome.

Thanks for reading
Luke

 

[lukx]

First thing I checked was whether the rear element was flipped. It wasn’t, same focus issue either way.

 

[Sonnar Brian]

I'm going to assume that the Distance Scale and the Rangefinder agree at all distances, based on the problem description. Best to check at close, medium, and infinity.

Does the optical block unscrew from the focus mount on this version? If so- and there is a shim, it needs to be thinner. No shim- it's grinding time. OR move the rear section closer to the image plane by putting a shim under the glass. The latter- how I optimized my Summarit 5cm F1.5 for close-up/wide-open.

 

[lukx]

Thanks, Brian. Yes, mechanically everything seems fine. I disassembled the lens from the back, it is actually rather straight forward to a certain point. I don’t think it’s a case of a wrongly assembled helicoid, there is really only one way to assemble it and have the distance markings line up.

So it must be a shim or optics related issue.

I found a thread on the L forum where someone accidentally unscrewed the optics, it looks exactly how one would expect (image from other forum):

But the lens is not one of those where this is a feature for Visoflex use. Others in the thread say Leica used to glue the optical block into the mount at this point in time, and OP claimed that once his became loose, it would frequently and easily unscrew.

The state of my lens currently it the exact opposite of what is pictured above. Everything stripped except the aperture casing (top) and the innermost part of the helicoid, both fused together. (Aperture ring and other parts of the outer barrel not shown.)



I tried with a lot of force, no chance to separate. Next step would be heat to crack the glue...

BUT this has me thinking: if the helicoid is really glued to the optical block, then it is likely that this was never separated before. Someone who does a hack job of a service, mixing up shims in the process, would likely not put in the effort to properly glue everything back together. And if that is the case, then it is unlikely that the issue stems from the shims between the two inseparable halves.

The fact that the three grub screws that are supposed to hold the front group in place were missing when I opened the lens (you can see one of the holes at the top of the aperture casing in the middle), and that there are considerable scratch marks where these screws would grab the front group tells me that a non-expert was inside this lens at some point. This supports my theory.

I will further investigate.

 

[Benjamin Marks]

This is a crazy question, but can the flange only be attached in one manner, or is it possible it was rotated 120 degrees when putting the lens back together by someone?

 

[TenEleven]

It would be very unlikely for the flange to be rotated, because if that was the case all indexes printed on the lens would appear upside down.

Anyway, if the lens severely front focuses and has no visible way to change the shimming I would assume it needs to be adjusted like the old collapsible Summicrons -- by changing the distance between the front and rear groups of the lens. Since the lens front-focuses it would mean its focal length is too short. (Too much displacement vs what is required.) So you could try to lengthen the lens focal length by screwing out the rear group maybe 1/2 a turn (just a total random guess) and see if that improves the situation any.

If it does just keep going until you find a setting that tracks. Then you can measure how far you have screwed out the rear group (VS completely screwed in) and manufacture a shim of the same thickness to put in there to make it a more permanent friction fit.

This is of course just an educated guess and is how I would try to proceed, not knowing how this type of lens ought to be put together for lack of technical drawings/repair manuals.

I guess the fundamental problem here is that you have some "expert" disassembling the lens but forgetting (or omitting) a crucial part such as a shim or standoff, giving up and then re-assembling it and selling it as-is. Then the lens changes hands a couple of times and you arrive at the place you're now.

 

[lukx]

I'm happy to report that I fixed the lens. In the end the front group was wrongly assembled, the middle doublet was loose because the retaining ring was installed backwards and the front element was not tightened correctly. Due to this, the doublet was not sitting in its correct position. I could have fixed this without completely dismantling the lens by just entering from the front and re-setting and tightening everything. Oh well...

Currently shooting a test film in my M2 after confirming focus accuracy on digital.



Some notes for others who try to service this lens
(I have not taken any more pictures, but maybe someone finds this useful regardless. Maybe even myself in a couple of years...)
The lens is okay-ish to work on. It's quite annoying that the optics cannot be serviced without completely dismantling the lens. DO NOT try to unscrew the optical block in the beginning. Anything you can hold onto at the front is held by tiny grub screws, including the front group itself. You will mar the threads if you try to twist things apart. You need good screwdrivers, a good lens spanner, correct helicoid lube, a suction cup, lens cleaning equipment.

Mechanically, the construction is straight forward, with a single helicoid and an easily removable rangefinder cam at the back. Unscrew the six screws from the lens mount, take it off. Then you can remove the rf cam by pulling it out. Afterwards, you can separate the helicoid. Make a mental note (better yet, a photo) where it separates but fear not: there is only one way really to put it back together and have everything line up. After separating the helicoid you can access the back element in case it needs to be removed for cleaning. You will likely need to clean and re-lube the helicoid before putting it back together once you're done.

Going in from the front, the name ring can be unscrewed after removing the single grub screw. Afterwards, the sliding hood can be taken off, unveiling three screws that hold the outer barrel with the aperture indicator dot. The front element sits tightly inside the barrel. Remove the retaining ring with a lens spanner, then use a strong suction cup to get it out. The front element pushes down onto the second (non screwable) retaining ring that holds the middle doublet in place. Again, the fit is very tight. When re-installing the elements, make sure that everything sits correctly inside the barrel. The middle doublet can feel solidly in place but actually be jammed at an angle. The bottom element of the front group is screwed in from the back, it can be accessed only after unscrewing the front group entirely from the inner barrel/aperture casing (see below).

The front group is held in place by hidden set screws behind the aperture ring that you need to remove before the group can be twisted off. (My lens is missing these screws but I'm writing as if they were there). If you have removed the outer barrel as described, you can access the screws holding the aperture ring. The ring actually consists of two pieces, the outer ring with the aperture index is what you grab, the inner ring is what actually engages the aperture mechanism. The two pieces are connected by said screws, loosening them will allow you to adjust the index position, or slide the outer ring down toward the helicoid and take it off.

PROCEED WITH CAUTION: there is a spring and a little bearing ball inside for the click stops. Once you pull off the outer aperture ring, the spring can catapult out, possibly taking the bearing ball with it (ask me how I know...). Do not lose these tiny parts! I suggest wrapping the lens in some cloth for this step so that nothing can escape... 😉

The inner aperture ring cannot be pulled off in the same way because there is a retaining ring that keeps it from dropping down (see photo below). This retaining ring can be taken off, but I think this requires complete disassembly. Once the outer aperture ring is off, you can remove the coupling screw that moves the aperture blades. The ring can now be turned freely.



BEWARE: at this point, nothing is holding the little cup that holds all 13 aperture blades in place. DO NOT TURN THE LENS UPSIDE DOWN. You'll scramble the aperture blades and putting them back is a major pain (again, ask me how I know). Generally try to keep the lens upright once you start working your way into the optical block.

There is a hole in the inner aperture ring through which you can (finally) access the mentioned grub screws holding the front group. Turn the ring and remove the screws one by one. The front optical group can be unscrewed now and serviced as required. See the second and third object on my image in the comment above for reference (notice the hole where one of the retaining screws goes). You may need a spanner to remove the inner-most element of the front group. Do not lose the rubber protection ring between the glass element and the metal retaining ring).

The point where the front group meets the inner barrel/aperture casing is a potential point of calibration. Putting a shim here to increase the spacing between front group and back element would slightly increase the focal length. This might be required if your lens is correctly assembled but still front focuses. My lens did not come with a shim and did not require one to be inserted.



Summicron-M 90mm 11136 lens design for reference.