[BigMackCam]

Four years ago, when I was in full-swing building my collection of lenses from the former Soviet Union, I bought the largest, heaviest, longest-focal-length lens I'd ever owned. Today, it's still the largest, heaviest, longest-focal-length lens I own... and I'm 99.9% certain it always will be

Allow me, if you will, to introduce my 1983-vintage MC MTO-11 10/1000 - a 1000mm f/10 Maksutov catadioptric mirror lens from the LZOS factory in Lytkarino, Moscow Oblast:



This all-metal behemoth weighs in at over 2.3kg with its caps and detachable M42 mount, and is so wide that it won't fit cameras with an overhanging prism hump (e.g. most - perhaps all? - Pentax DSLRs). Because of its size and weight, it's typically mounted to a tripod with the camera suspended by the mount... Unsupported, the weight of the lens would soon damage the camera's own mount.

Several excellent catadioptric lenses were manufactured in the former Soviet Union, and whilst the MC MTO-11 isn't perhaps the very best of them, it's nonetheless capable of impressive image quality... if, that is, you can focus it accurately. Despite the f/10 aperture and theoretical depth of field at any given distance, anything less than perfect focus accuracy results in soft images and loss of detail. That's been the case with every mirror lens I've used... but the MTO-11 is all the more challenging due to the diameter of its huge focus ring, and resistance from the focusing helicoid threads. One-handed focusing is a stretch (literally!) and only possible if the helicoid is properly lubricated.

This 1983 lens was little-used before it came into my posession, nor had it ever been serviced (apparently) since the screws still had factory thread-lock in place and none of them betrayed attempts at removal. When I received it, the focusing action was already quite stiff, generally requiring two hands to turn the focusing ring with ease. In the four years since, the factory grease gradually dried out further still, to the point where even two-handed focusing had become difficult. As a result, I decided to clean and re-lubricate the helicoid, and - after procrastinating for several weeks - I finally took the plunge today.

Disassembly - at least, sufficient disassembly for this purpose - is straightforward:



Removing screw A allows the rear plate to be removed. This isn't strictly necessary for the re-lube, but it gave me a chance to check that the mirror retaining ring wasn't too tight (as was sometimes the case straight from the factory), and since the tube is attached to the plate, removing it provides more space to work on the rear section's inner threads:



Screw B is the pin that prevents the two halves of the lens from unscrewing to the point of separation. Removing it, and unscrewing further, separates the halves, at which point the rear half's helicoid threads are exposed.

Screw C is one of three holding the focusing ring in place. Removing these allows the focusing ring to be slipped off the front half of the lens, exposing the helicoid threads. Before removing these screws, I used small triangles of low-tack masking tape to mark the position of the ring relative to thebody.

This is what the lens looks like when disassembled for helicoid cleaning and re-lubrication:







Cleaning the threads properly is a time consuming and unavoidably-messy process. I started by wiping all the excess, dried-up grease away with paper towel and cotton buds. There wasn't as much as I thought (perhaps why the focusing had become ultra-stiff), but I still got a reasonable harvest of infamous Soviet "ear-wax" :



I then used wooden cocktail sticks and more cotton buds (soaked in Zippo fluid) to get the remaing grease - some solid, some viscous - out of the threads. This took several passes, and after each one I wiped the threads with a lint-free pad dampened with isopropyl alcohol. Once the threads were clean (or as clean as I could reasonably make them), I gave them a final thorough clean with some lint-free alcohol wipes. Next, I applied a very thin coating of Helimax-XP grease to the threads on both halves of the lens, and mated them together to spread the grease and force out any excess, which I then wiped away, before final re-assembly.

At this point, I should show you the how nice the cleaned threads looked wearing their new coat of grease, but of course I forgot to take a photo Instead, I hope you'll be satisfied - not to say slightly amused - by this final photo of the reassembled lens, next to the pile of used cleaning materials :



After re-assembly, I racked the focusing back and forth from minimum to maximum focusing distance numerous times, then let the lens sit for a while before repeating. During this time, the grease spreads and settles in the threads, and the focusing action gradually becomes lighter and smoother.

What about the end result? Well, I can now focus the lens with one hand! I won't say it's "easy", as such, but I wouldn't expect that because of the size of focusing helicoid and number of threads. It's certainly much easier, a whole lot smoother, and the resistance is low enough that I can even focus one-handed with the camera and lens hand-held. I suspect it could be improved just a wee bit by an even-more-thorough cleaning of the threads with a toothbrush and soapy water, and perhaps even a little polishing of them... but for that I'd need to perform a complete disassembly to remove the optical elements, or risk getting those dirty (not a good idea with mirrored surfaces). As it stands, I'm very happy with the night-and-day improvement, and on reflection I think I'll forego the longer, messier job!

Thanks for reading

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Last edited by BigMackCam; 11-19-2021 at 12:45 AM.

[ismaelg]

WOW! That is discreet! Very cool!
Nice job.

Thanks,
Ismael

[bobbotron]

Fantastic! I enjoyed reading that, what a beast. I wonder, with a small m42 extension tube it'd probably mount up to a dslr?

Any chance you could post up some sample photos?

[c.a.m]

As it stands, I'm very happy with the night-and-day improvement, and on reflection I think I'll forego the longer, messier job!Thanks for reading

Great job, Mike. Thanks for taking us on the tour. That's quite the beast.

So, now you're fully prepared for your next street-shooting outing?

- Craig

[crazy4oldcars]

Great job, Mike. Thanks for taking us on the tour. That's quite the beast.

So, now you're fully prepared for your next street-shooting outing?

- Craig

Or night shots of Saturn...
That is an ...impressive sized lens. As noted above, I, too would be interested in seeing a few shots through this monster.

[BigMackCam]

Thanks for the kind feedback, chaps

So, now you're fully prepared for your next street-shooting outing?

Ha ha Yeah... the only minor inconvenience is its 8m minimum focus distance. Other than that, it's ideal

I wonder, with a small m42 extension tube it'd probably mount up to a dslr?

Yes, that works - but of course you lose the ability to focus at longer distances and infinity.

A far better choice for DSLRs is the ЗМ-5СА 8/500... It's compact, easier to handle, and image quality on a well-sorted example is excellent. If you can live with the bokeh, it's actually quite a practical long-focal-length lens... and the field of view is more versatile.

Or night shots of Saturn...

I'm pretty sure most folks use this kind of lens for precisely that purpose. Moreover, I suspect most 1000mm+ catadioptric Maksutov mirrors are being used as telescopes rather than camera lenses.

Any chance you could post up some sample photos?

I, too would be interested in seeing a few shots through this monster.

If the weather's OK between now and Monday, I'll endeavour to take some test shots and post them here

[PJ1]

with a small m42 extension tube it'd probably mount up to a dslr?

Yes. I had to do that with my Rubinar 500/5.6. It is now about a 503mm lens. But you need to shift the stop to get infinity focus.

[BigMackCam]

Yes. I had to do that with my Rubinar 500/5.6. It is now about a 503mm lens. But you need to shift the stop to get infinity focus.

Actually, I'll have to try it with a short extension on my K-3... The MTO-11 has a hard stop for minimum focusing (to stop the two lens halves from unthreading, obviously), but doesn't have a hard infinity stop... at least, not at infinity; it goes quite a way past. Maybe it's enough to allow for a short extension tube. I'll try to test that later today

[PJ1]

a short extension on my K-3

I think I used a 10mm edxtension tube to clear the flash housing. I am going to have to re-lube mine too. But when I did infinity (which is still not quite right) the helicoid was exposed so it shouldn't be too hard. Your pics will help.

[steephill]

I think most mirror lens are a Buzz Lightyear design. The intention is to allow for thermal expansion and contraction. A quick web search should find guides for collimating mirror lenses for maximum performance.

[BigMackCam]

I think most mirror lens are a Buzz Lightyear design. The intention is to allow for thermal expansion and contraction. A quick web search should find guides for collimating mirror lenses for maximum performance.

So far as I can tell, the MTO-11 has no means of collimation adjustment; I can't see any screws for that purpose - though I guess it might be possible to use shims... That aside, the most important adjustment in any of the Soviet mirror lenses is to ensure the primary mirror retaining ring isn't too tight - in fact, it shouldn't be tight, period. it needs to be adjusted such that the mirror doesn't move around, but no tighter than that, otherwise the mirror will be distorted. causing astigmatism. Many of the MTO and ЗМ lenses came from the factories with this retaining ring way too tight. My MTO-11 was already pretty good, but my ЗМ-5СА needed adjustment, and the improvement in image quality was huge...

[steephill]

My (fading) memory was that it was possible to reduce the tension of a spring ring supporting the secondary mirror as well as the primary mirror support you mention. I also read that you could buy slightly more expensive A coded versions of the Rubinars etc. which were much more accurately adjusted by the factory.

[BigMackCam]

My (fading) memory was that it was possible to reduce the tension of a spring ring supporting the secondary mirror as well as the primary mirror support you mention.

Interesting... I may check that at some point. Thanks for the info!

I also read that you could buy slightly more expensive A coded versions of the Rubinars etc. which were much more accurately adjusted by the factory.

I've read that too.

The main mirror retainer on my MTO-11 is more-or-less perfectly tensioned, and there's only one detent from the set screw in the retaining ring, so it obviously came from the factory that way. I guess I was just lucky

[bobbotron]

Yes, that works - but of course you lose the ability to focus at longer distances and infinity.

I feel like with a telephoto, infinity is overrated unless you're going for moon shots. Too bad you weren't close, I have a bunch of small m42 extension tubes I'd lend you to try it out. The small one would probably be super fun to play with, with this lens.

[BigMackCam]

I feel like with a telephoto, infinity is overrated unless you're going for moon shots. Too bad you weren't close, I have a bunch of small m42 extension tubes I'd lend you to try it out. The small one would probably be super fun to play with, with this lens.

That's kind of you Actually, I have a couple of sets of Zenit / KMZ M42 tubes, and the small one in each set is pretty short. Either that one or the next one up should provide enough clearance of the prism overhang...