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Info on MTO 500?
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PostPosted: Tue Nov 03, 2020 3:56 am    Post subject: Info on MTO 500? Reply with quote


I've been expanding my collection of old Soviet lenses and I've found myself the proud owner of a 1970 MTO 500. I didn't pay much as the lens is in need of some work. I ran across a few things I was curious about though.

I was under the impression that these only came in M39, and later in M42. Mine came with some kind of adapter attached, under which I thought I'd find M39 threads. What's underneath however are just genuine T threads (M42-0.75, not M39 or 'regular' M42-1.0 threads). Did these come from the factory with a T thread option? It looks factory to me. I don't mind using a different adapter, I just want to make sure I'm dealing with a real t thread setup with the standard 55mm focal flange distance and not some aftermarket shank that was installed where an M39 connection (and 45.2mm focal flange distance) should be. All the online ads I can find are M39 or M42(x1.0), though I've seen some talk of t threads on review sites. Anyone have one to compare? Almost all of the samples I see are stamped 'MTO' while mine says 'Mirror Telephoto'. Maybe it's just a different export model?

I'm hoping to have it all cleaned up and back together soon enough. It needed a lot more work than I figured it would! I can post pictures if it would help.

Thank you all!

PostPosted: Tue Nov 03, 2020 2:24 pm    Post subject: Reply with quote

The info here suggests that it can be found both as M39 (probably early ones) and t-mount. Usually the Russian "t-mount" isn't a true t-mount but like a t-mount with the male (lens) side being the inner collar of of a standard t-mount (so it won't unscrew). The pic is of a jupiter 11A 135mm.

Also the M39 screw thread mount is usually a ~44.5mm registration distance ie same as M42, not like a leica M39. So all that is needed is a cheap and easy M39 to M42 adapter collar.

PostPosted: Tue Nov 03, 2020 4:02 pm    Post subject: Reply with quote

I saw that post on the Pentax forum but I thought it was at least partially inaccurate because it indicates there are no M42x0.75 threads present, which isn't true. That's exactly what mine has. The t thread adapter I use for attaching a DSLR to my telescopes threads right on.

I've done the M39 to M42(x1.0) dance before. The former has a focal flange distance of 45.2mm while the latter is 45.46mm. You're right that usually a cheap M39 to M42 adapter will do the trick, but I've found that you can then lose infinity on an M39 lens due to the 0.26mm difference. Usually a quick shim adjustment is enough to get this back on an M39 though, or at least it's worked well for me with a Helios 44 and Industar 50 (both early silver M39 variants).

I suppose my concern with this MTO 500 is whether the Soviet implementation of 't threads' respects the typical 55mm of focal flange distance for that standard, or does something funky like Soviet M39 versus Leica M39. If the lens had arrived in working condition it wouldn't be too difficult to verify myself but unfortunately it was pretty rough.

I appreciate your reply - thank you!

PostPosted: Tue Nov 03, 2020 4:13 pm    Post subject: Reply with quote

Here are some photos of the threads and the adapter/cap that came off. I'm assuming this is the Soviet implementation of a t thread mount? I'm hoping the photos attach okay. I'm on my cell at work and had to downsize them to upload. Thank you all!

PostPosted: Tue Nov 03, 2020 4:50 pm    Post subject: Reply with quote

Yeah that's interesting and new on me. Thats certainly a standard CFD (old canon) t-mount. Thanks for the info. I have the facility to update the PF page.

PostPosted: Tue Nov 03, 2020 9:49 pm    Post subject: Reply with quote

AFAIK, soviet never used the t thread mount. Can you make photo from other angle of the lens mount, please?

PostPosted: Wed Nov 04, 2020 3:48 am    Post subject: Reply with quote

No problem. I'll add some more from different angles. I've heard of other Soviet lenses using T threads but it definitely doesn't seem common. The T thread to EOS adapter I have threads right on. Hopefully the lens was designed with the 55mm register distance and all will be well. Assuming I ever get it back together.

Thank you MarcusBMG for pointing out that the adapter was for Canon FD. I've looked up FD to t thread adapters and that looks exactly like it.

PostPosted: Sun Nov 08, 2020 9:49 pm    Post subject: Reply with quote

I had some updates on this and wanted to share in case anyone else comes along with similar questions.

Short version: Mine is likely a US import of the MTO-500 by Spiratone, sold with a standard t-ring mount and properly adjusted for the corresponding 55mm FFD. Despite having the bigger tripod mount section at the rear, it fits on a Canon crop sensor.

Long version, for those who want to read:
The MTO 500 came in several variants. The older ones are Soviet M39 (FFD of 45.2mm) and had the larger rear tripod mount section that hits prism housings on some DSLR cameras. Newer 3M-5A models were slimmer and have less fitment issues on DSLR cameras. They were still Soviet M39, though many came with M39-M42 adapters. The MTO 500 is a mirror lens, so it focuses past infinity by design. This means there's usually no infinity issue with the M39-M42 adapter rings. Apparently the M39 portion can screw off the back of the 3M-5A models to reveal a mount 'like the internal collar of a standard t-mount', per Pentax Forums. Pentax also notes that these models DO NOT have standard T-mount external threads (M42x0.75mm). The factory offered 6 different kinds of filters, though most lenses shipped with only four. The older models came in a wooden crate, while newer came in plastic boxes. The newer models also have a retractable hood, while the older one is a screw-off design. There are rumors and some posts of a few older models having an Exakta mount.

Mine is a bit of an oddball. Physically, it is most similar to the older style Soviet M39 mount, and it came in the wooden crate with four filters carrying the KMZ logo. The lens itself carries the LZOS logo, which was a KMZ satellite site. It is a 1970 model and does not carry the Brussels World Fair script. The beauty ring does not read 'MTO' like others, but rather 'Mirror Telephoto'. Lastly, the brass mount on the rear is a true T (Tamron) ring with external threads of M42x0.75mm (further differentiating it from the Pentax Forum notes). It is not Soviet M39 with an M42 screw mount (or t-ring) adapter, but rather is 'natively' M42x0.75mm.

Though physically very similar to the Soviet M39 variant, mine was also set up for a t-mount FFD of 55mm. The rear brass mount is no shorter than the Soviet M39 version, so the 9.8mm discrepancy is accounted for in the focusing helix. I had mine stripped down to the rafters as it was desperately in need of cleaning and repair. Inside it is very similar to a Maksutov telescope. The helix provides a wide range of focus and appears to be adjusted as short as possible for the t-mount version. I'd assume it is adjusted near the top of the adjustment range for the M39 variant (+9.8mm), but I don't have an M39 on my bench to measure. It would be possible to remove the limiting screw and perhaps gain a good amount of close-focus on this lens, but the single screw handles limitation of both inward and outward travel, so you'd run the risk of unscrewing the helix in this configuration. Limiting inward travel does not appear to be an issue without the screw given that it is near to 'bottoming out' as-is and will not strike the mirror. I don't see much use for closer focus with this lens, however.

As near as I can tell, what I have is a variant that was imported to the US by Spiratone from the late 60s into the early 70s. Though Spiratone pushed the very similar Minitel-M ( 500mm f8 ) mirror lens, it also imported the MTO 500 and made it available in one of their favorite mounts - the t-mount. I found the attached scanned ad that seems to confirm this.

This was a bit more work than I'd figured it would be, but I enjoy working on optics and this was easily the smallest catadioptric I've gotten to play with. The best part is that with a t-ring to EOS adapter, the lens can (just barely) be properly mounted to a Canon crop sensor DSLR (something the Soviet M39 version cannot do). That extra 9.8mm came in handy!

Last edited by jessebear on Tue Nov 10, 2020 6:47 pm; edited 1 time in total

PostPosted: Sun Nov 08, 2020 11:24 pm    Post subject: Reply with quote

Thanks for your post.
I have never heard of the special mount on this import version, but it's clearly possible. Interesting scan also!

Some corrections and adds :
I confirm the older ones are in exakta mount, not m39. They have slim body (without tripod mount) :

They were produced by KMZ from 1956 to 1959 (same like MTO 350 and MTO 1000).

LZOS is not a satellite of KMZ, but another factory. The production of the MTO was transfered from KMZ to LZOS in the mid 60's. LZOS was (and still is) the specialist of mirror (so mirror lens) in USSR / Russia . Interestingly, the "Mirror Telephoto" lens was produced by KMZ and later by LZOS. So it seems cooperation with Spiratone lasted for several years.

PostPosted: Mon Nov 09, 2020 7:16 am    Post subject: MTO in the 1960es Reply with quote

in the late 1960es a consortium of photographing friends bought a Maksutov 500 from "Mashpriborintorg". I used it directly on my Pentax, so it must have had a 42mm mount. Solid wooden chest with filters and not particularly expensive.A linguistically gifted friend managed the correspondence in cyrillic letters.

Interesting compressed pespectives, but somewhat cumbersome as hiking kit, especially as I had a Leitz IIIc with collapsible 50/2 for carrying in a large pocket and soon got the mistaken idea that a Minox would serve better.


PostPosted: Mon Nov 09, 2020 12:51 pm    Post subject: Reply with quote

$200 in 1970 is equivalent to about $1300 today!

PostPosted: Tue Nov 10, 2020 6:46 pm    Post subject: Reply with quote

Thank you all for the info! I apologize for not being more inclusive in my post regarding the Exakta mount options - I clearly hadn't researched that quite enough. And the bit about LZOS being a satellite of KMZ I had pulled from the Camerapedia page here, but perhaps that isn't a very reliable source.

I wouldn't be surprised if there were other import versions of this coming in other mounts. The focusing helix allows for a large range of motion, so I'd imagine it wouldn't be difficult to adapt to other registers. The bass mounting collar in the rear can be threaded off to reveal a much smaller thread immediately surrounding the rearmost lens assembly, but I don't recall the thread size (30-something mm). It seems this piece came in at least Soviet M39 and t-threads, as well as apparently standard M42 mount per paulhofseth.

PostPosted: Tue Nov 10, 2020 7:29 pm    Post subject: m42&mto Reply with quote


i notice that i can be interpreted as stating that the mto came with native M42 mount. I may not have been precise enough, it had an M42 mount "out of the box" , but I know nothing about whether that was due to an intermediate adapter ring. Somewhere in my disorderly paper archives I may have the original delivery documents; in the unlikely event that they do surface I will see if there are notes about the mount.