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MTO 10/1000 Mirror Lens
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PostPosted: Sat Feb 10, 2018 9:33 pm    Post subject: MTO 10/1000 Mirror Lens Reply with quote

I just picked up one of these cheap, the older brass barreled version that weighs a ton, made in 1970.

Got one problem with it - the 'T mount' will take a normal T mount adapter but doesn't then hit infinity, so the Russian version of a T mount must be thinner. Only time I've seen one of these Russian mounts in the flesh is on the bottom of a J11A.

Can you actually buy these mounts or will I have to modify a T mount in some way?

Any info on this lens is much appreciated, all I seem to be able to find is info on the later MTO-11CA.


PostPosted: Sat Feb 10, 2018 9:54 pm    Post subject: Reply with quote

My Jupiter 11a has a normal T mount - just to add to the confusion...


PostPosted: Sat Feb 10, 2018 10:24 pm    Post subject: Reply with quote

OOPS It's me whose confused. Embarassed

The Jupiter 11a does indeed have a different T mount, the dovetail is part of the lens and not a separate insert in the T mount.

The profile of the dovetail is different, the V is deeper on the Jupiter. The depth of the ring is different the Jupiter is 0.5mm thinner. The diameter is different - T mount = 50mm and Jupiter = 49mm .

Longer screws, and some careful centering, with a T mount outer might work ?

The Jupiter is on the right, with it's special T mount.




Last edited by Lloydy on Sat Feb 10, 2018 10:40 pm; edited 1 time in total


PostPosted: Sat Feb 10, 2018 10:36 pm    Post subject: Reply with quote

Cheers Dave.

Looks like I need to spend some quality time with a T mount and a grinder.


PostPosted: Sat Feb 10, 2018 10:44 pm    Post subject: Reply with quote

Is that the same mount? if it is there's always some dead J11a at the camera fair, and I'm selling at the next one on Fed 25th. So I'm there early and get to scavenge the boxes of crap that we all try and sell. Rolling Eyes


PostPosted: Sat Feb 10, 2018 11:29 pm    Post subject: Reply with quote

Here's the back of the lens in question, it has a screw rather than a dovetail:




PostPosted: Sun Feb 11, 2018 2:18 am    Post subject: Reply with quote

Why not adjust lens focus?


PostPosted: Sun Feb 11, 2018 6:25 am    Post subject: Reply with quote

Is the back of the MTO the same thread as a regular T-Mount, 42mm?

If so, do you have access to a lathe? You've got some extra "meat" at the base of the threads on that flange. I'd do some calculations to see if I could determine how much closer in a regular T-mount would have to come, and then I'd machine that much out of the flange at the base of the threads. It's true that lathes aren't really set up for exacting dimensions in a coaxial movement, but you might be able to rig up a dial indicator to show how much is being taken off, or just check periodically.

Or you could use an old tried and true method: a good file would take down that brass shoulder in a hurry. Measure as you go. If you wind up with your shoulder being a bit too short, well there's nothing wrong with that. Most long lenses focus past infinity anyway.


PostPosted: Sun Feb 11, 2018 11:02 am    Post subject: Reply with quote

This looks like the bit you need


PostPosted: Sun Feb 11, 2018 2:37 pm    Post subject: Reply with quote

I think you're right Dave. I shall have to dig in my box of bits and see what T mounts I have, I found an M42 one but it's missing the inner piece, I definitely have a complete one or more than one, just got to find them.

Then, as Michael says, a file is my friend. Smile


PostPosted: Mon Feb 12, 2018 12:20 am    Post subject: Reply with quote

To make things more complicated: I have an old 1000, this has a 39 mm mount and a copper ring to enlarge it to 42 mount. In my mind, that is also more logical. The Zenit camera's originally had a M39 mount, this was later changed to M42. A T mount lens came much later, I think and was probably only for foreign markets.


PostPosted: Mon Feb 12, 2018 1:42 am    Post subject: Reply with quote

Sounds like time to measure register distance of lens. Project bright window onto opposite wall; measure distance from lens flange to focused image on wall.

Another question, can lens or better camera be held to lens to achieve infinity?


PostPosted: Mon Feb 12, 2018 5:26 am    Post subject: Reply with quote

visualopsins wrote:
Sounds like time to measure register distance of lens. Project bright window onto opposite wall; measure distance from lens flange to focused image on wall.

Another question, can lens or better camera be held to lens to achieve infinity?


At that focal length it should rather be the sun or something at least 20x the focal length away!!


PostPosted: Mon Feb 12, 2018 1:15 pm    Post subject: Reply with quote

A church window, perhaps. Smile


PostPosted: Mon Feb 12, 2018 4:20 pm    Post subject: Reply with quote

visualopsins wrote:
Sounds like time to measure register distance of lens. Project bright window onto opposite wall; measure distance from lens flange to focused image on wall.

Another question, can lens or better camera be held to lens to achieve infinity?


I find this technique to be most useful for determining the size of the image circle and only generally the focal length of the lens, which obviously includes registration distance. You'll need to measure the distance with accuracy better than 1mm, and that, my friend, will be difficult. Better to calculate the registration distance based on known dimensions.


PostPosted: Mon Feb 12, 2018 5:10 pm    Post subject: Reply with quote

cooltouch wrote:
visualopsins wrote:
Sounds like time to measure register distance of lens. Project bright window onto opposite wall; measure distance from lens flange to focused image on wall.

Another question, can lens or better camera be held to lens to achieve infinity?


I find this technique to be most useful for determining the size of the image circle and only generally the focal length of the lens, which obviously includes registration distance. You'll need to measure the distance with accuracy better than 1mm, and that, my friend, will be difficult. Better to calculate the registration distance based on known dimensions.


Difficult but not impossible. Difference between m39 and M42 and T should be obvious... How to calculate based on known dimensions?


PostPosted: Mon Feb 12, 2018 6:17 pm    Post subject: Reply with quote

Evert wrote:
To make things more complicated: I have an old 1000, this has a 39 mm mount and a copper ring to enlarge it to 42 mount. In my mind, that is also more logical. The Zenit camera's originally had a M39 mount, this was later changed to M42.


Please do not confuse things even further. The Zenit M39 mount has a flange focal distance of 45.2 mm whereas M42 is 45.46mm. On simply adaption with a M39 to M42 ring without further adaption or modification you may loose the ability to focus correctly at infinity.


PostPosted: Mon Feb 12, 2018 7:36 pm    Post subject: Reply with quote

0.26mm isn't much @1000mm focal length, not enough to prevent infinity focus. 1mm on 500/4.5, yes.

Ian have you tried assuming the lens is M42? That would explain why a T adapter causes it to focus closer...