Threads and pitches

[KnipsOmat]

Hi there,

ever so often, all over the internet, one can read about thread pitches and thread angles of pre-war soviet M39 cameras and lenses not being LTM standard. Many say the threads would jam, as they were not compatible with LTM and post-war soviet rangefinders.

You read about pre-war threads being M39x1 instead of M39x26tpi as "true" LTM. Thread angle being 60° instead of 55° Whitworth.

An example for such a discussion can be found here:
http://www.rangefinderforum.com/forums/showthread.php?t=100876

I have many Soviet rangefinders, among them a couple of pre-war Trudkommuna and Kombinat FEDs. The oldest one so far is Trudkommuna NKVD-USSR #44563 from ~1937.

I've also got a couple of pre-war FED lenses. Three Industar-10 50/3,5 which came with the pre-war FED bodies, a ~1938 28/4.5 and a ~1939 100/6.3.

I can screw any post-war FED or Zorki lens I have (and I have plenty) into any of my pre-war FED bodies without any problems. And I can screw any of my pre-war FED lenses into any post-war FED, Zorki or Leningrad body I have. There is no noticeable difference in force to screw or unscrew, all is smooth.

Could it be the difference in pitch and angle of the threads is just an urban legend?

Or is it true, but the difference is small enough not to cause any problems?

Or was there a problematic difference, which had been corrected before my oldest FED stuff was built (before ~1937, that is)?

Anybody having any reliable information? Somebody actually measured precisely thread pitch and angle of pre and post war soviet M39 bodies / lenses?

Cheers,
Andreas

 

[Scrambler]

Great question.

I had/have an I61L/D that won't screw into a Leica standard thread but will fit a FED 2 that has no trouble with Leica thread lenses. I personally think that the depth and contour of the threads as well as the pitch and the true throat diameter might all come into play. I suspect, with very little evidence, that the camera threads had "slop" to deal with the less-than-precise lens threads. This may be hiding any subtle difference in lens thread pitch.

Have you tried your lenses on a Leica body? Or even a quality LTM-M adapter?

 

[Roger Hicks]

Great question.

I had/have an I61L/D that won't screw into a Leica standard thread but will fit a FED 2 that has no trouble with Leica thread lenses. I personally think that the depth and contour of the threads as well as the pitch and the true throat diameter might all come into play. I suspect, with very little evidence, that the camera threads had "slop" to deal with the less-than-precise lens threads. This may be hiding any subtle difference in lens thread pitch.

Have you tried your lenses on a Leica body? Or even a quality LTM-M adapter?

Same here. Likewise I have personally encountered lenses that fit one body but not another. All reasons as to why not are speculative -- precisely measuring an already-cut thread is a lot harder than setting up the lathe to cut it -- but another possibility is simple mechanical damage.Possibly at the factory, given Soviet QC.

Cheers,

R.

 

[David Hughes]

Hi,

I've no problems fitting lenses from the 30's to the 50's into bodies of the same vintage and mixing former USSR and Leitz products covering those years. And using all variations of screw threaded lens in a 50mm M bayonet adapter. I've just doubled checked with a pre-war and post war Leica and Zorki and all the 4 combinations of lens and body worked.

The trouble is, there's a lot of untested rumours floating around the internet and they get mixed and matched too...

As for checking the screw threads, all my tools were stolen years ago and, as most of them - the better ones - were pre-war, I've not bothered to replace them. I guess there'll be someone reading this who knows what a thread gauge is who could answer the query.

And I've often wondered if the Soviets followed the Japanese along the hybrid thread path. They were very good in the old USSR at being inspired by others.

BTW, I've had problems with body caps, both ancient and modern.

Regards, David

 

[Roger Hicks]

Hi,

I've no problems fitting lenses from the 30's to the 50's into bodies of the same vintage and mixing former USSR and Leitz products covering those years. And using all variations of screw threaded lens in a 50mm M bayonet adapter. I've just doubled checked with a pre-war and post war Leica and Zorki and all the 4 combinations of lens and body worked.

The trouble is, there's a lot of untested rumours floating around the internet and they get mixed and matched too...

As for checking the screw threads, all my tools were stolen years ago and, as most of them - the better ones - were pre-war, I've not bothered to replace them. I guess there'll be someone reading this who knows what a thread gauge is who could answer the query.

And I've often wondered if the Soviets followed the Japanese along the hybrid thread path. They were very good in the old USSR at being inspired by others.

BTW, I've had problems with body caps, both ancient and modern.

Regards, David

Dear David,

Well, I know what they are (I think -- I have my father's gauges) but alas I'm not sure how to use them, especially when it comes to such tiny differences as 26 tpi vs. 25.4 tpi and 55 degree vs 60 degree thread angles. Then there's the additional problem of actually having demonstrably incompatible threads to test, which I don't any more.

Cheers,

R.

 

[David Hughes]

Hi,

I hope you've locked them in the safe as pre-war stuff is generally vastly superior, when it comes to hand tools. I had the phone ringing continually when I sold off some of my father's old tools; if only ebay had existed then...

Regards, David

PS Back on subject, I don't think we'll ever solve this vexed Leitz/FED/Zorki problem.

 

[KnipsOmat]

Have you tried your lenses on a Leica body? Or even a quality LTM-M adapter?

No I haven't and I can't, as I neither own a single Leica body, nor any other non-soviet M39 body...

Cheers,
Andreas

 

[Scrambler]

No I haven't and I can't, as I neither own a single Leica body, nor any other non-soviet M39 body... Cheers, Andreas

For a modest cost you could buy a LTM-M adapter for the test. Cheaper than a thread gauge by the posts above! But of no use other than satisfying your curiosity. Perhaps you could borrow one? Otherwise your observation seems confirmed on one trial.

 

[wolves3012]

I don't know if there's any official documentation to say what FED used as thread spec, I've never seen anything online that wasn't assumption or speculation. However, there are some incompatibilities amongst the lenses I own. I have some I-61s that will not mount on a Leica IIIC and a couple of pre-war, uncoated FED 50 lenses that will, yet will not mount on certain post-war FEDs or Zorkis. Likewise, I have a pre-war FED that will take some post-war lenses but not all.

Certainly there's compatibility versus incompatibility in my few samples then. Reasons? Unfortunately a few variations:

1) Body/lens threads are compatible but one is damaged & they won't fit.
2) Compatible but body or lens thread is damaged & they won't fit.
3) Threads are to spec but body/lens are different specs & won't fit.
4) Threads are worn or damaged such that they fit despite being made to different specs. Either or both could exhibit the wear.

Based on the above and a small sample-size, I would not want to draw any conclusions from the gear I have.

 

[Scrambler]

I don't know if there's any official documentation to say what FED used as thread spec, I've never seen anything online that wasn't assumption or speculation. However, there are some incompatibilities amongst the lenses I own. I have some I-61s that will not mount on a Leica IIIC and a couple of pre-war, uncoated FED 50 lenses that will, yet will not mount on certain post-war FEDs or Zorkis. Likewise, I have a pre-war FED that will take some post-war lenses but not all. Certainly there's compatibility versus incompatibility in my few samples then. Reasons? Unfortunately a few variations: 1) Body/lens threads are compatible but one is damaged & they won't fit. 2) Compatible but body or lens thread is damaged & they won't fit. 3) Threads are to spec but body/lens are different specs & won't fit. 4) Threads are worn or damaged such that they fit despite being made to different specs. Either or both could exhibit the wear. Based on the above and a small sample-size, I would not want to draw any conclusions from the gear I have.

or 5) some or all are NOT to spec and left the factory that way.

 

[Livesteamer]

There is another important dimension here, possibly the most important. It's called pitch diameter. It's usually measured with a micrometer and some thin wire gauge rods that fit in the thread. It is not easy to measure in the home shop. In an industrial setting it would usually be measured on the shop floor with a set of go/no-go gauges that thread into or onto the part. Pitch diameter was not just a problem for the Soviets. A year ago I bought an adapter to put Pentax screw lens on my IIIc. It would not screw into my IIIc but fit all my Russian cameras. I suspect Leica makes their screw threads to very close standards. I have a Leica 50mm Summilux asph and the focusing helicoid is probably the most closely matched set of threads I have. No noticeable slop. Joe

 

[David Hughes]

The interesting thing is that the old USSR made ones get the most negative publicity. I've had problems with other makes but no one comes in with suspect stories about QC.

Of course, we've had 50, 60 or more years of reading PR material from the non-USSR makers and none from them...

Regards, David