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Steve_s
Tinkerer
Username: Steve_s
Post Number: 121
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 20, 2008 - 03:14 pm: | 
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Unfortunately Leicas are well outside my price-range, but I live in hope. Meanwhile I'm getting confused about Leica Thread Mount! From web searches, my understanding is that LTM is a 39mm diameter thread, but with 26 threads per inch (TPI). I also read that the early Russian copies used a 39mm thread, but with a 1mm pitch metric thread form, though later (post-war?) they changed to a true LTM.
Everyone seems to consider all the later Russian lenses to be LTM, but now I've acquired my first camera of this ilk, a Zorki 4k, I find that the instruction book describes the mount as being M39 x 1. Is this just a bit of poetic license by the manual writers, or is the mount, in fact, NOT a true LTM? |
Glenn
Tinkerer
Username: Glenn
Post Number: 354
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 20, 2008 - 06:08 pm: |
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I doubt 'poetic license', rather just plain ignorance of the actual specification of the LTM mount. Still the Russian engineering tolerances sometimes are way off - I have a number of Zorki bodies that quite happily accept M42xM39 lens adapters. These were supposed to be M42xLTM, but the person machining them was also ignorant of the facts, until he tried attaching them to a Leica! Still I got the benefit of the contents of his scrap bin. |
Dgillette4
Tinkerer
Username: Dgillette4
Post Number: 207
Registered: 04-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, May 20, 2008 - 06:40 pm: |
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The early Zorki and Feds had a different pitch of thread and had different back focus distances. The Zorki 1 on had the standard Leica thread, I have both zorkis 1,c,and Fed 4 and they all take ltm lenses and the lenses I have all line up on the rangefinder nicely. I believe 28.8mm comes to mind as standard bf on leica and zorki now. Some of the very early cameras had a hole in the back and pressure plate to see focus under test and to stip up or reduce shims in mount. Some parts even fit between Leica and Zorki , Fed and zorki lenses are super sharp. Some of the original lenses were hit and miss though. Don't under-estimate the Zorki I find them completely usable and cost a lot less...Good luck with yours..and fon't forget to tension shutter first then change speeds...he he he Don |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 122
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 21, 2008 - 02:39 am: |
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I hope that the KMZ and FED factories were a bit more precise in their knowledge of LTM than the manual writers (and the makers of your adapters, Glenn)! I've had a look at the thread on the Jupiter-8 with Whitworth and metric thread gauges. The thread isn't very well formed, and it is hard to be sure over just a couple of turns, but it does look more like 1mm than 26TPI to me.
In principle mixing a 26 TPI thread with a 1mm pitch (25.4 TPI) thread would be A Very Bad Thing! They would only contact over less than one turn, rather than the full length of the thread, which would be quite likely to cause damage. I've read that the LTM is Whitworth thread form which is 55º. Metric is 60º, so whichever component had the true LTM would probably be the one to suffer most because it would take the load at the top of the thread. Also, if the camera was 26TPI LTM and the lens 1mm pitch metric the larger core diameter of the 60º metric thread could worsen the problem.
This has me worried! If I ever do get my hands on a Leica I will think twice before I try my Jupiter on it. I suppose the answer is to use Russian lenses on Russian cameras, and don't buy a Leica unless you can afford the Leitz lenses to go with it!
From what you are saying, Don, I take it that when writers refer to the later Russian lenses as LTM they are really talking about standardisation on the correct back-focus distance more than the pitch of the screw-thread, which is what was causing me some confusion. I agree about the Zorki though. I haven't run it past my shutter tester yet, but as far as I can tell everything is working spot-on and it does seem eminently usable and well made. I'm impressed, and looking forward to running some film through it. |
Glenn
Tinkerer
Username: Glenn
Post Number: 355
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 22, 2008 - 06:50 pm: |
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Steve,
Yes the LTM is Whitworth thread form. I agree that the Russian threads can be very badly formed and difficult to check with gauges. What is noticeable on all my Russian lenses is that the lens thread is a very sloppy fit - diameter wise - in the body female thread until nipped up.
I have four Zorki 1 bodies which are mated to various modern wide angle lenses. They travel everywhere with me and are less of a worry than taking my Leicas. The Zorkis have proved to be utterly reliable despite some hard use, and they are very easy to CLA. |
John_shriver
Tinkerer
Username: John_shriver
Post Number: 30
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, June 02, 2008 - 07:53 pm: |
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It was Canon who made their earliest "LTM" cameras with M39x1 threads. Same with the earliest Serenar lenses. Sometimes called "J mount". When they realized the mistake, they made cameras with a "slop" mount, where the threads were a bit loose to take either M39x1 threads, or 39mm x 26 tpi. Eventually, when they didn't care about compatibility with the old lenses, they went to a pure LTM thread on the camera.
I think the Russian LTM cameras always used the standard 39mm by 26 tpi threads. But their rangefinders are apparently calibrated for the Contax nominal 50mm lens focal length, which is a little longer than the Leica nominal 50mm lens focal length. So you get focusing errors at close distances when you cross lenses. (Much like the Nikon/Contax problem.) |
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