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Br1078lum
Tinkerer
Username: Br1078lum
Post Number: 88
Registered: 11-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 18, 2011 - 06:59 pm: | 
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After a comment by Glenn in reply to one of my posts, I got to wondering what is the difference between an 'L39' mount, and the 'M39' mount. All I ever see is passing reference to this subject, but nothing really definitive. And what lenses does this pertain to? (mostly Soviet I assume)
PF |
Fredtheoyster
Tinkerer
Username: Fredtheoyster
Post Number: 14
Registered: 09-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 19, 2011 - 02:19 am: |
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As I've usually seen the terms used, L39 and M39 are the same screw mount - but the register distance (lens to film distance) is larger on M39. L39 are used on Leica rangefinder cameras, FED/Zorki and so on, whereas M39 have a gerater register distance because they are used on SLR cameras such as the early Zenit, where the mirror assembly adds extra depth. I hope that's helpful. |
Glenn
Tinkerer
Username: Glenn
Post Number: 925
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, May 19, 2011 - 05:16 am: |
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You are quite correct in explaining what the L and M designations mean in terms of register, but L39 is a very misleading term when you are talking early Leicas and Soviet clones. The correct terminology for the thread is LTM - no '39' comes into the definition. The mount thread is a 'bastard', a mixture of metric dimensions for the diameter and imperial for the pitch and thread form, with the orientation of the lens to mount obviously being standardised. This is a throw back to the old RMS - Royal Microscopical Society - thread form and as Leitz were already manufacturers of microscopes, it was logical that they just upped the diameter when they produced their first interchangeable lens body. Their machines and thread cutting tools were already set/ground to the RMS pitch and form.
Problems have arisen over the years when people have 'conveniently' forgotten the Imperial input into this thread when manufacturing lenses and adapters for Leica register cameras. This is compounded by the fact that it is possible to screw the two thread systems together in some circumstances.
The M39 screw thread as used on early SLR cameras is a purely metric thread in diameter, pitch and thread form. Problems arise when you enter the domain of the Leica 1 and its Soviet clones - you can come across lenses and various mount adapters that are certainly not threaded LTM, but are threaded with a true 39mm metric thread. So the term 'L39' is a modern invention that is actually meaningless when it comes to defining specifics. The problem is compounded by the fact that due to Soviet manufacturing tolerances one does find that the LTM and pure meteric systems will interchange - lens orientation and a tightness in screwing action being the usual pointers to 'something amiss here'. |
Br1078lum
Tinkerer
Username: Br1078lum
Post Number: 90
Registered: 11-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 20, 2011 - 06:08 pm: |
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Thank you Glenn. By the way, if you post over on NFf, your old buddies over there miss you.
PF |
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