I do not know if this helps or not as what you describe is rather odd and I have never heard of exactly this issue. I knew there were 39mm variants (such as the ones for Paxette and for Zorki cameras) but not similar mounts with slightly different diameters.
My personal thought is that this may be some kind of one-off experiment by a private owner if the throat diameter is different from the standard diameter of 39mm. I have had a Soviet rangefinder before, and it mounted LTM glass natively so any mod would have entailed modding both lens and camera. I have owned the Summaron 35mm f3.5 in LTM and it was absolutely standard size in its thread specifications. I also sometimes used it with a Leica LTM to M adapter and again it worked perfectly. (I later sold it because another Summaron 35mm f3.5 came into my hands and this one was in native M mount which was more useful to me. I have also owned several Canon rangefinder cameras and I can confirm that Leica LTM lenses all mounted and worked.
So, feeling curious, I typed the following into my AI Search Engine to see if anything came up:
"Other than the Leica Thread mount (LM) what other cameras used a 39mm thread mount which is the same or similar but may vary in thread pitch etc?"
The response (which I have not really analyzed yet - I just got up and have not yet had my "heart starter" (black coffee) was as follows:. There appears to be no mention of cameras/lenses with similar but smaller throat diameter than 39mm but this may be because my question was not explicit on this point.
"Several cameras used 39mm thread mounts that are similar to or identical in diameter to the Leica Thread Mount (LTM/L39), but many differ significantly in flange distance (the distance from the lens mount to the film plane), making them incompatible for focusing, or use different thread pitches.
Here are the main cameras and systems using 39mm threads, categorized by their relationship to the true 39mm x 26tpi (threads per inch) Leica standard:
1. True LTM/LSM/L39 Compatible (39mm x 26tpi~28.8mm Flange)
These cameras share the same thread diameter, pitch, and flange distance as Leica, allowing for direct, interchangeable use of lenses:
2. Incompatible 39mm Systems (Different Flange/Pitch)
These cameras use a 39mm thread, but lenses cannot be used interchangeably with Leica cameras without significant modification or extension tubes:
- Early Soviet Zenit SLRs: The Zenit 1, 3, 3M, and C used a 39mm mount, but with a ~45mm flange distance (similar to M42) rather than the 28.8mm rangefinder standard. These are sometimes called "ZM39".
- Braun Paxette: These rangefinder cameras use a 39mm thread, but the flange distance is different from Leica, and the lenses often have no rangefinder coupling cam.
- Soviet Chajka 2, 3, 2M: A half-frame camera with a 39mm thread that is not compatible with standard rangefinder flange distances.
- Great Wall DF (Chinese SLR): Used a 39mm screw mount.
3. Specialty/Other 39mm Usage
- Enlarger Lenses: Almost all photographic enlarger lenses use a standard M39 x 1/26" thread, which allows them to be physically screwed into Leica cameras, although they lack focusing mounts and cannot focus to infinity.
- Miranda Mirax: A reflex housing (mirror box) made by Orion Seiki/Miranda with a 39mm thread.
Key Differences to Note
- LTM/L39: 39mm diameter, 26 threads per inch, 28.8mm flange distance.
- Zenit M39 (ZM39): 39mm diameter, usually 1mm pitch (not 26 tpi)~45mm flange distance.
- Early Canon (J-mount): 39mm diameter, but with 24 threads per inch (incompatible with 26tpi).
- Canon Rangefinders: Models II, III, IV, V, VI, P, and 7.
- Soviet Rangefinders: FED (1, 2, 3, etc.), Zorki (1, 2, 3, 4, 5, 6), MIR, Drug, and Leningrad.
- Japanese "Leica Copies": Nicca, Leotax, Tanack, Yashica YE/YL, Melcon, and Honor.
- Other: Voigtländer Bessa (L, T, R), Corfield Periflex, and Reid "
