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04-22-2020, 04:53 AM   #1
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Did Pentax Asahi make a m39 to k mount converter?

I am asking if Pentax Asahi had ever made a m39 to k mount converter as I saw one for sale recently but could find no info that they had ever made one. Many other makers make such converters, but you can't get infinity focus with these. If anyone knows I would be very grateful.

04-22-2020, 05:12 AM - 2 Likes   #2
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Not that I'm aware of... and the reason being, the flange focal distance of K-mount (45.46mm) is greater than that of M39 (45.2mm).

You can use an M42 adapter and put an M39 to M42 step up ring on your M39 lenses (these are readily available on eBay). You won't be able to focus to infinity, though - the maximum focal distance will be somewhat limited; but it's fine for closer range work
04-22-2020, 05:32 AM - 1 Like   #3
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It appears Asahi made an M42 to L39 and a L39 to M42 adapters but not a L39 to K-mount adapter. See the posts in this thread: There are links to photos of the adapters in the thread.

M39 Leica mount adapter -

Note that the Fotodiox M39 to M42 adapter (it's simply a ring with an M42 outside thread with an M39 inside thread) does not thread into the OEM Phillipines made M42 adapter but threads fine into the Japan made OEM adapters, bellows and extension tubes. Since there is no stop on the ring I would hesitate to mount it directly on an screwmount body.

See also these threads:

Note: Minolta made a L39 to SR (MD) mount adapter. I have one in my collection.
04-22-2020, 06:23 AM   #4
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I have a Pentax-made M/L39 to M42 adapter. It was intended primarily to mount shorter FL enlarging lenses* onto tubes or bellows for macro photography.

*M39 became the standard thread for shorter (= generally ~105mm or less) enlarging lenses a long time ago. Several Nikon and Componon enlarging lenses are excellent for macro at 1/2X and greater magnification macro range, although above about life-size many work better in reversed orientation**. Specialty deep-macro/micro lenses such as the Zeiss Luminar series, Leitz Photar, and Canon 20mm macro use an RMS (Royal Microscope Society) thread. Pentax did make an RMS to K-Mount adapter for mounting these or microscope objectives onto tubes or bellows. I also have one of these adapters.

**This is using the lens in the manner intended, with a short distance from subject to lens, and a longer distance from lens to focus plane = the lens is being used to "project" the subject image onto the sensor just as it would project a negative onto a piece of enlarging paper.

AND FYI: High quality M/L39 to M42 and RMS to M42 adapters are available from Thor Labs.

04-22-2020, 11:03 AM   #5
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The Holy Grail of converters is the Pentax M37 to M42 converter.
04-22-2020, 12:58 PM - 4 Likes   #6
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There is a bit of confusion regarding these various screw mounts. Here are some bullet points:
  • Pentax never produced a 39mm thread mount lens.
  • Leica thread mount (abbr. LTM or L39) is 26tpi Whitworth* with a flange focal distance of 28.8mm. LTM lenses cannot be adapted to SLR cameras, but SLR lenses may be adaptable to LTM cameras. Many enlarger lenses are LTM.
  • M39 Zenit (aka M39 SLR) is 1mm metric and is found on some early Soviet-made cameras. M39 has a flange focal distance of 42.2mm. M39 lenses cannot be used on LTM cameras.
  • M42 (aka Praktica/Pentax thread mount) is 1mm metric with a flange focal distance of 45.6mm, the same as Pentax K.
  • M39-to-M42 adapters are widely available though with sacrifice of infinity focus on M42 cameras.
  • Some M39 lenses may be adjusted or modified to allow infinity focus on M42 cameras.


* There is some variation in the thread form, particularly in Soviet-made product.

Last edited by stevebrot; 04-22-2020 at 01:15 PM.

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