M42 to M39 Adapter

thuggins · Sep 5, 2019

I have an M42 lens that I'd like to use on an M39 rangefinder. I found a couple of adapters on that site, but they all say the lens won't focus at infinity. This makes no sense. The flange to film plane distance for an M42 is greater than for an M39 due to the mirror box, so an adapter should space it out a bit and allow infinity focus.

Oddly enough, the opposite adapter is quite common. Basically it is a step down ring with an M39 female thread and an M42 male thread. Since both threads are in the same plane there is no change in the mounting distance. This really makes no sense as the M39 lens would certainly not focus at infinity on an M42 body (apart from other issues such as automatic aperture control).

The only thing I can think of is that they just make the adapters too short. The spacer would need to be a bit over a half inch, and judging from the pictures that is not the case. So there are two mysteries.

1. Why is the M42 to M39 too short, when it could be easily made the correct length?
2. Why do they even make an M39 to M42 adapter when mounting and M39 lens on and M42 body would be essentially useless?

I'm almost tempted to buy two of the M42 to M39's and one of the M39 to M42's and stack them. But that would actually cost more than what I paid for the lens.

Dan Fromm · Sep 5, 2019

https://www.ebay.com/itm/Kipon-M42-...ax-Lens-to-Leica-M39-L39-Adapter/330771999802

https://www.ebay.com/itm/M42-Screw-...r-Type-701-601-Mirrorless-Camera/273183350168

AgX · Sep 5, 2019

First link is dead, second leads to a M42/bayonet adapter.

Dan Fromm · Sep 5, 2019

AgX said:
First link is dead, second leads to a M42/bayonet adapter.

Thanks for checking.

Cut-and-paste error with the first link. It should be: https://www.ebay.com/itm/Kipon-M42-...ax-Lens-to-Leica-M39-L39-Adapter/330771999802 I've corrected it in my post above.

As for the second link, the image doesn't agree with the text, the text is internally consistent. Given eBay's consumer protections, I think the thing is worth buying.

AgX · Sep 5, 2019

The text is for Leica-T mount which is a bayonet.

StepheKoontz · Sep 5, 2019

OK: the M39 to M42 ring is for adapting the super early Asahiflex (And I think some soviet model) lenses to a later M42 camera, they both share the same flange to film plane as they are both SLR's. It's not for LTM lenses/L39 mount to an SLR, which you are right, wouldn't work except for macro work. There are M42 to L39 adapters that do allow infinity focus, but won't have rangefinder coupling. M42 to M39 adapters won't focus to infinity because it's a step down adapter for a M42 SLR lens to a M39 SLR camera.

I think you are confused because you think M39 and L39 are the same mount, they aren't. The M is an SLR mount, the L is the leica/rangefinder mount.

GRHazelton · Sep 5, 2019

StepheKoontz said:
OK: the M39 to M42 ring is for adapting the super early Asahiflex (And I think some soviet model) lenses to a later M42 camera, they both share the same flange to film plane as they are both SLR's. It's not for LTM lenses/L39 mount to an SLR, which you are right, wouldn't work except for macro work. There are M42 to L39 adapters that do allow infinity focus, but won't have rangefinder coupling. M42 to M39 adapters won't focus to infinity because it's a step down adapter for a M42 SLR lens to a M39 SLR camera.

I think you are confused because you think M39 and L39 are the same mount, they aren't. The M is an SLR mount, the L is the leica/rangefinder mount.

Ummm..... My AsahiFlex IIa has a 37mm screw thread lens mount. I don't know what the flange to film distance is or even whether a M37 to M42 adapter is now available. I'd like to find one since I have my Father's 83mm f1.9 Takumar for the AsahiFlex. I've heard of a semi-mythical AsahiFlex made with a 42mm lens mount, but I've no proof of its existence. A pity that Asahi didn't choose the 42mm mount which had been introduced by the Contax S in 1949. Sporting a fixed pentaprism the Contax S was a handsome camera, influencing SLR design for decades.

The AsahiFlex is a lovely little camera. It resembles a Leica pre-M camera, but with a folding hood for focusing. Its fit and finish are impeccable, probably equal to Leicas'. Thank heaven the Asahi engineers gave it a proper hinged back for film loading.

StepheKoontz · Sep 5, 2019

My bad, it is 37... and yes there are M37 to M42 adapters on ebay, basically an internal and external thread. It was the Zenit that was a M39 SLR.

This chart should help. M39 is 39mm X 1mm. L39 is 39mm X 26 threads per inch, the common rangefinder threading.

https://fotodiox.freshdesk.com/support/solutions/articles/17000083341-m39-l39-ltm-lsm-whats-what-

GRHazelton · Sep 5, 2019

StepheKoontz said:
My bad, it is 37... and yes there are M37 to M42 adapters on ebay, basically an internal and external thread. It was the Zenit that was a M39 SLR.

This chart should help. M39 is 39mm X 1mm. L39 is 39mm X 26 threads per inch, the common rangefinder threading.

https://fotodiox.freshdesk.com/support/solutions/articles/17000083341-m39-l39-ltm-lsm-whats-what-

Not to worry. I'll have to look into the 37 to 42 mm adapters. BTW, since you are in Doraville, are you familiar with Wings Camera? A "dangerous" place for old camera nuts. Mike is my source for old stuff.

StepheKoontz · Sep 5, 2019

I went there today. Took a couple of light meters I didn't need, thinking I would walk out with a few $. Instead walked out with a mint Rolleiflex 3.5A lol He did give me a good price for my meters and on the camera. As you said, a dangerous place

reddesert · Sep 5, 2019

thuggins said:
1. Why is the M42 to M39 too short, when it could be easily made the correct length?
2. Why do they even make an M39 to M42 adapter when mounting and M39 lens on and M42 body would be essentially useless?

I'm almost tempted to buy two of the M42 to M39's and one of the M39 to M42's and stack them. But that would actually cost more than what I paid for the lens.

The base answer is that neither of these things is intended for what you want to do, but there are workarounds.

Q 1. Don't know, but some years ago when it was harder to get all these kinds of adapters, I made an M42 to Leica 39mm adapter by taking one of these short adapters and adding an old M42 extension tube. I filed the M42 extension tube to the right length. Some of these tubes have long internal threads, which you need so that there are still enough threads after filing. I suspect the original purpose of the M42 to M39 adapter is to put an M42 lens on another accessory that has 39mm threads, perhaps bellows and the like.

Q 2. StepheKoontz has it close. The thin M39 lens to M42 camera adapter rings are to adapt an M39 SLR thread mount lens such as certain East Bloc lenses, to an M42 SLR. For ex, Zenit started off making M39 SLRs and then switched to M42 SLRs.

GRHazelton · Sep 6, 2019

StepheKoontz said:
I went there today. Took a couple of light meters I didn't need, thinking I would walk out with a few $. Instead walked out with a mint Rolleiflex 3.5A lol He did give me a good price for my meters and on the camera. As you said, a dangerous place

Wowzer! Good on ya! BTW, Rollie Dan does good work, here on Photocrio. I have a Minolta Autocord he massaged. Looks and feels like a demo. Our Mike at Wings here in HotLanta is dangerous man to frequent, as you has discovered. I fear I am turning into a CAMERA COLLECTOR! Oh, the Horror!.... Good thing I have a forgiving Spouse. As Mike has said, "Photography is an expensive hobby. But it is cheaper than car collecting, and far, far cheaper and SAFER than having a mistress!" Truer words were never spoken! Not that I have personal experience.....!)

AgX · Sep 6, 2019

StepheKoontz said:
It was the Zenit that was a M39 SLR.

Not quite.

The pre E-family models have a M39 mount, few early samples of the E-family have it too. The vast majority of E-family samples have the M42 mount.
Successor Zenit models got a either M42 or bayonet mounts.

thuggins · Sep 6, 2019

Thanks for the replies; I certainly know a lot more about threaded mounts than I did before.

Armed with this new knowledge I went back to that site and noticed that the postings often conflate M39 and L39. Given that a 1mm pitch would be 25.4 tpi I am assuming that these threads are functionally interchangeable. There are a couple of adapters listed there that do what I want, but they cost more than the lens. Perhaps I'll stick with using this lens on my FTL.

StepheKoontz · Sep 6, 2019

GRHazelton said:
Wowzer! Good on ya! BTW, Rollie Dan does good work, here on Photocrio. I have a Minolta Autocord he massaged. Looks and feels like a demo. Our Mike at Wings here in HotLanta is dangerous man to frequent, as you has discovered. I fear I am turning into a CAMERA COLLECTOR! Oh, the Horror!.... Good thing I have a forgiving Spouse. As Mike has said, "Photography is an expensive hobby. But it is cheaper than car collecting, and far, far cheaper and SAFER than having a mistress!" Truer words were never spoken! Not that I have personal experience.....!)

I'm definitely a collector and as you said, it's a reasonable hobby compared to some others. And most of what I collect, I'm sure I could sell for close to what I paid for them if not more in the future. Buying the newest digital gear loses almost all of it's value in a short period of time.

abruzzi · Sep 10, 2019

thuggins said:
The only thing I can think of is that they just make the adapters too short. The spacer would need to be a bit over a half inch, and judging from the pictures that is not the case.

Just one small comment. If the adapter is too short, the lens will reach infinity and past, but the focus scale will be inaccurate and it won’t reach minimum focus distance. If the adapter is too long, then it won’t focus to infinity.

Wallendo · Sep 11, 2019

My personal experience is that lens adapters are best used with SLR's (or dSLR's and mirrorless cameras) where focus can be visually confirmed. When used on a rangefinder, everything in the optical path has to be perfectly calibrated to work well (the camera mount, the adapter length and the lens's mount.

AgX · Sep 11, 2019

If there is a camera back that can be taken off, one can check focus by groundglass or aerial image.

M42 to M39 Adapter

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