Using 50mm SLR lenses on your Leica M (with coupling)

[Ecar]

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Just a heads up for those who may have some legacy SLR lenses collecting dust in the basement.

I have recently received a couple of Shoten adapter - these came from Japan, although I suspect they are actually made, at least in part, in another Asian country...For the avoidance of doubt, I'll mention that I have bought these on their eBay store and have no relationship with the company.

Unlike other "dumb" adapters out there, these provide RF coupling on a Leica M for M42 and Pentax K-Mount lenses respectively. They come with their own helicoid, which allows the original lens helicoid to be used for close focus (requires LV/EVF). I believe that coupled adapters for other mounts, including Nikon-F, are at the prototype stage and will be available soon.
Some great glass was made in these mounts - and in very large volumes. This implies that used prices are (relatively) low: a fast 50mm in great condition will set you back less than $500 including the adapter...

Regarding the adapters: not much brass in there, but there's a focus tab, the fit is snug, the focus throw is short and they don't feel excessively cheap. Focus calibration with the lenses I mounted on them was 99% accurate out of the box but, in any event, fine focus is user-adjustable using the small screwdriver provided - although it can get a bit tricky and is not as straightforward as with other adapters (such as Kipon's Alpa adapter) or lenses (such as 7a's).
Worth noting also is that focus across the range will only be achievable with lenses whose focal length is 50mm. In particular, this excludes the somewhat popular SLR 55mm F/L. Another caveat is that you may occasionally run into lenses that require some minor mechanical modifications in order to mount properly (the lens pictured below is unfortunately one of them).

The adapters add about 15mm to the length of the lens. Pictures are easily available on the internet. To provide some scale, below are a couple of pictures of a Fujinon 50/1.4  EBC mounted on my M10M via the M42 to M adapter. For those who are interested, I will (slowly) post images taken with this and a few other adapted lenses in my favourite thread.

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[ocean2059]

Thank you very much for the write-up. Very interesting!

I recently saw a rangefinder coupled adapter for Leica R 35mm lenses, mainly the Elmarit-r 35 and Summicron-r 35 (not tested for the Summilux-r 35), from Taiwan. I am tempted to give it a try as I still have a few 35 R lenses which I like very much. 

Edited August 30, 2023 by ocean2059

[Ecar]

1 minute ago, ocean2059 said:

I recently saw a rangefinder coupled adapter for Leica R 35mm lenses, mainly the Elmarit-r 35 and Summicron-r 35 (not tested for the Summilux-r 35), from Taiwan. I am tempted to give it a try as I have few 35 R lenses which I like very much. 

Yes, the "rework" one. I'd try that too, but all my R lenses were sold many years ago. Obviously a mistake.

[jankap]

One could say, that the Asians have the ideas. But lens and mount should fit together.

Edited August 30, 2023 by jankap

[Ecar]

44 minutes ago, jankap said:

One could say, that the Asians have the ideas. But lens and mount should fit together.

Not sure I understand the point you are making. It's a bit too cryptic for my brain. Care to elaborate?

[jankap]

Firstly, the lens itself is set to infinity, if one uses the adapter for the range finding.

The mentioned focal length of 50 mm can in reality be from 49.5 to 50.4 mm. The thread of the distance adjustment must fit - within narrow tolerances - to the focal length. Namely, the construction must obey the Huygens rule: 1/f = 1/b + 1/v 

Where f is the real focal length of the lens; v the distance from camera to the object and b is the distance from the lens to the sensor.

One can see from the formula, that when v is infinity (far away), b must be equal to f. At shorter distances, b has to be greater than f. The picture distance b can be divided into three parts (seen in mm): part 1 is the focal length, part 2 is your mentioned 15mm and part 3 is the variable part of the adapter.

So, for the M system, the distance range runs from 0.7 meter to infinity.  Over this range, the formula must hold. That means, that say two lenses of 50mm, that - in reality - have different real focal lengths the adapter, that delivers the distance b should be thicker or thinner (part 2) AND have an adapted thread (part 3).

 

 

[Huss]

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It's a cool application, and perhaps appealing if you have a bunch of old SLR lenses.  But there are now many affordable M mount lenses being sold.  The choice no longer is just Leica.  Still neat that it is available for those interested.

I bought a whole bunch of adapters for my Nikon Z, Fuji X and Olympus M43.  Even my Leica M!  But after the initial novelty wore off, I quickly realized that all these cameras worked better, and gave better results, if I just used them with their native mount lenses.

[Ecar]

9 hours ago, jankap said:

Firstly, the lens itself is set to infinity, if one uses the adapter for the range finding.

The mentioned focal length of 50 mm can in reality be from 49.5 to 50.4 mm. The thread of the distance adjustment must fit - within narrow tolerances - to the focal length. Namely, the construction must obey the Huygens rule: 1/f = 1/b + 1/v 

Where f is the real focal length of the lens; v the distance from camera to the object and b is the distance from the lens to the sensor.

One can see from the formula, that when v is infinity (far away), b must be equal to f. At shorter distances, b has to be greater than f. The picture distance b can be divided into three parts (seen in mm): part 1 is the focal length, part 2 is your mentioned 15mm and part 3 is the variable part of the adapter.

So, for the M system, the distance range runs from 0.7 meter to infinity.  Over this range, the formula must hold. That means, that say two lenses of 50mm, that - in reality - have different real focal lengths the adapter, that delivers the distance b should be thicker or thinner (part 2) AND have an adapted thread (part 3).

Thanks. I think I understand now. And I fully agree: a given lens and a given adapter should be matched and calibrated together, since both are subject to manufacturing tolerances and deviations may add up. Most adapters do not allow for adjustment, leaving you with the only option left: adjust "part1" - i.e., the lens itself (usually by adding or removing shims), which is not ideal if you intend to keep using the lens on the system it was originally designed for. Case in point: the well-known Amedeo adapters for Nikon-S or Contax mounts are usually very well made but are also subject to small variations - and they are not adjustable.

The nice feature of these Shoten helicoids is that they allow you to achieve the required calibration by adjusting "part 3". Of course, as you imply, this means that for practical purposes each lens should be paired with its own adapter.

Edited August 31, 2023 by Ecar

[Ecar]

6 hours ago, Huss said:

It's a cool application, and perhaps appealing if you have a bunch of old SLR lenses.  But there are now many affordable M mount lenses being sold.  The choice no longer is just Leica.  Still neat that it is available for those interested.

I bought a whole bunch of adapters for my Nikon Z, Fuji X and Olympus M43.  Even my Leica M!  But after the initial novelty wore off, I quickly realized that all these cameras worked better, and gave better results, if I just used them with their native mount lenses.

It really depends on what you are looking for in terms of "results". For example, if you like the rendering of the Sonnar optical formula, you won't find many lenses in native M mount...

[Ecar]

29 minutes ago, Al Brown said:

Thank you @Ecar, I thought you of all vintage glass fans might notice these, I have one on the watchlist for my unique Porst K-Mount 50/1.2... I need to get a M42 coupled adapter they make for my 58 Biotar...

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Thanks. Yes, this one should work on the K-mount Porst.

Regarding the Biotar 58/2, you do realise though that the Shoten 50mm M42 will not enable you to focus accurately (see my opening post)? It's designed only for 50mm F/L lenses - not 55, not 58 and of course not for wider ones. Although I suspect that once their 50mm Nikon-F and C/Y adapters are released, the Shoten folks will start looking into other popular SLR F/L.

[Huss]

59 minutes ago, Ecar said:

It really depends on what you are looking for in terms of "results". For example, if you like the rendering of the Sonnar optical formula, you won't find many lenses in native M mount...

I have the ZM 50 1.5 and the Rollei 40mm 2.8.  M and LTM mount.  Also the 7A 50 1.1 which apparently is a Sonnar design.  Not sure what else I'd want.

[Ecar]

3 minutes ago, Huss said:

I have the ZM 50 1.5 and the Rollei 40mm 2.8.  M and LTM mount.  Also the 7A 50 1.1 which apparently is a Sonnar design.  Not sure what else I'd want.

Fair enough - most important thing is indeed being happy with what you get from what you have.

The 7a 35/2 v1 (not the v2) in M mount should also a be a Sonnar, I believe. And some of the MS-Optics too. Also, I don't consider LTM as "native" for the M system (still need adapters - and their tolerances vary, including the Leitz ones), but if you do, then of course there are many more Sonnars available...

[Huss]

20 hours ago, Ecar said:

Fair enough - most important thing is indeed being happy with what you get from what you have.

The 7a 35/2 v1 (not the v2) in M mount should also a be a Sonnar, I believe. And some of the MS-Optics too. Also, I don't consider LTM as "native" for the M system (still need adapters - and their tolerances vary, including the Leitz ones), but if you do, then of course there are many more Sonnars available...

I had that 7a 35 2 v1.  A really good lens.  I sold it because… not sure really.I think maybe because it wasn’t as nicely made as the CV 35 1.4 II.  Back on topic, while this adapter is not for me, it is a really cool piece.

[Ecar]

Another point worth mentioning is that focus on the adapter turns in the "Leica direction".

[Ecar]

2 hours ago, Huss said:

I had that 7a 35 2 v1.  A really good lens.  I sold it because… not sure really.I think maybe because it wasn’t as nicely made as the CV 35 1.4 II.  

My copy showed very visible red edges on some digital camera bodies (M9, M240) when used wide open against the light. It's much improved on the M10. Possibly entirely gone on the M11, but I don't have one to check. Apologies for going off-topic on the thread I started...🙄

Edited September 1, 2023 by Ecar

[TomB_tx]

It is an interesting adapter - making it possible to use the M RF with adapter 50mm lenses. I bought one to try, and it does work quite well as advertised - seems well designed and made. The focusing helical is rather heavily damped - if I were going to really use it I'd change to a lighter grease.

However, as the RF is only usable with 50mm lenses it is very limited, and as I have enough varied 50s in M mount I don't need it - I was just curious about how well it works.

I have a lot of old SLR lenses including Pentax K and M42, as well as Leica R. While Pentax dSLRs still support the K mount, they are really intended for autofocus lenses. I had better luck just adapting them to a base Sony A7 body, and with cheap adapters can use nearly all my old SLR lenses. (Haven't tried Exakta yet...) The smaller Pentax M lenses are nice on the small A7 body. Too bad no adapters operate the automatic diaphragms, but mirrorless can keep the VF bright when stopped down. Many of these old lenses are very good both mechanically and optically, and give very nice results on digital. As I get shakier I may have to try a newer A7 model with IBIS.

[Ecar]

If anyone is interested, Nikon-F and C/Y adapters now seem to be available.

Edited September 8, 2023 by Ecar

[250swb]

It’s an interesting and welcome idea, but I tend to agree with @Huss in that ultimately native lenses work hassle free a bit better. But there’d be some Leica diehards who’d be embarrassed if they could see how good a £40 eBay 50mm Takumar is. I’ll probably get one just for the hell of it.

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[Huss]

12 minutes ago, 250swb said:

It’s an interesting and welcome idea, but I tend to agree with @Huss in that ultimately native lenses work hassle free a bit better. But there’d be some Leica diehards who’d be embarrassed if they could see how good a £40 eBay 50mm Takumar is. I’ll probably get one just for the hell of it.

You don't even have to reach to a $50 Takumar.  My $20 SMC 50 f2 Pentax was embarrassingly good.  If I had to make a case for a Leica Summicron vs that Pentax to my accountant (if I had one), the best I could come up with is 'you just don't get it'...

[jankap]

Am 2.9.2023 um 15:06 schrieb TomB_tx:

However, as the RF is only usable with 50mm lenses it is very limited, and as I have enough varied 50s in M mount I don't need it - I was just curious about how well it works.

Did you try the adapter on an M camera wide open, at a distance of a few meters? Looking critical at the plane, where the rangefinder was set.

Edited September 9, 2023 by jankap