No serial Number 50mm F3.5 Elmar?

[pippy]

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45 minutes ago, jerzy said:

...To compensate this additional flange, when optics has been retained it must have been moved closer to the end of lens and respectively lens barrel must have been shortened. When during conversion optics has been renewed Elmar stayed unnumbered but the optical barrel has another construction that in early lenses and regular barrel length were used...

So if I understand you correctly the reason my un-numbered 11 o'clock Nickel has the same length barrel as my '35 Elmar is because the optical cell of the earlier lens was renewed? That would make sense.

As far as how the sizes of some of the 50mm f3.5 FSU lenses differ from the Elmar here is a quick snap I've just grabbed (rule is on edge-flange of 'supporting' lenses due to raised aperture ring).

Left to right c.1951(?) Industar-22; 1930 11 o'clock Nickel Elmar; 1935 Chrome Elmar; c.1948(?) 'f18-Scale' Un-Coated FED; 1959 Industar-50. Interestingly the FED has the shortest barrel of the bunch. Having also just carried out tests with all these lenses (at minimum focus and at f3.5 and f16/f18) the '48 FED performs almost exactly the same as the '35 Elmar; quite remarkable, really! Both Industars, however, back-focus to a degree which makes them completely unuseable;

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Philip.

Edited February 7, 2023 by pippy

[jerzy]

vor einer Stunde schrieb willeica:

To be certain about it, did they compensate for the marked different focal lengths by having a range of helicoids or am I picking that up the wrong way around?

this is a copy of spare part list, when ordering focal length group had to be specified. The whole mount consisting of flange with distance scale and movable part (with focusing knob) had to be ordered, both were matched to each other

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[willeica]

1 hour ago, jerzy said:

this is a copy of spare part list, when ordering focal length group had to be specified. The whole mount consisting of flange with distance scale and movable part (with focusing knob) had to be ordered, both were matched to each other

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Thanks Jerzy. That is exactly what I thought, that the mount had to be matched according to the focal length designation number. So, therefore, it is basically a matter of matching the focal length with an appropriate pitch in the mount.

William 

[Pyrogallol]

On a slightly different question. Does anyone know why they settled on 28.8mm as the lens flange distance ? Why not 29 or 30mm ?

[luigi bertolotti]

1 hour ago, Pyrogallol said:

On a slightly different question. Does anyone know why they settled on 28.8mm as the lens flange distance ? Why not 29 or 30mm ?

I think it's very difficult that a sure answer can emerge... was an engineering/manufacturing choice taken so many years ago... 😗 maybe (just an hipotesis) they took a "mean" flange distance of the current non standardized bodies, compared this with the mean real flange distance needed by the typical standard lens  - Elmar 5 cm - and found  28,8 as the best value considering mean manufacturing tolerances on both sides (body and lens) ; when (many years ago... 🙄) i studied the theory of tolerancing. there were many guidelines on statistics about machined parts to be coupled by thread... boring but deep matter...  and even the machine tools in use can be part of the analisys (and, who knows, there could be machines with Imperial specifications, even in a German factory...) 

Edited February 8, 2023 by luigi bertolotti

[willeica]

2 hours ago, Pyrogallol said:

On a slightly different question. Does anyone know why they settled on 28.8mm as the lens flange distance ? Why not 29 or 30mm ?

From Richter's (as translated by Fricke) book- see bottom left. The 28.8mm was fixed so that the I Model C could be used with the standard thread M39x1 that was on all the lenses made to this specification.

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This book also contains many handwritten notes from Zuhlcke to Barnack where a lot of the issues mentioned in this thread were tested and retested over a period of many years.

William 

[luigi bertolotti]

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Thanks ! Should be interesting to scrutinize the handwritten notes : indeed, the explanation about 28,8 is someway semplicistic in the text : as they say, there was already a "compensation point" for the Elmar (the lens' tube) so it should had been easy to set, for instance, the flange distance to 29 exactly and making the "0" lenses accordingly... (keeping to maintain the compensation for exact FL in the same way) ; I tend to think that there must have been some deeper reason to choose that 28,8...

 

[willeica]

1 hour ago, luigi bertolotti said:

Thanks ! Should be interesting to scrutinize the handwritten notes : indeed, the explanation about 28,8 is someway semplicistic in the text : as they say, there was already a "compensation point" for the Elmar (the lens' tube) so it should had been easy to set, for instance, the flange distance to 29 exactly and making the "0" lenses accordingly... (keeping to maintain the compensation for exact FL in the same way) ; I tend to think that there must have been some deeper reason to choose that 28,8...

 

Luigi, if I can find the time I will go through the hand written notes which are in old German script. I agree that what is printed is a summary of a lot of work that had gone on.

William 

[Chriseto]

Hi everyone, 
I'm totally beginning with Barnack cameras and bought a 1937 IIIa with a 3,5 Elmar 50. But this lens looks really weird and I found this thread when I was looking for some information. May be you'll know what this lens is actually.
Thank you in advance

Olivier 

 

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Edited February 20 by Chriseto

[willeica]

2 hours ago, Chriseto said:

Hi everyone, 
I'm totally beginning with Barnack cameras and bought a 1937 IIIa with a 3,5 Elmar 50. But this lens looks really weird and I found this thread when I was looking for some information. May be you'll know what this lens is actually.
Thank you in advance

Olivier 

 

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It looks like an 50mm Elmar lens for a I Model A which has been converted to an LTM mount. Does it stop at infinity when the knob is at 11 O'Clock or 7 O'Clock or at some other number? I see a screw at what looks like 9 or 10 O'Clock. 

William 

[luigi bertolotti]

The screw quoted by William is indeed oddly positioned (supposed that the Elmar is fully  screwed into the body); moreover, the screw itself has a not original look... I fear that the Elmar, taken by some old/damaged IA, was adapted/reworked by someone with no great care and precision... is it coupled to the rangefinder ? This a delicate rework,,,

Edited February 21 by luigi bertolotti

[pgk]

On 2/8/2023 at 8:29 AM, Pyrogallol said:

On a slightly different question. Does anyone know why they settled on 28.8mm as the lens flange distance ? Why not 29 or 30mm ?

Without having looked into the maths, my guess would be that this equated to a set of distances which an existing 50mm (exact focal length) lens required to work properly, fold into the body without hitting the shutter and which gave sufficient clearance to operate at infinity (when the optics are nearest the film plane). At a guess it was simply an engineered solution which also had to allow for marginal variation in focal length (a known tolerance). I don't think that it was actually anything to do with the mounting screw thread diameter or pitch other than that any focal length tolerance would still have to be allowed and would need to take thread pitch into account . At some point any slightly shorter than standard focal length lenses might not have been usable, so the need to accomodate the marginal, acceptable variation in focal length would have determined the minimal mount distance possible.

I suppose, as it has to be a specified distance, this was empirically based originally by Barnack and then refined when interchangablity was desired and could be engineered. I'm sure that it could have been slightly different but 28.8 was chosen because it fitted best with existing lenses and allowed them to be adjusted whilst establishing a future standard. The engineers chose extremely well.

[willeica]

7 minutes ago, pgk said:

but 28.8 was chosen because it fitted best with existing lenses and allowed them to be adjusted whilst establishing a future standard. The engineers chose extremely well.

Just one small correction, Paul. This distance was chosen based on tests done in Wetzlar by Barnack, Berek, Zuhlcke, Albert and others to achieve what you say was required. However, the distance was chosen before the LTM lenses were put on the market, or, you could say, 'just as' they were introduced. The 50mm Elmar on the I Model A was not an LTM M39 lens. It had a 33mm mount and each lens was adjusted as regards distance to ensure that that it provided a sharp image on the matched camera. I went into this at length in my recent video linked below. The British technicians, who adapted Leicas to take interchangeable lenses some years before Leitz in Wetzlar, did the same thing as Leitz was doing at that time and they matched lenses with cameras. They did not adopt a standard distance. As for why it is precisely 28.8 mm, I could not find an exact source, but it might be possible to determine the reasons for this if anyone was given full and free access to the full set of workshop papers from that time. The chances of that happening are slim. The Archive does not have the services of an archivist. They have a local archivist who can find things, if you ask all the right questions!  We met him on this expedition https://leicasocietyinternational.org/blog/a-visit-to-the-leica-archives-during-the-lsi-wetzlar-2023-conference?rq=WetzlarThere is nobody doing a comprehensive study in Wetzlar at the moment.  

William 

 

[pgk]

36 minutes ago, willeica said:

Just one small correction, Paul.

Yes, that makes good sense. Given that Barnack's base design was so good then engineers would have faced the problem of how to 'future proof' their standardised design. I'm sure that therir chosen flange to film distance took a lot of factors into account, and no doubt was based on existing requirements allied to currently being developed (lens) requirements, as well as potential (unknown) futue requirements. They would have quickly realised that a smaller 33mm mount would have been more restrictive and from then on it was no doubt about fitting a viably sized solution into a bodyshell which was acceptable. The thread and actual flange to film distance they chose have proven to be extremely effective. The M mount still allows for a simple adapter to retain full viability of early standardised lenses which means that we can use LTM even today as they were intended to be used. Quite an extraordinary achievment when all is considered.