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 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 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 

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Hallo,

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