Telyt-V 200mm marking.

[luigi bertolotti]

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Luigi, 208.5mm is too far away from the nominal focal length. I note that my "125mm" Hektor, which is really 120mm, has no marking.

 

208,5 = 200 + 4,25%

52,2 = 50 + 4,4% (Summicron) : but ok, this is academic... is clearly 198,5, seeing how is my item....

[luigi bertolotti]

Luigi, 208.5mm is too far away from the nominal focal length. I note that my "125mm" Hektor, which is really 120mm, has no marking.

 

My Hektor 125 (Wetzlar) too has no external marking, but has a "119,5" hand engraved on the inner barrel.

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[david werbeloff]

Hello, All,

 

I finally got around to unscrewing the optical unit of my lens. It's hand engraved "214" - upside down. So clearly, judging by the sampling mentioned here, the external engraving covers a range either longer or shorter than the nominal focal length of 200mm. Seems like there is a wider latitude for over than under. Mine is 214, K-H has 226, etc.

 

I wonder what the "basic" focal length of the lens blank was before the grinding and polishing process started. Does this imply that a slightly more skilled tech. was able to grind and polish the lens to spec. and still remove less material thus leaving it well above the nominal focal length?

 

Just a thought.

 

Best,

David

[Orient XI]

There are many variables that affect the focal length of a compound lens. These include individual lens curvature(s), slight variations in the refractive indices of the glasses used, thickness of each lens, and the thickness and refractive index of the cement between compound elements. Mechanical tolerances are usually under much better control than glass tolerances, but could include spacing between components. However, several very promising Leica lens designs have never made it beyond the prototype stage because their performance was too sensitive to inter lens spacings.

[jaapv]

I wonder what the "basic" focal length of the lens blank was before the grinding and polishing process started. Does this imply that a slightly more skilled tech. was able to grind and polish the lens to spec. and still remove less material thus leaving it well above the nominal focal length?

 

Just a thought.

 

Best,

David

No. It stems from the Leica habit of matching individual lens elements to reach the performance of the reference lens. Optical correction takes precedence over focal length. Edited July 27, 2014 by jaapv

[luigi bertolotti]

Hello, All,

 

I finally got around to unscrewing the optical unit of my lens. It's hand engraved "214" - upside down. ....

David

 

214mm and "85" on side... ... strange pair.... of course, it could have happened that one of the two parts has been exchanged for some maintenance/repair reason... and, after all, for Visoflex lenses the lenshead-focus unit coupling is much less critical than for RF lenses; anyway , seems one case which confirms the opinion of people who say that the Ontario factory was less careful to certain details (notice that also the "highly toleranced 226" quoted by KarlHeinz is a Canadian, whilst his "200 spot on" and my "199,5 just-0,25%" are from Wetzlar....)

Edited July 27, 2014 by luigi bertolotti