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Thread: What kind of lens has aperture scale in mm?

  1. #21

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    Re: What kind of lens has aperture scale in mm?

    I'd like to summarize what I've learned in this thread

    > Aperture used in the f/ number calculation it's not the physical hole in the iris, it's the effective aperture "seen" throught the front element side.

    > Taking lenses have the f?number for infinite focus, as we give bellows extension to focus close we use a compensantion factor for the modified aperture.

    > "Aperture in mm" in a repro lens allows to calculate aperture directly with using and bellows extension and the mm indicated in the aperture scale, those mm are not about the actual hole (I guess), but about the effective hole seen from the front element side. As those effective mm depends on the front glass then that scale is placed in the front casket, if we replace another front casket then we have the right readings in the scale...

  2. #22

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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Mark Sawyer View Post
    The difference being?

    I think if an f/stop is the ratio of focal length to aperture diameter as measured through the entrance pupil, that would be both the actual and the effective f/stop. But I'm willing to be educated...
    At infinity, the f/stop set is the f/stop you get. At closer distances the effective f/# is larger, the effective aperture smaller, than the f/stop set. In most situations the effective f/# is so close to the f/# set but when they differ by much the difference will bite you.

    effective f/# = f/# set * (1 + magnification)

    This is aperture adjusted for magnification, incorporates the dread and highly confusing bellows factor that becomes important only when magnification is greater than around 0.3.

  3. #23

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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Pere Casals View Post
    > "Aperture in mm" in a repro lens allows to calculate aperture directly with using and bellows extension and the mm indicated in the aperture scale, those mm are not about the actual hole (I guess), but about the effective hole seen from the front element side. As those effective mm depends on the front glass then that scale is placed in the front casket, if we replace another front casket then we have the right readings in the scale...
    Papi, why guess when you can look up Zeiss' own explanation? In post #2 above I directed the OP to two CZ catalogs. See p. 17 of the 1901 CZ London catalog.

  4. #24

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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Dan Fromm View Post
    Papi, why guess when you can look up Zeiss' own explanation? In post #2 above I directed the OP to two CZ catalogs. See p. 17 of the 1901 CZ London catalog.
    I was not finding the 1910 Catalog mentioned in Post #2 , the page 14 of the 1907 explains nicely, thanks.

    https://web.archive.org/web/20170123...o/zeiss_4.html

    Click image for larger version. 

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    In page 15 they name it Apparent Diameter, (nicer than effective diameter)

    Click image for larger version. 

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    True, better not guessing

  5. #25

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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Pere Casals View Post
    I was not finding the 1910 Catalog mentioned in Post #2
    Tiene que usar "the list," dodo pequenito.

  6. #26

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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Dan Fromm View Post
    Tiene que usar "the list," dodo pequenito.
    Dan, J'ai utilisÚ la liste, mais il y a une petite erreur, le catalogue CZ de 1910 il n'est pas en C.Eccentric, et " http://www.largeformatcameras.net/ " c'est cassÚ.


    La liste dit: "Zeiss 1891, 1892, 1910, 1927, 1932, no date" , mais 1910 n’est pas lÓ et il contient "1907, 1924, 1927, 1929 et 1933", seulement 1927 est correct.

    https://web.archive.org/web/20170120....com/info.html

  7. #27

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    Re: What kind of lens has aperture scale in mm?

    Papi, de la liste:

    Zeiss Jena:

    1901 Zeiss London catalog: http://books.google.com/books?id=cnk...gbs_navlinks_s CZ London, really. In English. Click on the little starry wheel in the upper right corner of the screen to download as a PDF.

    1910 catalog: http://cnum.cnam.fr/redir?M11192 In French. Not archived, alas.

    Post-WW II: http://www.arnecroell.com/czj.pdf

  8. #28

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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Dan Fromm View Post
    1910 catalog: http://cnum.cnam.fr/redir?M11192 In French. Not archived, alas.
    Just archived: https://ia601404.us.archive.org/24/i...num_M11192.pdf


    _________

    I found a Funny document, in 1951 C.I.A. made a list with key managers at Carl Zeiss Jena : https://archive.org/details/CIA-RDP8...0012-4/page/n1

  9. #29
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    Re: What kind of lens has aperture scale in mm?

    Quote Originally Posted by Dan Fromm View Post
    Papi, de la liste:

    Zeiss Jena:

    1901 Zeiss London catalog: http://books.google.com/books?id=cnk...gbs_navlinks_s CZ London, really. In English. Click on the little starry wheel in the upper right corner of the screen to download as a PDF.

    1910 catalog: http://cnum.cnam.fr/redir?M11192 In French. Not archived, alas.

    Post-WW II: http://www.arnecroell.com/czj.pdf
    Hi Dan, thanks for the links, however in my browser there is a starry wheel but without the option to download (therefore non of the pdf's in your listings can be downloaded). Could you insert a direct link to the 1901 pdf - like you've done with the post war II pdf?

    many thanks
    Ron
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  10. #30

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    Re: What kind of lens has aperture scale in mm?

    Ron, there is no easily copied direct link.

    I just clicked on the link in your post, got to https://books.google.com/books?id=cn...gbs_navlinks_s, clicked on the little starry wheel in the upper right corner of the screen, the drop down dropped down and I downloaded the file.

    Please try again.

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