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Thread: Portrait Euryscop Series III N4A

  1. #1

    Join Date
    Aug 2017
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    Switzerland
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    Portrait Euryscop Series III N4A

    Hello group,
    I have a Portrait Euryscop Series III N4A witch is upon the Voigtlander catalog a 10"5/6 : 275mm F/4.5
    I want to make some Waterhouse stop.
    When I mesure the full aperture at the Waterhouse stop place I get 55,5mm
    so I found that the full aperture of the lens is more F/4.95 than F/4.5 (275/55,5=4,95)
    does it sound right to you ?

    Laurent

  2. #2

    Join Date
    Aug 2018
    Posts
    212

    Re: Portrait Euryscop Series III N4A

    For a pinhole, it would be right. Once you get lenses involved, things change.

    If you place a SLR in back of your camera, you can find effective aperture pretty close when comparing with a modern lens you trust the aperture of.

    Sent fra min SM-G975F via Tapatalk

  3. #3

    Join Date
    Jan 2009
    Location
    Denmark
    Posts
    6,082

    Re: Portrait Euryscop Series III N4A

    Yes, it does Sound right!

    It is quite normal that the longer focal lengths do not quite met the formal speed give to a Series.
    For instance, the size 8A - focal length 25, front lens diameter 5 - is even further away from F.4.5.

    Or even more dramatic, size 9 series IV has a focal length of 46 and a diameter of 6.5 and doesnt come close to the promised F6!

  4. #4

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    Aug 2017
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    Re: Portrait Euryscop Series III N4A

    Quote Originally Posted by Steven Tribe View Post
    Yes, it does Sound right!
    focal length 25”, front lens diameter 5”
    yes you may be right, but I understand than you don't have to mesure the front lens diameter but the "entrance pupil" that it is placed at the diaphragm

  5. #5

    Join Date
    Jan 2009
    Location
    Denmark
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    Re: Portrait Euryscop Series III N4A

    Quote Originally Posted by Laurent Laval View Post
    yes you may be right, but I understand than you don't have to mesure the front lens diameter but the "entrance pupil" that it is placed at the diaphragm
    ………..as seen from in front of the front lens!

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