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Thread: Help with brass lens

  1. #1

    Join Date
    Jul 2020
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    7

    Help with brass lens

    I bought a 19th-century camera and was wondering if anyone by chance had some helpful info about the lens? I've searched from links here and my own research and not making much progress, and hoping someone here may know something. It has '18491 / C. Berthiot Fabricant Opticien Paris / No. 3' engraved. Would also like to know aperture size since it is not listed and I've tried doing the focal length/diameter but the math just doesn't seem right...any help is appreciated.
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  2. #2
    Foamer
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    Oct 2010
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    South Dakota
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    Re: Help with brass lens

    It looks like a rapid rectilinear lens. Set flat on a table with bright light above shining directly into it. Slowly raise the lens watching the spot of light focus below it. When the spot is sharpest measure from the spot to the middle of the lens. That's roughly the focal length. I would guess it will be 8 to 12 inches.


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  3. #3

    Join Date
    Jul 2020
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    7

    Re: Help with brass lens

    Yeah I tried that but I did it in a large room against a wall until the spot of light was sharp..but i used a flashlight so not sure if that messed up the test or not..because the spot was sharp on the wall and it was about 10 feet away haha. But I'll try again tomorrow using natural light from window and a smaller room and try it again.

  4. #4
    Foamer
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    Oct 2010
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    South Dakota
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    Re: Help with brass lens

    I think you'll find the lens is likely f8 too.


    Kent in SD
    Qui sedes ad dexteram Patris,
    miserere nobis.

  5. #5
    Philippe Grunchec's Avatar
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    Jul 2007
    Location
    Paris (France, not Texas)
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    342

    Re: Help with brass lens

    Patrice H. Pont & Jean-Loup Princelle:

    http://www.lereve-edition.fr/en/doss...sier-collector
    "I believe there is nothing more disturbing than a sharp image of a fuzzy concept!" (Ansel Adams)

    https://philippe.grunchec-photographe.over-blog.com/

  6. #6
    Alex Timmermans
    Join Date
    May 2008
    Location
    Holland
    Posts
    588

    Re: Help with brass lens

    http://https://www.facebook.com/100000725324881/posts/1191236357577197/?
    Here you can see how to measure it quite accurate.
    "You dont take a picture, it's given to you"

    www.alextimmermans.com
    www.collodion-art.blogspot.com
    email : collodion-art dot onsmail dot nl

  7. #7

    Join Date
    Jul 2020
    Posts
    7

    Re: Help with brass lens

    Yah it's about an F8 and then Waterhouse stop makes it approximately f18.

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