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Thread: Fixed focus 4x5 camera

  1. #41

    Join Date
    Jul 2008
    Posts
    91

    Re: Fixed focus 4x5 camera

    Bit by bit my camera comes together. It looks like crap (still). Sorry I don't have photo's yet. As good as I could I managed to get infinity in focus and subsequently have tried ever since to get a filmholder in the plane of focus :-) Just a bit more and then painting the insides black and go for a testride with the camera. Propably my second attempt will be one following all the advise I have gotten here :-). Will post some photo's soon though... to be continued...
    Stupid questions deserve stupid answers.
    allthingsanalogue.weebly.com
    http://www.new55project.com

  2. #42

    Join Date
    Jul 2008
    Posts
    91

    Re: Fixed focus 4x5 camera

    @Steve I use a 65mm super angulon wide angle lens. I decided to use the Sinar lens board because it is already on it and I don't have the proper tools to take it off.
    Stupid questions deserve stupid answers.
    allthingsanalogue.weebly.com
    http://www.new55project.com

  3. #43

    Join Date
    Oct 2015
    Posts
    33

    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Emmanuel BIGLER View Post
    From where do I measure de focal lenght of the lens? From the plate where the lens is attached?

    Hello from France!

    This is a frequently asked question

    What you want is to set the proper distance between the lens mount and the film.
    Hence, to do this, the knowledge of the focal length is not really useful, as strange as it may seem!
    What you need is a distance given by lens manufacturers, named "flange focal distance" or sometimes "Flange Focal Length" (e.g. in Fuji lenses documentation).
    This is the distance between the back side of the shutter and the focal point. The focal point is where an image of a far-distant object is projected sharp.
    Now in order to properly set your lens mount in front of your film holder, you have to take into account the film holder's depth, which is for modern film holders compliant with the ANSI standard
    - 2" x 3" and 4" x 5" : 5.0 mm +- 180 microns (0.197" +-0.007")
    - 5" x 7" : 5.8 +- 250 microns (0.228" + - 0.010")
    - 8" x 10" : 6.6 mm +- 400 microns (0.260" + - 0.016")

    If you already have a springback with ground glass, simply focus the image of a distant object, no computation is required.

    And if you wish to fix-focus at the hyperfocal distance, instead of infinity, starting from the flange focal distance, you'll need to slightly increase the length between the lens and film by a small amount, to be easily computed according to your working f/number, focal length and sharpness criterion.

    You can have a look at this article (in French) by Gilles Barbier who built a fix-focus camera for the 5x7" format.
    http://www.galerie-photo.com/barbier-hybis-90.html
    In this case, focal length was 90 mm, the sharpness criterion was 150 microns, the working aperture f/16, hence the offset required to focus at the hyperfocal distance instead of infinity was 3.3 mm.
    I've seen your replies a couple of times in different threads regarding this question, so OP excuse me if I highjack this one for a question. If I want to set up a fix-focus camera with a 90mm Super-Angulon, I have a Flange Focal Distance of 99mm and a Back Focal Distance of 67mm. Do those numbers change ragarding the F Stop? If I wanted to have the image sharp at f8, would the distance of the lens to the film change at f22? Or is f16 / f22 just a more "comfortable" area for the setup. The 67mm BFD should stay the same, no matter the how the lens is stopped down, correct?

  4. #44

    Join Date
    Dec 2001
    Location
    NJ
    Posts
    6,576

    Re: Fixed focus 4x5 camera

    FFD at infinity is FFD at infinity is FFD at infinity ...

    BFD at infinity is BFD at infinity is BFD at infinity ...

    Both are independent of aperture.

    When you set your camera up, focus the lens, don't rely on published FFD. Lenses as made rarely have the focal length engraved on them or the FFD published in the brochures. For best results, focus the lens or measure its FFD at infinity.

  5. #45

    Join Date
    Oct 2015
    Posts
    33

    Re: Fixed focus 4x5 camera

    Yes, first I will confirm the distance with my full plate camera, then with the one I am building. It's a custom 6x12 so no ground glass, but I am making one to confirm the focus. Thanks!

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