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Thread: Distortions Exposure and the ground glass

  1. #1

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    Distortions Exposure and the ground glass

    I shot my first distortion this weekend. I haven't had time to develop it yet. I noticed the amount of perceived light coming through the ground glass was reduced as I rotated the standards.

    Is this a result of less light actually making it to the film back thus requiring a lower aperture to compensate or simply a perceptual issue as the ground glass has swiveled off axis resulting in an anomaly as light passes through the fresnel.

    Thanks!

  2. #2

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    Re: Distortions Exposure and the ground glass

    If you are doing movements and your eye does not remain centered in the optical path the view will become dim.

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    Drew Bedo's Avatar
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    Re: Distortions Exposure and the ground glass

    I have done some shots of that involved both swing and tilt without noticible fall-off or other change in the negative or print.

    How much movement is involved in a "distortion" exposure.
    Drew Bedo
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    ic-racer's Avatar
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    Re: Distortions Exposure and the ground glass

    Quote Originally Posted by 1erCru View Post
    I shot my first distortion this weekend. I haven't had time to develop it yet. I noticed the amount of perceived light coming through the ground glass was reduced as I rotated the standards.

    Is this a result of less light actually making it to the film back thus requiring a lower aperture to compensate or simply a perceptual issue as the ground glass has swiveled off axis resulting in an anomaly as light passes through the fresnel.

    Thanks!
    The illuminance on the film plane falls off as the fourth power of the cosine of the off-axis angle.

  5. #5

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    Re: Distortions Exposure and the ground glass

    By distortion I meant an aggressive movement that hopefully will elongate part of the image.

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    Re: Distortions Exposure and the ground glass

    Quote Originally Posted by 1erCru View Post
    By distortion I meant an aggressive movement that hopefully will elongate part of the image.
    Two things going on here.

    1. Whichever part of the ground glass is farther from the lens will receive less light than the nearer part. Illumination decrease is due to the angular coverage decreasing. This is simply due to the increased "bellows draw" between one part of the viewing screen and the other. There will be a corresponding change of illumination at the film plane too, but this is seldom a problem.

    2. The viewing angle often changes significantly with extreme movements, taking your eye out of the "hot spot." If your eye isn't lined up with the angle of light projected by the lens, the ground glass can seem very dark. This can be exacerbated with a Fresnel screen. This "darkness" for viewing, however, doesn't affect illumination on the film. You can compensate for this by searching for a better viewing angle. You may need a loupe with a skirt that you can adjust the angle on, or a loupe that you don't have to rest on the ground glass so you can simply angle it to align with the line from lens-to-ground-glass.

    As for "hopefully" elongating part of the image: View cameras are WYSIWYG. You should easily be able to see the result of any movement. If your distortion is apparent on the ground glass, it'll be on the film; if not, it won't.

    Best,

    Doremus

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    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Distortions Exposure and the ground glass

    Quote Originally Posted by 1erCru View Post
    By distortion I meant an aggressive movement that hopefully will elongate part of the image.
    For that type of distortion (e.g. turning a circle into an oval) the film must be at an angle to the subject.

    You will likely need a wide-angle lens with significant coverage, perhaps 65mm or shorter on a 4x5.

    - Leigh
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  8. #8

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    Re: Distortions Exposure and the ground glass

    Yeah I should have used the term " slight elongation ". Nonetheless I can't believe have fascinating this camera is.

  9. #9

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    Re: Distortions Exposure and the ground glass

    Yes--to accentuate the effect of perspective, the rule is the closer you are to the subject, the more perspective "distortion" is enhanced--so shorter focus lenses produce more effect than longer focus lenses.

  10. #10

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    Re: Distortions Exposure and the ground glass

    Quote Originally Posted by Lou Baleur View Post
    Yes--to accentuate the effect of perspective, the rule is the closer you are to the subject, the more perspective "distortion" is enhanced--so shorter focus lenses produce more effect than longer focus lenses.
    You are not describing distortion. Distortion, at its most basic, makes lines curve.

    What you are describing is an effect due to optical physics. Foreshortening. That means things closer to the lens reproduce larger then things further from the lens. This is what creates large front shoulders, larger noses and foreheads in portraiture or that minnow that someone caught that looks like a trophy fish.

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