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  1. #1
    marciofs's Avatar
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    7x9in Pinhole camera test

    It seems the borders wasn't exposed. Could it be because it is too wide? Or maybe too short exposure?

    It has 0.350mm Pinhole Diameter and 88mm focal length.

    Click image for larger version. 

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  2. #2
    Dave Wooten's Avatar
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    The image is not evenly circular? Look for an "obstruction"
    Burr etc at the bottom and around lens. ?
    [FONT="Arial Black"][/FONT]

  3. #3
    marciofs's Avatar
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    I got it! I seems to be the tape around the hole. I think because it is so wide angle that the tape is blocking the borders.

    I Just gave more room and I am doing a last test today because the sun is going away (30min. exposure ouside).

    I show the result later on tonight.

  4. #4
    DWThomas's Avatar
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    As you get into really wide angles, it's amazing how many bits of mechanics can obstruct the light path. A pinhole is strictly a ray tracing situation, there is no retrofocus or other tricks like might be done with lenses.

    In another thread, one about converting a Brownie camera to a pinhole, I posted a diagram of how one might do a scale layout to determine what will or won't vignette. It was tailored to a 6x6 format, but the method could be adapted to any situation. The biggest problem is making accurate measurements if there is a an aperture at the bottom of a hole or some other stuff in the way of using normal measuring tools.

  5. #5
    marciofs's Avatar
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    Thank you DWThomas,

    I made the tape wide but it didn't changed much. I will check Thomas link:

    Click image for larger version. 

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  6. #6
    Joe VanCleave's Avatar
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    Another useful way to test a camera's angle of view for vignetting is to use a red laser pointer, aimed into the pinhole from outside the camera. You should be able to project the laser all the way into the corners of the image area at the film plane.

    ~Joe

  7. #7

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    It is not vignetting due to an obstruction it is because the distance from the pinhole to the film surface is greater at the edges than from the pinhole to the centre and the edges are underexposed. If you curved the film plane or made a centre filter you could reduce the problem. Or it could be done with careful dodging when printing.

  8. #8
    DWThomas's Avatar
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    Quote Originally Posted by NormanV View Post
    It is not vignetting due to an obstruction it is because the distance from the pinhole to the film surface is greater at the edges than from the pinhole to the centre and the edges are underexposed. If you curved the film plane or made a centre filter you could reduce the problem. Or it could be done with careful dodging when printing.
    Enh, it's true there is noticeable fall-off at wide angles off-axis, but to my eyes the images above show shadows of an irregular "edge" of some sort. The situation you're describing is more subtle and graduated (in my experience).

  9. #9
    Jim Jones's Avatar
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    The soft edges of the image circle and the non-circular shape suggest a pinhole with the edges too thick. The dimple, punch, and sand method usually does a good job of thinning this edge. Also, there will be several stops less exposure at the corners of a pinhole image with such a wide angle.

  10. #10
    marciofs's Avatar
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    There was a tape near the pinhole that was making this edge not circular.
    But the problem is that the box is too narrow which places the filme too near the hole.

    I am looking for a box which I can have 7x9in but I can't find any that will be deep enough to avoid vignetting. When I find it is too bit.

    Maybe I will have to make a box with woods.

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