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  1. #1

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    Hi all, I built a simple pinhole camera with my son made out of cardboard that uses 4X5 sheet film. The distance from the pinhole to the film is about 6 inches. I have been having trouble getting good images with my hand punched pinholes (sewing needle) exposure is OK but the focus seems poor. I am pretty careful to keep it steady.

    Is there are way to get more precise pinholes other than using a sewing needle? I may be mis-calculating the pinhole diameter needed for the focal distance.

    Thanks in advance for your advice.

    John

  2. #2
    glbeas's Avatar
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    Are you just pushing the pin through or using a piece of wood to back up the metal as you punch it? You should also deburr the hole very carefully with some very fine grit sandpaper.

  3. #3

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    also, what material are you using for the pinhole? if you'r eusing the cardboard the box is made from you're going to have a hard time getting a 'sharp' image. I make mine out of aluminium 'coke' cans. Cut a can up with some scissors and make the hole by swiveling the needle (drilling) rather than punching it through, and like Gary says, sand each side with the finest sandpaper your can lay your hands on.

  4. #4

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    Nige & glbeas, thanks for your response. I do use a cut coke can and sand down the burrs on both sides. I think the pinhole diameter is wrong. I think it should be .298mm for the 152mm focal length. Any idea what size needle to use?

    Thanks,
    John

  5. #5
    glbeas's Avatar
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    As a needle has a good bit of taper to it you should be able to use a hard piece of wood behind it to restrict the penetration and make a smaller hole as needed. Simple get a larger needle for bigger holes. If you have or know someone with a set of calipers you might could measure the needle diameter to get an idea how big the hole is going to be. If doing a smaller hole than the shaft of the needle the measure how far up the taper of the point the right size is and try to aim for that depth when "drilling" the hole.

  6. #6

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    have you measured your pinhole to confirm the 0.298mm?

  7. #7
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  8. #8

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    Project the pinhole as large as you can get it with your slide projector or enlarger and ratio the diameter of the projected image with something of known length projected to the same enlargement. This gives the actual pinhole diameter. The diameter of the pinhole is not all that critical as long as it's very small and reasonably clean-edged.

  9. #9
    Ed Sukach's Avatar
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    Quote Originally Posted by Lemastre
    Project the pinhole as large as you can get it with your slide projector or enlarger and ratio the diameter of the projected image with something of known length projected to the same enlargement. This gives the actual pinhole diameter. The diameter of the pinhole is not all that critical as long as it's very small and reasonably clean-edged.
    I don't think this would work - the theory behind the "pinhole" is to diffract the light passing through to the extent that it would give a "lens- like" effect... bending the rays to a "pseudo" focus plane. I've tried measuring small spaces on a Optical Comparator, and the edges become *extremely* fuzzy and indistinct. If they did not, it is likely that the "pinhole" is too large for use.
    Carpe erratum!!

    Ed Sukach, FFP.

  10. #10

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    I've used my enlarger and it worked really well.

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