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  1. #121
    barryjyoung's Avatar
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    If you are geek minded like some of us,,,,maybe not me,,,you can find a fascinating discussion (With cartoons) of how to determine correct pinhole size from an engineers perspective at:

    http://photondetector.com/blog/2006/03/28/pinhole-size/

    You have to download the .pdf file to see it. It is for guys with calculator holsters, but maybe the rest of us can glean something from it.

    As far as I know there are two age old formulae for determining pinhole size.

    .0073 times the square root of the focal length (I use this one and it works well for focal legths near the same length as the diagonal of the film).

    The other is Lord Rayleighs formula 1.9 times the square root of the focal length times the wavelength of light you want to bring to focus at that focal length.

    But then, why not just go to :

    http://www.pinhole.cz/en/pinholedesigner/

    and let the computer do all those nast calculations for you?
    Barry Young
    Young Camera Company

  2. #122

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    Thanks, Barry. I downloaded pinholedesigner a while ago, wanted to know what Chris had done.

  3. #123
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    Quote Originally Posted by barryjyoung
    .0073 times the square root of the focal length
    Just for clarification, this formula for calculating the optimum pinhole size measures the focal length in inches not millimeters.

  4. #124
    Steve Smith's Avatar
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    Quote Originally Posted by narsuitus
    Just for clarification, this formula for calculating the optimum pinhole size measures the focal length in inches not millimeters.

    It shouldn't make any difference. Measure the focal length in inches, the hole size will be in inches. Measure it in millimetres, the hole size will be in millimetres.

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  5. #125

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    seeing as I have no easy way of cutting or measuring a hole so small I enjoy simple guesswork!

    yay pinholes
    "Where is beauty? Where I must will with my whole Will; where I will love and perish, that an image may not remain merely an image."

  6. #126
    semeuse's Avatar
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    Haven't built a whole camera (yet) but I've built a couple of lenses for my 8x10 field camera.
    picture of 400mm lens with f16 stop installed: link
    picture taken with same: link

  7. #127
    barryjyoung's Avatar
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    Quote Originally Posted by Christopher Colley View Post
    seeing as I have no easy way of cutting or measuring a hole so small I enjoy simple guesswork!

    yay pinholes
    Oh yes, we do indeed have a way of both cutting and measuring pinholes.

    1. Get the book by Jim Shull entitled "The Hole Thing". What a great book! Your library can inerlibrary loan a copy for you if they don't have it. I sometimes see them on bookfinder.com and on ebay.com.

    2. If you cannot get the book because like me you are too tired cold or scared to do so, then get ye to the nearest fabric store and buy an assortment of hand sewing needles. Measure the needle with a micrometer or go to any machine shop where they will happily measure the needles for you and write the diameter on the handy masking tape tabs you have already attached to the needles so they don't have to.

    3. Push the desired needle eye first into a pencil eraser which is still attached to the pencil. It makes them muche easier to handle that way. Try to make it coaxial with the pencil which is now the handle for the needle.

    4. Put a piece of aluminum foil onto a piece of cardstock (Cap'n Crunch boxes are made from the industries finest card stock). Press the neddle into the foil while spinning the handle (pencil). This will make a very nice and perfectly round hole of the diameter you desire. If you believe this statement skip step 5 and imediately begin making breathtaking opinhole images.

    5. Oh ye of little faith. If you just HAVE to measure the pinhole, it can be done using a microscope. Focus the microscope on your calibrated needle. Tape a piece of velum (special drawing paper made from sheep intestines or something) over the eyepiece of a standard light microscope. mark the shadow cast on the velum by the needle. replace the needle with the pinhole and voila! you can compare the diameter of the calibrated needle to the diameter of the pinhole. Clever huh?

    Good luck.
    Barry Young
    Young Camera Company

  8. #128

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    Barry you just killed pinholes for me. God why do you people have to be so damn technical about everything? To me the beauty of a pinhole is in the soft image not another technical excersice is getting the perfect super sharp image creating pinhole. I use a regular lens for that.

    I just use a PIN and put a HOLE in some metal and put that on a box or a tube and have fun. Getting out the microscope to measure the hole just takes all the fun out of it for me.

  9. #129
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    Quote Originally Posted by Harrigan View Post
    Barry you just killed pinholes for me. God why do you people have to be so damn technical about everything? To me the beauty of a pinhole is in the soft image not another technical excersice is getting the perfect super sharp image creating pinhole. I use a regular lens for that.

    I just use a PIN and put a HOLE in some metal and put that on a box or a tube and have fun. Getting out the microscope to measure the hole just takes all the fun out of it for me.

    I didn't say you had to. So poke holes in foil with a pin and have fun.
    Barry Young
    Young Camera Company

  10. #130

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    OR, if you want a 'perfect' hole -- and it just HAS to be, for example, .432 mm in diameter, just have it laser drilled in a piece of .001 brass shim stock.



 

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