Pulling my hair out!

Discussion in 'Pinhole Photography' started by joeyk49, Apr 29, 2005.

  1. joeyk49

    joeyk49 Member

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    I build a rather simple pinhole using a large oatmeal box and a piece of punctured aluminum for the lens. The interior was painted flat black and the lid was covered and painted as well.

    I've attempted to expose some Ilford MG rc paper five or six times always with the same result. A twenty second exposure immediately turns completely black in the developer....aaargh!

    What might be going wrong?

    I'm pretty sure that the camera is light tight. The plastic lid was painted black, covered with cardboard and painted black again. Its also sealed with black electrical tape.

    My lens opening is tiny. I used the point of a small finishing nail to barely pierce the aluminum and lightly sanded the burs from the inside. It was sealed to the inside using super glue.

    My group of nine year old Cub Scouts are finishing up their cameras too, but I don't want them to start shooting, until I know that they will work for them.

    Any advise would be welcome.
     
  2. Nick Zentena

    Nick Zentena Member

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    So have you tried a shorter exposure? 20 seconds I guess is right for F/256 or so. How big is the box? Distance from the hole to the paper?
     
  3. Donald Qualls

    Donald Qualls Member

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    Well, let's check some obvious stuff (just in case). You're loading the camera and developing the paper in darkness or safelight suitable for the paper, correct (I never know what level people are working at when they're making oatmeal box pinhole cameras)? If you develop a sheet of the same paper straight out of the storage box, it should be completely white. Given this, put a sheet in your camera, put it out in the sun, and leave the pinhole covered. Let it sit there for five minutes or so, then take it into the darkroom and develop the sheet. If that sheet isn't also perfectly white, your camera has light leaks, and the solid black paper is just fogged from the time spent in the camera.

    If that paper isn't fogged, then your exposure is mongo too long, which suggests your pinhole is much too large. For a standard oatmeal box, the hole should be pretty close to .018" or about 0.45 mm, which would give around f/300; assuming ISO equivalent of 6 for the paper (few papers are actually this fast), "Sunny 16" exposures should run between about 60 and 90 seconds (without correcting for reciprocity failure -- paper should be okay in this range), but if your hole is 1 mm (about .040"), you'd get a correctly exposed (if unnecessarily fuzzy) negative at about 20 seconds, and if the hole is 2 mm it would only require about 5 seconds. To turn completely black, though, the paper would have to be overexposed by much more than the two stops you'd get with 20 seconds and a 2 mm hole, so I'd guess your oatmeal box isn't anything like as light tight as you think.

    Another quick test: with the hole closed, put a bright flashlight inside the box and close it, then look at it in your darkroom to check for leaks. Do it again with the flashlight the other direction, of course. If you see light anywhere other than the imaging pinhole, you need to seal up the leak.
     
  4. Tammyk

    Tammyk Member

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    I have a pinhole just like this with aluminum shim (is that the right word?)

    I used the tip of a beading needle #10 or #13 (not sure which).

    In bright sun, using RC paper, I get a pretty decent exposure at 60 secs.

    If you used a finishing nail, I'm just going to guess (even with just the tip) that you have a way bigger hole.

    Everything that Donald says above is exactly the things I had to go through in order to tweak my first tries- eliminating the obvious.

    My oatbox is my favorite pinhole. I love the distortion, so go have fun with it!
     
  5. rbarker

    rbarker Member

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    I suspect that Donald is onto something with the unexposed paper test he suggested. Although the inside of your oatmeal box has been painted black, my guess is that it may be surprisingly translucent in bright sunlight. You may need to cover the outside with foil to make it truly light-tight.
     
  6. Donald Qualls

    Donald Qualls Member

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    Actually, the plastic lid is the most likely culprit (IMO). Even with black paint inside and out, that lid will still be prone to leak light at the edges, where the paint doesn't cover well. For my time and effort, I plan to stick with steel cookie tins for my camera making; I've got a Starbuck's cofee tin (originally held four or five one-pound bags of coffee) that will become a 4x5 stereo camera. On all of these, I only need to blacken the interior, install film holders, pinholes, and shutters, and possibly a plug insert in the lid to block single reflections coming around the tin's seam under the lid. Never a question if the steel is lightproof.

    If you're more interested in results than appearance, or don't have access to folks who eat of lot of cookies around Christmas time, you should consider quart and gallon paint cans (the kind with the very tight lids). Very simple to work with, hold very large negatives, and the lid *is* light tight, without question, as long as it's not bent.
     
  7. Nige

    Nige Subscriber

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    I built one pinhole camera out of matt board, stappled together and black electrical tape over a couple of the seams. I have left paper in it for months and it's been fine. If you have an enlarger handy, use that to measure your pinhole accurately. Place the pinhole in the enlarger and project the hole on the baseboard. Measure the hole (you can also expose it onto some paper if you like to make it easier to measure and to examine for roundness and any daggy edges). If your enlarger column has the magnification on the column, read that and calc your pinhole size (measured circle / mag ratio) or work out the mag ratio by measuring your neg carrier (empty) and the projected rectangle and calculating (projected width / neg carrier hole width)
     
  8. joeyk49

    joeyk49 Member

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    Thanks guys.

    I'm thinking that its light leakage too. But I thought that I did pretty well with the lid. If it was an aperture or exposure time issue, I would think that I would get an image, just badly over/underexposed...not completely blown out.

    As I'm writing this, I'm starting to wonder about the seal around the aluminum sheet used for the aperture....hmmm

    The camera is made out of the larger size oatmeal cylinder, so distance to paper is about 5" or about 12,5 cm.

    I'll try some of your suggestions and see what happens.
     
  9. k_jupiter

    k_jupiter Member

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    Go down to the flghs (friendly local good hobby shop) and get a couple of #77 drill bits and a pinvise. Sand down your brass in the center till it's very thin than carefully drill the hole using the 78 drill. take a needle ro reem the hole just a bit to make sure it's ROUND.

    Cover your hole with duct tape (black is nice) with a paper punch hole in the middle. You center your small pinhole in the punch hole and tape your brass to the body of the camera box over the hole you cut in the box. Tape another piece of cardbord over top of that for a shutter.

    Now put your paper in, expose for 48 seconds. Should develop just fine.

    I use a converted 120 6x6 camera with a focal length of 75mm. It uses a
    #79 drill, and are they SMALL. The chromes I shoot with mine look like they come out of a Holga or something like that.



    tim in san jose