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  1. #1
    elangovans's Avatar
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    Pinhole beginner - help needed...

    Need help on this pinhole photography. I have made a pinhole camera at home using Oat meal tin.


    • Body: Oat meal tin


    • Lens (Hole) : #14 pin


    • Film: Ilford Multigrade IV Deluxe MGD.44M 5x7-25 Sheets B&W Variable Contrast RC (Resin Coated) Pearl Paper


    • Exposed for: 20 sec.


    • Result: I tried a picture today around 10am with sun light as my daughter as subject sitting in front of a wall. When I developed this paper tonight I got some kinda Black with bit of white textured paper and nothing else is visible.




    Whats wrong? Is it over exposed or under exposed. Why could I not see any sense of image in there?

    I need to try for tomorrow again. Any clue would be highly appreciated.

    Thanks
    Elangs.

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    Too short of an exposure most likely. It would be good if you could measure your pinhole diameter so you can work out the f-stop you should factor your exposures from. I have no idea what a #14 pin measures, maybe you can find that out somewhere. I use my enlarger to measure the pinhole by projecting it and measureing the circle then calcuating using the magnification factor. If I recall from usefilm correctly you don't have an enlarger yet, so you won't be able to do it that way. If yo have a slide projector you might be able to use that. If you can, there's a nifty exposure calculator at www.mrpinhole.com

    I use Agfa RC usually and it has an effective speed of 4-6. I actually also stick a Grade 00 filter across the pinhole to lower the contrast a little, but that slows the speed in half again, not that it really matters.

    If you can't work out the size of your pinhole accurately, I suggest doing tests shots, using a smaller piece of paper since there's no point wasting a whole piece, doubling the time until you get something reasonable, then fine tune They don't need to be too 'black' as I think you find they hold detail when being lighter than you think they should be. Contact print them to see how they really behave.

  3. #3
    elangovans's Avatar
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    Thansk for the quick tip, Nige.

    I researched the web and found that #14 needle is approx of 1/100th Inch size.

    Just want to confirm...
    Since it turned to kinda black with white patches of wall (bg), are you saying this is underexposed? Is this because, the paper that has come out the pinhole camera is the negative?

    Do you think I should increase the exposure? I tried in my bath(dark)room, if I expose the paper for 20 sec with 15w bulb (at about 2ft above), the paper turned to black once I developed. Doesnt this mean, it is overexposed?

    Please clarify.

    Elangs

  4. #4
    John Bartley's Avatar
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    Quote Originally Posted by elangovans

    Do you think I should increase the exposure? I tried in my bath(dark)room, if I expose the paper for 20 sec with 15w bulb (at about 2ft above), the paper turned to black once I developed. Doesnt this mean, it is overexposed?

    Please clarify.

    Elangs
    Hello,

    I think the idea is that a 0.01" (1/100'th) diameter hole really greatly restricts the amount of light that the paper can see compared to having NO restriction. This following is not exact I know, but it may help to think of it as a ratio. If the hole is 1" and it takes 1 second to expose properly, then a hole 1/100'th as big might take 100 times as long or, 100seconds (1-1/2 minutes). Remember that this is just an example and not the correct math. The link Nige gave will have lots of the correct info.

    regards
    .

  5. #5
    John Bartley's Avatar
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    Quote Originally Posted by elangovans

    the paper turned to black once I developed. Doesnt this mean, it is overexposed?

    Please clarify.

    Elangs
    Oops - forgot one thing - paper turning black in the developer is exposed - not turning black (staying white) is underexposed or not exposed

  6. #6

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    Quote Originally Posted by elangovans
    Thansk for the quick tip, Nige.
    I researched the web and found that #14 needle is approx of 1/100th Inch size.
    ok, measure your focal length (from pinhole to paper) and poke those numbers into the calculator at mrpinhole to get your f-stop to use for exposure calcs (there's a exposure calculator there too, so have a play with that too)

    Just want to confirm...
    Since it turned to kinda black with white patches of wall (bg), are you saying this is underexposed? Is this because, the paper that has come out the pinhole camera is the negative?
    yep, its a negative, which you'll need to contact print to a positive. The highlights in your scene will go black on the paper neg, so you're trying to expose so that you get some 'black' (hopefully it's grey's) in the shadow areas of the scene, however paper is contrasty so this can be difficult without blowing the highlights clean off the paper!


    Do you think I should increase the exposure? I tried in my bath(dark)room, if I expose the paper for 20 sec with 15w bulb (at about 2ft above), the paper turned to black once I developed. Doesnt this mean, it is overexposed?
    You're not taking the aperture of the pinhole into account if I understand you right here. Do the calcs mentioned above and you'll be able to meter with your normal camera, then extrapolate to get a pretty accurate time at your f-stop (which might be f200 or something like that). My base exposures are 1min for one camera, 2mins for another. I make guestimates if I think I should.

    Yell out if any of this doesn't make sense!

  7. #7
    Ed Sukach's Avatar
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    Quote Originally Posted by John Bartley
    This following is not exact I know, but it may help to think of it as a ratio. If the hole is 1" and it takes 1 second to expose properly, then a hole 1/100'th as big might take 100 times as long or, 100seconds (1-1/2 minutes). .... This is just an example and not the correct math. The link Nige gave will have lots of the correct info.
    The math is actually correct, ... BUT ...

    The "size" of the "hole" (aperture) must be considered in terms of hole area, not diameter. A hole with a diameter of 0.010 (we are talking ratios here, so I won't bother with metric conversions) will have an area 1/10,000 as "large" as one with a diameter of 1.0" (0.000 078 54 / 0.7854). It will admit 1/10 000 as much light - so (praying that I have all my decimal points in the right places) ten thousand times more time is necessary for the same amount of light to reach the light sensitive surface. That would be 10 000 seconds (~ 14.5 "stops") or about 2 hours, 46 minutes, 12 seconds.

    Reciprocity - additional time necessary due to the extended exposure - comes into play . I have not addressed that here.

    I'm going to check all this with the "Pinhole Calculator" program. I may return - very quickly - with massive editing ... all this is "back of an envelope" calculating.
    Carpe erratum!!

    Ed Sukach, FFP.

  8. #8
    John Bartley's Avatar
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    Quote Originally Posted by Ed Sukach
    The math is actually correct, ... BUT ...

    The "size" of the "hole" (aperture) must be considered in terms of hole area,
    Right on!! "exponential" is the word I couldn't think of before coffee this morning

    Maybe though, when Nige and Elangs finish up calc'ing for the 0.01" needle size, they'd share the exposure time with us?

    regards

  9. #9
    smieglitz's Avatar
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    I have to disagree with the previous posts. This sounds like overexposure or fogging to me if I am reading you correctly. You are getting an image out of the camera on the original paper that becomes largely black with only a few area remaining white when the sheet is developed Is this correct? If so, the paper is receiving too much exposure somehow.

    You state you are using an "oatmeal tin" for the camera. Is this an actual metal cylinder or is it a standard cardboard oatmeal box? The latter needs to be painted black inside to become opaque. Even then, the lids usually leak light.

    The description of your image with the patches of "white textured paper and nothing else" sounds like the texture that might result from exposing through the wrong side of the paper like when you make a contact sheet through the base rather than on the emulsion side of the sheet. Such an image looks very unsharp and mottled due to the paper fibers. Could that be what you are seeing?

    By all means determine the pinhole diameter to try and narrow the correct exposure, but from what I'm reading, you have too much and not too little already. I suspect you are getting exposure fog rather than image exposure.

  10. #10
    Mongo's Avatar
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    Just a quick note here on determining pinhole diameter: If you have a flatbed scanner it's pretty easy to scan the pinhole at a known resolution and figure out the size of the pinhole from the circle that you see on-screen. This can be helpful information when using pinhole exposure calculators.

    Although you know your needle size, if the needle moved at all in the horizontal direction when you made the pinhole then you really don't know the pinhole size without measuring it. I've used the flatbed trick for years and it's helped me a lot.
    Film is cheap. Opportunities are priceless.

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