Pinhole beginner - help needed...

Discussion in 'Pinhole Photography' started by elangovans, Jan 30, 2005.

  1. elangovans

    elangovans Member

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    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.
     
  2. Nige

    Nige Subscriber

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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. :smile:

    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. elangovans

    elangovans Member

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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. John Bartley

    John Bartley Member

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    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. John Bartley

    John Bartley Member

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

    Nige Subscriber

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    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)

    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!


    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. Ed Sukach

    Ed Sukach Member

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    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.
     
  8. John Bartley

    John Bartley Member

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    Right on!! "exponential" is the word I couldn't think of before coffee this morning:smile:

    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. smieglitz

    smieglitz Subscriber

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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. Mongo

    Mongo Member

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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.
     
  11. mdohoney

    mdohoney Member

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    When I made oatmeal carton (cardboard) cameras I found that, in spite of sealing the base, covering the lid with contact paper and painting the inside black I still had leaks. I solve it by giving each carton an aluminum foil 'bonnet'.

    It's possible to determine the size of a pinhole by using a scanner. I copied the following from a thread on the f295 website (http://f295.tompersinger.com) It was posted by Dvoracek.

    "Put in on the scanner, set the resolution to the highest it will go, select as little area around the pinhole as possible and scan. Once you have the scan, look at it at 100%, 1:1, or Actual Pixels., enlarging it to 200 per cent doesn't hurt.

    I you're using photoshop or photoshops elements, crop it down to just the hole itself, using select, cut, paste and then look at Image Size under the Image menu and it will tell you what size it is."

    Once you get the size of your pinhole the calculators linked to the f295 site are quite useful.
     
  12. Nige

    Nige Subscriber

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    I've used the scanner method but I didn't get a distinct cut off point (where the pixels go white to black... there were lots of grey ones even when bumping the contrast during scanning. Maybe scanning as line-art would fix that but at the time I didn't think of that and was too eager to try the pinhole out anyway) so had to guess a bit, not that it really matters as you'll still need to experiment with the final exposure anyway.

    Ummm, I don't think that paragraph would pass a grammer checker! :smile:
     
  13. Nige

    Nige Subscriber

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    oops, just re-read your original description again at some other site :smile: and I must have read it wrong the 1st time. So, I'll amend this to, most likely a light leak! The paper gets blacker with more exposure. The rest (f-stop, paper speed, etc) stands as a method to determine likely exposures.
     
  14. elangovans

    elangovans Member

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    I am kinda convinced that the cause could have been the light leak. Overall, I learned a lot but of course got confused a lot too. Did not think this would get this complecated. well... should go back to the clean slate. :smile: and start fresh, I guess.

    Elangs
     
  15. elangovans

    elangovans Member

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    Thanks all you guys. Here is what I have come back with. I tried agian yesterday... I scanned the negative and inverted using PS.

    I know this is no where near to perfect, however, here is for you to view and comment it. I think, there is still some light leak or some issues in the picture.

    Thanks
    Elangs.
     

    Attached Files:

  16. elangovans

    elangovans Member

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    Forgot to mention... this is picture of the swimming pool. The things that are shown up here are the rails in the swimming pool... :smile:
     
  17. smieglitz

    smieglitz Subscriber

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    This looks very mottled and I suspect part of that could be the result of a light leak through the camera material or exposing through the wrong side of the paper as mentioned earlier. But, it appears to me that the development is also very uneven and I suspect that much of the mottling is coming from poor development technique. How long was your development? Also, it looks like there is a development line meandering through the image from not immersing it in developer quick enough. Be sure to give the image full development with constant agitation.

    Is the paper you are using outdated? That could be another factor in the overall grayness/fog and mottled appearence.
     
  18. John Bartley

    John Bartley Member

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    Ok - call me a wierd nut, but....that almost looks like multiple, enderexposed images to me.
    I can see a wrought iron fence if I look hard enough and once I am told what it is supposed to be, but what I see first and without suggestion, is a bridge in the upper half of the photo, and a face in the centre, with the mouth in the bottom centre.
    Below the bridge and in what looks like a background is a cityscape?

    Oooh - I gotta see what I put in my coffee this morning......
     
  19. mark

    mark Member

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    Looks like serious fogging to me. You never said what the material you made this from was. Was it card board or metal. I would spray both flat black in side as, if I remember the inside of the one metal oatmeal tin I have seen it was a copper color. Copper will reflect light and have it bouncing all over the inside of your camera.
     
  20. Donald Qualls

    Donald Qualls Member

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    I'm in agreement here -- the long curved line across the sheet, especially, is almost certainly due to getting into the developer unevenly. Also, is it possible you pulled the paper after a lot less than the full development time (typically 2 minutes in Dektol 1:2, 68 F)? That will give a muddy appearance, where the shadows (or in the case of a paper negative, the highlights) aren't fully developed and are gray instead of black. And you have a lot of fog -- for which others have made good suggestions.

    The mottling looks very much like an effect I once saw when trying to contact print paper to paper to get a negative print, caused by variations in the density of the paper and/or the reflective backing behind the emulsion. Is it remotely possible you could have exposed the backing side of the paper, instead of the emulsion side? Under safelight, most papers are glossier on the emulsion side, but a few matte surface RC papers are actually shinier on the back...
     
  21. elangovans

    elangovans Member

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    You are right.. this is a iron rods - around the swimming pool. in the bg, you see some bush and apartments doors.

    Also, the oatmeal box is cardboad box. which is spray painted inside and covered with black contact paper. The lid is spray painted and on top a black paper taped. Still dont know where could be the light leak...

    About the back side of paper ... I m going to do a test on it, maybe this week end.

    You guys have been of great help.

    Thanks a ton...
    Elangs.

    Elangs.