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Thread: Less is pinhole

  1. #1

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    Less is pinhole

    A trip with Obscura.
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  2. #2

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    Less is pinhole

    2nd part.
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  3. #3

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    Hope you guys have some tips for me.I want improve it more.I think now it's all about the focal length, because now I use a real pinhole, made from a cheap chinese watch.It is from metal , very thin, and has the perfect small hole, sort of ~0.4mm.
    I really love my Obscura camera.Next film that goes in must be better than this one , wish me luck!

  4. #4
    Romary's Avatar
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    What is the focal length?

  5. #5

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    Sort of ~ 50mm-51mm.I just have to go closer or further.Tricky!Any advices?

  6. #6
    bsdunek's Avatar
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    Looks like your effective f-stop is about f125. In my experience, I find that you need at least f200 to get a reasonably sharp photo. Just a suggestion.
    Bruce

    Moma don't take my Kodachrome away!
    Oops, Kodak just did!
    For all practical purposes, they've taken Kodak away.


    BruceCSdunekPhotography.zenfolio.com

  7. #7

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    Your pictures are very soft. Pinhole pictures are always a bit soft - and maybe this is what you want?

    But if you want sharper - there is a mathematical relationship between the hole to film distance and the diameter.
    The idea is that the circle of confusion gets smaller as the diameter decreases, but as the diameter decreases diffraction gets worse, so there will be some ideal compromise diameter for best sharpness.

    If you use the formula d = SQR( F/k)

    where F = film to hole distance, and k is a constant, about 1300.
    (SQR means square root)
    Different people use different constants and formulas, but it gets you in the right area.

    For a film to hole distance of 50mm - you want about a hole diameter of about 0.2 mm, I reckon.

    Or... to work that backwards from a hole size of 0.4 mm, F = (0.4*0.4) * 1300 = 208.

    So, I reckon that pinhole is ideal for being about 200 mm from the film. (If I've got my maths right?!!!)

    What size film are you using? That would be a 'Normal lens' on 5 X 4"
    Steve

  8. #8
    Romary's Avatar
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    I do not believe in the formulae for the holes there are more than 50 formulas for that hole. All these formulas give very differente result with a sometime a factor two betweens the results. I wrote an article in my blog with formula from various great specialists of optic, physics etc which give totally deferent results. The article is in franch, but you can have a look at the fomulas and the curves)

    But saying that, that does not means the size of the hole is not important. If you want a sharper results, 0.4 mm for a focal length of 51 mm seems to me a bit too big. A hole with a diameter of 0.2 or 0.3 mm should improve clearly the results in term of sharpness.

    Second thing, you said that you used a part of a Chinese watch. How thin is the material. I doute it is a thin as for example a piece of beverage can. The thickness is clearly also important (an taken in account in the formulas).

  9. #9

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    pinhole or any "soft" image enlarged ..
    require a larger viewing distance.
    the thumbnails look sharp as nails,
    and if you take a few steps back
    the enlarged jpg's look nice as well
    from a distance ..
    nice work !
    my only suggestion would be to make the images less "tippy"
    unless angled composition is what you were going for

    have fun !
    john

  10. #10
    SMBooth's Avatar
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    Your exposures look ok so what ever exposure calc your using is working for you. At 50mm a .3 pinhole is around the right mark so your .4 is not so far off to worry greatly. I would expect sharper pinhole image for this setup unless you where not using a tripod or other support. Maybe the material of the pinhole is to thick, I use a soft drink can and sand in back with some 1000grit wet and dry sandpaper. If this effect, which is not unpleasant is what your looking for then keep going.
    f295.org is an active pinhole site that you may wish to visit as well.

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