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Thread: Big pinholes

  1. #1

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    Big pinholes

    Currently, I'm using a borrowed Zero Image 2000 (f138), photographing slightly moving people/objects inside, generally getting 5min exposure times with FP4. I'd like to use a curved plane 120 panoramic but without the ?25min times that the usual f250+ would give me.


    I would like it to be somewhere around f140 - for an 80mm focal length that would mean a 0.6mm pinhole. How might that affect things? Would I start to see unwanted artefacts?

    Thanks,
    Mark

  2. #2
    SMBooth's Avatar
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    The image would be softer because if the larger pinhole

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    An example of what I'm aiming for: http://www.apug.org/gallery1/showima...mageuser=33351

    And I think the question I was trying to ask was 'does the absolute size of the pinhole make the difference or is it just relative?'. If it is only relative then the effect for f138 would be the same at both 25mm and 80mm focal length. At what point does the absolute size of the pinhole start to cause problems, 1mm, 2mm, 10mm?
    Last edited by MkII; 12-11-2012 at 06:07 AM. Click to view previous post history.

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    I don't know all the theory, but I made a makeshift pinhole out of an old 35mm Fujica and some cardstock last week.

    Focal length was 45mm, and the pinhole ended up being 1mm ... so I guess that's f/45 ... and the results were much too blurry for my liking. I took the camera out for a test without measuring the hole, which was foolish indeed.

    This was the best result from my test:
    Click image for larger version. 

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    I've since made a second attempt at a pinhole which seems to be around 0.28mm which hopefully will give much better results.

    No idea if the problem here is absolute or relative size, though - I think f/45 is waaay to big for a pinhole regardless the absolute size that works out to be.

  5. #5
    SMBooth's Avatar
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    For very film to pinhole distance there is a "correct" pinhole diameter. So a .6mm pinhole at one distance will give a different result if used at a longer or shorter distance. The field of view will also change. You could just use faster (HP5) film to reduce your exposure times.

  6. #6
    Joe VanCleave's Avatar
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    If you're comparing a small film-format pinhole image enlarged to the same size as a large format pinhole image, you will see enlarged pinhole artifacts in the enlarged image. For one, the image "blur" will be enhanced by the enlargement factor, such that an f138 pinhole image enlarged 4x would give an apparent blur in the final print equivalent to (138/4=34.5) shooting a f34.5 pinhole in the larger format camera directly. However, attempting to compensate for this enhanced blur in the final print by using an abnormally small pinhole in the f138 camera merely results in more diffraction in the image, if the abnormally small pinhole is smaller than that recommended by Rayleigh, et al. The net effect is that larger film formats will have intrinsically better sharpness characteristics to the image if optimized.

    MkII, your suggestion of a larger format camera with the f140 aperture actually sounds reasonable, because in the real world of practical pinhole photography the exposure time can affect image sharpness at least as much as absolute aperture, due to subject and camera support movement, plus the problems with compensating for reciprocity failure at these extended exposure times.

    I understand that Fuji Acros has improved reciprocity characteristics over more traditional emulsions like FP4, so you might want to give that a try, for reducing your exposure times at smaller apertures.

    There's also a certain crossover point where paper negatives end up giving you shorter exposure times than traditional film, since, although they have an intrinsically lower base ISO, exhibit virtually no reciprocity failure.

    ~Joe

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    Thanks for the replies. Useful things to think about.

  8. #8
    RalphLambrecht's Avatar
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    to me the softness is part of the pinhole charme. a pin-sharp pinhole is not desirable. that said there are two optimal pinhole diameters, one for resolutionand one for contrast. the contrast equationhas the larger following among lens shooters.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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    Have you considered a zone plate?



 

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