Circle of confusion and Hyperfocal distance of a pinhole camera

Discussion in 'Pinhole Photography' started by Samuel Hotton, Feb 6, 2006.

  1. Samuel Hotton

    Samuel Hotton Member

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    I am using a Zero Image 75B Deluxe 4x5 pinhole camera with a fixed 3 inches (75mm) focal length pinhole at a calculated f216 aperture.
    I have no idea IF a pinhole has a Circle of Confusion nor what the near focus of its Hyperfocal distance would be.
    Does any one have any idea what would be the closest distance acceptable focus could be had with this camera configured as described?

    Many thanks,
    Sam Hotton
     
  2. Nige

    Nige Subscriber

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    it's equally sharp (or fuzzy as may be the case) throughout the DOF

    checkout www.mrpinhole.com for some good info, calculators and links
     
  3. Poptart

    Poptart Member

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    Circle of confusion is a term that applies to the image on the film plane; it has more to do with the depth-of-focus than the type of lens. That said, a pinhole will create a standardized focus throughout its range--generally about 9"-infinity. The limitations on sharp focus are the result of refraction against the edge of the pinhole in the smallest apertures.
     
  4. Donald Qualls

    Donald Qualls Member

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    It's commonly said that pinhole cameras are equally "sharp" over all distances, but it's easy to show geometically that they lose sharpness as the subject gets "close" to the pinhole. This is not a matter of refraction (not present in the absence of a lens) or diffraction (which is a function of hole size, light wavelength, and projection distance, independent of subject distance), but simple geometry; the diverging light rays from a close object will produce a larger "spot" at the image plane than the more nearly parallel rays from a "distant" object, and the larger image spots from closer objects will make those objects less sharp, just as the circle of confusion does for objects further from the plane of focus when using a lens.

    In practice, depending on the format and focal length, this effect starts to make itself visible inside a distance of anywhere from 3x to 10x the projection distance (incorrectly called focal length by most). If you routinely make macro images, it can pay to make the pinhole smaller, and there's a version of the optimum hole size equation around that accounts for hole-to-subject distance as well as hole-to-film -- but if you mostly make images of objects more than a foot or two beyond the pinhole, you can ignore this effect.
     
  5. manjo

    manjo Member

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  6. Christopher Walrath

    Christopher Walrath Subscriber

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    I would keep the subject 10 feet out just to be safe.
     
  7. Donald Qualls

    Donald Qualls Member

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    Ten feet is many times what's needed. Common pinhole cameras, with a projection distance of, say, 20 to 100 mm, give very acceptable results with subjects down to a foot or closer; if you make the pinhole a little smaller than the commonly calculated "optimum" figure you can cut that minimum distance in half with little loss at longer distances.
     
  8. eddie gunks

    eddie gunks Member

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    hello, i also have the same set up as you do. i have not tried a close up with the 75mm on. but as mentioned about about a foot or so should do it for you. may i also suggest you shoot with the 25mm? i find it is simply awesome. here are two links you may enjoy. notice on the first i also put pictures of me shooting the scene. get closer always. http://www.photo.net/photodb/folder?folder_id=565448
    http://f295.tompersinger.com/cgi-bin/Blah/Blah.pl?b-cc/m-1138897213/
    also be sure and check out f295. http://f295.tompersinger.com/cgi-bin/Blah/Blah.pl? it is a very helpful and friendly group. enjoy.

    eddie
     
  9. eddie gunks

    eddie gunks Member

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  10. Jim Jones

    Jim Jones Subscriber

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    Donald Qualls' comments agree with my research. The basic simplicity of pinhole photography has lured many practitioners into believing that precision is unnecessary. Where optimum sharpness is needed, the diameter of the pinhole should be calculated, and the pinhole fabricated (or purchased) within a few percent of the ideal size. When the diameters of the pinhole and the Airy disc are nearly the same size, there is a distinct increase in on-axis resolution. Then, line pairs smaller than the pinhole diameter can clearly be resolved. The image suffers from reduced resolution and slight astigmatism at angles away from the axis. Maximum pinhole image quality is obtained with large format wide angle cameras. Enlarging the pinhole of a wide angle camera fairly well evens out the sharpness across the image at a considerable loss of on-axis resolution. Fortunately, a good photographer can often create fine pinhole photos with little regard to the quest for optimum resolution.

    Traditional hyperfocal and DOF formulae don't always apply to pinhole photography. The discrepancies between the many charts and formulae for pinhole diameters should be resolved by each photographer based on his own preferences. Someone with a modest understanding of physics and math and a drive for perfection may find an in-depth study of pinhole optics rewarding. Others may find just making pinhole photos more useful.
     
  11. Poptart

    Poptart Member

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    O boy. Pinhole photography is, by nature, low-res; it's an aesthetic of d.i.y. and has no need for precise focus. That noted, pinholes have approximately the same depth at any given distance from 9"-infinity if they are properly fabricated, and so, the circle of confusion is standardized throughout that range. As I said earlier before my stalker added his convoluted two cents. And I repeat, if you make the hole too small you begin to get interference from the edge--regardless of what you choose to call that distortion.