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I have a homemade pinhole camera (film) that I use for taking super long exposures (multiple months). And while the results are fun, I would like to improve the sharpness of the image. Is diffraction my only problem?

Are there lens designs which are sharper than a pinhole image while also allowing for long exposure times?

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  • \$\begingroup\$ If there's a lens, doesn't that mean it's no longer a pinhole camera? :) \$\endgroup\$
    – laurencemadill
    Commented Jun 25, 2015 at 15:39
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    \$\begingroup\$ @laurencemadill Yup. I'm not a purist. It doesn't have technically be a "pinhole" to make me happy. \$\endgroup\$
    – john_science
    Commented Jun 25, 2015 at 15:42
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    \$\begingroup\$ en.wikipedia.org/wiki/Coded_aperture "In a coded aperture more complicated than a pinhole camera, images from multiple apertures will overlap at the plate or detector array. It is thus necessary to use a computational algorithm (which depends on the precise configuration of the aperture arrays) to reconstruct the original image. In this way a sharp image can be achieved without a lens." \$\endgroup\$
    – Count Iblis
    Commented Jun 25, 2015 at 17:11
  • \$\begingroup\$ This is my question. Please delete it. The question has been edited by someone else and no longer really reflects my question. Also, the answers no longer reflect my question. Perhaps my question was poorly phrased, or the answer is just "no". \$\endgroup\$
    – john_science
    Commented Jun 25, 2015 at 18:44
  • \$\begingroup\$ Does the current version (with more edits) now reflect what you're looking for? \$\endgroup\$
    – mattdm
    Commented Jun 25, 2015 at 19:13

4 Answers 4

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No, there is no lens design that allows for sharpening a pinhole image. This is because pinhole cameras by definition don't have lenses.

You can replace the pinhole with a lens to get more sharpness with lower f-stops. That's why normal cameras have lenses instead of pinholes.

With a pinhole, the sharpness gets better as the pinhole gets smaller, which also decreases the amount of light getting thru. Eventually as you make the pinhole smaller, diffraction effects dominate and sharpness gets worse again. This is basic physics that you can't get around. Note that diffraction effects are a function of the pinhole size to the wavelength of light. You can get a sharper picture (use a smaller pinhole before diffraction makes sharpness worse) if you are only imaging with blue light, for example.

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  • \$\begingroup\$ Obviously I understand that adding a lens means it will no longer be purely a "pinhole". I am not interested in "pinhole purity". I just want to know if I can improve the sharpness of my image, but keep my very long (multi-month) exposures. \$\endgroup\$
    – john_science
    Commented Jun 25, 2015 at 17:19
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    \$\begingroup\$ I think most photographers use ND filters for extremely long exposures. You could use a lens in your design and stack on filters to give the exposures you want. Or you could use an optimum sized pinhole with ND filter material in front of it. \$\endgroup\$
    – BobT
    Commented Jun 25, 2015 at 18:22
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There are basically two ways to make a pinhole camera sharper. as Olin Lathrop said, the smaller the pinhole the sharper the image, but if it gets too small, diffraction come into play. There is an optimal diameter of the pinhole and this formula calculates it:

Diameter = Constant x sqrt(Focal Length x Wavelength of light)

There is a bit of mess about what the value of Constant should be. If you're interested, this answer summaries the issue nicely.

The other factor is how round the hole is. Perfectly round holes will give the best results. You can even order laser drilled holes online.

You can also use bigger film, but I guess it's not very useful since you probably need a bigger camera too.

I've not suggested using a lens because as I've read in a comment you are interested in maintaining very long exposures and adding a lens will dramatically shorten the exposure time.

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As @BobT suggests, a sharp lens with neutral-density filter(s) could do the job, or you might use multiple short exposures. In any case, take into account reciprocity failure, which will; require yet longer exposures in very dim lighting, and which causes color shifts on most emulsions.

It should be interesting to see the photos here, showing only really permamnent objects, with all else blurred (e.g. watching the grass grow).

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    \$\begingroup\$ You might be interested in the photographs of Michael Wesley with images such as this (the streaks in the sky? that's the sun's path - each path traced out over multiple days (the exposure was about a year and a half long)). \$\endgroup\$
    – user13451
    Commented Jun 27, 2015 at 3:32
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Assuming a "medium" brightness (averaging day & night), ISO 25, f/64, with a 9-stop ND should get you to about 30 days. I haven't seen a reciprocity failure chart that goes that high, but I would assume that would carry you out as far as you want to go. A lot of assumptions, but it sounds possible to me.

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