Some time ago I discussed the optimum size for a pinhole to be used in digital pinhole-camera photography. Iu2019ve now done some practical work, the results of which are presented hereu2026
I had a commercially-supplied pinhole sitting in a drawer – I think it came from The Pinhole Resource (www.thepinholeresource.com) – and decided to try this on a Nikon D700. Running some framing tests alongside a conventional lens revealed that the pinhole had roughly the same angle of view as a 55mm lens (on the full-frame body). Similarly, exposure tests found that at ISO400 the lens gave a correct exposure at f/8 and 1/250s whereas the pinhole required 2s for the best exposure, giving an effective aperture some nine stops smaller than f/8. This works out to be about f/180, which is exactly the number that was printed on the box containing the pinhole assembly.
It’s worth saying that Pinhole Resource’s pinholes come mounted in a camera dust-cap and are therefore very easy to use: for greater versatility, I have double-mounted the pinhole so that one side of the dust-cap has a Sigma mount and the other has a Nikon mount.
Returning to the figures, f/180 on a 55mm lens suggests a pinhole diameter of 0.3mm (55/180) – which is slightly bigger than the diameter that was derived as the optimum value in a previous blog.
Out of interest, I put the pinhole through its MTF paces and returned a resolution figure of about 0.03 cycles-per-pixel, which is around an order of magnitude lower than would be expected with a glass lens. I also got a picture-height/line-width ratio of about 160: given that the full-frame picture-height is 24mm, this suggests that the minimum resolvable detail on the sensor will be 0.15mm (24/160).
Of course the line is only visible if there is space to each side of it and this means that the 0.15mm line requires a 0.15mm space, giving a total minimum detail size of 0.3mm. This perfectly matches the 0.3mm pinhole diameter, which is a bit suspicious given that diffraction should have enlarged the “dot” projected by the pinhole.
In fact there is probably nothing suspicious because we have at no time measured the actual pinhole diameter and all the calculations undertaken include the effect of diffraction. If we were to measure the pinhole then we might very well expect it to be close to the 0.24mm optimum size previously calculated and the apparent increase reported here might well simply be the effect of diffraction.
Whatever the science, the fact is that digital pinhole photography is remarkably easy to do, not least thanks to the instant feedback that the medium provides, and also produces some very pleasant images. So why not give it a go – and perhaps post a comment here in due course to share your results with other readers?