Pinhole photography is arguably the most simple form of photography. Instead of using an actual lens, a simple hole is all that is needed. All rays of light from the scene pass through this hole, forming an inverted image inside of the camera. Pinhole photos are blurry, but this is somewhat compensated by their depth of field being practically unlimited. I use a 0.3 mm pinhole with a Nikon D70 digital camera (self-portrait of the camera, which is part of the Pinhole series). It may seem a bit strange that I use a digital camera with such a primitive lens, but this is not really relevant. The film is replaced by a sensor, but the rest of the camera is exactly the same. It is also noteworthy that a pinhole works at all frequencies, which is certainly not the case for normal lenses. Pinholes are therefore sometimes used to focus X-rays, which are difficult to focus using normal lenses. Although you also need an X-ray camera for this, of course.

The following sections answer some particular questions about my personal pinhole camera. They are formulated as questions because they are also linked from the About page.

## Pinhole Size

*Why did I use a pinhole size of 0.3 mm for my pinhole camera?*

One of the classical formulas to calculate the optimal diameter of the pinhole, is the one by Lord Rayleigh (this is the same Lord Rayleigh from, for example, the Rayleigh distribution, and the 1904 Nobel Prize in Physics),

\[d=1.9\sqrt{f\lambda}\]

where \(d\) is the diameter of the pinhole, \(f\) is the focal length and \(\lambda\) is the wavelength of the light. The focal length of my pinhole camera is 49 mm. For an average wavelength of light of 550 nm, this results in (all numbers converted to mm)

\[d=1.9\sqrt{49\times 0.00055}\approx 0.31\,\mathrm{mm}\]

The closest easily available size to that is, of course, 0.3 mm. So that's what I picked.

## f-number

*Why is the f-number of my pinhole camera f/163?*

The f-number (\(N\)) is defined to be

\[N=f/d\]

where \(f\) is the focal length and \(d\) is the aperture diameter. The focal length of my pinhole camera is 49 mm and the aperture diameter is 0.3 mm, so in this case

\[N=49\,\mathrm{mm}/0.3\,\mathrm{mm}\approx 163\]

## Aperture Difference

*Why is the difference between f/163 and f/10 about 8 stops?*

The relation between f-number (\(N\)) and aperture (\(a\)) is

\[N=\sqrt{2}^{\,a}\]

This means that the aperture difference between f/163 and f/10 is

\[\log_{\sqrt{2}}(163)-\log_{\sqrt{2}}(10)\approx 8\]

Calculate this using the log button on a calculator by doing

\[\log_{\sqrt{2}}(163)=\log(163)/\log(\sqrt{2})\]

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