Photography Calculators

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Pinhole Diameter Calculator

A pinhole has an optimum: too small and diffraction takes over, too large and the image never sharpens. This uses d = 1.9 √(f·λ) with λ in millimetres — the Rayleigh-style fit many pinhole cameras are built on. Drill close, then take a test shot; foil thickness and a ragged hole matter more than the third decimal.

Inputs

Units
mm

Pinhole-to-sensor (or film) distance, not a lens marking.

nm

550 nm green is the visual default. For an infrared-converted camera, enter the filter wavelength, e.g. 720 or 850 nm.

Results

Optimal diameter
0.3151mm

Rayleigh optimum 1.9 × √(f × λ), in millimetres.

f-number
158.7f/

Pinhole-to-sensor distance ÷ hole diameter.

Airy diameter
213.0µm

2.44 × λ × N: the diffraction blur spot of that hole.

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

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Calculation method

Convert wavelength from nanometres to millimetres (divide by one million). Optimal diameter is 1.9 times the square root of focal length times that wavelength, both in millimetres. f-number is focal length over that diameter — often f/150 to f/300. Airy diameter in micrometres is 2.44 times wavelength in micrometres times that f-number, so you can compare to a CoC or a pixel.

Exact formula

diameterMm = 1.9 × √(f_mm × λ_mm), λ_mm = nm/1e6. fNumber = f/d. airyUm = 2.44 × (nm/1000) × N. Limits: Optimal-diffraction hole, not a drilled-foil guarantee; material thickness, ragged edges and vignetting omitted.

Coverage

A pinhole has huge angle of view if the ‘sensor’ is large relative to f. Vignetting comes from the hole’s thickness and from the natural cos⁴ falloff at wide angles, not from an image circle of glass.

Diffraction vs CoC

The Airy disk at these f-numbers is huge compared with a 0.03 mm CoC. Pinhole ‘sharpness’ is a different game than a 50 mm f/8 lens. Pair with the diffraction calculator if you want the comparison.

Frequently asked questions

Needle or laser-cut?

Laser-cut or a purpose-made disk is rounder. A needle through foil is cheap and usually a bit large. Measure with a loupe if you care; then shoot a test frame.

Exposure?

Treat it as a tiny f-number. From sunny 16, count stops to your f/180 and lengthen shutter. Reciprocity on film will steal even more time; digital just needs a tripod.

Why 1.9?

It is a common Rayleigh-style coefficient for visual pinhole work (some texts use 1.6–2.0). Changing the constant a little changes diameter less than a ragged hole does.

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