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. IR pinholes want a longer λ.

Results

Optimal diameter
0.3151mm
f-number
158.7f/
Airy diameter
213.0µm

Recommended gear

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 is from the hole’s thickness, 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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