Pinhole Camera Calculator

A pinhole camera has no lens: a tiny hole projects an image onto film or a sensor. The results are soft, dreamy and have endless depth of field, and a camera can be built from a box or a tin. Getting good pictures depends on the right hole size and long, correctly calculated exposures. This calculator handles both.

Optimum pinhole size

Too large a hole makes the image blurry; too small and diffraction blurs it instead. The best size depends on the distance from the hole to the film, the focal length. The calculator uses Lord Rayleigh’s classic formula, d = 1.9 √(f λ), considered the sharpest, or Petzval’s smaller constant of 1.56, for green light with a wavelength of 550 nanometers. A 50 mm camera needs a hole of about 0.31 mm, a 150 mm camera about 0.55 mm.

Measuring the actual hole

Hand-made pinholes rarely match the target exactly. Measure yours with a flatbed scanner at high resolution or under a loupe with a scale, enter the actual diameter, and the calculator uses it for the working f-number. A small difference in diameter changes the exposure noticeably.

Working f-number

The f-number is the focal length divided by the hole diameter: typically between f/150 and f/300. Light meters rarely go that far, so meter at a normal aperture such as f/16 or f/22 and let the calculator translate the time. It shows how many stops darker the pinhole is than the metered aperture.

Film format and angle of view

Choose 35 mm, 120 film in 6 × 6 or 6 × 9, or sheet film in 4 × 5 or 8 × 10 inches. The calculator gives the diagonal angle of view and warns when the design is very wide, because pinholes darken strongly toward the corners at wide angles, an effect many pinhole photographers enjoy.

Reciprocity failure

Film becomes less sensitive in exposures longer than about a second. Ilford publishes exponents for its films: corrected time equals metered time to the power p. For HP5 Plus, with p = 1.31, a metered 10 seconds becomes about 20, and a metered minute becomes about three and a half. Choose the film to apply its value. For digital sensors and paper negatives, choose no correction.

Exposure in practice

In bright sun, pinhole exposures on ISO 400 film are often a second or two; in shade, many seconds; indoors, minutes or hours. Use a tripod or a steady surface, and a dark cloth or tape as a shutter. Bracket by doubling and halving times.

Building tips

Use thin brass shim or aluminum from a drink can, dimple it with a fine needle, sand the bump flat, and push through gently while rotating. Blacken the inside of the camera to avoid reflections.

Paper negatives

Photographic paper is a cheap, fun alternative to film in a pinhole camera. It is roughly ISO 3 to 12, has no reciprocity data from the maker and sees mainly blue light, so skies turn white. Make test exposures and develop in trays under a safelight.

Related tools

Convert light-meter readings for neutral density filters with the ND Filter Calculator. For enlarging pinhole negatives, the Darkroom Timer calculates print exposures.