Pinhole Camera Exposure Calculator
Calculate equivalent pinhole f-number and square-law shutter-time scaling from a known reference exposure. Film reciprocity, diffraction and optimal diameter are outside the model.
Interactive calculator · Method PINHOLEEXPOSURE-2.0 · Last reviewed: 2026-10-05
Estimate pinhole f-number and exposure time
Enter the pinhole-to-image distance, hole diameter, and a reference exposure from a normal lens or meter. Keep ISO and scene brightness the same when comparing the times.
Your inputs
Default worked example. Edit the inputs to calculate your scenario.
Default worked example
A f/192.31 pinhole needs about 577.85× the reference exposure time, or 4.62 s, at the same ISO and scene brightness.
How to use the calculator
Measure the pinhole-to-image-plane distance and hole diameter in millimeters. Enter a known reference f-number and shutter time for the same scene brightness and ISO.
What the result means
This gives an exposure starting point from a reference measurement. It does not optimize the hole diameter or model diffraction, image quality or film reciprocity.
Formula and units
Equivalent f-number N = focal distance/diameter. Aperture area scales with diameter squared, so estimated shutter = reference shutter × (N/reference f-number)² under equal scene brightness and ISO.
Worked examples
Pinhole-to-image distance (mm): 50 mm; Pinhole diameter (mm): 0.26 mm: Pinhole-to-image distance (mm): 50 mm; Pinhole diameter (mm): 0.26 mm; Reference lens f-number: 8 f-number; Reference shutter time (seconds): 0.008 seconds.
Example result: Equivalent f-number: f/192.31; Exposure multiplier vs reference: 577.85×; Estimated shutter time: 4.62 s; Reference exposure: f/8 at 0.008 s.
Pinhole-to-image distance (mm): 75 mm; Pinhole diameter (mm): 0.39 mm: Pinhole-to-image distance (mm): 75 mm; Pinhole diameter (mm): 0.39 mm; Reference lens f-number: 12 f-number; Reference shutter time (seconds): 0.008 seconds.
Example result: Equivalent f-number: f/192.31; Exposure multiplier vs reference: 256.82×; Estimated shutter time: 2.05 s; Reference exposure: f/12 at 0.008 s.
Limitations and common mistakes
Lens transmission, stray light, subject brightness, photographic response and long-exposure reciprocity can change actual exposure. Apply film-specific reciprocity guidance and bracket test exposures. No fixed optimal-diameter coefficient is used.
Do not confuse diameter with radius, change ISO without adjusting the reference exposure, or treat geometric exposure scaling as a complete photographic response model.
Sources and assumptions
The geometric and exposure scaling is a declared model; reciprocity failure and diffraction require camera-specific validation.
Method PINHOLEEXPOSURE-2.0; last formula review 2026-10-05. Sources and their supported claims. Calculation methodology.