Pinhole Optics for Makers and Solargraphy
Geometry first: diameter, distance, and diffraction decide sharpness before aesthetics.
A pinhole is a lens-free aperture. Image size scales with focal length (pinhole-to-plane). Sharpness peaks near an optimal diameter for that focal length, larger holes blur geometrically; tiny holes diffract.
Key relationships
- Focal length (f): box depth.
- Diameter (d): hole size.
- f-number ≈ f / d, larger f/# is dimmer.
- Optimal d grows with √f (order-of-magnitude rule used by many calculators).
Use the Pinhole Optics Calculator to iterate before cutting foil.
Practical trade-offs
| Goal | Bias | |------|------| | Solargraphy detail | Smaller hole, longer total exposure, careful sealing | | Classroom demo / camera obscura | Larger hole, brighter, softer | | Room obscura | Large f, carefully sized aperture |
Field tips (Guyana STEM)
- Foil tears create oval apertures, re-punch.
- Measure depth from foil plane to paper, not outer box wall.
- Tropical cardboard softens, reinforce and reseal after rain season mounts.
Real paper results (soft trails, cloud gaps) look like this west-facing scan:
Interactive below
Play the blur tradeoff demo under this article: larger holes blur geometrically; tiny holes diffract; optimum grows with √focal length. Then cut foil with real millimetres in the calculator.