Formulas#
| Quantity | Formula | Notes |
|---|---|---|
| Crop factor | 43.27 ÷ √(w² + h²) | Diagonal ratio to 36×24 mm |
| Circle of confusion | 0.030 mm ÷ crop | 8×10 in print at ~25 cm |
| Hyperfocal distance | H = f²/(N·c) + f | Thin-lens approximation |
| Depth of field | near = s(H−f)/(H+s−2f); far = s(H−f)/(H−s) | Far = ∞ when s ≥ H |
| Background blur | b = f²/(N(s−f)) | Disc for a point at infinity, % of frame width |
| Field of view | 2·atan(d/2f) | d = sensor width, height or diagonal |
| Diffraction (Airy disk) | 2.44·λ·N, λ = 550 nm | Visible above ≈2 pixel pitches |
| 500 rule | 500 ÷ (f × crop) | Classic star-trail limit |
| NPF rule | (35·N + 30·p) ÷ f | p = pixel pitch in µm |
| Exposure value | EV = log₂(N²/t) − log₂(ISO/100) | |
| Print size | pixels ÷ DPI | |
| Sun position | NOAA solar calculator equations | Golden hour −4°…+6°, blue hour −6°…−4° |
| Motion blur | v·t·f ÷ d on the sensor | Compared with 6 µm pixels |
Editorial principles#
We publish only what we can source or compute. Specs come from the sources listed on each page; when sources disagree, we prefer manufacturer-backed Wikipedia infobox data, then Wikidata, Lensfun and openMVG. Field-craft advice is written by photographers and reviewed for safety (e.g. solar eclipses) and animal welfare. We do not accept payment for coverage.
Last updated October 03, 2026 · How we calculate · Sources