About Blue Hour Club
Calculators for the photographer's working day: when the light is good, and how to expose for it.
What it is
Blue Hour Club has five free tools: a golden hour and blue hour calculator, an exposure value calculator, a depth of field calculator, an ND filter calculator with a long-exposure timer and a print size and DPI calculator. They are made for planning a shoot and for the arithmetic you would otherwise do on the back of a lens cap.
How it works
Everything is calculated in your browser. The Sun's position follows Jean Meeus's Astronomical Algorithms (2nd edition, 1998) and twilight follows the US Naval Observatory's definitions; we checked sunrise, sunset and twilight against the Naval Observatory's 2026 tables for London, Sydney and Tromsø, and they agree to within about a minute. The photography formulas are the standard ones, and each page shows them with its sources. A built-in list of cities and your browser's own time zone data give local times, so nothing is looked up online.
What it is not
Light times assume a flat horizon at sea level, and exposure tables describe typical scenes. Your camera's histogram, the weather and the hills on your horizon have the final say.
Sources
US Naval Observatory, rise, set and twilight definitions. Wikipedia articles on golden hour, blue hour, exposure value, hyperfocal distance and neutral-density filters. DOFMaster's depth of field equations.