Astrophotography Calculators

Astrophotography presents unique technical challenges. The Earth rotates at approximately 15 degrees per hour, causing stars to trail in long exposures. The classic 500 Rule divides 500 by the effective focal length to give the maximum exposure time in seconds before stars begin to visibly trail: for a 24mm lens on full-frame, that is about 20 seconds.

The more precise NPF Rule accounts for pixel pitch, aperture, and declination to give a tighter limit for modern high-resolution sensors. It typically produces shorter maximum exposure times than the 500 Rule but ensures pin-sharp stars when pixel-peeping.

Moon phase directly affects astrophotography planning. A new moon provides the darkest skies for deep-sky and Milky Way photography, while a full moon washes out faint nebulae and the galactic core. The Milky Way core is best visible from the UK between April and September, when it rises high enough above the southern horizon.

For deep-sky work with tracked mounts, total integration time (the sum of all sub-exposures) determines signal-to-noise ratio. Stacking many shorter exposures reduces noise while preserving detail. Our calculators help you plan every aspect of your night sky photography.