Astro Exposure Calculator — Deep-Sky Integration Time

Integration time is the total combined exposure time of all your light frames. For example, 60 frames of 2 minutes each gives 120 minutes (2 hours) of integration time. More integration time means better signal-to-noise ratio and smoother, more detailed images.

Random noise is different in every frame, but the astronomical signal is consistent. When you stack N frames, the signal adds up proportionally (N×) but noise only increases by √N, giving an SNR improvement of √N. Doubling from 30 to 60 frames improves SNR by about 41%.

Calibration frames remove systematic errors. Darks (same exposure, lens cap on) subtract thermal noise and hot pixels. Flats (evenly lit, short exposure) correct vignetting and dust spots. Biases (shortest possible exposure, lens cap on) measure the readout noise pattern.

A common recommendation is 20-30 dark frames, 20-50 flat frames, and 50+ bias frames. More calibration frames produce a cleaner master calibration frame, reducing the noise they add to the final stack. At minimum, aim for 15-20 of each type.

Sub-exposure length depends on your sky brightness and mount tracking. From light-polluted sites, 30-120 seconds prevents the background from clipping. From dark sites with good tracking, 3-10 minutes captures more signal per frame. The total integration time matters more than individual sub length.