What is 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.

How does stacking improve image quality?

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%.

What are darks, flats and biases?

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.

How many calibration frames do I need?

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.

How long should each sub-exposure be?

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.

Astro Exposure Calculator — Deep-Sky Integration Time

Calculate total integration time, SNR improvement and storage requirements for deep-sky stacking sessions.

Sub-Exposure Duration

Duration of each light frame

Number of Light Frames

Total light frames to capture

Dark Frames

Calibration: same exposure, lens cap on

Flat Frames

Calibration: even illumination, short exposure

Bias Frames

Calibration: shortest exposure, lens cap on

How We Calculate This

Stacking multiple exposures improves the signal-to-noise ratio (SNR) of deep-sky images:

Total integration = sub-exposure time × number of light frames

SNR improvement = √N (where N = number of stacked frames)

Calibration frames (darks, flats, biases) are used by stacking software to remove systematic noise, vignetting, and sensor artefacts. They add to shooting time and storage requirements but do not contribute to integration time.

Storage is estimated at approximately 25 MB per RAW frame for a typical 24MP camera.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.