Calculator
Exposure Calculator
Deep-sky imaging is a signal-to-noise problem. This calculator takes your optics, your sky and your target type and returns a working exposure plan — sub-exposure length, gain, number of frames and total integration time — plus an estimate of the signal-to-noise ratio you can expect from it.
Result
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Measure
How to read these numbers
- Sub-exposure length is a compromise: long enough that read noise is small compared with sky noise, short enough that guiding error and satellite trails do not ruin frames.
- Total integration time matters more than any single exposure. Doubling the number of frames improves signal-to-noise by roughly the square root of two.
- The 500 rule for wide-field star photography is an approximation: maximum exposure seconds ≈ 500 ÷ (focal length × crop factor). Modern high-resolution sensors show trailing well before that limit.
These are planning figures computed from standard approximations, not measurements of your equipment. Atmospheric seeing, optical quality, collimation and sky brightness move the real numbers, sometimes a lot.