Calculators · sub-exposure & SNR
Exposure Calculator
A risk-aware sub length — most of the SNR, in frames you won't lose to wind, satellites or clouds — plus a gain advisor and integration-to-SNR, driven by your camera's real read noise, full-well, and QE.
Example site
Setup
Rig & sky
Telescope
Reducer / Flatteneroptional
Camera
Sky · Bortle21.30 mag/arcsec²
Bortle 4 · Rural/suburban transition · light pollution 0.9× natural (155 µcd/m²)
Filter · effective bandwidth
Read noise defaults to the sensor minimum (HCG). The sub limit is your longest safe exposure — what your mount holds round in wind/gusts before trailing, plus satellite/cloud risk. It caps the recommended sub and drives the gain advisor. The default tracks your sky (≈10 min in Bortle 1, ≈5 min or less by Bortle 5); type to override.
Pick a telescope and camera to compute the optimal sub — or .