How long can you shoot untracked?
Estimate the maximum exposure before star trailing exceeds your tolerance — useful for wide-field Milky Way shots without a tracker.
Inputs
Higher dec = slower trailing (90° = none)
Acceptable star elongation on screen
Results
Adjust the inputs to see results.
Max exposure ≈ (max trail arcsec) / (15 × cos(dec)). Trail arcsec = max trail pixels × image scale. Scale = 206.265 × pixel size / focal length.
All formulas verified by automated tests.