How long should guide subs be?
Balance guide star SNR against mount correction frequency — subs should be short enough to catch periodic error before it smears your main camera.
Inputs
From your guiding ratio or image scale calc
Typical PE cycle length for your mount
Results
Adjust the inputs to see results.
Min exposure ≈ mount period / 4 (clamped 0.5–4s). Max ≈ period / 2 (clamped 2–10s). Recommended = midpoint of min and max.
All formulas verified by automated tests.