NPF Rule: This tool utilizes the NPF rule, which is significantly more accurate than the traditional "500 Rule". It considers your lens aperture, sensor pixel pitch, and focal length to minimize star trailing.
Declination: Exposure times are longer near the celestial pole (90° Declination) because stars move slower in the frame. We adjust the calculation accordingly.
Comet Drift: Comets move independently of background stars. An estimated 2.0"/min motion is applied to this calculation. Keep exposure times below the "Comet Drift" threshold to avoid blurring the comet nucleus.