Optimum S/N Photometry Calculator


This page will calculate the optimum exposure time and telescope focus to obtain optimum signal-to-noise for photomtery. It takes into account both photon noise and scintillation noise, with detailed calculations involving the camera read noise, sky brightness, etc. Just input the values below and hit submit! If you get an answer that's a better seeing than you can achieve, then the optimum solution is to focus as best as possible.


Read Noise (e- per pixel):
Gain (e- per ADU):
Read Time (seconds):
Telescope Diameter (centimeters):
Height of Observatory Above Sea Level (meters):
Airmass of Observation:
On this instrument, a mag star yields a total of ADU per second.
Target star mag:
Sky flux in ADU per second per pixel:
Max counts in ADU before saturation or non-linearity:
Number of co-adds (usually 1 unless you're using an infrared array):




Please send any suggestions for improvements or any other comments to jefflcoughlin@gmail.com