Astronomical Optics - Daniel J. Schroeder - Google Books

https://books.google.de/books?id=v7E25646wz0C&pg=PA433&dq=snr%2Bmean%2Bstandard-deviation%2Bratio#v=onepage

This book provides a unified treatment of the characteristics of telescopes of all types, both those whose performance is set by geometrical aberrations and the effect of the atmosphere, and those diffraction-limited telescopes designed for observations…