Astronomical Optics

The increasing rate of growth in astronomical knowledge during the past few decades is a direct consequence of the increase in the number and size of telescopes and the efficiency with which they are used. Most celestial sources are intrinsically faint, and observations that required hours of observing time with small refracting telescopes and insensitive photographic plates are now done in minutes with large reflecting telescopes and efficient solid-state detectors. The increased efficiency with which photons are collected and recorded by modern instruments has indeed revolutionized the field of observational astronomy.