The UVOT mirror system consists of three mirrors. Light enters the baffle and is reflected from
the biggest mirror - the primary mirror - to a smaller secondary mirror and on to a third
mirror. The inclined third mirror reflects light through the filter wheel and on to the
UVOt detector.
The primary mirror is 30 cm in diameter, making the optical monitor a 30 cm telescope (12" aperture). However, because the UVOT operates beyond the Earth's atmosphere, the reduced background light allows the instrument to detect faint objects that can only be seen with a 4 meter telescope on Earth. The primary and secondary mirrors are both hyperbolic mirrors arranged in a Ritchey-Chretien configuration. The Ritchey-Chretien design eliminates almost all the effects of coma, an optical aberration that makes point sources of light look like fuzzy comets. Removing coma effects gives a high quality image over a wide field of view.
