primary mirror

The primary mirror is a crucial component of reflecting telescopes, which use mirrors to gather and focus light from celestial objects. Unlike refracting telescopes that use lenses, reflectors employ a concave mirror, typically parabolic, to reflect light. This design avoids chromatic aberration, a distortion caused by lenses dispersing light by wavelength.1

Early reflecting telescopes, like those developed by Isaac Newton, used a small plane mirror to redirect the light to the side of the tube for observation. Later designs, such as the Cassegrain and Gregorian telescopes, involved secondary mirrors to reflect light back through a hole in the primary mirror. Modern large reflecting telescopes, like the Hale Telescope, utilize advanced materials such as Pyrex and Cer-Vit for their primary mirrors to minimize expansion and maintain optical stability across temperature changes.21