Peilitähystin

A peilitähystin, often translated as a reflecting telescope, is an optical instrument that uses mirrors to form a magnified image of distant objects. Unlike refractors which use lenses, reflectors primarily employ curved mirrors to gather and focus light. The main mirror, known as the primary mirror, is concave and collects light from the object being viewed. This light is then directed towards a smaller, secondary mirror, which in turn reflects the light path to an eyepiece where the observer looks.

The simplest and most common type of reflector is the Newtonian telescope, invented by Sir Isaac Newton. In a Newtonian design, the secondary mirror is placed at an angle, directing the light beam out of the side of the telescope tube, usually near the top. Other reflector designs include the Cassegrain telescope, which uses a convex secondary mirror to reflect light back through a hole in the center of the primary mirror, resulting in a more compact design.

Reflecting telescopes are popular for astronomical observation due to several advantages. Mirrors are generally easier to manufacture in very large sizes compared to lenses, allowing for greater light-gathering capabilities. They also do not suffer from chromatic aberration, a phenomenon where different colors of light are focused at slightly different points by lenses, leading to color fringing. This makes reflectors particularly well-suited for observing faint and distant celestial objects. Modern large ground-based and space telescopes, such as the Hubble Space Telescope, predominantly utilize mirror technology.