Katadioptrikus

Katadioptrikus is a term that refers to optical systems that use both reflection and refraction to form an image. The name itself is derived from Greek words: "kata" meaning down, "dioptron" meaning to see through, and "optikos" meaning visual. Therefore, katadioptrikus systems are essentially mirrors that also bend light.

These systems are commonly found in telescopes, particularly reflecting telescopes that incorporate lenses. A classic example is the Schmidt-Cassegrain telescope. In such a design, light first encounters a correcting lens, often called a Schmidt corrector plate, which is a aspheric lens. This plate is placed at the entrance of the telescope tube. After passing through the corrector plate, the light strikes a primary mirror. This primary mirror is typically parabolic or spherical. Following reflection from the primary mirror, the light is directed towards a secondary mirror. This secondary mirror then reflects the light back through a central hole in the primary mirror to the eyepiece or camera.

The advantage of katadioptrikus designs lies in their ability to correct for optical aberrations, such as spherical aberration and coma, which can plague simpler mirror systems. The corrector plate, by its specific shape, compensates for the distortions introduced by the primary mirror, resulting in sharper and clearer images, especially at the edges of the field of view. This makes them popular choices for amateur astronomers and astrophotographers who seek compact, high-performance instruments.