Quarz Zenitspiegel 90°, dielektrische Vergütung, 2'' SC-Gewinde

The position in which an observer looks into the telescope or through the accessory. Usually the position is at an angle of 90°, 45°, or is straight.

The optical elements are treated with ultra-thin coatings. Among others, there are anti-reflective coatings for reducing, and dielectric coatings for increasing reflection.

The amount of light that is reflected after striking the optical surface.

The telescope image is always upside down, but can be corrected using correction optics or mirrors.

Telescopes with a focuser at the rear end require an erecting lens to ensure a comfortable viewing position.