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2. Three-mirror anastigmat - Wikipedia

   en.wikipedia.org/wiki/Three-mirror_anastigmat

   A three-mirror anastigmat is an anastigmat telescope built with three curved mirrors, enabling it to minimize all three main optical aberrations – spherical aberration, coma, and astigmatism. This is primarily used to enable wide fields of view, much larger than possible with telescopes with just one or two curved surfaces.

3. Curved mirror - Wikipedia

   en.wikipedia.org/wiki/Curved_mirror

   Spherical mirrors, however, suffer from spherical aberration—parallel rays reflected from such mirrors do not focus to a single point. For parallel rays, such as those coming from a very distant object, a parabolic reflector can do a better job. Such a mirror can focus incoming parallel rays to a much smaller spot than a spherical mirror can.

4. Coma (optics) - Wikipedia

   en.wikipedia.org/wiki/Coma_(optics)

   Coma is an inherent property of telescopes using parabolic mirrors. Unlike a spherical mirror, a bundle of parallel rays parallel to the optical axis will be perfectly focused to a point (the mirror is free of spherical aberration), no matter where they strike the mirror. However, this is only true if the rays are parallel to the axis of the ...

5. Foucault knife-edge test - Wikipedia

   en.wikipedia.org/wiki/Foucault_knife-edge_test

   Viewing the mirror from behind the knife edge shows a pattern on the mirror surface. If the mirror surface is part of a perfect sphere, the mirror appears evenly lighted across the entire surface. If the mirror is spherical but with defects such as bumps or depressions, the defects appear greatly magnified in height.

6. Ritchey–Chrétien telescope - Wikipedia

   en.wikipedia.org/wiki/Ritchey–Chrétien_telescope

   With two non-spherical mirrors, such as the Ritchey–Chrétien telescope, coma can be eliminated as well, by making the two mirrors' contribution to total coma cancel. This allows a larger useful field of view. However, such designs still suffer from astigmatism. The basic Ritchey–Chrétien two-surface design is free of third-order coma and ...

7. List of phobias - Wikipedia

   en.wikipedia.org/wiki/List_of_phobias

   The English suffixes -phobia, -phobic, -phobe (from Greek φόβος phobos, "fear") occur in technical usage in psychiatry to construct words that describe irrational, abnormal, unwarranted, persistent, or disabling fear as a mental disorder (e.g. agoraphobia), in chemistry to describe chemical aversions (e.g. hydrophobic), in biology to describe organisms that dislike certain conditions (e.g ...