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A plane mirror is a mirror with a flat reflective surface. [ 1 ] [ 2 ] For light rays striking a plane mirror, the angle of reflection equals the angle of incidence. [ 3 ] The angle of the incidence is the angle between the incident ray and the surface normal (an imaginary line perpendicular to the surface).
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.
Thus reflection is a reversal of the coordinate axis perpendicular to the mirror's surface. Although a plane mirror reverses an object only in the direction normal to the mirror surface, this turns the entire three-dimensional image seen in the mirror inside-out, so there is a perception of a left-right reversal. Hence, the reversal is somewhat ...
A Paul design has a parabolic primary with spherical secondary and tertiary mirrors; a Paul–Baker design modifies the secondary slightly to flatten the focal plane. 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 ...
The second plane used in the analysis is the sagittal plane, defined as the plane orthogonal to the tangential plane and containing the chief ray before refraction (so along the original chief ray direction). This plane intersects the optical axis at the entrance pupil of the optical system.
For mirrors with parabolic surfaces, parallel rays incident on the mirror produce reflected rays that converge at a common focus. Other curved surfaces may also focus light, but with aberrations due to the diverging shape causing the focus to be smeared out in space. In particular, spherical mirrors exhibit spherical aberration. Curved mirrors ...
The image in a plane mirror is not magnified (that is, the image is the same size as the object) and appears to be as far behind the mirror as the object is in front of the mirror. A diverging lens (one that is thicker at the edges than the middle) or a concave mirror forms a virtual image. Such an image is reduced in size when compared to the ...
The needed amount of toroidal shape can be transferred entirely or partially to the primary mirror. In large focal ratios optical assemblies, both primary and secondary mirror can be left spherical and a spectacle correcting lens is added between the secondary mirror and the focal plane (catadioptric Yolo).