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# Spherical aberration

Spherical aberration is an optical effect observed in an optical device (lens, mirror, etc.) that occurs due to the increased refraction of light rays when they strike a lens or a reflection of light rays when they strike a mirror near its edge, in comparison with those that strike close to the centre. [1]

## Achromatic lens

An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration.

## Aspheric lens

An aspheric lens or asphere is a lens whose surface profiles are not portions of a sphere or cylinder.

## Cartesian oval

In geometry, a Cartesian oval, named after René Descartes, is a plane curve, the set of points that have the same linear combination of distances from two fixed points.

## Curved mirror

A curved mirror is a mirror with a curved reflecting surface.

## Distortion (optics)

In geometric optics, distortion is a deviation from rectilinear projection; a projection in which straight lines in a scene remain straight in an image.

## F-number

The f-number of an optical system (such as a camera lens) is the ratio of the system's focal length to the diameter of the entrance pupil.

## Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.

## Hubble Space Telescope

The Hubble Space Telescope (HST) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation.

## Lens (optics)

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.

## List of refractive indices

Many materials have a well-characterized refractive index, but these indexes depend strongly upon the frequency of light.

## Maksutov telescope

The Maksutov (also called a "Mak") is a catadioptric telescope design that combines a spherical mirror with a weakly negative meniscus lens in a design that takes advantage of all the surfaces being nearly "spherically symmetrical".

## Mirror

A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection.

## Optical aberration

Aberration in optics refers to a defect in a lens such that light is not focused to a point, but is spread out over some region of space, and hence an image formed by a lens with aberration is blurred or distorted, with the nature of the distortion depending on the type of aberration.

## Optical axis

An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens or microscope.

## Optics

Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

## Parabolic reflector

A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves.

## Reflection (physics)

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.

## Refraction

Refraction is the change in direction of wave propagation due to a change in its transmission medium.

## Ritchey–Chrétien telescope

A Ritchey–Chrétien telescope (RCT or simply RC) is a specialized variant of the Cassegrain telescope that has a hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors (coma).

## Schmidt corrector plate

A Schmidt corrector plate is an aspheric lens which is designed to correct the spherical aberration in the spherical primary mirror it is combined with.

## Soft focus

In photography, soft focus is a lens flaw, in which the lens forms images that are blurred due to spherical aberration.

## Sphere

A sphere (from Greek σφαῖρα — sphaira, "globe, ball") is a perfectly round geometrical object in three-dimensional space that is the surface of a completely round ball (viz., analogous to the circular objects in two dimensions, where a "circle" circumscribes its "disk").

## Star

A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.

## Telescope

A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light).

## References

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