Photonics Dictionary: C

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Cassegrain lens system

A two-mirror lens design used in astronomical telescopes, the primary being a parabola, the secondary a smaller hyperbola. The image formed is free of spherical aberration and color and is located...

cathetometer

A type of comparator with a telescope equipped with a cross wire mounted on a vertical sliding column. It is used to measure vertical distances on fairly near objects.

central obstruction

In a reflecting telescope, the obstruction of the primary mirror by a secondary mirror which blocks a small amount of the light reflected by the primary mirror and introduces additional diffraction.

chromatic dispersion -> dispersion

Dispersion refers to the phenomenon where different wavelengths (colors) of light travel at different speeds when passing through a medium. This variation in the speed of light for different colors...

cinetheodolite -> phototheodolite

A camera equipped with angular scales in altitude and azimuth. The scale readings are imprinted on the film when an exposure is made. The exact point indicated by the scale readings is shown by...

coelostat

A plane mirror mounted on a polar axis that lies parallel to the plane of the mirror. When the mirror is rotated once in 48 hours, celestial objects can be made to appear stationary and are...

collimating telescope -> collimator

An optical instrument consisting of a well- corrected objective lens or mirror with a light source and or object/image (i.e. illuminated slit or retical) at its focal plane. Collimators are used to...

compensating wedge -> measuring wedge

A wedge in a rangefinder or heightfinder used to displace the image produced by one telescope so that it coincides with that produced by the other telescope, thus affording a measurement of the...

concave

Concave is an adjective used to describe a surface or shape that curves inward or has a hollow or recessed appearance. In the context of geometry or optics, a concave shape is one that curves or...

concave and convex spherical mirror

Concave and convex spherical mirrors are types of curved mirrors that have surfaces shaped like segments of spheres. These mirrors are commonly used in optics for various applications, including...

cosmic ray telescope

A system consisting of two or more Geiger-Müller counters, connected in coincidence with their centers on an axis. The only particles recorded are those traversing all counters, near the axis,...

coudé

A set of mirrors along a telescope's polar axis designed to redirect light to a fixed position without being affected by the motion or position of the telescope. From the French word for "elbow."

Photonics DictionaryC

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