An old name for the rotating arm moving about an axis of rotation over a divided circle used to measure angles. Now the term refers to a small stadia telescope mounted over a ruler for use in plane-table surveying.

A satellite-borne remote sensing device capable of transmitting images at 10 and 20 m resolution from an altitude of 830 km,...

A technique used in astronomy that requires a radio telescope to be directed at a point in the sky west of the object under...

A type of telescope mount that permits direct azimuth and elevation adjustments.

The angular subtense of the field of view in the image space of a telescope, as differentiated from that in the object space...

A grazing incidence mirror telescope with concentric conic surfaces having a single common point: a paraboloid-hyperboloid...

Optical phase distortion refers to a phenomenon where the phase of an optical wavefront is altered as it propagates through...

A small defocused Galilean telescope mounted in a hole in a door. Viewed from inside through the positive lens, a wide-angle...

The image of the aperture stop, usually the objective lens, that is produced by the eye lens. When the exit pupil of the...

An artificial star used to aid in adaptive optics imaging of the sky. The guide star is provided from a telescope system on...

The optical phenomenon that causes relative motion between two objects when the eyepoint is moved laterally. When parallax...

With respect to a lens, the reciprocal of its focal length. The term power, as applied to a telescope or microscope, often...

A spatial light modulator (SLM) is an optical device that modulates or manipulates the amplitude, phase, or polarization of...

An antireflection coating (AR coating) is a thin film or coating applied to optical surfaces, such as lenses or windows, to...

An interferometer constructed to be positioned on a telescope to measure the angular separation of the components of double...

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...

A phase screen, in the context of optics and wave optics, refers to a surface or medium that introduces a phase delay to an...

A camera equipped with angular scales in altitude and azimuth. The scale readings are imprinted on the film when an exposure...

A form of Cassegrain telescope having a concave hyperbolic primary and a convex hyperbolic secondary. This form permits the...

1. A prism used in some instruments to bend light 90° before it enters the objective. 2. A dispersing prism located in...

A device attached to the end of an alignment telescope that detects and calculates a plane mirror's rotation axis that is...

Optical cements and adhesives are specialized materials used in the assembly and bonding of optical components in optical...

A system consisting of two or more Geiger-Müller counters, connected in coincidence with their centers on an axis. The only...

A pair of stars (double star) that can be seen separately with a telescope, generally by setting a filar micrometer for the...

A lens blank is a piece of optical material in a raw, unfinished state, typically in the form of a disk or block, from which...

A negative lens used to increase the effective focal length of a telescope objective.

An optical instrument used to track and image a test vehicle (target) throughout its flight. The cinesextant frequently...

Any form of lens, optical system (camera, telescope, microscope, etc.), or opto-electronics utilized for the purpose of...

An afocal optical device made up of lenses or mirrors, usually with a magnification greater than unity, that renders distant...

A telescope stand equipped with a polar axis that can be set parallel to the Earth's axis of rotation and a declination axis...

The base used to hold an astronomical telescope. It may be either altazimuth, with horizontal and vertical axes of rotation,...

A telescope that transmits, enlarges and converts infrared images.

A telescope with an ellipsoidal secondary concave mirror that reflects rays from a parabolic primary mirror through an...

Concave is an adjective used to describe a surface or shape that curves inward or has a hollow or recessed appearance. In...

Instruments used for measuring angles and occasionally lengths on the ground. The principal surveying instruments are the...

A telescope so manufactured that the image remains erect and the position of the eyepiece is unchanged as the line of sight...

A photon sieve is an optical device used in the field of optics and imaging. It's designed to focus and shape light,...

1. The focal point. 2. To adjust the eyepiece or objective of a telescope so that the image is clearly seen by the observer....

Dispersion refers to the phenomenon where different wavelengths (colors) of light travel at different speeds when passing...

A low-power telescope placed at the eyepiece of an optical system to increase overall magnification. Most often used to...

A handheld binocular telescope that is commonly of the Galilean type.

MTF analysis/measurement equipment refers to instruments and tools used to measure and analyze the modulation transfer...

An aspheric mirror is an optical mirror surface that deviates from the shape of a perfect sphere, having a non-spherical...

A large telescope mirror fabricated from several smaller sections.

The line of vision; the optical axis of a telescope or other observation system. The straight line connecting the object and...

A telescope that is fixed or has a limited degree of movement in a vertical plane; primarily used to determine the position...

A refracting telescope that uses a prism to bend the line of sight 90°.

An optical testing instrument is a device or system used to evaluate and measure the performance, quality, and...

The adjustment of a binocular instrument so that the lines of sight of both telescopes are parallel.

A type of glass used in telescope mirrors, formed by adding a nucleating agent to standard glass and then heating it until...

An image-forming system that uses mirrors rather than lenses. Such objectives are frequently used for astronomical...

Concave and convex spherical mirrors are types of curved mirrors that have surfaces shaped like segments of spheres. These...

Chromatic aberration is an optical phenomenon that occurs when different wavelengths (colors) of light are refracted by a...

Two stars so close together that they cannot be resolved by telescopes. They are proved to be double stars by the doubling...

A refracting telescope that yields an erect image by the use of a positive lens for its objective and a negative lens for...

A defect of a binocular instrument causing two images to be seen separately instead of being fused. It is caused when the...

A two-mirror corrector for a parabolic primary mirror that provides anastigmatic performance for large astronomical...

Optical coatings are thin layers of materials applied to optical components, such as lenses, mirrors, filters, and prisms,...

A passive infrared system that uses two line-of-sight telescopes to generate both narrow and wide field-of-view images of...

An optical assembly refers to a collection of optical components that are carefully arranged and aligned to perform a...

A simple form of astronomical telescope that uses a fixed objective and a focusable eyepiece. The objective forms an...

A telescope that produces an erect image. Erection is achieved either by a lens (for a long instrument) or a prism (for a...

Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effects of...

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

A hemispherical covering that is rotatable about a central axis. There is a slit opening along one side wide enough to allow...

A small low-power microscope or magnifier with a scale that is used to measure the exit pupil diameter and eye relief on...

A device for the internal inspection of hard-to-get-at mechanical parts, such as rifle barrels, sewer pipes, oil wells, or...

An instrument designed to collect naturally formed extraterrestrial electromagnetic radiation within the radio frequency...

A telescope that corrects dispersion and spherical aberration through the use of one or more lenses, usually smaller than...

An instrument that serves to produce an enlarged electron image on a fluorescent screen by focusing an infrared image of a...

A controlled motion system that may use a telescope, camera or antenna to follow accurately a satellite, missile, vehicle or...

The ability of an optical system to make an object appear larger. An optical element or optical system causing an object to...

In a reflecting telescope, the obstruction of the primary mirror by a secondary mirror which blocks a small amount of the...

A pair of telescopes with prismatically erected images, mounted side by side with the eyepieces at the interocular distance...

The field of view (FOV) refers to the extent of the observable world or the visible area that can be seen at any given...

Freeform optics refers to the design and fabrication of optical surfaces that do not follow traditional symmetric shapes,...

A telescope lens is a primary optical component of a telescope system that gathers and focuses light to form an image. It is...

Consists of a pair of radio telescopes concentrated on a single celestial object. This technique creates a single radio...

An achromat, in the context of optics, refers to a type of lens or lens system designed to reduce chromatic aberration....

A set of mirrors along a telescope's polar axis designed to redirect light to a fixed position without being affected by the...

A telescope objective with excellent spherochromatic correction, consisting of a meniscus crown and a meniscus flint, both...

An aspheric lens is a type of lens whose surface profiles deviate from the traditional spherical shape. Unlike spherical...

The point spread function (PSF) is a fundamental concept in imaging that describes the response of an imaging system to a...

A wedge in a rangefinder or heightfinder used to displace the image produced by one telescope so that it coincides with that...

A coarse diffraction grating that is used to form a scale of intensities to determine the relative magnitudes of stars. The...

A liquid crystal light valve (LCLV), also known as a spatial light modulator (SLM), is an optical device that modulates the...

A sensing or image-forming detector that serves to convert infrared rays into visible signals for communication purposes....

Off-axis paraboloid and ellipsoid mirrors are specialized optical components used in various optical systems, particularly...

A reticle, also known as a reticule or graticule, is a pattern or set of markings placed in the focal plane of an optical...

A telescope that uses a reflecting objective to focus an image of a distant object at a focal point.

Multi-axis alignment refers to the process of aligning or adjusting components or systems in multiple spatial dimensions or...

A handheld navigational instrument used to measure the elevation angle of celestial bodies such as the sun. An image of the...

The optical element that receives light from the object and forms the first or primary image in telescopes and microscopes....

An aplanatic surface is an optical surface that is specifically designed or shaped to minimize spherical aberration and...

A telescope with a concave paraboloidal objective mirror and a small plane (diagonal) mirror that reflects rays from the...

A mirror mount is a mechanical device used to secure and precisely position mirrors in optical systems. Mirrors are...

Freeform mirrors refer to reflective optical components that deviate from traditional symmetric or rotationally symmetric...

An instrument for measuring the vertical angle of an object. It usually contains an accurately made protractor, a sensitive...

A small telescope mounted on a tripod and free to rotate about a vertical axis. A spirit level is mounted over the telescope...

Optics is the branch of physics that studies the behavior and properties of light, including its interactions with matter...

The process of using a spectrograph with a telescope to acquire information on an astronomical object's speed and physical...

A two-mirror lens design used in astronomical telescopes, the primary being a parabola, the secondary a smaller hyperbola....

A telescope similar to the customary Cassegrain telescope, but having a primary mirror that is ellipsoidal and a secondary...

A mirror blank refers to the initial piece of material from which a mirror is made. It is typically a flat or slightly...

Diamond turning refers to a precision machining process used to produce complex optical components, particularly lenses and...

An astronomical telescope is a type of optical instrument designed to gather and magnify light from distant celestial...

A precise telescope set on a pair of rotation axes, the horizontal and vertical axes equipped with two divided circles. One...

A lens is a transparent optical device that focuses or diverges light, allowing it to pass through and form an image. Lenses...

A spheric lens, also known as a spherical lens, is a type of optical lens with at least one surface that is part of a...

A corrective lens system that is placed near the focal plane of a Newtonian telescope to increase its effective field of...

A telescope that is mounted on an equatorial mount.

A small erect-image telescope for use as a sighting device on a rifle. The chief requirement is a long eye relief to avoid...

The Mills Cross telescope is a two dimensional radio telescope in which the two antenna arrays are positioned perpendicular...

A CCD sensor that provides feedback to the motion control system for a telescope, allowing the telescope to follow a...

Also known as roof prism. A type of prism designed by G.B. Amici. It consists of a roof edge produced upon the long...

Magnification that is above the level of maximum useful magnification and does not contribute useful resolving power. In a...

A technique for obtaining improved resolution of images produced by large telescopes and distorted by the effects of...

A Cassegrain telescope having a parabolic primary mirror, a spherical secondary mirror and a zero-power doublet in the...

An optical instrument containing a gimballed sighting telescope, used to measure angular relationships in horizontal and...

A flat, round micrometer that is placed in the focal plane of a telescope to measure difference in right ascension and...

An airspaced achromatic doublet telescope objective.

An instrument used to measure the luminance (brightness) of a distant object. The object is viewed through a small...

Technology that corrects the shape of reflective optics; primarily applied in large telescope systems, in order to...

A low-power telescope with a wide field of view, typically attached to a higher power telescope with a narrower field of...

An optical tooling instrument consisting of an objective lens, a focusing lens, an optical micrometer, a reticle and an...

A telescope in which a mask occults the solar disk, generating an artificial eclipse and allowing observation and recording...

An astronomical mirror, also known as a telescope mirror or primary mirror, is a key component of a reflecting telescope. It...