Photonics Dictionary: F

A set of rays through a lens originating at a common point and contained in one plane.

In image processing and machine vision, the process in which an initial measurement pattern or some subsequence of measurement patterns is transformed to a new pattern feature. In image pattern...

The principle that a light ray extending from one point to another will, after any number of reflections and refractions, follow the path requiring the least transit time. This is also known as the...

A phenomenon in which high optical power, encountering an imperfection in an optical fiber, destroys the fiber's core and causes damage to back-propagate down the fiber. It is caused by classic...

A fiber optic spectrometer is a device used for measuring the spectral content of light. It utilizes optical fibers to transmit light from a source to a spectrometer unit, where the light is...

The face of a cathode-ray tube (CRT) that has a fiber optic sheet attached to its surface. The sheet's fibers are at right angles to the face, allowing the transmittance of the fluorescent trace...

A wide-field multiobject spectroscopy system used in astronomy, in which a bundle of low-loss optical fibers positioned on the target images is rearranged at its other end into a linear array along...

An X-Y electrically addressable series of arrays with individual electron emitters bombarding a phosphor-coated transparent plate. The phosphor is induced into luminescence, similar to traditional...

The field of view (FOV) refers to the extent of the observable world or the visible area that can be seen at any given moment through a device, such as an optical instrument, camera, or sensor. It is...

A technique used in radiography to obtain an unblurred image of a moving object by the use of very short x-ray exposures, such as one microsecond, to record the image.

An electronic display in which a flat screen is formed by an orthogonal array of display devices, such as electroluminescent devices, light-emitting diodes or liquid crystal cells.

An instrument designed to give a visual indication to the pilot when the plane has strayed from a specific flight path.

Fluence is a term used in various scientific and technical disciplines to describe the amount of something per unit area. The specific meaning of fluence can vary depending on the context in which it...

The photographic recording of a subject that exhibits luminescence only for an extremely short time (10-8 s) after the exciting source is removed. In the process, the subject may be illuminated by...

A fluorescent screen refers to a phosphorescent or fluorescent-coated surface that emits visible light when exposed to other forms of electromagnetic radiation, such as x-rays or ultraviolet light....

A camera with a very high aperture lens or mirror system for photographing x-ray fluorescent screen images, mainly to save the cost of large pieces of 11 x 14-in. film. The film may be 4 x 5-in. cut...

A lens having an extremely high aperture and used in the recording of x-ray fluorescent screen images. It often is specially designed for the camera, the color of the light and the image...

The time it takes a cathode-ray tube's electron beam to return to its starting point after completing one line, one field or one trace.

The moving spot of light emitted by a source, generally a cathode-ray tube, to illuminate specific points of an area carrying light and dark regions according to a specific pattern.

A microscope that uses a flying spot scanner, directed through the eyepiece, as a light source to determine the features of a transparent specimen. The flying spot is modulated by the varying density...

The focal length of a lens is the distance between the lens's optical center (or principal point) and the image sensor or film when the lens is focused at infinity. In simple terms, it is the...

A linear or two-dimensional matrix of individual detector elements, typically used at the focus of an imaging system.

An infrared imaging device composed of a detector array and readout electronics. It may include a cryogenic cooling system. The assemblies are used in meteorological and surveillance satellites,...

That point on the optical axis of a lens, to which an incident bundle of parallel light rays will converge.

In a symmetrical optical system this is a measure of the influence of the system upon the focus of a pencil of rays passing through it.

1. A mechanism that permits the focusing of an optical system.2. A means of obtaining the sharpest image from a cathode-ray tube display by adjusting the size of the spot where it reaches the screen.

One of the electrodes used to focus the electron beam of a cathode-ray tube. As the electrode's voltage is changed, its electrical field is changed, resulting in a change of the electron beam's spot...

Decrease in cosmic ray activity that is observed approximately 24 hours after a solar flare, attributed to a shielding effect produced by magnetic fields contained in the plasma of the cloud emitted...

The application of ultraviolet, x-ray, infrared and conventional photography to law enforcement.

Frame rate refers to the frequency at which consecutive images, or frames, are displayed in a video sequence. It is typically measured in frames per second (fps) and determines the smoothness and...

A Fresnel lens is a type of optical lens that consists of a series of concentric grooves or steps carved into a flat, thin piece of transparent material, typically plastic or glass. This design...

Optical fibers fused together to form a solid, vacuum-tight assembly in the form of a slab or rod. Discs or rectangular shapes having ground and polished surfaces perpendicular to the fiber lengths...