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Photonics Dictionary

Clear All Filters x vision x
diffraction grating

A diffraction grating is an optical component consisting of a surface with a periodic structure of equally spaced, parallel grooves or rulings. These rulings act as an array of closely spaced slits...

diplopia

A defect of vision where a single object appears as two. Also known as double vision.

direct scanning

A scanning technique in which the object is illuminated the entire time, and in which picture elements of the object are viewed singly by the television camera.

direct viewing

The observation of a reproduced television picture on the face of a cathode-ray tube.

discrimination

The degree to which a vision system is capable of sensing differences in light intensity between two regions.

dispersive lens -> diverging lens

A diverging lens is a type of lens that causes parallel rays of light to spread out or diverge. It is thinner in the center than at the edges and is commonly referred to as a concave lens. The most...

display primaries -> receiver primaries

Also known as display primaries. Colors formed by a television receiver that are of constant chromaticity and variable luminance, and that, mixed in certain proportions, form other colors. Red, green...

DIVAD

division air defense

divergent lens -> diverging lens

diverging lens

double-Gauss lens

A fast, wide-angle lens used in television and photographic cameras, with excellent overall correction, but subject to residual oblique spherical aberration.

DWDM

dense wavelength division multiplexing

edge contrast -> acutance

In photography, the density gradient across an edge separating light from darkness, a physically measurable quantity that correlates well with subjectively observed sharpness of definition. By...

electron speckle pattern interferometry

A method for detecting vibration amplitudes analogous to image holography, except that the film emulsion is replaced by a television target.

electron-beam film scanning

The method by which photographic film is scanned by an electron beam. One technique uses the uniform light of a television screen, focused by a lens onto the processed film, as a means of creating a...

electron-gun system

An electron-gun system is an assembly used to generate and control a focused beam of electrons. Electron guns find applications in various fields, including cathode ray tubes (CRTs), electron...

electronic viewfinder

A small television monitor that replaces the reflex viewfinder in a television camera.

emmetropia

The normal condition of vision where an object at infinity is in sharp focus with the eye lens in a neutral or relaxed state.

eye

The organ of vision or light sensitivity.

eye test apparatus

Instruments used by ophthalmologists and optometrists to study the eye. There are, for instance, the ophthalmoscope to observe and photograph the retina; the retinoscope and optometer to determine...

Farnsworth-Munsell test -> color perception test equipment

Equipment for testing an observer's color vision. Some tests require the identification or ordering of colored samples. The commercially available examples include: the Ishihara plates, on which...

FDM

frequency division multiplex

feature extraction

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...

femtosecond laser

A femtosecond laser is a type of laser that emits ultrashort pulses of light with durations on the order of femtoseconds, where one femtosecond is equal to 10-15 seconds. These lasers are capable of...

fiber -> optical fiber

Optical fiber is a thin, flexible, transparent strand or filament made of glass or plastic used for transmitting light signals over long distances with minimal loss of signal quality. It serves as a...

fiber Bragg grating

A fiber Bragg grating (FBG) is a type of optical filter that is inscribed or "written" into the core of an optical fiber. It consists of a periodic modulation of the refractive index along the length...

field

1. In raster scan television, one of the two scans that are interlaced to make up a frame. 2. See field of view.

field frequency -> field repetition rate

The number of fields scanned per second in a television system. The US standard is 60. Also called field frequency.

field of view

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...

field repetition rate

The number of fields scanned per second in a television system. The US standard is 60. Also called field frequency.

first-side meniscus

The process of grinding the concave surface of a single-vision spherical lens.

first-side toric

The process of grinding the toric surface of a single vision sphero-cylindrical lens.

flicker

The fluctuation in apparent illumination that has a rate comparable to the reciprocal of the period of persistence in vision.

fluorescent screen

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....

focal plane assembly

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,...

forward-looking infrared

A night-vision device that uses one or more infrared transducers to scan a scene in the 3- to 5-µm or 8- to 12-µm spectral region, convert the infrared radiation to electronic data and...

frame

1. To center an image or place it in any part of the television screen desired. Also applies to stills. 2. A single image of the connected multiple images on motion-picture film. 3. The size of the...

frame frequency

The number of times per second that the frame of a television system is completely scanned. In the United States, 30 per second is the standard frame frequency.

frame rate

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...

Fresnel lens

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...

fusion

1. The combination of the effects of two or more stimuli in any given sense to form a single sensation. With respect to vision, the perception of continuous illumination formed by the rapid...

gamma

A numerical value representing the degree of contrast in a television picture: the exponent of the power law used to approximate the curve of output magnitude vs. input magnitude over the region of...

gamma correction

Modification of a system to provide for a linear transfer characteristic from an input to an output device. A circuit for this purpose is built into a television camera to compensate for display tube...

genlock

A device used to lock the internal synchronization generator of a television camera to an external source.

germanium crystal

Germanium crystal refers to a crystalline form of the element germanium (Ge), which is a metalloid and semiconductor commonly used in various electronic and optical applications. Germanium crystals...

gradient

In image processing and machine vision, the rate of change of pixel intensity.

gray levels

In image processing, machine vision and television, discrete brightness values quantized for a group of pixels. They can range from white, through various shades of gray, to black.

Harting Dove prism

A direct-vision prism made in one piece that can be used only in parallel light.

HDWDM

high-density wavelength division multiplex

high contrast

A term used to describe a photograph, film or television picture where the values for black and white areas are at or near their limits, thereby giving the maximum degree of difference between them.

Photonics Dictionary