Photonics Dictionary: F

An optical instrument consisting of an objective lens, a coherent (usually flexible) fiber bundle and an eyepiece to examine the output of the fiber bundle.

Relation between a material's transport rate and the material's concentration gradient and the diffusion coefficient.

One or more spots placed in the field of view of an optical system to provide a means of reference.

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

A photodetector employing photoregeneration of carriers in the channel region of an FET structure to provide photodetection with current gain.

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...

An image-forming instrument in which a strong electrostatic field causes cold emission of electrons from a sharply rounded point or from an object that is located on that point. The electrons are...

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

An extremely powerful microscope that renders individual ionized atoms visible by using an electric field to propel the ions to a fluorescent screen where they are magnified.

1. A lens situated at or near the plane of an internal image to project the aperture of a previous objective or erector upon the aperture of a following lens. 2. A lens at or near the plane of a...

An expression of the tolerance of decentration of a laser diode from the optical axis: the region around the axis in the focal plane of the collimator in which the facet can be located and still...

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...

Intensity of emission as a function of direction in a given plane.

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

An aperture located at an image plane of an optical system that determines the size and shape of the image.

The angle measured between the focal surface containing the image and a plane normal to the optical axis.

Secondary aberrations remaining after the primary (Seidel) aberrations have been corrected.

The allowable departure from the given figure or geometrical form. It may be described in terms of fringes or wavelengths.

In optics, the geometrical form of an optical surface.

The process whereby the shape of an optical surface is altered by polishing.

The freeing of electrons from a filament in an electron tube as the result of the filament being heated by an electric current.

A transformer that is designed to regulate the amount of current that passes through an electron tube's filament.

A measuring eyepiece with a screw-micrometer-driven crosshair used to measure the size of the image.

In solar energy technology, the percent of usable land covered by collectors. The horizontal collector is the only design that exhibits 100 percent fill factor.

The ratio of active to inactive areas on a pixel.

The site behind the lens system in a camera where photographic media are positioned for exposure.

A mechanism in a camera designed to position the film in the focal plane for exposure.

A device used to scan images or information on photographic film for the subsequent relay of information.

An instrument designed to place nongraphic information, usually generated by a computer, onto photographic film. The information is generally encoded as a series of opaque and translucent spots, or...

The process by which the light from the images of photographic film is encoded into electrical signals for video transmission.

An interferometer spectrometer designed to measure thicknesses of thin films or layers by recording the interferogram and by having a computer within the instrument to establish the distance between...

The butt (edge to edge) splice of two pieces of film produced by a heat splicer that melts the edges together; used in editing motion picture film.

Filoviruses are a family of viruses that are responsible for severe and often fatal hemorrhagic fevers in humans and non-human primates. The name "filovirus" is derived from their filamentous...

1. With respect to radiation, a device used to attenuate particular wavelengths or frequencies while passing others with relatively no change. 2. See digital filter.

The necessary increase of a photograph's exposure time as the result of the additional absorption of light by the filter being used.

A grating used as a reflectance filter, particularly in the far-infrared. Small plane gratings, blazed for the wavelength of the unwanted radiation, are produced for this purpose.

A function used in a convolution filtering operation. The image to be filtered is convolved with the filtering kernel to obtain the enhanced image.

A spectrophotometer that makes use of filters to isolate narrow bands of the spectrum.

A device that holds a number of filters and allows the filter with the desired characteristics to be rotated into an optical aperture.

A low-power telescope with a wide field of view, typically attached to a higher power telescope with a narrower field of view. This enables an observer to locate a celestial object with the...

For a Fabry-Perot interferometer or etalon, a value for the transmission bandwidth which can be calculated as the ratio of the free spectral range to the full width half maximum of the transmission...

A fixed-focus camera designed to record the ink impression of fingerprints that have been impressed on a card or form for record purposes.

A grinding process that employs fine emery.

A method used to produce precision spherical and aspheric molded glass lenses without grinding or polishing.