Photonics Dictionary: F

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

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

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

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.

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

A finite version of Shannon's sampling theorem that states that a class of functions can be reconstructed exactly by a sufficient number of spectral samples; the reconstructed function is an explicit...

The spectral transmission window in silica-based fibers between 830 and 850 nm.

The separate spectral lines formed by a diffraction grating that are characterized by one wavelength difference in path length between adjacent slits.

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

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

A type of wide-angle lens that has an angular field above 140° and that exhibits barrel distortion. The most commonly used fish-eye lenses have a field of about 180°, though they are...

The locus of points in a system along a line that remains stationary while the remainder of the system rotates.

Fizeau fringes are interference fringes observed in an interferometer, specifically in a Fizeau interferometer. The Fizeau interferometer is named after the French physicist Armand Fizeau, who...

A type of interferometer noted for producing narrow multiple-beam interference fringes. As a result, when compared with the Twyman-Green, the Fizeau interferometer has fewer optical components, does...

A device used to measure the speed of light by adjusting the rotation of a toothed wheel so that light passing through one tooth opening is reflected through the next. This device has since been...

A technique in photometry that uses an oxyhydrogen or oxyacetylene flame to optically excite a solution containing the sample to be analyzed.

The use of high temperatures, between 2000 and 3000 °C, to excite emission lines from a sample in spectroscopic analysis.

Any of a number of instruments that uses a flame to vaporize a solution of the chemical being analyzed so that light may be passed through the vapor. Monochromation of the transmitted light is...

A part of the spectrochemical analysis of a sample that deals with the excitation of that sample by flame analysis.

The procedure applied to flame-excited line emissions to determine spectra and wavelengths.

The study of the reflection or transmission properties of specimens as a function of wavelength after they have been excited by flame-analysis techniques.

The emission spectrum formed by the radiation from a sample that has been evaporated by a nonluminous flame.

Nonimage-forming light, concentrated or diffuse, that is transmitted through the lens to the image. It is frequently the result of reflections from lens surfaces, a lens barrel, shutter or lens mount.

A filter, partially opaque to near-ultraviolet, visible and infrared radiation, that may be made by exposing and processing photographic film. Such materials are almost equally opaque to radiation of...

A spectroscopic technique used in the detection of free radicals by virtue of their electronic spectra. In this method, an intense light flash is used to form extensive photolysis and yield a high...

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.

A sensitometer that utilizes an electronic flashtube or a photoflash lamp as both the light source and the shutter for obtaining short-duration exposures.

The study and interpretation of the spectra of substances after they have absorbed the radiant energy emitted by a brief, intense light source.

The inverse peak voltage that produces ionization in a gas tube.

A device that is designed to automatically turn electric lamps on and off in a rapidly repeating sequence. The device may use a motor-driven mechanism or a combination heater filament and bimetallic...

A pulsed dye laser in which the excitation is provided by means of a flashlamp. Output is tunable from 335 to 850 nm, with peak power up to 7000 kW.