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Definitions: T

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t number
The equivalent f number of a fictitious lens that has a circular opening and 100 percent transmittance, which would give the same central illumination as the lens being considered: where...
T stop -> t number
The equivalent f number of a fictitious lens that has a circular opening and 100 percent transmittance, which would give the same central illumination as the lens being considered: where...
table
See honeycomb table; indexing table.
tachometer
An instrument designed to measure the rate of rotation of components, such as shafts.
talbot
One lumen-second, the SI unit of the quantity of light.
Talbot's bands
The series of interference bands that appear in the spectrum when a specified glass plate is inserted into a spectroscope, from the side of the blue portion of the spectrum, so that the plate...
Talbot's law
The law stating that the brightness of an object that is examined through a slotted disc, rotating over a critical frequency, is proportional to the angular aperture divided by the opaque sectors.
tangent ogive
In optics, a shape often given to the leading edge of a projectile. In any side view it appears as a pointed arc, while any cross section perpendicular to its long axis appears as a circle.
tangential distortion
Optical aberration such that image magnification varies with ray distance from the optical axis in a radial distortion.
tap
A device for extracting a portion of the optical signal from a fiber.
tapered transmission line -> tapered waveguide
A waveguide having a characteristic that is altered continuously with the distance traveled, relative to the axis of its path.
tapered undulator -> undulator magnet
A device used in a free-electron laser to convert the electron-beam's energy into microwave laser radiation by creating a magnetic field of alternating polarity through which the free electrons are...
tapered waveguide
A waveguide having a characteristic that is altered continuously with the distance traveled, relative to the axis of its path.
target
1. The anode or anticathode of an x-ray tube that emits x-rays when bombarded by electrons. 2. The screen in a television imaging tube that is scanned by an electron beam to determine the...
target angular position
Measurement estimated from the position of the image's centroid.
target size and orientation
Angular tracking measurement estimated from the properly normalized image second-moment tensor.
Taylor criterion
States that in interferometers in which the separation of the maxima is equal to the half-value width, a slight drop in intensity between fringes is distinguishable and the fringes can be considered...
TEA laser -> transversely excited atmosphere laser
Also known as TEA laser. A coherent optical source with a wide wavelength range in the infrared, visible and ultraviolet that uses an electrical discharge transverse to (across) the optical axis to...
tearing
In television, a lateral displacement of the lines from their normal position due to the instability of a synchronizing circuit. Visually, it appears as though parts of the images had been torn away.
technicolor
The color process that is used to form positive color cine films by dye transfer or imbibition, based on the use of separate matrices that superimpose yellow, magenta and cyan dye images on the final...
tee coupler
A passive coupler that connects three ports.
telecentric lens
There are three types of telecentric lenses: -Image-space telecentric lenses are those in which the aperture stop is located at the front focus, resulting in the chief rays being parallel to the...
telemeter
1. The term used to describe any of the many instruments used to remotely record physical dimensions, such as strain, temperature or pressure, and transmit this data to a receiving station. 2. A...
telemetry
The science of sensing and measuring information at some remote location and transmitting the data to a convenient location for reading or recording.
teleobjective -> telephoto lens
A compound lens so constructed that its overall length is equal to or less than its effective focal length.
telephoto lens
A compound lens so constructed that its overall length is equal to or less than its effective focal length.
telephoto magnification -> telephoto ratio
In a telephoto lens, the ratio of the overall length to the focal length of the lens. It is generally about 0.8 to 0.9 in magnitude.
telephoto power
The ratio between the focal length of a lens having a longer focal length than that of the standard lens used with a camera, and the focal length of the standard lens. It is used to provide an...
telephoto ratio
In a telephoto lens, the ratio of the overall length to the focal length of the lens. It is generally about 0.8 to 0.9 in magnitude.
telephotography
1. A method of photographing distant objects with a lens of long focal length. 2. The reproduction of photographs over a distance by means of electricity.
telephotometer
An instrument used to measure the luminance (brightness) of a distant object. The object is viewed through a small telescope, and a mirror in the focal plane reflects an internal illuminated surface...
telephotometry
The principles and techniques involved in the use of telephotometers to measure atmospheric extinction.
telepresence
The use of head-mounted displays and body-operated remote actuators to control distant machinery. Provides a virtual environment for humans to control devices, robots, etc., in a hostile real...
teleradiography
A method of taking radiographs at a distance from the object being photographed to decrease distortion.
telescope
An afocal optical device made up of lenses or mirrors, usually with a magnification greater than unity, that renders distant objects more distinct, by enlarging their images on the retina.
telescope exit pupil
The image of the aperture stop, usually the objective lens, that is produced by the eye lens. When the exit pupil of the telescope coincides with the entrance pupil of the eye of the observer, the...
telescope lens
A telescope lens is a primary optical component of a telescope system that gathers and focuses light to form an image. It is typically a curved, transparent piece of glass or other optical material...
telescope mount
The base used to hold an astronomical telescope. It may be either altazimuth, with horizontal and vertical axes of rotation, or equatorial, with one axis parallel to the Earth's axis of rotation and...
telescopic sight -> riflescope
A small erect-image telescope for use as a sighting device on a rifle. The chief requirement is a long eye relief to avoid damage to the eye due to recoil. The power may lie anywhere between 1 and...
televise
To transform a picture or image field into a television signal for transmission.
television aperture
The term that represents the size of one of the many small elements into which a television image is necessarily broken down for transmission.
television bandwidth
The span of frequencies within which a single channel of broadcast television must fall; in the US, it is 6 MHz.
television camera
A camera containing an electronic image sensor that converts the image to an electronic signal suitable for television applications.
television line number
The value equal to the raster height divided by the half-period of a periodic test pattern.
television microscope
A device designed to enlarge the image of a microscopic object by television process. It may be a flying spot scanner that is used to scan the microscope slide, or a camera tube-microscope...
television monitor
A television receiver that receives the signals generated by a television camera directly, or remotely through a radio signal. It may be used to continuously check image and sound reception; as a...
television projection
A television display system in which the television signal is converted to an image that is projected onto either a front or rear projection screen.
television signal
The combination of the audio and visual signals that are transmitted and received at the same time, correlating the scene and sound in a television picture.
television transmitter
An electronic device used to encode video and audio signals of a television camera into radio waves that are broadcast to remote receivers. The video and audio components are transmitted...
television waveform
The graph of the oscillating variations composing the wave of a video signal.

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