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Dictionary T - End

Tangential Meridian

Tangential Meridian:
In an optical system of revolution, the tangential, or meridional, plane is defined as the plane containing the optical axis
and the specified object point.
Telecentric Lens:
A multi-component system whose aperture stop is located at the front focus so that the chief rays are parallel to the
optical axis in image space. For a telecentric lens, the exit pupil is at infinity.
Telephoto Lens:
A multi-component lens arranged so that the overall length of the compound system is less than or equal to the effective
focal length.
Test Glass:
See Optical Flat.
Total Internal Reflection:
When the angle of incidence of light striking the boundary surface of a substance exceeds the critical angle, the result is
total internal reflection.
To admit the passage of light through a medium; light not reflected back to its source is transmitted through the medium.
Transverse Ray Error:
Errors, or departures from ideal, measured in a direction perpendicular to the optical axis.
Truncation Ratio:
The dimensionless ratio of the Gaussian beam diameter at the 1/eČ intensity point to the limiting aperture of the lens.
The range of the electromagnetic spectrum from 10 to 400 nanometers.
A narrowband coating for specific laser wavelengths.
The gradual reduction of image illuminance with an increasing off-axis angle, resulting from limitations of the clear
apertures of elements within an optical system.
Virtual Image:
Light rays reproduce an object, called an image, by gathering a beam of light diverging from a point source and
transforming it into a beam converging toward or diverging from another point; if the beam is diverging, it produces a
virtual image.
Visible Spectrum:
That part of the electromagnetic spectrum that the human eye can perceive, between the ultraviolet and the infrared
(range = .4 microns to .76 microns).
Wave Phenomena:
The characteristics of radiant energy.
Wavefront Deformation:
Departure of a wavefront from ideal (usually spherical or planar) caused by surface errors or design limitations.
The distance light travels in one wave cycle. Electromagnetic energy travels in waves.
An optical element with its faces inclined toward each other at very small angles, diverting light toward the thicker parts
of the element.
Young's Modulus:
Modulus of elasticity; the amount of stress required to produce a unit change in length (strain). Expressed in pounds per
square inch (PSI) or dynes per square cm.


Dictionary continued ...

Common optical terms
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