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.
Transmission:
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.
Ultraviolet:
The range of the electromagnetic spectrum from 10 to 400 nanometers.
V-Coating:
A narrowband coating for specific laser wavelengths.
Vignetting:
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.
Wavelength:
The distance light travels in one wave cycle. Electromagnetic energy travels in waves.
Wedge:
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.
EMAIL : luton.leica@virgin.net
Dictionary continued ...
Common optical terms
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