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Earth science
Any of several geological sciences that are concerned with the earth, its origins, and all of its various structures and physical forms and phenomena.
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Astigmatic power lens
Eyewear; Optometry
Lens bringing a paraxial pencil of parallel light to two separate line foci mutually at right angles and hence having vertex power in only the two principal meridians.
Astronomical telescope
Eyewear; Optometry
Compound optical system, afocal in normal adjustment, consisting of a positive objective element or group and a positive ocular element or group forming a magnified, inverted ...
Condensing lens
Eyewear; Optometry
A convex lens used to condense the illuminating beam into the patient's eye and to form a real inverted image of the retina thus illuminated.
Concave lens
Eyewear; Optometry
Lens which causes parallel incident light to diverge from a virtual focus. Also known as minus-power lens.
Abbe number
Eyewear; Optometry
Mathematical expression for determining the correction for chromatic aberration of an optical material of component.
Astigmatic difference
Eyewear; Optometry
Vertex power in the second principal meridian minus that in the first principal meridian.
Optical drive
Multimedia;
An optical drive is an electronic device used to seek, read, and write data on an optical disc. An optical drive may reside in an optical library or as a stand-alone unit.
