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Natural environment

Related to any physical feature of the earth's natural environment.

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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.

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