calcium fluoride

Definition: Cystalline substance displaying anormalous dispersion i.e. its refractive index does not change consistently with varying wavelength. * It may be used as optical material to produce lenses with extremely high correction of chromatic aberrations. * Expensive to utilise as it is extremely difficult to manufacture to high quality as large crystals; it is relatively soft; it exhibits high coefficient of thermal expansion; and it absorbs moisture. * Where used for camera lenses, it is enclosed air-tight and is never an outer element.

Related Terms: dispersion

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