Crown glass (optics)
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Crown glass is a type of optical
low dispersion glasses
.
History
The term originated from
Types
The
boric oxide, have good optical and mechanical characteristics, and are resistant to chemical and environmental damage. Other additives used in crown glasses include zinc oxide, phosphorus pentoxide, barium oxide, fluorite and lanthanum oxide
. The crown/flint distinction is so important to optical glass technology that many glass names, notably Schott glasses, incorporate it. A K in a Schott name indicates a crown glass (Krone in German). The B in BK7 indicates that it is a borosilicate glass composition.
BAK-4 barium crown glass (glass code 569560) has a higher index of refraction than BK7, and is used for prisms in high-end binoculars. In that application, it gives better image quality and a round exit pupil.
A
singlet lens with the same focal length
.
See also
- History of the achromatic telescope
- John Dollond, who patented and commercialised the crown/flint doublet