K9 glass is a glass product made of K9 material, used in optics and telescopes.
The composition of K9 is as follows: SiO2-69.13% B203=10.75% Ba0=3.07% Na20=10.40% K20-6.29% As203=0.36%
Its optical constants are: refractive index=1.51630 dispersion=0.00806 Abbe number=64.06
The national standard for optical glass is classified by Abbe number. Glass with Abbe number>50 is defined as crown glass and is represented by "K", and glass with Abbe number<50 is defined as flint glass and is represented by "F".
Under these two categories, light "Q"; heavy "Z"; special "T" and chemical element symbols plus prefixes, numbers plus suffixes are used for subdivision, and there are 18 categories and 141 grades. For example: QF8 (light flint) BaK11 (barium crown) K9 (crown) Generally speaking, crown glass belongs to the alkali silicate system, and most flint glasses belong to the lead silicate system. Currently, most reflecting objective lenses and some refracting telescope components use K9 optical glass.

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