Optical Glass Classification

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As the most important component of optical instruments, optical glass has a direct impact on the imaging quality of mirrors. optical Glass is first divided into Mian brand glass and Firestone glass according to the content of lead oxide. less than 3% of these are Mian brand glass and more than 3% are Firestone glass, later, as the number of glass types increased, the refractive index and dispersion were used. The refractive index of the crown glass was usually smaller than 1.6, and the dispersion coefficient (also called the Abbe number) was larger, the smaller the dispersion), the more 50, the opposite of flint glass.

Crown Glass (k is the last letter in the abbreviation): This name is easy to misunderstand as a brand. It is actually just a production process, so some people translate it into crown glass: it is to first blow the glass liquid into a crown or hollow ball, and then put in a fast rotating flat center re-heating, the use of centrifugal force to expand it to form a glass circle about 1.5 in diameter, A relatively thin edge is cut into a proper shape for window glass. The circular bulge in the middle is the prototype of the lens, but some people do not mind the image distortion, it is also called bullseye windows ). This production method was developed and matured by glass craftsmen near Ruang in France around 1320, but it was not announced as a trade secret. As a result, the British who were separated by water imported windows for three hundred years, the same process did not appear in London until 1628.

Flint glass (Flint glass): In the middle of the 17th century, the Firestone mine in the lower-period deposits in the southeastern England region is widely used in the manufacture of lead glass (usually 4%-60% of lead content. However, lead glass may cause environmental pollution in the production and treatment process. At present, it is generally replaced by titanium dioxide and zirconia.

Because the German company Zeiss has a complete set of glass models and stable performance, it generally follows its Naming Standard. K Represents the Crown card, f Represents the rock, z is heavy, B Represents boron, BA represents barium, l represents La, p represents phosphorus, N represents lead-free, for example, the BK7 prism widely used in the dual-tube telescope is No. 7th in borkron glass (borosilicate German; the brighter bak4 prism uses light Barium Crown, Which is baritleichtkron in German ). Other types include fluenton (FK), qk, zpk, ZK, TK, and QF) heavy Firestone (ZF), heavy barium Firestone
(Zbaf), Firestone (kf), special Firestone (TF) and so on.

In the Abbe diagram with the dispersion coefficient as the abscissa and refractive index as the ordinate, the distribution is as follows:

 

Another material that has to be mentioned is fluorite-fluorite, which is actually a calcium fluoride crystal (this material exists in our teeth and plays an important role in the prevention and treatment of dental caries ), its dispersion is very low (the number of abits is 95.3), which makes it very suitable for use as an optical material. The fluorite ore is widely distributed, but it can meet the requirements of optical accuracy, in addition, it is very expensive because of its poor processing and chemical stability (slightly soluble in water. In addition to optical glass, there are also common composite lenses that combine several lenses with different optical properties to overcome single types of defects: for example, Nikon's ultra-low dispersion (extra-low dispersion), Canon's ud (ultra dispersion), and tenglong's LD (low
Dispersion), the SLD developed by the company, and the ad developed by the company. It may be convenient to speculate. I don't know more technical details, so I won't start it anymore.