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The glass originally used to make the lens was the lumps on the ordinary window glass or wine bottle, and the shape resembled a "crown". The name of the crown glass or crown glass was derived from this. The glass at that time was extremely uneven and foamy. In addition to crown glass, there is another flint glass that contains more lead. Around 1790, the Frenchman Pierre-Louis Junard discovered that stirring glass sauce can make glass with uniform texture.
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Optical glass is mixed with high-purity oxides of silicon, boron, sodium, potassium, zinc, lead, magnesium, calcium, barium, etc. according to a specific formula, melted in a platinum crucible at high temperature, and stirred evenly with ultrasonic to remove air bubbles; Cool down slowly over time to avoid internal stress in the glass block. The cooled glass block must be measured by optical instruments to check whether the purity, transparency, uniformity, refractive index and dispersion rate meet specifications. The qualified glass block is heated and forged to form an optical lens blank.
The earliest lenses were uncoated, and some did not even have the matting inside the lens barrel and the blackening of the edge of the lens, and then a single-layer coating appeared, but this is mainly used in military telescopes to achieve lens matting and reduce the enemy The possibility of discovery. In the field of civilian cameras, 1941 Kodak produced the first camera Ektra with a coated lens. However, the development of coating technology should start from the early 1970s. Pentax's SMC-coated lens began to count.
The coatings on modern optical lenses can be divided into two types. One is called antireflection coating, which increases light transmittance, while the other coating changes the color spectrum transmission characteristics of optical lenses, such as one Although the optical material used in a certain lens of the lens has good index of refractive index and other optical lens, it has a yellowish phenomenon, then coat it with a spectrum blocking film to correct the color cast back, and the development of coating technology can compensate for the shortcomings of some relatively inexpensive optical materials, and the design of the lens does not need to use expensive special formula optical glass to complete it as in the past. Therefore, new lenses generally have multiple layers of coating on the air contact surface of each lens. This also highlights the important role of coating for the lens.
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