The difference between optical glass and other glass is that it is a part of the optical system and must satisfy the requirements of optical imaging. Therefore, the determination of the quality of optical glass also includes some special and more stringent indicators. The optical glass has the following requirements:
One, the specific optical constants and the same batch of glass optical constants
Each variety of optical glass has a prescribed standard refractive index for different wavelengths of light, as the basis for the design of optical systems. The optical constants of the optical glass so the factory production must be in the certain value tolerance range, otherwise it will make the actual quality of the imaging quality and the results of expected design does not match the influence of optical instruments. At the same time, because the same batch of instruments are often used in the same batch of optical glass manufacturing, in order to facilitate the uniform calibration of the instrument, the deviation of the refractive index of the same batch of glass is more strict than their standard deviation.
Two, a high degree of transparency
The relationship between the brightness of the optical system and the transparency of the glass. Optical glass to a certain wavelength of light transparency in the light absorption coefficient K. Light passes through a series of lenses and lenses, whose energy is partially absorbed by the interface of the optical part and the other part is absorbed by the medium (glass). Increase the former with refractive index increasing, the value of very high refractive index glass, such as a heavy flint glass surface light reflection loss is approximately 6%. Therefore, the main way to improve the transmission efficiency is to reduce the reflection loss on the surface of the lens, such as the coating surface coating, and so on. For large size optical components such as the telescopes objective, due to its great thickness, the optical systems transmission rate is mainly determined by the optical absorption coefficient of the glass itself. By improving the purity of glass raw materials and in the whole process from the ingredients to the melting in preventing any coloring impurities mixed, can usually make the glass light absorption coefficient is less than 0.01 (that is, the thickness of 1 cm on the glass light transmittance is higher than 99%).