What are the quality requirements of our optical glass in general?

1. The specific optical constants and the consistency of the optical constants of the same batch of glass

Each type of optical glass has a specified standard refractive index value for different wavelengths of light, which is used as the basis for optical designers to design optical systems. Therefore, the optical constant of the optical glass produced by the factory must be within a certain allowable deviation range of these values, otherwise the actual image quality will not be consistent with the expected results at the time of design and affect the quality of the optical instrument.

At the same time, because the same batch of instruments are often made of the same batch of optical glass, in order to facilitate the unified calibration of the instrument, the allowable deviation of the refractive index of the same batch of glass is more stringent than their deviation from the standard value.

2. High degree of transparency

The brightness of the optical system image is proportional to the transparency of the glass. The transparency of optical glass to a certain wavelength of light is expressed by the optical absorption coefficient Kλ. After light passes through a series of prisms and lenses, part of its energy is lost by reflection at the interface of the optical part and the other part is absorbed by the medium (glass) itself. The former increases with the increase of the refractive index of the glass, and this value is very large for high refractive index glass, such as a surface light reflection loss of about 6% for heavy flintlock glass.

Therefore, for the optical system containing multiple thin lenses, the main way to improve the transmittance is to reduce the reflection loss of the lens surface, such as coating the surface anti-reflection film. For large-size optical parts such as the objective lens of an astronomical telescope, due to its large thickness, the transmittance of the optical system is mainly determined by the light absorption coefficient of the glass itself. By improving the purity of the glass raw material and preventing any coloring impurities from mixing in the entire process from mixing to melting, it is generally possible to make the light absorption coefficient of the glass less than 0.01(that is, the light transmittance of the glass with a thickness of 1 cm is greater than 99%).