1. （Flat window）Colorless optical glass is almost transparent in the visible and near-infrared wave band, which is widely used. According to the different refractive index and dispersion, there are more than 100 brands, which can be divided into two types, namely, coronal optical glass (represented by K) and flint optical glass (represented by F). The crown glass is borosilicate glass, which becomes flint glass after adding alumina.
（Flat window）The main difference between the two is that the refractive index and dispersion of flint glass are large, so the spectral elements are mostly made of it.
2. Radiation resistant optical glass -- it has the properties of colorless optical glass, and can not change its function under radiation. The type and grade of optical instruments used for V irradiation are the same as those of colorless optical glass. Its chemical composition is based on the colorless optical glass, adding cerium dioxide to eliminate the color center formed by high-energy radiation in the glass, so that the light absorption of this glass is changed little after being irradiated.
3. （Flat window）Colored optical glass has specific absorption or transmission function for some wavelengths of light. Also known as filter glass, there are more than 100 kinds. The color filter can selectively absorb some colors, while the neutral filter can only reduce the intensity of the beam without changing its color. Dry and filter is based on the principle of dry and light, will not need to reflect off the color rather than absorption.
