The difference between optical glass and other glasses is that it is a component of the optical system. Each type of optical glass has a specified standard refractive index value for different wavelengths of light. The transmittance of the optical system is mainly Determined by the light absorption coefficient of the glass itself, as the basis for designing the optical system of the optical lens, the optical constant of the optical glass must be within a certain tolerance range of these values, otherwise the actual imaging quality will not match the expected result during the design. Affect the quality of optical lenses. Optical glass has a high degree of transparency, a high degree of physical and chemical uniformity, and specific and precise optical coefficients.
Physical properties of optical glass:
1. Refractive index (ND)
The refractive index of glass is measured by the characteristic line of sodium element Du003d589.3nm , Expressed in ND.
2. Specific gravity (s)
Measure the specific gravity of glass by hydrostatic weighing method.
3. Chromaticity value (x, y, Y)
According to the method specified by the International Commission on Illumination (CIE) in 1931 and 1964, the standard illuminants in A and D65 were measured The chromaticity value of the glass under illumination.
4. Thermal characteristics
When the temperature of the glass increases by 1℃, the relative change rate of its length.
5. Transition temperature (Tg)
When the swelling amount of the glass changes suddenly, the corresponding temperature is the transition temperature of the sample. At this temperature, the viscosity of the glass is close to 10 13 Pa.sec.
6. Softening temperature (Ts)
When the physical properties of glass change drastically, its swelling volume also approaches zero temperature (the softening temperature of glass, at this time The viscosity of glass approaches 10 11 Pa/sec).
7. Color temperature conversion capability (V)
Color temperature glass is divided into two types: increasing color temperature glass and decreasing color temperature glass, and its conversion capability is expressed by the Mired value.
The color temperature rising glass is blue, the grade is SSB, and its Millard is negative. The color temperature glass is amber, the grade is SJB, and its Millard is positive.
Spectral characteristics of optical glass
According to the spectral characteristics of colored optical glass, it can be divided into three categories
1, cut-off glass
Their spectral characteristic indexes are expressed by the transmission limit wavelength λtj, the allowable deviation of the transmission limit, the transmittance Tλo and the curvature slope K at a prescribed wavelength.
2. Choose absorbing glass
Glass only transmits (or absorbs) light in a certain (or several) wavelength range, and its The spectral characteristic index is expressed by the transmittance value and the allowable transmittance deviation value of the specified glass thickness at a specific wavelength λ.
3. Neutral glass
Glass absorbs light of various wavelengths in the visible light uniformly and indiscriminately, and its spectral characteristic index is based on the average transmittance Tp, the allowable deviation range of average transmittance △Tp. The maximum allowable deviation is expressed by Qz