A3.1 OPTICAL GLASSES
Optical glass is mainly determined by the value of two constants, namely, the refractive index and the Abbe constant. A diagram of the Abbe number Vd versus the refractive index nd for Schott glasses is shown in Figure A3.1. Besides the refractive index for the d line, several other quantities define the main refractive characteristics of the glass. The difference (nF – nC) is called the principal dispersion. The Abbe value expresses the way in which the refractive index changes with wavelength. The Abbe value Vd for the d line is defined as
There are many types of glass, but a common broad classification is as follows:
a. Crown glasses are those with a relatively ...