Optical glasses with certain inner quality e.g. low striae content are essential for good optical systems. A stria is a small
local change in the refractive index inside the glass resulting in a wave front distortion that can cause blurring of the image.
During the production process of optical glass, striae are observed by measuring it with the so-called shadow graph method.
This simple measurement displays a stria as a shadow on an observation screen. A human operator evaluates the contrast
by comparing it with references. The new proposed approach uses a digital camera and image processing to measure human
independent the stria level. A first repeatability measurement shows wave front deviation (maximum deviation, peak-topeak)
of less than +/- 8 nm.