Paul S. Schmitt

Scatter ratio test for lens surface quality measurement

The surface quality of an optical lens can be quantitatively measured using a scatter ratio test. A collimated light beam is focused by the test lens upon an opaque spot. A detector behind the spot measures light scattered past the spot. The spot is then displaced to the side so that total energy out of the lens is measured by the detector. The scatter ratio is the ratio of the two detector outputs. The test is shown to be reproducible and insensitive to operator effects. It is shown to be an effective process control tool for detecting changes in surface finish. The relationship between stylus measurements of lens surface roughness and the scatter ratios is shown.