Patent US 3,963,348

A device for detecting a strain and foreign matters in a glass container is designed to amplify the electrical output obtained by bringing vertical scanning lines into intersection with the image of horizontally rotating strain polarized light. A polarizer and an analyzer are disposed in such a manner that their optical axes cross each other at right angles, and polarized light from the polarizer is projected upon a rotating glass container under inspection and is allowed to pass through the analyzer only when strain and/or foreign matter is found in the glass container. The resulting strain polarized light is projected upon a non-storage camera tube through a lens so as to vertically scan with a line through the center of an image of the glass container on the photoelectric surface of the tube at a speed proportional to the moving speed of the glass container to thereby bring the vertical scanning lines into intersection with the image of the horizontally rotating strain polarized light.