In transmitted light DIC, light from the lamp is passed through a  polarizer located beneath the substage condenser, in a manner similar to polarized light microscopy. Next in the light path (but still beneath the condenser) is a modified Wollaston prism that splits the entering beam of polarized light into two beams traveling in slightly different directions. The Wollaston prism is composed of two quartz wedges cemented together, from which emerging light rays vibrate at 90 degrees relative to each other with a slight path  difference. A different Wollaston prism is needed for each  objective of different magnification. Wollaston prisms are usually  loaded into a revolving turret on the condenser, which allows the  microscopist to rotate the appropriate prism into the light path when changing magnifications.