Dove prism to erect projected images using arc lamp.

Dove prism to erect projected images using arc lamp. Collimated white light is sent through an 'arrow' slit and then focused on a projection screen with a lens. The arrow on the screen is the 'upside-down' version of the arrow object due to the lens. If a Dove erecting prism is placed at position 1, then the arrow on the screen is flipped so that the upright version of the arrow object is projected. See figure 1. Light from the 'arrow' slit is sent into a Dove 45 deg -45 deg -90 deg prism. The light refracts through the first face of the prism, is totally internally reflected from the second face of the prism, and is refracted out of the third face of the prism. The exiting beam is parallel to the entering beam, and the 'arrow' is flipped. The prism is called an 'erecting' prism when used in this fashion. Ref: Modern College Physics by Harvey White, 6th ed., p.496-497