Abstract: Couples an additional optical system to an existing system having viewing optics, including an eyepiece. A pivoted mirror reflects the image scene from the imaging optics of the existing system to the viewing optics. The added system transmits a second image scene through a Pechan prism to the mirror, which when pivoted to a second position, reflects it to the viewing optics. The prism has internal reflecting paths to increase the optical path length of the added system to equal the path length of the existing system so that both image scenes are in focus at the eyepiece. An image intensifier may be employed between the prism and the imaging optics of the added system to brighten the image, and a reticle may be placed at the output of the intensifier to provide for boresighting and alignment of the added system.

Abstract: A scanning mirror position sensor operable from the back side of a scanning mirror which utilizes the front side of the mirror for scanning a scene to be interrogated or displayed. A rectangular uniformly distributed light source is reflected from the back surface of the scanning mirror across a grating consisting of alternate transparent and opaque regions placed in the focal plane in front of a single large area photodetector. As the light from the light source sweeps across the grating, the detector is alternately energized and deenergized to form a serial pulse train which is coupled to a pulse counter which accumulates the pulse count to thereby provide a continual and accurate measure of the mirror position.