Abstract: A mechanical step scanner which moves an image in discrete steps relative to a detector array by displacing, rather than by deflecting, the optical path. The scanner includes first and second rotatable reflector discs that are in optical alignment with each other, with the optical path of the image, and with the detector array. Each reflector disc has a plurality of flat surfaces which are in parallel-spaced relationship (i.e., are "stepped"); and, the rotation of each disc is at a preselected synchronized speed. Unlike the prior art, this scanner can be placed at any point in the optical path forward of the first disc; avoids complex optical surfaces and the aberrations resulting from the use thereof; and, is not critically dependent on the angular orientation of the optical path, but is only dependent on the stability of the angle selected.