Method of forward motion compensation in an aerial reconnaissance camera

Forward motion compensation techniques are described for an aerial reconnaissance camera having a Cassegrain objective optical subassembly consisting of a primary mirror, a secondary mirror and a flat azimuth mirror located between the secondary mirror and the Cassegrain image plane. The camera includes a camera housing oriented such that the camera housing is substantially parallel to the roll axis of the aircraft. The primary and secondary mirror are rotated about an axis orthogonal to the roll axis in the direction of flight of the aircraft, while maintaining the image recording medium in a fixed condition relative to the camera housing. While the primary and secondary mirror are rotating, the azimuth mirror is rotated in the direction of flight at a rate one half the rate of rotation of the primary and secondary mirror.