The purpose of an analytical orthoprojector is the computer-controlled rectification of aerial photographs into a parallel perspective orthophoto. For the optical transformation the aerial photographs are scanned with a small slit. Each picture element must be exposed onto a specific position in the orthophoto at a specific magnification and orientation (rotation). The density of the orthophoto must be uniform without visible strips. Hence the basic requirements for the optical system are: large range zoom, uniform slit illumination independent of zoom position, image rotation, high boresight stability for projecting beam. The optical design of the Zeiss orthoprojector ORTHOCOMP Z 2 is discussed.
There are zoom system applications in which transverse image displacement caused by centring errors can be disturbing. By choosing an optimum reference point (adjustment of reference mark) image displacement is minimized. Formulae are given which permit residual image displacement to be already calculated from the design with thin lenses. Examples show that different types of zoom system differ markedly in sensitivity to this effect of centring errors.
