Anamorph: ANAMORPH.LEN - An Anamorphic Telextender

Anamorph shows the use of cylindrical lenses, special apertures, and the pickup-length-minus (pkp lnm) command that holds the image in a fixed location, despite the motion of intermediate lenses.This type of system is often used as a telextender to change the focal length of an existing lens. This example shows a simple Bravais system, which is a system where the object coincides with the image. The system goes on the back end of an ordinary lens to create a sharp image with different magnification in the x and y directions. This is accomplished using cylindrical lenses with power in the yz meridian. The Bravais condition is imposed using a pk lnm command on surface 4. Actually, the condition cannot be precisely satisfied using cylindrical lenses because the thickness of the lenses displaces the image in the xz meridian. Therefore, the lens powers were chosen to make the image in the yz meridian lie on the same surface as the xz image.

Note the use of special apertures on surfaces 3 and 4 to model the rectangular lens.