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A saddle mirror has opposite curvatures in the two principal sections. Such an optical element has some very interesting properties, the important one being that it gives a nonreversed image for an object located in front of and some distance away from it. However, once such a mirror is made, it is difficult to vary the two powers in the two principal sections to enable one to change the size of the image. This paper considers the possibility of combining two separate cylindrical surfaces, in the form of a lens and a mirror, that can be rotated to change the effective curvatures in the principal sections of the equivalent saddle mirror. Several methods for achieving this type of system are described.
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