Three-lens system providing a variable focal power along one principal meridian

Claim 1

An optical system for varying focal power along one principal meridian comprising, in alignment along an optical axis, two-spaced cylinder lenses I and II having their axis of cylinder in a plane passing through the optical axis and an axially-slidable cylindrical lens III having an axis of cylinder perpendicular to said plane, said lenses having values set forth in the following table wherein axial thicknesses of successive lenses are designated T 1 to T 3 , successive axial spaces are designated S 1 to S 2 , successive lens radii are designated R 1 to R 6 wherein the radius denotes cylinder curvature about a line lying on the side opposite the focal-plane side of the lenses, refractive indices and Abbe numbers of the glasses in the successive lenses are absolute values designated ND 1 to ND 3 and ν 1 to ν 3 , ______________________________________ Index of Thick- Refrac- Abbe Lens Cyl. Radius ness(T) Spacing(S) tion(ND) No. (ν) ______________________________________ R.sub.1 =∞ I T.sub.1 =5.0mm ND.sub.1 =1.523 ν.sub.1 =58 R.sub.2 =261.5mm S.sub.1 = 28.3 to 139.4mm R.sub.3 =∞ II T.sub.2 =5.0mm ND.sub.2 =1.523 ν.sub.2 =58 R.sub.4 =174.33mm S.sub.2 =160.4S.sub.1 R.sub.5 =∞ III T.sub.3 =5.0mm ND.sub.3 =1.523 ν.sub.3 =58 R.sub.6 =348.67mm ______________________________________