Abstract: The surface of a lens for reading out an optical recording medium facing the optical recording medium is formed as a convex aspheric surface which is rotationally asymmetrical with respect to the optical axis and defined by a predetermined aspheric surface equation, whereby, even when a light beam having an astigmatic aberration is emitted from a light source, a signal surface of the optical recording medium can be irradiated with a light beam whose astigmatic difference has been favorably corrected, while the lens can be easily manufactured.

Abstract: A reading lens system consists of a first lens element which is a positive meniscus lens convex toward the object side, a stop and a second lens element which is a meniscus lens convex toward the image plane side. The first lens element, the stop and the second lens element are arranged in this order from the object side. Each of the faces of the second lens element is an aspheric surface represented by formula (1), and satisfying formula (2), as follows: ##EQU1## wherein B.sub.3 =1-k.sub.3 c.sub.3.sup.2 y'.sub.3.sup.2,B.sub.4 =1-k.sub.4 c.sub.4.sup.2 y'.sub.4.sup.2,k.sub.i =a value which gives the conic constant of an i-th face as numbered from the object side as k.sub.i -1,C.sub.i =the curvature at the vertex of the aspheric plane of an i-th face,y.sub.i =the height above the optical axis of an i-th face,y'.sub.3 =the effective radius of the third face,y'.sub.4 =the effective radius of the fourth face, andA.sub.j =2.sub.j order aspheric coefficient (j=2.about.5).

Abstract: Described herein is a variable magnification duplicator lens system which is provided with, on the subject side of a stop, a front lens group including a 1st lens element consisting of a meniscus lens of positive power and facing the convex side thereof toward the subject, a 2nd lens element consisting of a meniscus lens of negative power facing the convex side thereof toward the subject, a 3rd lens element with positive power, and a 4th lens element with negative power, and on the image-forming side of the stop, a rear lens group including 5th, 6th, 7th, and 8th lens elements arranged symmetrically with the 1st to 4th lens elements of the front lens group, respectively. Of these lens elements, the 3rd to 6th lens elements and at least one of the 1st and 8th lens elements are movable.