Abstract: In an optical lens system for use in combination with a bar code sensor, first and second meniscus lenses are arranged back to back along an optical axis on object and image sides, respectively, and are identical in configuration and optical charcteristics with each other. Each meniscus lens has effective aspherical surfaces defined by predetermined formulae. On the assumption that the first and the second meniscus lenses have the same refractive index, the optical lens system satisfies the following formulae:0.25<(r1/r2)/(n/(n-1))<0.5.1.2<f1/f<1.8,0.3<D/f<0.6, and1.

Abstract: In an aspherical glass lens element which has an optical axis, a focal length f, a thickness along the optical axis, and first and second aspherical convex surfaces defined by first and second predetermined formulae represented as functions of first and second radii of curvature r.sub.1 and r.sub.2 at apexes of the first and the second aspherical convex surfaces and first and second conical coefficients k.sub.1 and k.sub.2, a first factor of f/D, a second factor of (r.sub.1 /r.sub.2)D, and a third factor of k.sub.1 /k.sub.2 fall within the following ranges:1.68<f/D<1.75,-0.18<(r.sub.1 /r.sub.2)D<-0.10, and-0.08<k.sub.1 /k.sub.2 <0.04,where an absolute value of the second coefficient k.sub.2 is smaller than 1000.

Abstract: In an aspherical glass lens element which has an optical axis, a focal length f, a thickness along the optical axis, and first and second aspherical convex surfaces defined by first and second predetermined formulae represented as functions of first and second radii r.sub.1 and r.sub.2 of curvature at apexes of the first and the second aspherical convex surfaces and first and second coefficients k.sub.1 and k.sub.2 of cones, f/D, r.sub.1 /r.sub.2, and k.sub.1 /k.sub.2 fall within the following ranges:2.0<f/D<4.0,-0.5<r.sub.1 /r.sub.2 <-0.1,-2<k.sub.1 <1, and-80<k.sub.2 <-10.A glass material of the aspherical glass lens element has a refractive index nd and an Abbe number .nu.d selected within the following ranges:1.45<nd<1.55 and75<.nu.d<90.

Abstract: In an aspherical lens element which has an optical axis, a focal length f, a thickness D along the optical axis, and first and second aspherical convex surfaces defined by first and second predetermined formulae represented as functions of first and second radii r.sub.1 and r.sub.2 of curvature at apexes of the first and the second aspherical convex surfaces and first and second coefficients k.sub.1 and k.sub.2 of cones, the aspherical lens element is formed by a low dispersion glass material which has a refractive index n and an Abbe number .nu. specified by:1.44<n<1.55,and75<.nu.<90.In addition, the aspherical lens element is defined by:1.5<(f/D)<1.9,-0.4<(r.sub.1 /r.sub.2)<-0.2,and10<k.sub.1 .multidot.k.sub.2 -1000E.sub.1 <30.