Reproducing objective lens for videodiscs

A reproducing objective for videodiscs comprising:

• a first, second, third, fourth and fifth lens;
• said first lens being a positive lens, said second lens being a positive lens, said third lens being a negative meniscus lens with its convex surface positioned toward the object side, said fourth lens being a negative meniscus lens with its convex surface positioned toward the object side, said fifth lens being a positive meniscus lens with its concave surface positioned toward the object side, said reproducing objective lens for videodiscs satisfying the following conditions:
• ______________________________________ 1. 0.30 .DELTA.r.sub.6 /f .gtoreq. 0.23 2. 0.27 .gtoreq. d.sub.1 /f .gtoreq. 0.15 3. 1.4 .gtoreq. r.sub.6 /.vertline.r.sub.7 .vertline. .gtoreq. 0.9 4. 6.0 .gtoreq. .vertline.f.sub.3 .vertline./.vertline.f.sub.4 .vertline. .gtoreq. 2.5 5. 0.31 .gtoreq. d.sub.5 /f .gtoreq. 0.21 ______________________________________
• wherein
• reference symbol f represents the focal length of the lens system as a whole, reference symbol f.sub.3 represents the focal length of the third lens, reference symbol f.sub.4 represents the focal length of the fourth lens, reference symbol r.sub.6 represents the radius of curvature of the surface on the image side of the third lens, reference symbol r.sub.7 represents the radius of curvature of the surface on the object side of the fourth lens, reference symbol d.sub.1 represents the thickness of the first lens and reference symbol d.sub.5 represents the thickness of the third lens;
• and wherein
• said reproducing objective for videodiscs has the following numerical data:
• ______________________________________ r.sub.1 = .infin. d.sub.1 = 2.7726 n.sub.1 = 1.547 .nu..sub.1 = 54.0 r.sub.2 = -5.6308 d.sub.2 = 0.2500 r.sub.3 = 15.9099 d.sub.3 = 2.2050 n.sub.2 = 1.672 .nu..sub.2 = 64.0 r.sub.4 = -14.0644 d.sub.4 = 1.9386 r.sub.5 = 5.4115 d.sub.5 = 3.7500 n.sub.3 = 1.667 .nu..sub.3 = 33.0 r.sub.6 = 3.4870 d.sub.6 = 3.8136 r.sub.7 = -2.8396 d.sub.7 = 3.5075 n.sub.4 = 1.667 .nu..sub.4 = 33.0 r.sub.8 = -5.2742 d.sub.8 = 0.2500 r.sub.9 = -69.2660 d.sub.9 = 3.0721 n.sub.5 = 1.667 .nu..sub.5 = 33.0 r.sub.10 = -10.2729 f = 13.1297 f.sub.3 = -66.667 f.sub.4 = -21.786 RMS wavefront errors = .021 1 = 2 ______________________________________
• wherein
• reference symbols r.sub.1 through r.sub.10, respectively, represent radii of curvature of respective lens surfaces, reference symbols d.sub.1 through d.sub.9, respectively, represent thicknesses of respective lenses and air spaces between respective lenses, reference symbols n.sub.1 through n.sub.5, respectively, represent refractive indices of respective lenses, reference symbols .nu..sub.1 through .nu..sub.5, respectively, represent Abbe's numbers of respective lenses, reference symbol f represents the focal length of the lens system as a whole, reference symbol f.sub.3 represents the focal length of the third lens, reference symbol f.sub.4 represents the focal length of the fourth lens and reference symbol 1 represents the working distance of the lens system as a whole.