Objective lens system for endoscopes having an image transfer optical fiber bundle

Claim 2

An objective lens system for an endoscope having an image transfer optical fiber bundle, which comprises from the object end to the image end a negative powered first lens element L1 having a concave image side surface, a positive powered second lens element L2 having a radius of curvature greater on an image side than on an object side, a positive powered third lens element L3 having a radius of curvature greater on the object side than on the image side, a positive powered doublet lens component comprising fourth lens element L4 and fifth lens element L5, and an aperture diaphragm interposed between the second lens element and the third lens element, said objective lens system satisfying the following relations: |d·f/f.sub.R.sup.2 |<0.11 v2<45.0 where f is the equivalent focal length of the entire objective lens system, f R is the equivalent focal length of the rear lens group including the third, fourth and fifth lens elements; d is the axial distance between the aperture diaphragm and the front focal point of the rear lens group, and v2 is the Abbe number of glass for the second lens element.

Claim 3

An objective lens system as defined in claim 1, wherein said first lens element consists of a plano-concave lens.

Claim 4

An objective lens system as defined in claim 1, wherein said second lens element consists of a plano-convex lens.

Claim 5

An objective lens system as defined in claim 1, wherein said third lens element consists of a plano-convex lens.

Claim 6

An objective lens system as defined in claim 1, wherein said fourth lens element consists of a bi-convex lens having a radius of curvature greater on the image side than on the object side.

Claim 7

An objective lens system as defined in claim 1, wherein said fifth lens element consists of a negative powered meniscus lens having a convex image side surface.

Claim 8

An objective lens system as defined in claim 1 described substantially as follows: ______________________________________ Radius of Axial Distance Element Curvature (mm) Between Surfaces n.sub.d V.sub.d ______________________________________ R1 = ∞ L1 d1 = 0.5363 1.81550 44.4 R2 = 1.155 d2 = 1.3274 R3 = 13.8639 L2 d3 = 1.9174 1.80518 25.4 R4 = ∞ d4 = 0.0536 R5 = ∞ L3 d5 = 1.5151 1.71300 53.9 R6 = -2.4590 d6 = 1.2738 R7 = 2.9887 L4 d7 = 1.6760 1.62041 60.3 R8 = -1.9857 L5 d8 = 0.5363 1.80517 25.4 R9 = -4.7894 ______________________________________ where the lens elements L1 to L5 have surfaces R1 to R10, the index of refraction is given by n d , the dispersion measured by the Abbe number is given by v d , and axial distance between each adjacent surfaces is given by d.

Claim 9

An objective lens system as defined in claim 1 described substantially as follows: ______________________________________ Radius of Axial Distance Element Curvature (mm) Between Surfaces n.sub.d v.sub.d ______________________________________ R1 = ∞ L1 d1 = 0.5423 1.79950 44.4 R2 = 1.1665 d2 = 1.0884 R3 = 21.3740 L2 d3 = 2.0381 1.80518 25.4 R4 = ∞ d4 = 0.0542 R5 = ∞ L3 d5 = 2.0337 1.62041 60.3 R6 = -2.136 d6 = 1.3558 R7 = 3.0220 L4 d7 = 1.6947 1.62041 60.3 R8 = -2.0079 L5 d9 = 0.5423 1.80517 25.4 R10 = -4.8428 ______________________________________ where the lens elements L1 to L5 have surfaces R1 to R10, the index of refraction is given by n d , the dispersion measured by the Abbe number is given by v d , and axial distance between each adjacent surfaces is given by d.