Disposable endoscope employing positive and negative gradient index of refraction optical materials

Claim 1

An objective for an endoscope comprising distal and proximal optical elements and having distal and proximal optical surfaces symmetrical about an optical axis, said distal element being formed of a material exhibiting a negative radial gradient in its index of refraction, and said proximal element being formed of a material exhibiting a positive radial gradient in its index of refraction, and wherein the radii of the optical surfaces of said distal and proximal elements and the spacings of the optical surfaces thereof from one another are specified by the following optical prescription: ______________________________________ SURFACE RADIUS (mm) THICKNESS (mm) MEDIUM ______________________________________ OBJ: INFINITY 2.000000 AIR 1: INFINITY 0.500000 "NEGRIN" 2: 1.24839 2.224813 STO: INFINITY 1.387962 4: 11.48559 2.781881 "POGRIN" 5: -7.30623 3.210405 IMG: INFINITY 0.000000 ______________________________________ in which surfaces 1 and 2 are the distal and proximal optical surfaces of the distal element, respectively, and surfaces 3 and 4 are the distal and proximal optical surfaces of the proximal element, respectively, and wherein the variation of the indices of refraction of the "negrin" and "pogrin" materials of said distal and proximal elements, respectively, are specified by the following values therefor: ______________________________________ PWL 656.00 588.00 486.00 "NEGRIN" n.sub.00 1.504730 1.507410 1.514000 c.sub.10 0.6934E-01 0.6790E-01 0.6456E-01 c.sub.01 = c.sub.02 = c.sub.03 = c.sub.04 = 0; c.sub.20 = c.sub.30 = c.sub.40 = 0 PWL 656.00 588.00 486.00 "POGRIN" n.sub.00 1.661300 1.667200 1.682100 c.sub.10 -0.6369E-01 -0.6350E-01 -0.6298E-01 c.sub.01 = c.sub.02 = c.sub.03 = c.sub.04 = 0; c.sub.20 = c.sub.30 = c.sub.40 = 0 ______________________________________ wherein: PWL refers to the wavelength of light in nm to which a particular specified value for the index of refraction n refers, and the index of refraction n of the material of each of the proximal and distal elements at any point (r,z) therein is specified by the following equation (1) n(r,z)=n.sub.00 +c.sub.01 z+c.sub.02 z.sup.2 +c.sub.03 z.sup.3 +c.sub.04 z.sup.4 +c.sub.10 r.sup.2 +c.sub.20 r.sup.4 +c.sub.30 r.sup.6 +c.sub.40 r.sup.8 ( 1) in which: n(r,z)=refractive index of the material at radius r in mm from the optical axis and elevation z in mm from a plane tangent to one optical surface of the element at the optical axis; n 00 =refractive index at r=0, z=0; c 0i =coefficient of axial variation of refractive index; c i0 =coefficient of radial variation of refractive index.