Rear conversion lens

Claim 2

A rear conversion lens mountable to the image side of a photographic lens to make the composite focal length of the rear conversion lens and the photographic lens greater than the focal length of the photographic lens, comprising: a divergent forward lens group comprising three components which are, in order from the object side, a biconvex positive lens, a biconcave negative lens with its more curved surface facing the image side, and a positive lens with its more curved surface facing the object side; and a divergent rearward lens group disposed on the image side of said forward lens group and comprising two components which are, in order from the object side, a biconcave negative lens with its more curved surface facing the image side and a biconvex positive lens with its more curved surface facing the object side.

Claim 3

A rear conversion lens according to claim 1, satisfying the following conditions: ##EQU11## where f Pi represents the focal length of the ith lens from the object side (i=1, 2, . . . , 5), q i represents the shape factor, n i the refractive index, ν i the Abbe number, the shape factor q being defined by ##EQU12## where r a represents the radius of curvature of the object side surface of that lens and r b the radius of curvature of the image side surface of that lens.

Claim 4

A rear conversion lens according to claim 1 or 2, wherein said biconcave negative lens and said biconvex positive lens in said rearward group are cemented together.

Claim 5

A rear conversion lens according to claim 1, wherein the numerical data are follows: ______________________________________ Forward lens group: r.sub.1 = 121.015 d.sub.1 = 4.000 n.sub.1 = 1.59507 ν.sub.1 = 35.6 r.sub.2 = -100.184 d.sub.2 = 2.008 r.sub.3 = -118.420 d.sub.3 = 1.800 n.sub.2 = 1.79668 ν.sub.2 = 45.4 r.sub.4 = 35.500 d.sub.4 = 1.800 r.sub.5 = 36.800 d.sub.5 = 6.000 n.sub.3 = 1.59507 ν.sub.3 = 35.6 r.sub.6 = -5196.816 d.sub.6 = 4.575 Rearward lens group: r.sub.7 = -99.964 d.sub.7 = 1.500 n.sub.4 = 1.79668 ν.sub.4 = 45.4 r.sub.8 = 70.033 d.sub.8 = 0.200 r.sub.9 = 53.938 d.sub.9 = 9.000 n.sub.5 = 1.51009 ν.sub.5 = 63.4 r.sub.10 = - 180.939 ______________________________________ where r 1 , r 2 , r 3 , . . . r 10 , represent the radii of curvature of the successive lens surfaces from the object side; d 1 , d 2 , d 3 , . . . d 9 , represent the center thicknesses of or separations between the lenses; n 1 , n 2 , . . . n 5 , and ν 1 , ν 2 , . . . ν 5 , represent the refractive indices and Abbe numbers, respectively, of the lenses: ______________________________________ Distance between the image plane of the photo- graphic lens and the surface of said rear conversion lens closest to the object d.sub.O = - 48.968 Magnification of said rear conversion lens β = 1.4 Apparent refractive index of the forward lens group N.sub.1 = -14.47 Focal length of the forward lens group f.sub.1 = -886.066 Apparent refractive index of the rearward lens group N.sub.2 = 2.59 Focal length of the rearward lens group f.sub.2 =-145.988 Distance between principal points of said forward and said rearward lens groups e = -0.537 Composite focal length of the rear con- version lens f.sub.R = -125.403 Distance from the principal point of the forward lens group to the image point of the photographic lens a = 35.368 Petzval sum P = -0.00186 Distance from the lens surface which is most adjacent to the object to the final image plane L = 71.001 ______________________________________

Claim 6

A rear conversion lens according to claim 1, wherein the numerical data are as follows: ______________________________________ Forward group: r.sub.1 = 120.000 d.sub.1 = 4.000 n.sub.1 = 1.59507 ν.sub.1 = 35.6 r.sub.2 = -104.724 d.sub.2 = 1.800 r.sub.3 = -113.000 d.sub.3 = 1.800 n.sub.2 = 1.79668 ν.sub.2 = 45.4 r.sub.4 = 35.800 d.sub.4 = 1.800 r.sub.5 = 35.500 d.sub.5 = 6.000 n.sub.3 = 1.59507 ν.sub.3 = 35.6 r.sub.6 = 1200.000 d.sub.6 = 2.500 Rearward group: r.sub.7 = -128.000 d.sub.7 = 1.500 n.sub.4 = 1.79668 ν.sub.4 = 45.4 r.sub.8 = 61.000 d.sub.8 = 9.000 n.sub.5 = 1.51009 ν.sub.5 = 63.4 r.sub.9 = -118.428, ______________________________________ where r 1 , r 2 , r 3 , . . . r 10 , represent the radii of curvature of the successive lens surfaces from the object side; d 1 , d 2 , d 3 , . . . d 9 , represent the center thicknesses of or separations between the lenses; n 1 , n 2 , . . . n 5 , and ν 1 , ν 2 , . . . ν 5 , represent the refractive indices and Abbe numbers, respectively, of the lenses: ______________________________________ Distance between the image plane of the photo- graphic lens and the surface of said rear conversion lens closest to the object d.sub.0 = -46.279 Magnification of said rear conversion lens β = 1.4 Apparent refractive index of the forward lens group N.sub.1 = -2.70879 Focal length of the forward lens group f.sub.1 = -659.232 Apparent refractive index of the rearward lens group N.sub.2 = 2.7077 Focal length of the rearward lens group f.sub.2 = - 157.826 Distance between principal points of said forward and said rearward lens groups e = -1.160 Composite focal length of the rear con- version lens f.sub.R = -127.521 Distance from the principal point of the forward lens group to the image point of the photographic lens a = 35.497 Petzval sum P = -0.00178 Distance from the lens surface which is most adjacent to the object to the final image plane L = 68.516 ______________________________________