Inverted-telephoto type wide angle lens system

Claim 2

An inverted-telephoto type wide angle lens system, comprising from the object side to the image side: a first lens group of a negative refractive power; a second lens group of a positive refractive power; and a third lens group of a positive refractive power; wherein the second and third lens groups are shiftable to the object side along the optical axis of the lens system at different speeds from one another in a focusing operation to a closer object, while the first lens group is stationary on the optical axis in the focusing operation and wherein the lens system fulfills the following conditions: 1.0<R<1.5 wherein: R represents a ratio of shifting speed beyond the second and third lens groups in the focusing operation.

Claim 3

An inverted-telephoto type wide angle lens system as claimed in claim 1, wherein the lens system fulfills the following conditions; 0.12<L/f<0.38 wherein; L represents an axial distance between the first and second lens groups in infinity focusing condition; and f represents a compound focal length of the whole lens system.

Claim 4

An inverted-telephoto type wide angle lens system as claimed in claim 1, wherein the lens system fulfills the following conditions; 0.1<f/-f.sub.1 <0.35 1.5<-f.sub.1 /f.sub.2 <3.5 2.1<-f.sub.1 /f.sub.3 <5.0 wherein; f 1 represents a focal length of the first lens group; f 2 represents a focal length of the second lens group; and f 3 represents a focal length of the third lens group.

Claim 5

An inverted-telephoto type wide angle lens system as claimed in claim 1, wherein the first lens group consists of, from the object side, a first lens component of a negative refractive power, a second lens component of a negative refractive power, and a third lens component of a positive refractive power.

Claim 6

An inverted-telephoto type wide angle lens system as claimed in claim 4, wherein the second lens group consists of, from the object side, a fouth lens component of a positive refractive power, a fifth lens component of a negative refractive power consisting of either a single lens element or compound lens unit.

Claim 7

An inverted-telephoto type wide angle lens system as claimed in claim 5, wherein the third lens group consists of, from the object side, a sixth lens component of a negative compound lens element, a seventh lens component of a positive refractive power, and a eighth lens component of a positive refractive power.

Claim 8

An inverted-telephoto type wide angle lens system according to the following design parameters: ______________________________________ f = 100 2ω = 64° F.sub.NO = 1.45 Radius of Axial Refractive Abbe curvature distance index (Nd) number (νd) ______________________________________ r.sub.1 319.422 d.sub.1 5.364 N.sub.1 1.56883 ν.sub.1 56.04 r.sub.2 80.323 d.sub.2 24.047 r.sub.3 -840.794 d.sub.3 5.634 N.sub.2 1.56883 ν.sub.2 56.04 r.sub.4 131.189 d.sub.4 9.299 r.sub.5 140.886 d.sub.5 14.085 N.sub.3 1.81100 ν.sub.3 44.86 r.sub.6 -1270.195 d.sub.6 22.535 r.sub.7 148.309 d.sub.7 15.775 N.sub.4 1.78100 ν.sub.4 44.55 r.sub.8 -808.126 d.sub.8 0.555 r.sub.9 149.979 d.sub.9 28.169 N.sub.5 1.78850 ν.sub.5 45.68 r.sub.10 -78.957 d.sub.10 5.634 N.sub.6 1.74000 ν.sub.6 37.53 r.sub.11 90.835 d.sub.11 33.442 r.sub.12 -53.609 d.sub.12 5.634 N.sub.7 1.75520 ν.sub.7 27.51 r.sub.13 338.641 d.sub.13 18.310 N.sub.8 1.72000 ν.sub.8 52.14 r.sub.14 -105.234 d.sub.14 0.845 r.sub.15 -7252.156 d.sub.15 10.704 N.sub.9 1.72000 ν.sub.9 52.14 r.sub.16 -133.792 d.sub.16 0.845 r.sub.17 * -507.797 d.sub.17 16.901 N.sub.10 1.72000 ν.sub.10 52.14 r.sub.18 -97.502 Aspheric coefficients (r.sub.17): A.sub.4 = 0.32795 × 10.sup.-6 A.sub.6 = 0.10126 × 10.sup.-10 A.sub.8 = 0.13405 × 10.sup.-14 ______________________________________ wherein, the asterisk (*) represents the aspheric surface, and the apsheric coefficients A 1 , A 2 , - - - are defined by the following equation; ##EQU2## wherein A 0 represents the paraxial radius of curvature of the basic spheric surface, X represents the coordinate along the optical surface measured from the top of the basic surface, and Y represents the coordinate perpendicular to the optical axis measured from the optical axis.

Claim 9

An inverted-telephoto type wide angle lens system according to the following design parameters: ______________________________________ f = 100 2ω = 64° F.sub.NO = 1.45 Radius of Axial Refractive Abbe curvature distance index (Nd) number (νd) ______________________________________ r.sub.1 319.422 d.sub.1 5.364 N.sub.1 1.56883 ν.sub.1 56.04 r.sub.2 80.323 d.sub.2 24.047 r.sub.3 -840.794 d.sub.3 5.634 N.sub.2 1.56883 ν.sub.2 56.04 r.sub.4 131.189 d.sub.4 9.299 r.sub.5 140.886 d.sub.5 14.085 N.sub.3 1.81100 ν.sub.3 44.86 r.sub.6 -1270.195 d.sub.6 22.535 r.sub.7 148.309 d.sub.7 15.775 N.sub.4 1.78100 ν.sub.4 44.55 r.sub.8 -808.126 d.sub.8 0.555 r.sub.9 149.979 d.sub.9 28.169 N.sub.5 1.78850 ν.sub.5 45.68 r.sub.10 -78.957 d.sub.10 5.634 N.sub.6 1.74000 ν.sub.6 37.53 r.sub.11 90.835 d.sub.11 33.442 r.sub.12 -53.609 d.sub.12 5.634 N.sub.7 1.75520 ν.sub.7 27.51 r.sub.13 338.641 d.sub.13 18.310 N.sub.8 1.72000 ν.sub.8 52.14 r.sub.14 -105.234 d.sub.14 0.845 r.sub.15 -7252.156 d.sub.15 10.704 N.sub.9 1.72000 ν.sub.9 52.14 r.sub.16 -133.792 d.sub.16 0.845 r.sub.17 * -507.797 d.sub.17 16.901 N.sub.10 1.72000 ν.sub.10 52.14 r.sub.18 -97.502 Aspheric coefficients (r.sub.17): A.sub.4 = 0.32795 × 10.sup.-6 A.sub.6 = 0.10126 × 10.sup.-10 A.sub.8 = 0.13405 × 10.sup.-14 ______________________________________ wherein, the asterisk (*) represents the aspheric surface, and the apsheric coefficients A 1 , A 2 , - - - are defined by the following equation; ##EQU2## wherein A 0 represents the paraxial radius of curvature of the basic spheric surface, X represents the coordinate along the optical surface measured from the top of the basic surface, and Y represents the coordinate perpendicular to the optical axis measured from the optical axis.

Claim 10

An inverted-telephoto type wide angle lens system comprising, from the object side to the image side: a first lens group of a negative refractive power, consisting of, a first lens component of a negative refractive power, a second lens component of a negative refractive power, and a third lens component of a positive refractive power; a second lens group of a positive refractive power, consisting of, a fourth lens component of a positive refractive power, a fifth lens component of a negative refractive power containing a single lens element or compound lens element; and a third lens group of a positive refractive power, consisting of, a sixth lens component of a negative compound lens element, a seventh lens component of a positive refractive power, and an eighth lens component of a positive refractive power; wherein the second and third lens groups are shiftable to the object side along the optical axis of the lens system at different speeds from one another in a focusing operation to a closer object, while the first lens group is stationary on the optical axis in the focusing operation.

Claim 11

An inverted-telephoto type wide angle lens system comprising, from the object side to the image side: a first lens group of a negative refractive power, consisting of, a first lens component of a negative refractive power, a second lens component of a negative refractive power, and a third lens component of a positive refractive power; a second lens group of a positive refractive power, consisting of, a fourth lens component of a positive refractive power, a fifth lens component of a negative refractive power containing a single lens element or compound lens element; and a third lens group of a positive refractive power, consisting of, a sixth lens component of a negative compound lens element, a seventh lens component of a positive refractive power, and an eighth lens component of a positive refractive power; wherein the second and third lens groups are shiftable to the object side along the optical axis of the lens system at different speeds from one another in a focusing operation to a closer object, while the first lens group is stationary on the optical axis in the focusing operation.

Claim 12

An inverted-telephoto type wide angle lens system as claimed in claim 8, wherein the lens system fulfills the following conditions; 1.0<R<1.5 0.12<L/f<0.38 wherein; R represents a ratio of shifting speed between the second and third lens group in the focusing operation; L represents an axial distance between the first and second lens group in infinity focusing condition; and f represents a compound focal length of the whole lens system.

Claim 13

An inverted-telephoto type wide angle lens system as claimed in claim 9, wherein the lens fulfills the following conditions; 0.1<f/-f.sub.1 <0.35 1.5<-f.sub.1 /f.sub.2 <3.5 2.1<-f.sub.1 /f.sub.3 <5.0 wherein; f 1 represents a focal length of the first lens group; f 2 represents a focal length of the second lens group; and f 3 represents a focal length of the third lens group.