Large aperature ratio zoom lens system

Claim 2

A large aperture ratio zoom lens system, comprising from the object side to the image side; a first lens unit of a positive refractive power fixed in the zooming operation; a second lens unit of a negative refractive power; a third lens unit of a negative refractive power; a fourth lens unit of a positive refractive power; an aperture diaphragm; and a fifth lens unit of positive refractive power, including a front lens unit consisting of a positive first lens component whose object side surface has stronger refractive power than its image side surface has and a negative second lens component whose object side surface has stronger refractive power than its image side surface has, and a rear lens unit consisting of a biconvex third lens component, a negative meniscus fourth lens component whose image side surface has stronger refractive power than its object side surface has, and a positive fifth lens component whose object side surface has stronger refractive power than its image side surface has; wherein the second lens unit and the third lens unit are shiftable along the optical axis in the zooming operation; and wherein the lens system fulfills the following conditions: ##EQU3## wherein, F V : the focal length of the fifth lens unit, N B : the refractive index of the second lens component, Nc: the refractive index of the third lens component, r BP : the radius of curvature of the object side surface of the second lens component, r CF : the radius of curvature of the image side surface of the third lens component, φ BP : the refractive power of the object side surface of the second lens component, and φ CF : the refractive power of the image side surface of the third lens component.

Claim 3

A large aperture ratio zoom lens system as claimed in claim 1, wherein the lens system fulfills the following condition: 0.15<(T.sub.BC +T.sub.CD)/F.sub.V <0.6 wherein, T BC : the axial distance between the second lens component and the third lens component in the fifth lens unit; and T CD : the axial distance between the third lens component and the fourth lens component in the fifth lens unit.

Claim 4

A large aperture ratio zoom lens system as claimed in claim 2, wherein the lens system fulfills the following conditions: 1.0<r.sub.DP /r.sub.DF <3.0 r.sub.DP, r.sub.DF >0 ν.sub.B, ν.sub.D <35 wherein, r DP ; the radius of curvature of the object side surface of the fourth lens component, r DF ; the radius of curvature of the image side surface of the fourth lens component, ν B ; the Abbe number of the second lens component, and ν D ; the Abbe number of the fourth lens component.

Claim 5

A large aperture ratio zoom lens system as claimed in claim 1, wherein the lens system defined the following design parameters: __________________________________________________________________________ radius of refractive Abbe curvature axial distance index(Nd) number(νd) __________________________________________________________________________ r.sub.1 71.522 d1 1.600 N1 1.80518 ν1 25.43 r.sub.2 33.291 d2 7.800 N2 1.51680 ν2 64.12 I r.sub.3 -225.050 d3 0.100 r.sub.4 35.574 d4 5.250 N3 1.69100 ν3 54.75 r.sub.5 331.979 d5* (Variable) r.sub.6 1065.109 d6 0.800 N4 1.77250 ν4 49.77 r.sub.7 13.142 d7 3.500 II r.sub.8 -17.737 d8 0.800 N5 1.71700 ν5 47.86 r.sub.9 13.217 d9 3.800 N6 1.80518 ν6 25.43 r.sub.10 -64.206 d10* (Variable) r.sub.11 -29.135 d11 0.900 III N7 1.66998 ν7 39.23 r.sub.12 -425.067 d12* (Variable) r.sub.13 106.558 d13 3.400 N8 1.72000 ν8 50.31 IV r.sub.14 -26.686 d14 2.500 r.sub.15 (aperature) d15 4.500 r.sub.16 22.581 D16 3.700 N9 1.69100 ν9 54.75 V.sub.F r.sub.17 -973.434 d17 2.800 r.sub.18 -19.172 d18 1.300 N10 1.80518 ν10 25.43 r.sub.19 -105.306 d19 7.600 V r.sub.20 47.566 d20 4.300 N11 1.72900 ν11 53.48 r.sub.21 -31.532 d21 0.100 r.sub.22 23.741 d22 1.000 N12 1.76182 ν12 26.55 V.sub.R r.sub.23 11.655 d23 2.200 r.sub.24 17.917 d24 3.400 N13 1.69100 ν13 54.75 r.sub.25 -130.240 d25 5.000 r.sub.26 ∞ d26 4.000 N14 1.51680 ν14 64.12 r.sub.27 ∞ f 8.60 20.00 50.40 d5* 1.00 14.734 23.654 d10* 22.780 6.139 3.200 d12* 4.574 7.480 1.500 total length = 107.0 mm exit pupil position = -355 mm __________________________________________________________________________