Variable focal length lens system

Claim 2

A variable focal length lens system comprising from object side to image side: a first lens unit of a positive refractive power; a second lens untin of a negative refractive power with a first variable air space formed between the first and second lens units; a third lens unit of a positive refractive power; and a fourth lens unit of a negative refractive power with a second variable air space formed between the third lens unit and fourth lens unit; wherein the back focal length of the whole lens system for the shortest focal length is less than half of the diagonal length of the image plane; wherein the first lens unit is shiftable from the image side to the object side while increasing the first variable air space in the zooming operation from the shortest focal length to the longest focal length; and wherein the fourth lens unit is shiftable from the image side to the object side while decreasing the second variable air space in the zooming operation from the shortest focal length to the longest focal length.

Claim 3

A variable focal length lens system as claimed in claim 1, wherein the lens system fulfills the following condition: ##EQU8## wherein, f S represents the focal length of the whole lens system for the shortest focal length, and f 4 represents the focal length of the fourth lens unit.

Claim 4

A variable focal length lens system as claimed in claim 1, wherein the fourth lens unit is shiftable along the optical axis in the focusing operation, and wherein the lens system further fulfills the following condition; ##EQU9## wherein, β L4 represents the lateral magnification of the fourth lens unit for the longest focal length, β S4 represents the lateral magnification of the fourth lens unit for the shortest focal length, and Z represents the zoom ratio of the whole lens system.

Claim 5

A variable focal length lens system as claimed in claim 1, wherein the first lens unit includes a negative lens element having an object side surface convex to the object side, and a positive lens element having an image side surface concave to the image side.

Claim 6

A variable focal length lens system as claimed in claim 1, wherein the second unit includes a negative lens element and a positive lens element.

Claim 7

A variable focal length lens system as claimed in claim 1, wherein the third lens unit includes from the object side to the image side, a positive lens element, a negative lens element and a positive lens element.

Claim 8

A variable focal length lens system as claimed in claim 1, wherein the fourth lens unit includes a negative meniscus lens element located at the rearmost side.

Claim 9

A variable focal length lens system as claimed in claim 1, wherein the third lens unit is shiftable during the zooming operation while changing a third variable air space formed between the second and third lens units.

Claim 10

A variable focal length lens system as claimed in claim 2, wherein the second lens unit is stationary along the optical axis of the whole lens system in the zooming operation, and the lens system further includes an aperture stop fixed to the second lens unit.

Claim 11

A variable focal length lens system as claimed in claim 1, wherein the lens system fulfills the following condition; ##EQU10## wherein, f S123 represents the compound focal length of the first to third lens units for the shortest focal length, and f 4 represents the focal length of the fourth lens unit.

Claim 12

A variable focal length lens system as claimed in claim 10, wherein the lens system further fulfills the following conditions: ##EQU11## wherein, β L4 represents the lateral magnification of the fourth lens unit for the longest focal length, β S4 represents the lateral magnification of the fourth lens unit for the shortest focal length, Δd34 represents the decreased distance of the second variable air space by the zooming operation from the shortest focal length to the longest focal length, and f S represents the focal length of the whole lens system for the shortest focal length.

Claim 13

A variable focal length lens system comprising the following design parameters: ______________________________________ f = 39.0˜50.0˜62.0 F.sub.No = 3.6˜4.1˜4.2 radius of axial refractive Abbe curvature distance index (Nd) number (νd) ______________________________________ r1 57.985 d1 1.500 N.sub.1 1.84666 ν1 23.88 r2 29.417 d2 3.300 N.sub.2 1.69680 ν2 56.47 r3 76.987 d3 0.150 r4 20.517 d4 3.700 N.sub.3 1.69680 ν3 56.47 r5 45.102 d5 2.000˜7.109˜13.059 r6 -46.081 d6 1.100 N.sub.4 1.74250 ν4 52.51 r7 18.868 d7 1.700 N.sub.5 1.80518 ν5 25.43 r8 43.670 d8 5.870˜4.265˜3.000 r9 48.677 d9 1.708 N.sub.6 1.77250 ν6 49.77 r10 -54.163 d10 0.150 r11 20.458 d11 1.815 N.sub.7 1.71300 ν7 53.93 r12 122.565 d12 0.360 r13 -84.395 d13 1.603 N.sub.8 1.80518 ν8 25.43 r14 23.349 d14 2.523 r15 57.734 d15 2.576 N.sub.9 1.66446 ν9 35.84 r16 -37.964 d16 15.158˜8.813˜3.028 r17 -18.162 d17 2.500 .sup. N.sub.10 1.69680 ν10 56.47 r18 -69.675 ______________________________________

Claim 14

A variable focal length lens system comprising the following design parameters: ______________________________________ f = 39.0˜50.0˜62.0 F.sub.No = 3.6˜4.1˜4.2 radius of axial refractive Abbe curvature distance index (Nd) number (νd) ______________________________________ r1 57.985 d1 1.500 N.sub.1 1.84666 ν1 23.88 r2 29.417 d2 3.300 N.sub.2 1.69680 ν2 56.47 r3 76.987 d3 0.150 r4 20.517 d4 3.700 N.sub.3 1.69680 ν3 56.47 r5 45.102 d5 2.000˜7.109˜13.059 r6 -46.081 d6 1.100 N.sub.4 1.74250 ν4 52.51 r7 18.868 d7 1.700 N.sub.5 1.80518 ν5 25.43 r8 43.670 d8 5.870˜4.265˜3.000 r9 48.677 d9 1.708 N.sub.6 1.77250 ν6 49.77 r10 -54.163 d10 0.150 r11 20.458 d11 1.815 N.sub.7 1.71300 ν7 53.93 r12 122.565 d12 0.360 r13 -84.395 d13 1.603 N.sub.8 1.80518 ν8 25.43 r14 23.349 d14 2.523 r15 57.734 d15 2.576 N.sub.9 1.66446 ν9 35.84 r16 -37.964 d16 15.158˜8.813˜3.028 r17 -18.162 d17 2.500 .sup. N.sub.10 1.69680 ν10 56.47 r18 -69.675 ______________________________________

Claim 15

A variable focal length lens system comprising the following design parameters: ______________________________________ f = 39.0˜62.0 F.sub.No = 3.5 radius of axial refractive Abbe curvature distance index (Nd) number (νd) ______________________________________ r1 72.389 d1 1.500 N.sub.1 1.84666 ν1 23.88 r2 36.269 d2 3.300 N.sub.2 1.75450 ν2 51.57 r3 32.027 d3 0.150 r4 21.276 d4 3.200 N.sub.3 1.69680 ν3 56.47 r5 36.442 d5 2.000˜17.284 r6 -71.032 d6 1.100 N.sub.4 1.69680 ν4 56.47 r7 26.695 d7 1.700 N.sub.5 1.84666 ν5 23.83 r8 81.505 d8 6.743˜2.243 r9 26.757 d9 2.200 N.sub.6 1.77250 ν6 49.77 r10 -28.036 d10 0.550 r11 -15.975 d11 0.800 N.sub.7 1.75000 ν7 25.14 r12 30.496 d12 2.373 r13 106.499 d13 3.280 N.sub.8 1.80750 ν8 35.45 r14 -18.217 d14 12.557˜3.028 r15 -28.199 d15 2.000 N.sub.9 1.77250 ν9 49.77 r16 -25.090 d16 0.800 r17 -23.072 d17 1.200 .sup. N.sub.10 1.77250 ν10 49.77 r18 -603.500 ______________________________________

Claim 16

A variable focal length lens system comprising the following design parameters: ______________________________________ f = 39.0˜62.0 F.sub.No = 3.5 radius of axial refractive Abbe curvature distance index (Nd) number (νd) ______________________________________ r1 72.389 d1 1.500 N.sub.1 1.84666 ν1 23.88 r2 36.269 d2 3.300 N.sub.2 1.75450 ν2 51.57 r3 32.027 d3 0.150 r4 21.276 d4 3.200 N.sub.3 1.69680 ν3 56.47 r5 36.442 d5 2.000˜17.284 r6 -71.032 d6 1.100 N.sub.4 1.69680 ν4 56.47 r7 26.695 d7 1.700 N.sub.5 1.84666 ν5 23.83 r8 81.505 d8 6.743˜2.243 r9 26.757 d9 2.200 N.sub.6 1.77250 ν6 49.77 r10 -28.036 d10 0.550 r11 -15.975 d11 0.800 N.sub.7 1.75000 ν7 25.14 r12 30.496 d12 2.373 r13 106.499 d13 3.280 N.sub.8 1.80750 ν8 35.45 r14 -18.217 d14 12.557˜3.028 r15 -28.199 d15 2.000 N.sub.9 1.77250 ν9 49.77 r16 -25.090 d16 0.800 r17 -23.072 d17 1.200 .sup. N.sub.10 1.77250 ν10 49.77 r18 -603.500 ______________________________________

Claim 17

A variable focal length lens system, comprising from object side to image side: a first lens unit of a positive refractive power; a second lens unit of a negative refractive power with a first variable air space formed between the first and second lens units; a third lens unit of a positive refractive power; and a fourth lens element of a negative refractive power with a second variable air space formed between the third lens unit and the fourth lens element; wherein the back focal length of the whole lens system for the shortest focal length is less than half of the diagonal length of the image plane; wherein the first lens unit is shiftable from the image side to the object side while increasing the first variable air space in the zooming operation from the shortest focal length to the longest focal length; and wherein the fourth lens element is shiftable from the image side to the object side while decreasing the second variable air space in the zooming operation from the shortest focal length to the longest focal length.

Claim 18

A variable focal length lens system, comprising from object side to image side: a first lens unit of a positive refractive power; a second lens unit of a negative refractive power with a first variable air space formed between the first and second lens units; a third lens unit of a positive refractive power; and a fourth lens element of a negative refractive power with a second variable air space formed between the third lens unit and the fourth lens element; wherein the back focal length of the whole lens system for the shortest focal length is less than half of the diagonal length of the image plane; wherein the first lens unit is shiftable from the image side to the object side while increasing the first variable air space in the zooming operation from the shortest focal length to the longest focal length; and wherein the fourth lens element is shiftable from the image side to the object side while decreasing the second variable air space in the zooming operation from the shortest focal length to the longest focal length.

Claim 19

A variable focal length lens system as claimed in claim 14, wherein the lens system fulfills the following condition: ##EQU12## wherein: f S represents the focal length of the whole lens system for the shortest focal length, and f 4 represents the focal length of the fourth lens element.

Claim 20

A variable focal length lens system as claimed in claim 14, wherein the first lens unit includes a negative lens element having an object side surface convex to the object side, and a positive lens element having an image side surface concave to the image side.

Claim 21

A variable focal length lens system as claimed in claim 14, wherein the second lens unit includes a negative lens element and a positive lens element.

Claim 22

A variable focal length lens system as claimed in claim 14, wherein the third lens unit includes from the object side to the image side, a positive lens element, a negative lens element and a positive lens element.

Claim 23

A variable focal length lens system as claimed in claim 14, wherein at least one of the second and third lens units is shiftable in the zooming operation.

Claim 24

A variable focal length lens system as claimed in claim 19, wherein the second lens unit is stationary along the optical axis of the whole lens system in the zooming operation, and the lens system further includes an aperture stop fixed to the second lens unit.

Claim 25

A variable focal length lens system as claimed in claim 14, wherein the lens system fulfills the following condition: ##EQU13## wherein, f S represents the compound focal length of the first to third lens units for the shortest focal length, and f 4 represents the focal length of the fourth lens element.

Claim 26

A variable focal length lens system as claimed in claim 21, wherein the lens system further fulfills the following conditions: ##EQU14## wherein, β L4 represents the lateral magnification of the fourth lens element for the shortest focal length, β S4 represents the lateral magnification of the fourth lens element for the shortest focal length, Δd34 represents the decreased distance of the second variable air space by the zooming operation from the shortest focal length to the longest focal length, and f S represents the focal length of the whole lens system for the shortest focal length.