Zoom lens system

Claim 2

A zoom lens system comprising: a first lens unit of a negative refractive power; a second lens unit of a positive refractive power located on the image side of the first lens unit with a first variable air space between the first and second lens unit; a third lens unit of a negative refractive power located on the image side of the second lens unit with a second variable air space between the second and third lens units; and a fourth lens unit of a positive refractive power located on the image side of the third lens unit with a third variable air space between the third lens unit and the fourth lens unit, wherein the first and third variable air spaces are reduced and the second variable air space is increased in accordance with an increase of the focal length of the whole lens system during zooming, wherein the lens system fulfills the following condition: ##EQU3## whereby: f 2 represents the focal length of the second lens unit; and f 3 represents the focal length of the third lens unit.

Claim 3

The invention of claim 1, wherein the lens system further fulfills the following condition: 1.5f.sub.w <f.sub.4 <10f.sub.w wherein: f 4 represents the focal length of the fourth lens unit; and f w represents the shortest focal length of the whole lens system.

Claim 4

The invention of claim 1, wherein the lens system further fulfills the following conditions: ##EQU4## wherein: f 1 represents the focal length of the first lens unit; and f 4 represents the focal length of the fourth lens unit.

Claim 5

The invention of claim 1, wherein the lens system further fulfills the following condition: 7 mm<l.sub.3 <20 mm wherein: l 3 represents the greatest value for the third variable air space.

Claim 6

The invention of claim 1, wherein the second and fourth lens units are moved in a body during the zooming.

Claim 7

The invention of claim 1, wherein the third lens unit is left stationary during the zooming.

Claim 8

The invention of claim 1, wherein at least a part of the second to fourth lens units are movable for macrofocusing with the remaining part of the lens system left stationary.

Claim 9

The invention of claim 7, wherein all the second to fourth lens units are movable toward the object side for macrofocusing.

Claim 10

The invention of claim 8, wherein the movement of the third lens unit for macrofocusing is different from those of the second and fourth lens units.

Claim 11

The invention of claim 7, wherein the second and fourth lens units are movable toward the object side in a body for macrofocusing with the third lens unit left stationary.

Claim 12

The invention of claim 7, wherein only the third lens unit is movable toward the image side for macrofocusing.

Claim 13

A zoom lens system comprising: a first lens unit of a negative refractive power; a second lens unit of a positive refractive power located on the image side of the first lens unit with a first variable air space between the first and second lens units; a third lens unit of a negative refractive power located on the image side of the second lens unit with a second variable air space between the second and third lens units; and a fourth lens unit of a positive refractive power located on the image side of the third lens unit with a third variable air space between the third lens unit and fourth lens unit, wherein the first and third variable air spaces are reduced and the second variable air space is increased in accordance with an increase of the focal length of the whole lens system upon zooming, and wherein the lens system fulfills the following condition: 1.5f.sub.w <f.sub.4 <10f.sub.w wherein: f 4 represents the focal length of the fourth lens unit; and f w represents the shortest focal length of the whole lens system.

Claim 14

A zoom lens system comprising: a first lens unit of a negative refractive power; a second lens unit of a positive refractive power located on the image side of the first lens unit with a first variable air space between the first and second lens units; a third lens unit of a negative refractive power located on the image side of the second lens unit with a second variable air space between the second and third lens units; and a fourth lens unit of a positive refractive power located on the image side of the third lens unit with a third variable air space between the third lens unit and fourth lens unit, wherein the first and third variable air spaces are reduced and the second variable air space is increased in accordance with an increase of the focal length of the whole lens system upon zooming, and wherein the lens system fulfills the following condition: 1.5f.sub.w <f.sub.4 <10f.sub.w wherein: f 4 represents the focal length of the fourth lens unit; and f w represents the shortest focal length of the whole lens system.

Claim 15

A zoom lens system comprising the following design parameters: ______________________________________ f = 28.7˜50.0˜83.0 F.sub.No. = 4.1 Radius of Axial Refractive Abbe Curvature Distance Index Number ______________________________________ r.sub.1 -1346.691 d.sub.1 4.000 N.sub.1 1.51680 ν.sub.1 64.12 r.sub.2 -175.382 d.sub.2 0.150 r.sub.3 518.632 d.sub.3 2.500 N.sub.2 1.80741 ν.sub.2 31.59 L.sub.1 r.sub.4 28.654 d.sub.4 8.600 r.sub.5 193.102 d.sub.5 2.100 N.sub.3 1.51680 ν.sub.3 64.12 r.sub.6 27.382 d.sub.6 7.100 N.sub.4 1.80518 ν.sub.4 25.43 r.sub.7 78.340 d.sub.7 59.086˜22.095˜1.000 r.sub.8 39.131 d.sub.8 1.500 N.sub.5 1.80518 ν.sub.5 25.43 r.sub.9 20.790 d.sub.9 7.500 N.sub.6 1.67000 ν.sub.6 57.07 L.sub.2 r.sub.10 -76.684 d.sub.10 0.150 r.sub.11 30.675 d.sub.11 4.000 N.sub.7 1.67000 ν.sub.7 57.07 r.sub.12 100.011 d.sub.12 3.000˜5.763˜10.823 r.sub.13 -183.420 d.sub.13 3.000 N.sub.8 1.75520 ν.sub.8 27.51 r.sub.14 -38.057 d.sub.14 1.300 N.sub.9 1.69680 ν.sub.9 55.43 L.sub.3 r.sub.15 57.414 d.sub.15 1.800 r.sub.16 -410.268 d.sub.16 1.300 N.sub.10 1.60311 ν.sub.10 60.74 r.sub.17 69.570 d.sub.17 9.322˜6.559˜1.499 r.sub.18 188.113 d.sub.18 1.200 N.sub.11 1.80700 ν.sub.11 39.71 L.sub.4 r.sub.19 15.601 d.sub.19 6.000 N.sub.12 1.60000 ν.sub.12 64.38 r.sub.20 -43.142 Σd = 123.608˜86.617˜65.522 f.sub.1 = -48.309, f.sub.2 = 27.201, f.sub.3 = -39.318, f.sub.4 = ______________________________________ 185.391

Claim 16

A zoom lens system comprising the following design parameters: ______________________________________ f = 28.7˜50.0˜83.0 F.sub.No. = 4.1 Radius of Axial Refractive Abbe Curvature Distance Index Number ______________________________________ r.sub.1 -1346.691 d.sub.1 4.000 N.sub.1 1.51680 ν.sub.1 64.12 r.sub.2 -175.382 d.sub.2 0.150 r.sub.3 518.632 d.sub.3 2.500 N.sub.2 1.80741 ν.sub.2 31.59 L.sub.1 r.sub.4 28.654 d.sub.4 8.600 r.sub.5 193.102 d.sub.5 2.100 N.sub.3 1.51680 ν.sub.3 64.12 r.sub.6 27.382 d.sub.6 7.100 N.sub.4 1.80518 ν.sub.4 25.43 r.sub.7 78.340 d.sub.7 59.086˜22.095˜1.000 r.sub.8 39.131 d.sub.8 1.500 N.sub.5 1.80518 ν.sub.5 25.43 r.sub.9 20.790 d.sub.9 7.500 N.sub.6 1.67000 ν.sub.6 57.07 L.sub.2 r.sub.10 -76.684 d.sub.10 0.150 r.sub.11 30.675 d.sub.11 4.000 N.sub.7 1.67000 ν.sub.7 57.07 r.sub.12 100.011 d.sub.12 3.000˜5.763˜10.823 r.sub.13 -183.420 d.sub.13 3.000 N.sub.8 1.75520 ν.sub.8 27.51 r.sub.14 -38.057 d.sub.14 1.300 N.sub.9 1.69680 ν.sub.9 55.43 L.sub.3 r.sub.15 57.414 d.sub.15 1.800 r.sub.16 -410.268 d.sub.16 1.300 N.sub.10 1.60311 ν.sub.10 60.74 r.sub.17 69.570 d.sub.17 9.322˜6.559˜1.499 r.sub.18 188.113 d.sub.18 1.200 N.sub.11 1.80700 ν.sub.11 39.71 L.sub.4 r.sub.19 15.601 d.sub.19 6.000 N.sub.12 1.60000 ν.sub.12 64.38 r.sub.20 -43.142 Σd = 123.608˜86.617˜65.522 f.sub.1 = -48.309, f.sub.2 = 27.201, f.sub.3 = -39.318, f.sub.4 = ______________________________________ 185.391