Zoom lens

Abstract

A zoom lens has, in succession from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power. The second and third lens units are moved to thereby effect zooming. When variations in the magnifications of the second and third lens units from the wide angle end to the telephoto end are Z.sub.2 and Z.sub.3, respectively, the zoom lens satisfies the condition that Z.sub.3 /Z.sub.2 >1.4. The zoom lens is compact and yet covers a wide angle range of an angle of view of 60.degree.-80.degree..

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a zoom lens suitable for a camera for photographic film, a video camera and a still video camera, and particularly to a compact zoom lens of three-unit construction.

2. Related Background Art

In recent years, with the tendency of home video cameras toward compactness and light weight, compactness and lighter weight and particularly, a shorter full length and reduced diameter of the front lens have been required of not only camera bodies, but also zoom lenses.

On the other hand, with the compactness of zoom lenses, demand is increasing for zoom lenses in which the angle of view at the wide angle end covers a wide angle range of the order of 60.degree.-80.degree..

Zoom lenses which have, in succession from the object side, a first lens unit having positive refractive power, a second lens unit having negative refractive power and a third lens unit having positive refractive power and in which the second lens unit and third lens unit are moved to thereby effect zooming are disclosed, for example, in Japanese Laid-Open Patent Application No. 51-56645, Japanese Laid-Open Patent Application No. 51-68244 and Japanese Laid-Open Patent Application No. 63-304218.

These zoom lenses, however, could hardly be said to satisfy the aforementioned requirement, i.e., the requirement for being compact and yet securing a sufficiently wide angle range.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a zoom lens which is compact and yet covers a wide angle range, and the feature of the present invention is that the zoom lens has, in succession from an object side, a first lens unit having positive power, a second lens unit having negative refractive power and a third lens unit having positive refractive power, the second lens unit and the third lens unit being moved to thereby effect zooming, and when variations in the magnifications of the second lens unit and the third lens unit from the wide angle end to the telephoto end are Z.sub.2 and Z.sub.3, respectively, the zoom lens satisfies the following condition: ##EQU1##

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a zoom lens according to a first embodiment of the present invention.

FIGS. 2A-1, 2A-2, 2A-3, 2B-1, 2B-2 and 2B-3 show aberrations in the zoom lens according to the first embodiment.

FIG. 3 is a cross-sectional view of a zoom lens according to a second embodiment of the present invention.

FIGS. 4A-1, 4A-2, 4A-3, 4B-1, 4B-2 and 4B-3 show aberrations in the zoom lens according to the second embodiment.

FIG. 5 is a cross-sectional view of a zoom lens according to a third embodiment of the present invention.

FIGS. 6A-1, 6A-2, 6A-3, 6B-1, 6B-2 and 6B-3 show aberrations in the zoom lens according to the third embodiment.

FIG. 7 is a cross-sectional view of a zoom lens according to a fourth embodiment of the present invention.

FIGS. 8A-1, 8A-2, 8A-3, 8B-1, 8B-2 and 8B-3 show aberrations in the zoom lens according to the fourth embodiment.

FIG. 9 is a cross-sectional view of a zoom lens according to a fifth embodiment of the present invention.

FIGS. 10A-1, 10A-2, 10A-3, 10B-1, 10B-2 and 10B-3 show aberrations in the zoom lens according to the fifth embodiment.

FIG. 11 is a cross-sectional view of a zoom lens according to a sixth embodiment of the present invention.

FIGS. 12A-1, 12A-2, 12A-3, 12B-1, 12B-2 and 12B-3 show aberrations in the zoom lens according to the sixth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1, 3, 5, 7, 9 and 11 are cross-sectional views of zoom lenses according to the present invention. The reference character I designates a first lens unit having positive refractive power, the reference character II denotes a second lens unit having negative refractive power, the reference character III designates a third lens unit having positive refractive power, and the reference character SP denotes a stop. During zooming from the wide angle end to the telephoto end, the second lens unit and the third lens unit are moved along zoom loci as indicated by the arrow. During the zooming, the first lens unit remains stationary. The reference character G designates a filter member such as an infrared cut filter or an optical low-pass filter.

When variations in the magnifications of the second lens unit and the third lens unit from the wide angle end to the telephoto end are Z.sub.2 and Z.sub.3, respectively, the following condition is satisfied: ##EQU2##

The conditional formulation (1) prescribes the ratio of the magnification variation to the zooming of the second lens unit and the third lens unit, and is a condition for achieving the wide angle and compactness of a zoom lens of three-unit construction, and yet correcting aberrations, particularly distortion and curvature of image field, well. If this range is departed from, the amount of movement of the second lens unit will tend to become great in order to obtain a desired zoom ratio, and if moreover, an attempt is made to shorten the focal length at the wide angle end, i.e., to achieve a wide angle, the diameter of the front lens as the first lens unit will tend to become large. Further, the negative refractive power of the second lens unit will become strong, and at the wide angle end, barrel-shaped distortion and Petzval sum will be in the negative direction, and the image plane will tend to become over.

Also, to secure the angle of view widely in a wide angle state, it is desirable that the following conditional expression be satisfied:

1.40<.vertline.F.sub.2 /F.sub.W .vertline.<2.60, (2) where F.sub.2 is the focal length of the second lens unit, and F.sub.W is the focal length of the whole system at the wide angle end. If this range is departed from, it will become difficult to draw near the wide angle side and yet maintain a good performance. If the upper limit of this conditional expression is exceeded, the diameter of the front lens will become large or the amount of movement of the second lens unit will become great, and this is not suitable for compactness. Also, if the lower limit of this conditional expression is exceeded, the refractive power of the second lens unit will become too strong and Petzval sum will become great in the negative direction and thus, the fluctuation of the image plane will become unable to be eliminated.

Further, to optimize the sharing of magnification change by the lens units, it is preferable that the amounts of movement of the lens units satisfy the following conditional expressions:

0.5<.vertline.M.sub.2 .vertline./(F.sub.T -F.sub.W)<1.6 (3) 0.5<.vertline.M.sub.3 .vertline./(F.sub.T -F.sub.W)<1.0, (4) where M.sub.2 and M.sub.3 are respectively the amounts of movement of the second lens unit and the third lens unit during the zooming from the wide angle end to the telephoto end, and F.sub.T is the focal length of the whole system at the telephoto end.

If these ranges are departed from, the sharing of magnification change by the lens units will not only become ill-balanced, but also the size of the zoom lens and aberrations created in each lens unit will be affected. If the upper limits of these expressions (3) and (4) are exceeded, the whole system will become bulky, and if the lower limits of these expressions are exceeded, the amounts of movement for obtaining a desired magnification ratio will become small and it will become necessary to strengthen the refractive power of each lens unit and the correction of aberrations will become difficult.

Further, it is desirable that the amounts of movement of the lens units be within the following range:

0.7<.vertline.M.sub.2 /M.sub.3 .vertline.<2.5 (5) If this range is departed from, the whole system will become large and the balance of the sharing of magnification change by the lens units will be aggravated, and this is not suitable.

Also, to set the focal length at the wide angle side shortly, it is desirable that the following conditional expressions be further satisfied:

5<F.sub.1 /F.sub.W <53 (6) 1<F.sub.3 /F.sub.W <3 (7) 0.4<E.sub.1W /F.sub.W <1.8, (8) where F.sub.1 and F.sub.3 are respectively the focal lengths of the first lens unit and the third lens unit and E.sub.1W is the principal point spacing between the first lens unit and the second lens unit at the wide angle end.

Conditional expression (6) is concerned in the refractive power of the first lens unit, and if the upper limit of this conditional expression is exceeded, it will become difficult to correct barrel-shaped distortion. Also, if the lower limit of this conditional expression is exceeded, the refractive power of the first lens unit will become strong and Petzval sum will tend to assume a positive value and the image plane will tend to become under.

Also, it is preferable that the first lens unit be comprised of a positive lens, and particularly, to correct distortion as described above, it is desirable that the first lens unit be a positive lens having its convex surface facing the object side.

Conditional expression (7) is concerned in the refractive power of the third lens unit, and if the upper limit of this conditional expression is exceeded, the amount of movement for obtaining a desired magnification change ratio will become great and the zoom lens will become bulky, and this is not preferable. Also, if the lower limit of this conditional expression is exceeded, the refractive power of the third lens unit will become strong and the image plane will tend to become under or the back focal length at the wide angle end will become short, and there will be no room for containing a glass black such as a filter. Further, the principal ray will not perpendicularly (telecentrically) enter an imaging element such as a CCD and it will cause so-called shading, and this is not preferable.

Conditional expression (8) prescribes the ratio of the principal point spacing between the first lens unit and the second lens unit to the focal length at the wide angle end, and is a condition for achieving the compactness of the zoom lens system and yet maintaining good aberrations.

Further, when the focal length of the whole system at the telephoto end is F.sub.T, it is desirable in the relation to conditional expression (6) to provide such a degree of focal length that satisfies the following conditional expression:

F.sub.1 <30F.sub.T (9)

If the upper limit of this conditional expression is exceeded, the full length of the zoom lens will increase, and this is not preferable. If the lower limit of this conditional expression is exceeded, the correction of coma will become particularly difficult.

Finally, to reduce the number of lenses in the zoom lens according to the present invention and yet maintain good aberrations, it is desirable that the first lens unit be comprised of a single positive lens having its convex surface facing the object side in order to correct effectively correct distortion by the first lens unit, and for the same purpose, a fixed stop be disposed between the second lens unit and the third lens unit.

The focusing of the zoom lens of the present invention can be accomplished by moving any of the first, second and third lens units.

The numerical value embodiments of the present invention will be shown below. In the numerical value embodiments below, ri represents the radius of curvature of the ith lens surface from the object side, di represents the thickness and air gap of the ith lens from the object side, and ni and .mu.i represent the refractive index and Abbe number, respectively of the glass of the ith lens from the object side. R.sub.28 and R.sub.29 are face plates, filters or the like.

Also, the relations between the aforementioned conditional expressions and the numerical values in the numerical value embodiments will be shown in Table 1 below.

When the direction of the optical axis is X-axis and the direction perpendicular to the optical axis is H-axis and the direction of travel of light is positive and paraxial radii of curvature B, C, D and E are aspherical surface coefficients, the aspherical surface shape is indicated by the following equation:

______________________________________ ##STR1## ______________________________________Embodiment 1f = 1 to 3.0 fno = 1:(2.49 to 3.6) 2.omega. = 74.5.degree. to28.5.degree.______________________________________ r1 = 5.935 d1 = 0.72 n1 = 1.51633 .upsilon.1 = 64.2 r2 = 114.032 d2 = changeable r3 = 3.497 d3 = 0.24 n2 = 1.77250 .upsilon.2 = 49.6 r4 = 1.147 d4 = 0.58 r5 = -4.799 d5 = 0.19 n3 = 1.80400 .upsilon.3 = 46.6 r6 = 2.491 d6 = 0.25 r7 = 2.433 d7 = 0.53 n4 = 1.69895 .upsilon.4 = 30.l r8 = -51.970 d8 = changeable r9 = (stop) d9 = changeable r10 = 6.674 d10 = 0.33 n5 = 1.83481 .upsilon.5 = 42.7 r11 = -6.674 d11 = 0.04 r12 = 1.540 d12 = 0.58 n6 = 1.72000 .upsilon.6 = 50.3 r13 = 6.308 d13 = 0.07 r14 = -7.120 d14 = 0.33 n7 = 1.84666 .upsilon.7 = 23.8 r15 = 1.423 d15 = 0.12 r16 = 5.516 d16 = 0.62 n8 = 1.80400 .upsilon.8 = 46.6 r17 = -2.394 d17 = changeable r18 = .infin. d18 = 1.19 n9 = 1.51633 .upsilon.9 = 64.2 r19 = .infin.______________________________________ FOCAL LENGTHCHANGEABLE W M TINTERVAL 1.00 2.39 2.99______________________________________d2 0.24 1.80 1.79d8 1.93 0.36 0.38d9 1.93 0.88 0.33 d17 0.71 1.77 2.31______________________________________Embodiment 2f = 1 to 2.92 fno = 1:(2.30 to 3.30) 2.omega. = 64.2.degree. to24.2.degree.______________________________________ r1 = 3.578 d1 = 0.47 n1 = 1.51633 .upsilon.1 = 64.2 r2 = 21.337 d2 = changeable r3 = 3.688 d3 = 0.20 n2 = 1.83481 .upsilon.2 = 42.7 r4 = 1.006 d4 = 0.34 r5 = -4.683 d5 = 0.16 n3 = 1.83481 .upsilon.3 = 42.7 r6 = 2.112 d6 = 0.18 r7 = 2.046 d7 = 0.39 n4 = 1.69895 .upsilon.4 = 30.1 r8 = -7.857 d8 = changeable r9 = (stop) d9 = changeable r10 = 6.793 d10 = 0.29 n5 = 1.83400 .upsilon.5 = 37.2 r11 = -6.793 d11 = 0.03 r12 = 1.171 d12 = 0.41 n6 = 1.72000 .upsilon.6 = 50.3 r13 = 13.242 d13 = 0.04 r14 = -9.959 d14 = 0.43 n7 = 1.84666 .upsilon.7 = 23.8 r15 = 0.976 d15 = 0.11 r16 = 3.088 d16 = 0.33 n8 = 1.83481 .upsilon.8 = 42.7 r17 = -3.088 d17 = changeable r18 = .infin. d18 = 0.98 n9 = 1.51633 .upsilon.9 = 64.2 r19 = .infin.______________________________________ FOCAL LENGTHCHANGEABLE W M TINTERVAL 1.00 2.34 2.92______________________________________d2 0.20 1.46 1.50d8 1.59 0.33 0.30d9 1.44 0.67 0.28 d17 0.59 1.36 1.75______________________________________Embodiment 3f = 1 to 1.61 fno = 1:(2.09 to 2.91) 2.omega. = 63.7.degree. to29.6.degree.______________________________________ r1 = 17.554 d1 = 0.31 n1 = 1.51633 .upsilon.1 = 64.2 r2 = 263.217 d2 = changeable r3 = 2.789 d3 = 0.19 n2 = 1.80400 .upsilon.2 = 46.6 r4 = 1.233 d4 = 0.44 r5 = -42.527 d5 = 0.16 n3 = 1.80400 .upsilon.3 = 46.6 r6 = 1.952 d6 = 0.17 r7 = 1.886 d7 = 0.41 n4 = 1.68893 .upsilon.4 = 31.1 r8 = 17.734 d8 = changeable r9 = (stop) d9 = changeable r10 = 5.212 d10 = 0.31 n5 = 1.83481 .upsilon.5 = 42.7 r11 = -5.212 d11 = 0.03 r12 = 1.251 d12 = 0.45 n6 = 1.71300 .upsilon.6 = 53.8 r13 = 12.044 d13 = 0.03 r14 = -14.574 d14 = 0.56 n7 = 1.84666 .upsilon.7 = 23.8 r15 = 0.930 d15 = 0.14 r16 = 3.101 d16 = 0.41 n8 = 1.80400 .upsilon.8 = 46.6 r17 = -3.100 d17 = changeable r18 = .infin. d18 = 0.97 n9 = 1.51633 .upsilon.9 = 64.2 r19 = .infin.______________________________________ FOCAL LENGTHCHANGEABLE W M TINTERVAL 1.00 2.36 1.61______________________________________d2 0.17 1.95 1.48d8 2.03 0.26 0.73d9 1.15 0.27 0.76 d17 0.19 1.07 0.58______________________________________Embodiment 4f = 1 to 3.98 fno = 1:(2.3 to 3.6) 2.omega. = 74.4.degree. to21.6.degree.______________________________________ r1 = 5.381 d1 = 0.99 n1 = 1.51633 .upsilon.1 = 64.2 r2 = 39.933 d2 = changeable r3 = 3.995 d3 = 0.24 n2 = 1.77250 .upsilon.2 = 49.6 r4 = 1.317 d4 = 0.73 r5 = -6.892 d5 = 0.19 n3 = 1.80400 .upsilon.3 = 46.6 r6 = 2.434 d6 = 0.23 r7 = 2.412 d7 = 0.53 n4 = 1.69895 .upsilon.4 = 30.1 r8 = 47.272 d8 = changeable r9 = (stop) d9 = changeable r10 = 7.011 d10 = 0.32 n5 = 1.80400 .upsilon.5 = 46.6 r11 = -7.011 d11 = 0.04 r12 = 1.440 d12 = 0.62 n6 = 1.69680 .upsilon.6 = 55.5 r13 = 5.617 d13 = 0.08 r14 = -9.201 d14 = 0.24 n7 = 1.84666 .upsilon.7 = 23.8 r15 = 1.364 d15 = 0.14 r16 = 5.547 d16 = 0.55 n8 = 1.83400 .upsilon.8 = 37.2 r17 = -2.806 d17 = changeable r18 = .infin. d18 = 1.19 n9 = 1.51633 .upsilon.9 = 64.2 r19 = .infin.______________________________________ FOCAL LENGTHCHANGEABLE W M TINTERVAL 1.00 3.11 3.98______________________________________d2 0.24 2.58 2.54d8 2.68 0.34 0.38d9 2.20 0.95 0.31 d17 0.71 1.96 2.61______________________________________Embodiment 5f = 5.15 to 12.12 FNO = 2 to 2.8 2.omega. = 60.4.degree. to______________________________________27.8.degree.r1 = 93.483 d1 = 1.60 n1 = 1.51633 .upsilon.1 = 64.2r2 = 279.352 d2 = changeable*r3 = -202.847 d3 = 1.00 n2 = 1.80400 .upsilon.2 = 46.6r4 = 6.116 d4 = 2.09r5 = 9.395 d5 = 1.90 n3 = 1.67270 .upsilon.3 = 32.1r6 = 28.200 d6 = changeabler7 = (stop) d7 = changeabler8 = 26.334 d8 = 1.60 n4 = 1.83481 .upsilon.4 = 42.7r9 = -26.636 d9 = 0.15r10 = 6.569 d10 = 2.30 n5 = 1.71300 .upsilon.5 = 53.8r11 = 72.494 d11 = 0.15r12 = -75.741 d12 = 2.87 n6 = 1.84666 .upsilon.6 = 23.8r13 = 4.789 d13 = 0.72r14 = 14.872 d14 = 2.10 n7 = 1.80400 .upsilon.7 = 46.6r15 = -17.513 d15 = changeabler16 = .infin. d16 = 5.00 n8 = 1.51633 .upsilon.8 = 64.2r17 = .infin.______________________________________ FOCAL LENGTHCHANGEABLE W TINTERVAL 5.15 12.12______________________________________d2 3.18 13.45d8 11.56 1.29d9 5.92 1.55 d17 1.00 5.36______________________________________Third Surface: Aspherical SurfaceR.sub.0 = -202.847, B = 2.010 .times. 10.sup.-4, C = -6.716 .times.10.sup.-7,D = -5.130 .times. 10.sup.-10, E = -1.396 .times. 10.sup.-10Embodiment 6f = 5.15 to 12.39 FNO = 1:(2 to 2.8) 2.omega. = 60.4.degree. to27.2.degree.______________________________________r1 = 55.506 d1 = 1.60 n1 = 1.51633 .upsilon.1 = 64.2r2 = -171.365 d2 = changeabler3 = 14.530 d3 = 1.00 n2 = 1.80400 .upsilon.2 = 46.6r4 = 6.071 d4 = 2.28r5 = -443.467 d5 = 0.80 n3 = 1.80400 .upsilon.3 = 46.6r6 = 9.031 d6 = 0.88r7 = 8.921 d7 = 2.10 n4 = 1.68893 .upsilon.4 = 31.1r8 = 59.057 d8 = changeabler9 = (stop) d9 = changeable*r10 = 7.139 d10 = 2.30 n5 = 1.80400 .upsilon.5 = 46.6r11 = -42.369 d11 = 0.15r12 = -93.663 d12 = 2.87 n6 = 1.84666 .upsilon.6 = 23.8r13 = 6.292 d13 = 0.72r14 = 18.851 d14 = 2.10 n7 = 1.80400 .upsilon.7 = 46.6r15 = -11.000 d15 = changeabler16 = .infin. d16 = 5.00 n8 = 1.51633 .upsilon.8 = 64.2r17 = .infin.______________________________________ FOCAL LENGTHCHANGEABLE W MINTERVAL 5.15 12.39______________________________________d2 2.89 12.17d8 10.66 1.38d9 5.92 1.80 d17 1.00 5.12______________________________________Tenth Surface: Aspherical SurfaceR.sub.0 = 7.139, B = -3.828 .times. 10.sup.-4, C = -6.742 .times.10.sup.-7,D = 1.339 .times. 10.sup.-7, E = -1.787 .times. 10.sup.-8______________________________________ TABLE 1__________________________________________________________________________ Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment 1 2 3 4 5 6__________________________________________________________________________Cond. Ex. (1): Z.sub.3 /Z.sub.2 2.089 1.804 2.117 2.173 2.168 1.793Cond. Ex. (2): .vertline.F.sub.2 /F.sub.W .vertline. 1.710 1.580 2.370 1.854 2.574 2.081Cond. Ex. (3): .vertline.M.sub.2 .vertline./(F.sub.T -F.sub.W) 0.779 0.698 1.310 0.771 1.474 1.281Cond. Ex. (4): .vertline.M.sub.3 .vertline./(F.sub.T -F.sub.W) 0.806 0.625 0.648 0.635 0.625 0.568Cond. Ex. (5): .vertline.M.sub.2 /M.sub.3 .vertline. 0.967 1.117 2.023 1.214 2.357 2.256Cond. Ex. (6): F.sub.1 /F.sub.W 12.09 8.237 36.41 11.93 52.73 15.81Cond. Ex. (7): F.sub.3 /F.sub.W 2.347 1.935 1.850 2.449 1.851 1.9297Cond. Ex. (8): E.sub.1W /F.sub.W 0.940 0.596 0.593 1.404 0.830 0.915Cond. Ex. (9): F.sub.1 /F.sub.T 4.03 2.826 15.46 2.995 22.39 6.56__________________________________________________________________________

Claims

1. A zoom lens consisting of, in succession from an object side, a first lens unit having positive refractive power and consisting of a single positive lens element, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, said second lens unit and said third lens unit being moved to thereby effect zooming, said zoom lens satisfying the following condition:

0.5<.vertline.M.sub.3 .vertline./(F.sub.T -F.sub.W)<1.0,

wherein M.sub.3 is an amount of movement of zooming from a wide angle end to a telephoto end of said third lens unit and F.sub.W and F.sub.T are respectively focal lengths of said zoom lens at the wide angle end and the telephoto end.

2. The zoom lens according to claim 1 satisfying the following condition:

1.4<.vertline.F.sub.2 /F.sub.W .vertline.<2.6,

where F.sub.2 is the focal length of said second lens unit.

3. The zoom lens according to claim 2 satisfying the following condition:

0.5<.vertline.(M.sub.2 .vertline./(F.sub.T -F.sub.W)<1.6,

where F.sub.T is the focal length of said zoom lens at the telephoto end, and .vertline.M.sub.2 .vertline. is the amount of zoom movement of said second lens unit from the wide angle end to the telephoto end.

4. The zoom lens according to claim 1 satisfying the following conditions:

5<F.sub.1 /F.sub.W <53

1<F.sub.3 /F.sub.W <3,

where F.sub.1 and F.sub.3 are respectively the focal lengths of said first and third lens units.

5. The zoom lens according to claim 4 satisfying the following condition:

0.4<E.sub.1W /F.sub.W <1.8,

where E.sub.1W is the principal point distance between said first lens unit and said second lens unit at the wide angle end.

6. The zoom lens according to claim 1 satisfying the following condition:

0.7<.vertline.M.sub.2 /M.sub.3 .vertline.<2.5,

where M.sub.2 and M.sub.3 are respectively the amounts of movement of said second and third lens units from the wide angle end to the telephoto end.

7. A zoom lens consisting of, in succession from an object side, a first lens unit consisting of a single lens element having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, said second lens unit and said third lens unit being moved to thereby effect magnification change.

8. The zoom lens according to claim 7 satisfying the following condition:

1.4<.vertline.F.sub.2 /F.sub.W .vertline.<2.6,

where F.sub.2 is the focal length of said second lens unit, and F.sub.W is the focal length of said zoom lens at the wide angle end.

9. The zoom lens according to claim 7 satisfying the following condition:

0.4<E.sub.1W /F.sub.W <1.8,

where E.sub.1W is the principal point distance between said first lens unit and said second lens unit at the wide angle end, and F.sub.W is the focal length of the whole system at the wide angle end.

10. The zoom lens according to claim 7 satisfying the following condition:

0.7<.vertline.M.sub.2 /M.sub.3 .vertline.<2.5,

where M.sub.2 and M.sub.3 are respectively the amounts of movement of said second and third lens units from the wide angle end to the telephoto end.

11. The zoom lens of claim 7 wherein the object side surface of said single lens element is shaped as being convex toward the object side.

12. A zoom lens according to claim 7, wherein when the magnification change is effected, said second lens unit and said third lens unit are moved in opposite directions.

13. A zoom lens consisting of, in succession from an object side, a first lens unit consisting of a single lens element having positive refractive power, a second lens unit having negative refractive power, a stop, and a third lens unit having positive refractive power, said second lens unit and said third lens unit being moved to thereby effect magnification change.

14. A zoom lens according to claim 13, wherein when the magnification change is effected, said second lens unit and said third lens unit are moved in opposite directions.

15. A zoom lens comprising, in succession from an object side, a first lens unit having positive refractive power and consisting of a single positive lens element, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, said second lens unit and said third lens unit being moved to thereby effect zooming, and said zoom lens satisfying the following condition:

0.5<.vertline.M.sub.3 .vertline./(F.sub.T -F.sub.W)<1.0,

wherein M.sub.3 is an amount of movement of zooming from a wide angle end to a telephoto end of said third lens unit, and F.sub.W and F.sub.T are respectively focal lengths of said zoom lens at the wide angle end and the telephoto end.

16. A zoom lens comprising, in succession from an object side, a first lens unit consisting of a single lens element having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, said second lens unit and said third lens unit being moved to thereby effect magnification change,

said zoom lens further comprising a stop disposed between said second lens unit and said third lens unit.

17. The zoom lens of claim 16, wherein the object side surface of said single lens element is shaped as being convex toward the object side.

18. A zoom lens according to claim 16, wherein when the magnification change is effected, said second lens unit and said third lens unit are moved in opposite directions.

19. A zoom lens comprising, in succession from an object side, a first lens unit consisting of a single lens element having positive refractive power, a second lens unit having negative refractive power, and a third lens unit having positive refractive power, said second lens unit and said third lens unit being moved to thereby effect magnification change,

wherein said third lens unit has three or more lens elements.