Zoom lens

Description

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens that is small in size and suitable for a camera with a lens shutter or a video camera.
2. Background Arts
A camera with a lens shutter conventionally uses a zoom lens consisting of a front lens group having a positive power and a rear lens group having a negative power. As an example of small size zoom lens consisting of two lens groups, JPA 3-158815 discloses a zoom lens whose front lens group consists of two lens elements and whose rear lens group consists of a single lens element. In this zoom lens, the first and second lenses of the front lens group are spaced from each other by a relatively long distance in order to balance various aberrations well.
Indeed the zoom lens of the prior art uses merely three lens elements, but the larger spacing between the two lenses of the front lens group makes the total length of the zoom lens relatively large even in its retracted or collapsed position. Moreover, as the spacing between the two lens of the front lens group increases, the first lens must have a larger effective aperture and thus a larger diameter. As a result, also the diameter of the zoom lens of the prior art is relatively large.
OBJECT OF THE INVENTION
In view of the foregoing, a prime object of the present invention is to provide a zoom lens that consists of a small number of lens elements and is small in size.
DETAILED DESCRIPTION OF THE INVENTION
To achieve the above object, the present invention provides a zoom lens of a front lens group having a positive power and a rear lens group having a negative power, wherein the front lens group consists of a first lens having negative power and a second lens having a positive power. The first lens has at least one aspherical surface, and is spaced from the second lens by an air gap D2, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the air gap between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle terminal.
Above the upper limit of the condition (1), spherical aberration would be too large to correct. Also, the air gap between the first and second lenses would be as large as conventional, and the effective aperture of the first lens would be as large as conventional. Below the lower limit of the condition (1), it is impossible to provide an air gap between the first and second lenses.
To balance various aberrations well, the one aspherical surface of the first lens of the zoom lens of the present invention preferably satisfies the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7 Y.sub.max <Y<1.0 Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
It is to be noted that the local radius of curvature C.sub.as at the height Y relative to the optical axis may be calculated according to the following equation:
C.sub.as =D2.sup.2 X(Y)/D2Y.sup.2
wherein X(Y) represents the surface contour of the aspherical surface, and X is an amount of displacement from the base surface in the direction of the optical axis.
Above the upper limit of the condition (2), coma aberration would be over-compensated, while astigmatism and spherical aberration would be worsen. Below the lower limit of the condition (2), coma aberration would be too large to compensate.

BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become apparent from the following detailed description of the preferred embodiments when read in connection with the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention, wherein like reference numerals designate like or corresponding parts throughout the several views, and wherein:
FIG. 1 is a schematic diagram showing a zoom lens according to Example 1 of the present invention, at a wide-angle terminal;
FIGS. 2A, 2B and 2C are diagrams showing aberration curves of the zoom lens according to Example 1 at the wide-angle terminal;
FIGS. 3A, 3B and 3C are diagrams showing aberration curves of the zoom lens according to Example 1 at a middle focal length;
FIGS. 4A, 4B and 4C are diagrams showing aberration curves of the zoom lens according to Example 1 at a telephoto terminal;
FIG. 5 is a schematic diagram showing a zoom lens according to Example 2 of the present invention, at a wide-angle terminal;
FIGS. 6A, 6B and 6C are diagrams showing aberration curves of the zoom lens according to Example 2 at the wide-angle terminal;
FIGS. 7A, 7B and 7C are diagrams showing aberration curves of the zoom lens according to Example 2 at a middle focal length;
FIGS. 8A, 8B and 8C are diagrams showing aberration curves of the zoom lens according to Example 2 at a telephoto terminal;
FIG. 9 is a schematic diagram showing a zoom lens according to Example 3 of the present invention, at a wide-angle terminal;
FIGS. 10A, 10B and 10C are diagrams showing aberration curves of the zoom lens according to Example 3 at the wide-angle terminal;
FIGS. 11A, 11B and 11C are diagrams showing aberration curves of the zoom lens according to Example 3 at a middle focal length;
FIGS. 12A, 12B and 12C are diagrams showing aberration curves of the zoom lens according to Example 3 at a telephoto terminal;
FIG. 13 is a schematic diagram showing a zoom lens according to Example 4 of the present invention, at a wide-angle terminal;
FIGS. 14A, 14B and 14C are diagrams showing aberration curves of the zoom lens according to Example 4 at the wide-angle terminal;
FIGS. 15A, 15B and 15C are diagrams showing aberration curves of the zoom lens according to Example 4 at a middle focal length;
FIGS. 16A, 16B and 16C are diagrams showing aberration curves of the zoom lens according to Example 4 at a telephoto terminal;
FIG. 17 is a schematic diagram showing a zoom lens according to Example 5 of the present invention, at a wide-angle terminal;
FIGS. 18A, 18B and 18C are diagrams showing aberration curves of the zoom lens according to Example 5 at the wide-angle terminal;
FIGS. 19A, 19B and 19C are diagrams showing aberration curves of the zoom lens according to Example 5 at a middle focal length;
FIGS. 20A, 20B and 20C are diagrams showing aberration curves of the zoom lens according to Example 5 at a telephoto terminal;
FIG. 21 is a schematic diagram showing a zoom lens according to Example 6 of the present invention, at a wide-angle terminal;
FIGS. 22A, 22B and 22C are diagrams showing aberration curves of the zoom lens according to Example 6 at the wide-angle terminal;
FIGS. 23A, 23B and 23C are diagrams showing aberration curves of the zoom lens according to Example 6 at a middle focal length;
FIGS. 24A, 24B and 24C are diagrams showing aberration curves of the zoom lens according to Example 6, at a telephoto terminal;
FIG. 25 is a schematic diagram showing a zoom lens according to Example 7 of the present invention, at a wide-angle terminal;
FIGS. 26A, 26B and 26C are diagrams showing aberration curves of the zoom lens according to Example 7 at the wide-angle terminal;
FIGS. 27A, 27B and 27C are diagrams showing aberration curves of the zoom lens according to Example 7 at a middle focal length; and
FIGS. 28A, 28B and 28C are diagrams showing aberration curves of the zoom lens according to Example 7, at a telephoto terminal.

In FIGS. 1, 5, 9, 13, 17, 21, 25, the arrows indicate the directions of movements of front and rear lens groups of the respective zoom lenses when zooming to the wide angle terminal.
In the drawings, the curves S and T represent astigmatisms in the sagittal image surface and the tangential image surface respectively. The curves C, d, F, g represent spherical aberrations relative to the C-rays (656.3 nm), the d-rays (587.6 nm), the F-rays (486.1 nm) and the g-rays (435.8 nm).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
EXAMPLE 1
The zoom lens 5 of the first Example of the present invention, as shown in FIG. 1, is composed of a front lens group 10 with a positive power, and a rear lens group 20 with a negative power, arranged in this order from the object side. The front and rear lens groups 10 and 20 are moved relative to each other along an optical axis for zooming. The front lens group 10 includes a first lens 11 of a negative power and a second lens 12 of a positive power, arranged in this order from the object side. The rear lens group 20 consists of a third lens 23 of a negative power. Object side surfaces R1 and R3 and image side surfaces R2 and R4 of the first and second lenses 11 and 12 are aspherical.
Numerical values of the first Example will be described below.
In the following numerical values of any Examples, R is the radius of curvature of the respective surfaces of the lens elements 11, 12 and 23, i is the surface number in the order from the object side, D is the spacing between two adjacent surfaces, N is the refractive index, and v is the Abbe number.
EXAMPLE 1______________________________________i R (mm) D (mm) N .nu.______________________________________1 -17.0045 (aspherical) 3.26454 1.747509 37.26112 76.7339 (aspherical) 1.325933 23.8927 (aspherical) 3 1.487000 70.44 -6.99216 (aspherical) variable5 -11.8156 1 1.620000 60.36 -280.601______________________________________
The aspherical surfaces satisfy the following definition:
X=(Y.sup.2 /R)/[1+.sqroot. {1-(1+K).multidot.(Y.sup.2 /R.sup.2)}]+aY.sup.2 +bY.sup.6 +cY.sup.8 +dY.sup.10 (3)
wherein X is the displacement from the base surface in the axial direction, Y is the height relative to the optical axis in the perpendicular direction to the optical axis, K is the conical constant, R is the radius of curvature, a, b, c and d are the coefficients of the aspherical surfaces. It is possible to use another definition on the aspherical surfaces in place of the above definition (3) without interring the inventive effect.
Aspherical coefficients of the first Example are as follows:
__________________________________________________________________________i 1 2 3 4__________________________________________________________________________K 2 10.219621 -17.66172 -0.13992a -1.637320E-04 3.945130E-04 2.224290E-04 -5.948580E-05b 1.032190E-05 5.300960E-05 4.085390E-05 1.050960E-05c -1.702140E-07 -8.482370E-07 3.390040E-07 -4.891900E-07d -1.964640E-09 1.462760E-07 1.358250E-07 1.342110E-07__________________________________________________________________________
The total focal length F and the f-number of the zoom lens 5 of the first Example are designed to vary within the following ranges:
F: 24.00 to 34.00 to 45.12
f-number: 5.77 to 8.17 to 10.85
In correspondence with the variation of the focal length F, the distance D4 between the front lens group 10 and the rear lens group 20 varies as follows:
D4: 18.1643 to 10.9392 to 13.6239
In the first Example, the image side aspherical surface R2 of the first lens 11 satisfies the condition (1):
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10
wherein C is a radius of curvature of a base surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7 Y.sub.max <Y<1.0Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
With regard to the image side aspherical surface R2 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 1.266510.8 Y.sub.max 2.193310.9 Y.sub.max 3.826211.0 Y.sub.max 6.73237______________________________________
In the first Example, the distance D2 between the first and second lenses 11 and 12, and the total focal length Fw of the zoom lens 5 at its wide-angle terminal are:
D2=1.32593, Fw=24.00.
D2/Fw=1.32593/24.00.apprxeq.0.05524
Accordingly, the first Example satisfies the condition (1) for the first characteristic value of the invention: 0<D2/Fw<0.1.
Aberration curves of the first Example at the wide-angle terminal (F=24.00), at the middle focal length (F=34.00) and at the telephoto terminal (F=45.12) are shown in FIGS. 2A, 2B and 2C, FIGS. 3A, 3B and 3C and FIGS. 4A, 4B and 4C, respectively.
EXAMPLE 2
The composition of the zoom lens 5 of the second Example of the present invention, as shown in FIG. 5, is fundamentally equal to that of the first Example, as shown by the same reference numbers as used in FIG. 1. In the second Example, all surfaces R1 to R6 of first to third lenses 11, 12 and 23 are aspherical.
Numerical values and aspherical coefficients of the second Example are set forth below. In any of the following Examples, any aspherical surface satisfies the above definition (3).
EXAMPLE 2______________________________________1 R (mm) D (mm) N .nu.______________________________________1 -13.6495 (aspherical) 1.10013 1.734826 36.96152 1621.7 (aspherical) 0.796213 87.2737 (aspherical) 2.922 1.492609 67.06444 -6.04327 (aspherical) variable5 -13.3418 (aspherical) 1 1.553850 64.33116 -1907.72 (aspherical)______________________________________i 1 2 3______________________________________K 1.794321 -29.88028 -20a -3.460850E-04 1.423570E-04 -6.738340E-04b 5.677900E-05 9.800520E-05 -7.002920E-06c -6.502610E-07 2.916050E-06 8.824960E-06d -8.760530E-08 3.357760E-08 -4.543920E-07______________________________________i 4 5 6______________________________________K 0.219663 -0.296758 -2064.763a -2.868550E-04 -1.069860E-04 -7.517050E-05b -6.996320E-06 -2.359670E-06 8.452880E-07c -8.839490E-07 6.522560E-08 -4.224640E-09d 7.858180E-09 -4.937130E-10 5.073310E-12______________________________________
As for the second Example, the total focal length F, the f-number of the zoom lens 5 and the distance D4 between the front lens group 10 and the rear lens group 20 vary as follows:
F: 26.39 to 34.19 to 49.60
f-number: 6.35 to 8.22 to 11.93
D4: 19.9535 to 15.5227 to 10.8598
In the second Example, the image side aspherical surface R2 of the first lens 11 satisfies the condition (2): 0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10 in the range of 0.7Y.sub.max <Y<1.0Y.sub.max. With regard to the image side aspherical surface R2 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 0.946870.8 Y.sub.max 1.66060.9 Y.sub.max 2.781141.0 Y.sub.max 4.4887______________________________________
In the second Example, the distance D2 between the first and second lenses 11 and 12, and the total focal length Fw of the zoom lens 5 at the wide-angle terminal are:
D2=0.79621, Fw=26.39
D2/Fw=0.79621/26.39.apprxeq.0.03017
Accordingly, the second Example satisfies the condition (1).
Aberration curves of the second Example at the wide-angle terminal (F=26.39), at the middle focal length (F=34.19) and at the telephoto terminal (F=49.60) are shown in FIGS. 6A, 6B and 6C, FIGS. 7A, 7B and 7C and FIGS. 8A, 8B and 8C, respectively.
EXAMPLE 3
The composition of the zoom lens 5 of the third Example of the present invention, as shown in FIG. 9, is fundamentally equal to that of the first Example, as shown by the same reference numbers as used in FIG. 1. In the third Example, all surfaces R1 to R4 of first to second lenses 11 and 12 and an image side surface R6 of a third lens 23 are aspherical. From the third example, the reference numerals D1 to D5 designating distances between the lens surfaces R1 to R6 are omitted from the drawings for clarity sake.
Numerical values and aspherical coefficients of the third Example will be described below.
EXAMPLE 3______________________________________i R (mm) D (mm) N .nu.______________________________________1 -16.4866 (aspherical) 1.52301 1.776099 33.8592 1000 (aspherical) 0.9956833 63.3212 (aspherical) 3 1.5168 64.24 -6.92786 (aspherical) variable5 -12.5532 1 1.642041 60.36 -71.5476 (aspherical)______________________________________i 1 2 3______________________________________K 3.403018 -30 -20a -5.812270E-04 -2.666420E-04 -4.362150E-04b 4.009680E-05 7.391780E-05 2.996020E-05c -4.193460E-07 1.064830E-06 2.925480E-06d -2.825340E-08 -9.456040E-09 -1.247370E-07______________________________________i 4 6______________________________________K 0.045604 -32.72678a -1.745750E-04 1.124000E-05b -6.874410E-06 -4.776440E-08c 8.372820E-07 -7.166160E-10d -4.249550E-08 3.409470E-12______________________________________
As for the third Example, the total focal length F, the f-number of the zoom lens 5 and the distance D4 between the front lens group 10 and the rear lens group 20 vary as follows:
F: 26.00 to 36.40 to 48.88
f-number: 6.25 to 8.75 to 11.75
D4: 19.7362 to 14.2619 to 10.7677
In the third Example, the image side aspherical surface R2 of the first lens 11 satisfies the condition (2): 0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10 in the range of 0.7Y.sub.max <Y<1.0Y.sub.max. With regard to the image side aspherical surface R2 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 1.005250.8 Y.sub.max 1.889060.9 Y.sub.max 3.256041.0 Y.sub.max 5.26734______________________________________
In the third Example, the characteristic value D2/Fw=0.995683/26.00.apprxeq.0.0383. Accordingly, the third Example satisfies the condition (1).
Aberration curves of the third Example at the wide-angle terminal (F=26.00), at the middle focal length (F=36.40) and at the telephoto terminal (F=48.88) are shown in FIGS. 10A, 10B and 10C, FIGS. 11A, 11B and 11C and FIGS. 12A, 12B and 12C, respectively.
EXAMPLE 4
The composition of the zoom lens 5 of the fourth Example of the present invention, as shown in FIG. 13, is fundamentally equal to that of the first example, as shown by the same reference numbers as used in FIG. 1. In fourth Example, all surfaces R1 to R4 of first to second lenses 11 and 12 and an object side surface R5 of a third lens 23 are aspherical.
Numerical values and aspherical coefficients of the fourth Example are as set forth below.
EXAMPLE 4______________________________________i R (mm) D (mm) N .nu.______________________________________1 -13.8628 (aspherical) 1.79176 1.745816 40.50672 2644.19 (aspherical) 0.6371723 79.7756 (aspherical) 3 1.487000 70.44 -6.35765 (aspherical) variable5 -13.9 (aspherical) 1 1.514065 67.62026 -3428.52______________________________________i 1 2 3______________________________________K 2 -30 -20a -1.199810E-04 3.701540E-04 -4.132980E-04b 6.795730E-06 2.609930E-05 -1.100600E-05c 1.955710E-06 7.062610E-06 8.229290E-06d -1.117460E-07 -4.284410E-08 -1.804600E-07______________________________________i 4 5______________________________________K 0.192031 -1.032804a -2.401940E-04 -6.478060E-05b -7.728600E-06 -6.126400E-07c -6.010100E-07 8.171070E-09d 2.751090E-08 -4.635400E-11______________________________________
As for the fourth Example, the total focal length F, the f-number of the zoom lens 5 and the distance D4 between the front lens group 10 and the rear lens group 20 vary as follows:
F: 28.00 to 34.19 to 52.63
f-number: 6.73 to 9.42 to 12.66
D4: 22.5567 to 16.1664 to 12.0877
In the fourth Example, the image side aspherical surface R2 of the first lens 11 satisfies the condition (2): 0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10 in the range of 0.7Y.sub.max <Y<1.0Y.sub.max. With regard to the image side aspherical surface R2 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 0.94620.8 Y.sub.max 1.716780.9 Y.sub.max 3.003411.0 Y.sub.max 5.0599______________________________________
In the fourth Example, the characteristic value D2/Fw=0.637172/28.00.apprxeq.0.023. Accordingly, the fourth Example satisfies the condition (1).
Aberration curves of the fourth Example at the wide-angle terminal (F=28.00), at the middle focal length (F=34.19) and at the telephoto terminal (F=52.63) are shown in FIGS. 14A, 14B and 14C, FIGS. 15A, 15B and 15C and FIGS. 16A, 16B and 16C, respectively.
EXAMPLE 5
The composition of the zoom lens 5 of the fifth Example of the present invention, as shown in FIG. 17, is fundamentally equal to that of the first Example, as shown by the same reference numbers as used in FIG. 1. In the fifth Example, both surfaces R1 to R2 of a first lens 11 are aspherical.
Numerical values and aspherical coefficients of the fifth Example will be described below.
EXAMPLE 5______________________________________i R (mm) D (mm) N .nu.______________________________________1 -50.2903 (aspherical) 1.1 1.747898 36.59072 24.7752 (aspherical) 2.139993 37.8499 3 1.488893 70.18784 -7.44993 variable5 -13.8326 1 1.588121 62.06746 495.329______________________________________i 1 2______________________________________K -0.492914 -14.1429a -9.673020E-04 -4.167430E-04b 2.088140E-05 3.567870E-05c -9.425970E-07 -2.053300E-06d 3.639970E-08 1.287310E-07______________________________________
As for the fifth Example, the total focal length F, the f-number of the zoom lens 5 and the distance D4 between the front lens group 10 and the rear lens group 20 vary as follows:
F: 28.00 to 34.19 to 52.63
f-number: 6.73 to 9.42 to 12.66
D4: 20.6029 to 15.4922 to 12.2319
In the fifth Example, the object side aspherical surface R1 of the first lens 11 satisfies the condition (2): 0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10 in the range of 0.7Y.sub.max <Y<1.0Y.sub.max. With regard to the object side aspherical surface R1 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 0.9489950.8 Y.sub.max 1.1289030.9 Y.sub.max 1.2225691.0 Y.sub.max 1.095134______________________________________
In the fifth Example, the characteristic value D2/Fw=2.13999/28.00.apprxeq.0.076. Accordingly, the fifth Example satisfies the condition (1).
Aberration curves of the fifth Example at the wide-angle terminal (F=28.00), at the middle focal length (F=34.19) and at the telephoto terminal (F=52.63) are shown in FIGS. 18A, 18B and 18C, FIGS. 19A, 19B and 19C and FIGS. 20A, 20B and 20C, respectively.
EXAMPLE 6
The composition of the zoom lens 5 of the sixth example of the present invention, as shown in FIG. 21, is fundamentally equal to that of the first Example, as shown by the same reference numbers as used in FIG. 1. In sixth example, respective object side surfaces R1, R3 and R5 of first to third lenses 11, 12 and 23 are aspherical.
Numerical values and aspherical coefficients of the sixth example be described below.
EXAMPLE 6______________________________________i R (mm) D (mm) N .nu.______________________________________1 -20.6222 (aspherical) 1.94774 1.749145 34.59662 61.8776 0.4494943 47.4541 (aspherical) 3 1.55994 60.85044 -7.9449 variable5 -12.7133 (aspherical) 1 1.487 70.46 -361.145______________________________________i 1 3 5______________________________________K -15.16338 119.9333 0.056179a -1.021410E-03 3.333290E-04 -2.093480E-05b 9.159980E-06 -2.001340E-05 -4.749710E-07c -9.120820E-07 1.104570E-06 1.086950E-08d 3.757890E-08 -1.100160E-07 -3.666320E-11______________________________________
As for the sixth example, the total focal length F, the f-number of the zoom lens 5 and the distance D4 between the front lens group 10 and the rear lens group 20 vary as follows:
F: 28.00 to 34.20 to 52.64
f-number: 6.73 to 9.42 to 12.66
D4: 21.2939 to 14.9301 to 10.8678
In the sixth Example, the object side aspherical surface R1 of the first lens 11 satisfies the condition (2): 0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10 in the range of 0.7Y.sub.max <Y<1.0Y.sub.max. With regard to the object side aspherical surface R1 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 1.0642150.8 Y.sub.max 1.3620970.9 Y.sub.max 1.5894651.0 Y.sub.max 1.55097______________________________________
In the sixth example, the characteristic value D2/Fw=0.449494/28.00.apprxeq.0.0160. Accordingly, the sixth example satisfies the condition (1).
Aberration curves of the sixth example at the wide-angle terminal (F=28.00), at the middle focal length (F=34.20) and at the telephoto terminal (F=52.64) are shown in FIGS. 22A, 22B and 22C, FIGS. 23A, 23B and 23C and FIGS. 24A, 24B and 24C, respectively.
EXAMPLE 7
The composition of the zoom lens 5 of the seventh example of the present invention, as shown in FIG. 25, is fundamentally equal to that of the first Example, as shown by the same reference numbers as used in FIG. 1. In the seventh example, both surfaces R1 and R2 of a first lens 11 and an object side surface R5 of a third lense 23 are aspherical.The object side aspherical surface R1 of the first lens 11 satisfies the condition (1) in the range of 0.7Y.sub.max <Y<1.0Y.sub.max.
Numerical values and aspherical coefficients of the seventh example will be described below.
EXAMPLE 7______________________________________i R (mm) D (mm) N .nu.______________________________________1 -19.8996 (aspherical) 3 1.755 27.62 487.302 (aspherical) 1.083 53.2066 3 1.62668 58.98354 -9.06012 variable5 -12.2814 (aspherical) 1 1.624288 59.4456 -187.372______________________________________i 1 2 5______________________________________K 6.21525 -30 0.553798a -4.453040E-04 -1.371070E-04 1.942520E-05b 4.704620E-06 5.865720E-06 -7.415740E-08c -3.823140E-07 -1.754670E-07 4.702170E-09d 1.038880E-08 1.233490E-08 8.320360E-11______________________________________
As for the seventh example, the total focal length F, the f-number of the zoom lens 5 and the distance D4 between the front lens group 10 and the rear lens group 20 vary as follows:
F: 28.00 to 34.20 to 52.64
f-number: 6.73 to 9.42 to 12.66
D4: 17.0273 to 12.3284 to 9.32904
In the seventh Example, the object side aspherical surface R1 of the first lens 11 satisfies the condition (2): 0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10 in the range of 0.7Y.sub.max <Y<1.0Y.sup.max. With regard to the object side aspherical surface R1 of the first lens 11, the value .vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline. varies with the value Y in the range of 0.7Y.sub.max <Y<1.0Y.sub.max in the following manner.
______________________________________ .vertline.(C.sub.as - C)/(N - 1)/.PHI..sub.G1 .vertline.______________________________________0.7 Y.sub.max 1.3615510.8 Y.sub.max 1.7867490.9 Y.sub.max 2.1468581.0 Y.sub.max 2.176913______________________________________
In the seventh example, the characteristic value D2/Fw=1.08/28.00.apprxeq.0.039. Accordingly, the seventh example satisfies the condition (1).
Aberration curves of the seventh example at the wide-angle terminal (F=28.00), at the middle focal length (F=34.20) and at the telephoto terminal (F=52.64) are shown in FIGS. 26A, 26B and 26C, FIGS. 27A, 27B and 27C and FIGS. 28A, 28B and 28C, respectively.

Claims

1. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power, the first lens and second lens being separated by an air gap; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein the rear lens group consists of a third lens having a negative power.
2. A zoom lens according to claim 1, further satisfying the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7 Y.sub.max <Y<1.0 Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
3. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein image side surfaces and object side surfaces of the first to third lenses are aspherical.
4. The zoom lens of claim 3, wherein the zoom lens satisfies the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7Y.sub.max <Y<1.0Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
5. The zoom lens of claim 4, wherein the rear lens group consists of a third lens having a negative power.
6. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein image side surfaces and object side surfaces of the first and second lenses and an image side surface of the third lens are aspherical.
7. The zoom lens of claim 6, wherein the zoom lens satisfies the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7Y.sub.max <Y<1.0Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
8. The zoom lens of claim 7, wherein the rear lens group consists of a third lens having a negative power.
9. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein image side surfaces and object side surfaces of the first and second lenses and an object side surface of the third lens are aspherical.
10. The zoom lens of claim 9, wherein the zoom lens satisfies the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7Y.sub.max <Y<1.0Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
11. The zoom lens of claim 10, wherein the rear lens group consists of a third lens having a negative power.
12. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein object side surfaces of the first to third lenses are aspherical.
13. The zoom lens of claim 12, wherein the zoom lens satisfies the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7Y.sub.max <Y<1.0Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
14. The zoom lens of claim 13, wherein the rear lens group consists of a third lens having a negative power.
15. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein the rear lens group consists of a third lens having a negative power;
said zoom lens further satisfying the following condition:
0.5<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7Y.sub.max <Y<1.0Y.sub.max, and Y.sub.max is a maximum effective aperture of the first lens.
16. A zoom lens according to claim 15, wherein image side surfaces and object side surfaces of the first and second lenses are aspherical, and the image side surface of the first lens satisfies the above condition (2).
17. A zoom lens according to claim 15, wherein an image side surface and an object side surface of the first lens are aspherical, and the object side surface of the first lens satisfies the above condition (2).
18. A zoom lens according to claim 15, wherein an image side surface and an object side surface of the first lens and an object side surface of the third lens are aspherical, and the object side surface of the first lens satisfies the above condition (2).
19. A zoom lens comprising:
a front lens group having a positive power, the front lens group consisting of a first lens having a negative power and a second lens having a positive power; and
a rear lens group having a negative power, the rear lens group being movable relative to the front lens group along an optical axis for zooming;
wherein the first lens has at least one aspherical surface, and is spaced from the second lens by a distance, wherein the zoom lens satisfies the following condition:
0<D2/Fw<0.1 (1)
wherein D2 is the distance between the first and second lenses, and Fw is a total focal length of the zoom lens at a wide-angle end;
wherein the rear lens group consists of a third lens having a negative power;
said zoom lens further satisfying the following condition:
1.8<.vertline.(C.sub.as -C)/(N-1)/.PHI..sub.G1 .vertline.<10(2)
wherein C is a radius of curvature of a base surface of the aspherical surface, N is an index of refraction of a medium forming the first lens, .PHI..sub.G1 is a power of refraction of the first lens, and C.sub.as is a local radius of curvature at a height Y relative to an optical axis, wherein 0.7Y.sub.max <Y<1.0Y.sub.max and Y.sub.max is a maximum effective aperture of the first lens.
20. A zoom lens according to claim 19, wherein image side surfaces and object side surfaces of the first and second lenses are aspherical, and the image side surface of the first lens satisfies the above condition (2).
21. A zoom lens according to claim 19, wherein an image side surface and an object side surface of the first lens are aspherical, and the object side surface of the first lens satisfies the above condition (2).
22. A zoom lens according to claim 19, wherein an image side surface and an object side surface of the first lens and an object side surface of the third lens are aspherical, and the object side surface of the first lens satisfies the above condition (2).

Priority Claims (1)

Number	Date	Country	Kind
9-314748	Nov 1997	JPX

US Referenced Citations (5)

Number	Name	Date
5602676	Estelle	Feb 1997
5633758	Ueda	May 1997
5805352	Kawamura	Sep 1998
5808811	Iyama	Sep 1998
5995298	Ohno	Nov 1999

Foreign Referenced Citations (1)

Number	Date	Country
3-158815	Jul 1991	JPX

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Abstract

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Priority Claims (1)

US Referenced Citations (5)

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