ZOOM LENS

Abstract

A zoom lens includes sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power. The zoom lens satisfies given conditions to implement a compact, large aperture ratio zoom lens having excellent optical performance and compatible with solid state image sensors capable of recording full high vision images.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens suitable for an imaging apparatus equipped with a solid state image sensor, such as digital still camera and a digital video camera.

2. Description of the Related Art

Zoom lenses that are configured by 4 lens groups, capable of high zoom ratios, and used as imaging lens on digital still cameras and digital video cameras equipped with a solid state image sensor such as such as a charge-coupled device (CCD) and a complementary metal-oxide-semiconductor (CMOS) are commonly known (see, for example, Japanese Patent No. 4672860).

The zoom lens recited in Japanese Patent No. 4672860 includes sequentially from a side nearest an object (object side), first to fourth lens groups respectively having a positive, negative, positive, and positive refractive powers. In the zoom lens, the first and third lens groups are stationary, while the second lens group is moved in one direction to perform zooming and the fourth lens group is moved in a back and forth direction to correct image plane variation accompanying zooming and to perform focusing. The zoom ratio of the zoom lens is on the order of 25×; and the maximum angle of view is on the order of 58 degrees. With such a zoom lens formed by 4 lens groups, since there are 2 movable groups, configuration of the lens barrel can be simplified and the size of the lens system overall can be reduced.

A zoom lens that incorporates a stationary fifth lens group into the 4 lens group configuration above is further known (see, for example, Japanese Patent Nos. 4542933, 4823680, and 4823684). The zoom lenses recited in Japanese Patent Nos. 4542933, 4823680, and 4823684 each include from the object side, first to fifth lens groups respectively having a positive, negative, positive, positive, and negative refractive power. In the zoom lenses, the first, third, and fifth lens groups are stationary, while the second lens group is moved in one direction to perform zooming and the fourth lens group is moved in a back and forth direction to correct image plane variation accompanying zooming and to perform focusing.

The zoom ratio of the zoom lens recited in Japanese Patent No. 4542933 is on the order of 30×; and the maximum angle of view is on the order of 60 degrees. The zoom ratio of the zoom lens recited in Japanese Patent No. 4823680 is on the order of 35×; and the maximum angle of view is on the order of 73 degrees. The zoom ratio of the zoom leas recited in Japanese Patent No. 4823604 is on the order of 14×; and the maximum angle of view is on the order of 70 degrees.

Nonetheless, in addition to favorably correcting various types of aberration over the entire zoom range, large aperture ratios for wide angle views enabling the recording of images at dimly lit locations over a wider range are demanded of lens systems for surveillance cameras. Furthermore, accompanying the increased prevalence of solid state image sensors capable of full high vision image recording, lens systems compatible with full high vision solid state image sensors are demanded. Conventionally, demand has increased for a lens system for a surveillance camera equipped with a full high vision solid state image sensor to have extremely high optical performance capable of favorably correcting various types of aberration over the entire zoom range.

As conventional technologies, the zoom lenses above have a problem in that accompanying increased aperture ratios and higher zoom ratios, at the telephoto edge where the zoom ratio is high, image plane curvature becomes prominent when the object distance changes. As a result, particularly at the telephoto edge, as the object distance becomes closer, a peripheral portion of the image gradually becomes out of focus. Of course, the greater the image height, i.e., the larger the size of the solid state image sensor, the more prominent the blur becomes.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the above problems in the conventional technologies.

A zoom lens according to one aspect of the present invention includes sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power. The first lens group, the third lens group, and the fifth lens group remain stationary. The second lens group is moved along an optical axis, from the object side toward an image side, whereby zooming from a wide angle edge to a telephoto edge is performed. The fourth lens group is moved along the optical axis, whereby image plane variation accompanying zooming is corrected and focusing is performed. The fifth lens group includes sequentially from the object side, a negative first lens having at least one aspheric surface and a positive second lens. The zoom lens satisfies a conditional expression (1) 1.5<|f51|/Y<3, and a conditional expression (2) 0.2<|F5/Ft|<0.8, where, f51 is a focal length of the first lens in the fifth lens group, Y is an image height for the entire optical system, F5 is a focal length of the fifth lens group, and Ft is a focal length of the entire optical system at the telephoto edge.

The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view (along the optical axis) of a zoom lens according to a first embodiment;

FIG. 2 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the first embodiment;

FIG. 3 is a cross sectional view (along the optical axis) of the zoom lens according to a second embodiment;

FIG. 4 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the second embodiment;

FIG. 5 is a cross sectional view (along the optical axis) of the zoom lens according to a third embodiment;

FIG. 6 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the third embodiment;

FIG. 7 is a cross sectional view (along the optical axis) of the zoom lens according to a fourth embodiment; and

FIG. 8 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of a zoom lens according to the present invention are explained in detail with reference to the accompanying drawings.

The zoom lens according to the present invention includes sequentially from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power. The second lens group is moved along an optical axis, whereby zooming is performed from the wide angle edge to the telephoto edge. The fourth lens group is moved along the optical axis whereby image plane variation accompanying zooming is corrected and focusing is performed. The first lens group, the third lens group, and the fifth lens group remain stationary (the configuration above is referred to as a basic configuration).

An object of the present invention is to provide a high zoom ratio zoom lens that is compact, has a large aperture ratio and excellent optical performance, e.g., a zoom lens that is optimal for a compact imaging apparatus equipped with a solid state image sensor capable of recording images in full high vision. To achieve such an object, various conditions are set as indicated below.

In addition to the basic configuration, in the zoom lens according to the present invention, the fifth lens group includes sequentially from the object side, a negative first lens having at least one aspheric surface and a positive second lens. By forming an aspheric surface on the first lens disposed farthest on the object side of the fifth lens group, coma, astigmatism, and image plane curvature that accompany high zoom ratios and large aperture ratios and occur when the object distance changes, can be easily corrected. As a result, the advantages of high zoom ratios and large aperture ratios can be realized.

The zoom lens according to the present invention preferably satisfies the following conditional expressions, where f51 is the focal length of the first lens in the fifth lens group, Y is the image height for the entire optical system, F5 is the focal length of the fifth lens group, and Ft is the focal length of the entire optical system at the telephoto edge.

1.5<|f51|/Y<3  (1)

0.2<|F5/Ft|<0.8  (2)

Conditional expression (1) prescribes a proper range of the ratio of the focal length f51 of the first lens disposed farthest on the object side of the fifth lens group and the image height Y of the entire optical system. Satisfaction of conditional expression (1) establishes a proper refractive power of the negative first lens disposed farthest on the object side of the fifth lens group, enabling implementation of a high-resolution optical system of a high zoom ratio and favorably correcting various types of aberration.

Below the lower limit of conditional expression (1), the negative refractive power of the first lens disposed farthest on the object side of the fifth lens group becomes too strong, making correction of various aberration of a peripheral portion of an image difficult. Meanwhile, above the upper limit of conditional expression (1), the negative refractive power of the first lens disposed farthest on the object side of the fifth lens group becomes too weak, increasing the Petzval sum for the entire fifth lens group and making image plane curvature prominent, whereby a flat imaging plane cannot be obtained. In particular, the correction of chromatic aberration occurring on the telephoto side becomes difficult.

More favorable results can be expected if the zoom lens satisfies conditional expression (1) within the range indicated below.

1.7<|f51|/Y<2.8  (1a)

By satisfying conditional expression (1) within the range prescribed by conditional expression (1a), the zoom lens can more favorably correct various types of aberration of the peripheral portion of an image since the Petzval sum for the entire fifth lens group can be decreased.

Conditional expression (2) prescribes a proper range of the ratio of the focal length F5 of the fifth lens group and the focal length Ft of the entire optical system at the telephoto edge. Below the lower limit of conditional expression (2), the refractive power of the fifth lens group becomes too strong, the exit pupil position on the telephoto side becomes extremely close to the image plane, and relative illumination (shading) deteriorates. Further, spherical aberration and coma on the wide angle side or the telephoto side becomes prominent, inviting drops in resolution. Meanwhile, above the upper limit of conditional expression (2), the refractive power of the fifth lens group becomes too weak, requiring the fourth lens group to be moved over a greater distance to perform focusing and thereby, making size reductions of the optical system difficult.

To achieve high resolution, the zoom lens according to the present invention preferably satisfies the following conditional expression, where nd51 is the refractive index (with respect to the d-line) of the first lens in the fifth lens group and nd52 is refractive index (with respect to the d-line) of the second lens in the fifth lens group.

nd51−nd52>0.2  (3)

Conditional expression (3) prescribes a proper range of the difference of the refractive indexes (with respect to the d-line) of the negative lens (the first lens) and the positive lens (the second lens) in the fifth lens group. Below the lower limit of conditional expression (3), the Petzval sum for the entire fifth lens group increases and image plane curvature becomes prominent, whereby a flat imaging plane cannot be obtained. As a result, resolution of the optical system drops.

In the zoom lens according to the present invention, the first lens group includes sequentially from the object side, a negative first lens, a positive second lens, a positive third lens, and a positive fourth lens. In the configuration, to favorably correct chromatic aberration at the telephoto edge of the optical system, the first lens and second lens in the first lens group are cemented. In addition, the zoom lens preferably satisfies the following conditional expression, where υd12 is the Abbe number (with respect to the d-line) of the second lens in the first lens group, and υd13 is the Abbe number (with respect to the d-line) of the third lens in the first lens group.

υd12>75  (4)

υd13>63  (5)

Conditional expressions (4) and (5) express conditions necessary to favorably correct chromatic aberration occurring at the telephoto edge of the optical system. Below the lower limit of either conditional expression (4) or conditional expression (5), chromatic aberration occurring at the telephoto edge of the optical system cannot be corrected.

In the zoom lens according to the present invention, the third lens group preferably includes sequentially from the object side, a positive first lens having at least one aspheric surface, and a negative second lens that is a meniscus lens having a convex surface on the object side. Configuration of the third lens group in this manner enables spherical aberration and coma occurring over the entire zoom range to be favorably corrected.

As described, the zoom lens according to the present invention has the configuration described above, enabling size reductions, a greater aperture ratio, and a higher zoom ratio to be achieved as well as favorable correction of various types of aberration over the entire zoom range and compatibility with a solid state image sensor capable of recording full high vision images. In particular, by satisfying the conditions above, the zoom lens enables size reductions, greater aperture ratios, higher zoom ratios, and the maintenance of high optical performance to be achieved.

With reference to the accompanying drawings, embodiments of the zoom lens according to the present invention will be described in detail. Nonetheless, the present invention is not limited by the embodiments below.

FIG. 1 is a cross sectional view (along the optical axis) of the zoom lens according to a first embodiment. The zoom lens includes sequentially from a side nearest a non-depicted object (the object side), a first lens group G₁₁ having a positive refractive power, a second lens group G₁₂ having a negative refractive power, a third lens group G₁₃ having a positive refractive power, a fourth lens group G₁₄ having a positive refractive power, and a fifth lens group G₁₅ having a negative refractive power.

An aperture stop STP prescribing a given aperture is disposed between the second lens group G₁₂ and the third lens group G₁₃. A cover glass CG is disposed between the fifth lens group G₁₅ and an imaging plane IMG. The cover glass CG is disposed as necessary and may be omitted accordingly. At the image plane IMG, the light receiving surface of a solid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₁₁ includes sequentially from the object side, a negative first lens L₁₁₁, a positive second lens L₁₁₂, a positive third lens L₁₁₃, and a positive fourth lens L₁₁₄. The first lens L₁₁₁ and the second lens L₁₁₂ are cemented.

The second lens group G₁₂ includes sequentially from the object side, a negative first lens L₁₂₁, a negative second lens L₁₂₂, a positive third lens L₁₂₃, and a negative fourth lens L₁₂₄. The first lens L₁₂₁ is a meniscus lens having a convex surface on the object side and both surfaces of the first lens L₁₂₁ are aspheric. The third lens L₁₂₃ and the fourth lens L₁₂₄ are cemented.

The third lens group G₁₃ includes sequentially from the object side, a positive first lens L₁₃₁ and a negative second lens L₁₃₂. Both surfaces of the first lens L₁₃₁ are aspheric. The second lens L₁₃₂ is a meniscus lens having a convex surface on the object side.

The fourth lens group G₁₄ includes sequentially from the object side, a positive first lens L₁₄₁ and a negative second lens L₁₄₂. The surface on the object side of the first lens L₁₁₁ aspheric. The first lens L₁₄₁ and the second lens L₁₄₂ are cemented.

The fifth lens group G₁₅ includes sequentially from the object side, a negative first lens L₁₅₁ and a positive second lens L₁₅₂. Both surfaces of the first lens L₁₅₁ are aspheric.

The second lens group G₁₂ is moved along the optical axis from the object side toward the imaging plane IMG side, whereby the zoom lens zooms from the wide angle edge to the telephoto edge. The fourth lens group G₁₄ is moved along the optical axis, whereby the zoom lens corrects image plane variations accompanying zooming and performs focusing. The first lens group G₁₁, the third lens group G₁₃, and the fifth lens group G₁₅ remain stationary.

Here, various values related to the zoom lens according to the first embodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to
24.0 (intermediate focal position) to 129.0 (Ft: telephoto edge)
F number = 1.6 (wide angle edge) to 3.8 (intermediate focal
position) to 4.9 (telephoto edge)
Half-angle (ω) = 38.03 (wide angle edge) to 7.10
(intermediate focal position) to 1.32 (telephoto edge)
(Lens Data)
	r1 = 155.252
	d1 = 1.00	nd1 = 1.84666	νd1 = 23.78
	r2 = 40.511
	d2 = 5.75	nd2 = 1.49700	νd2 = 81.60
	r3 = −245.543
	d3 = 0.10
	r4 = 55.154
	d4 = 3.20	nd3 = 1.59282	νd3 = 68.63
	r5 = 382.377
	d5 = 0.10
	r6 = 31.841
	d6 = 3.50	nd4 = 1.83481	νd4 = 42.72
	r7 = 95.333
	d7 = D(7) (variable)
	r8 = 73.450 (aspheric)
	d8 = 0.70	nd5 = 1.85135	νd5 = 40.10
	r9 = 6.869 (aspheric)
	d9 = 3.52
	r10 = −11.337
	d10 = 0.50	nd6 = 1.88300	νd6 = 40.80
	r11 = 339.750
	d11 = 0.10
	r12 = 23.770
	d12 = 2.00	nd7 = 1.95906	νd7 = 17.47
	r13 = −24.162
	d13 = 0.50	nd8 = 1.88300	νd8 = 40.80
	r14 = 104.181
	d14 = D(14) (variable)
	r15 = ∞ (aperture stop)
	d15 = 0.50
	r16 = 11.539 (aspheric)
	d16 = 4.20	nd9 = 1.61881	νd9 = 63.85
	r17 = −30.000 (aspheric)
	d17 = 0.10
	r18 = 19.101
	d18 = 0.80	nd10 = 2.001	νd10 = 29.13
	r19 = 10.836
	d19 = D(19) (variable)
	r20 = 12.791 (aspheric)
	d20 = 4.20	nd11 = 1.4971	νd11 = 81.56
	r21 = −9.500
	d21 = 0.60	nd12 = 1.90366	νd12 = 31.31
	r22 = −14.070
	d22 = D(22) (variable)
	r23 = 28.595 (aspheric)
	d23 = 0.50	nd13 = 1.85135	νd13 = 40.10
	r24 = 5.300 (aspheric)
	d24 = 0.30
	r25 = 7.909
	d25 = 2.26	nd14 = 1.56732	νd14 = 42.80
	r26 = −16.411
	d26 = 1.00
	r27 = ∞
	d27 = 2.00	nd15 = 1.51633	νd15 = 64.14
	r28 = ∞
	d28 = 3.50
	r29 = ∞ (imaging plane)
Constants of the cone (k) and aspheric coefficients (A, B, C, D)
	(eighth plane)
	k = 0,
	A = −4.57687 × 10−5, B = 6.79061 × 10−6,
	C = −2.31578 × 10−7, D = 2.42224 × 10−9
	(ninth plane)
	k = 0.5967,
	A = −3.17031 × 10−4, B = −4.17155 × 10−6,
	C = 5.67706 × 10−7, D = −3.92278 × 10−8
	(sixteenth plane)
	k = −0.1306,
	A = −4.08183 × 10−5, B = −1.15089 × 10−6,
	C = 1.15662 × 10−8, D = −6.70182 × 10−11
	(seventeenth plane)
	k = −8.2910,
	A = 7.81968 × 10−5, B = −1.89538 × 10−6,
	C = 2.76889 × 10−8, D = −1.55839 × 10−10
	(twentieth plane)
	k = −0.1487,
	A = −4.90625 × 10−5, B = −1.02186 × 10−6,
	C = 5.04342 × 10−10, D = 4.85594 × 10−10
	(twenty-third plane)
	k = 0,
	A = −4.98290 × 10−4, B = −1.45444 × 10−5,
	C = 3.32964 × 10−6, D = −1.57350 × 10−7
	(twenty-fourth plane)
	k = −0.1993,
	A = −4.77089 × 10−4, B = −3.50309 × 10−5,
	C = 3.89261 × 10−6, D = −2.07190 × 10−7
(Zoom Data)
		wide angle	intermediate	telephoto
		edge	focal position	edge
	D(7)	0.719	19.460	27.823
	D(14)	28.930	10.189	1.825
	D(19)	10.283	4.604	14.356
	D(22)	4.687	10.366	0.614
	(Values related to conditional expression (1))
	f51 (focal length of first lens L151) = −7.718
	Y (image height) = 3.4
	|f51|/Y = 2.27
	(Values related to conditional expression (2))
	F5 (focal length of fifth lens group G15) = −58.051
	|F5/Ft| = 0.45
	(Values related to conditional expression (3))
	nd51 (refractive index of first lens L151, with respect to d-line) = 1.85135
	nd52 (refractive index of second lens L152, with respect to d-line) = 1.56732
	nd51 − nd52 = 0.284
	(Values related to conditional expression (4))
	νd12 (Abbe number of second lens L112, with respect to d-line) = 81.60
	(Values related to conditional expression (5))
	νd13 (Abbe number of third lens L113, with respect to d-line) = 68.63

FIG. 2 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the first embodiment. S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.

FIG. 3 is a cross sectional view (along the optical axis) of the zoom lens according to a second embodiment. The zoom lens includes sequentially from the object side, a first lens group G₂₁ having a positive refractive power, a second lens group G₂₂ having a negative refractive power, a third lens group G₂₃ having a positive refractive power, a fourth lens group G₂₄ having a positive refractive power, and a fifth lens group G₂₅ having a negative refractive power.

The aperture stop STP prescribing a given aperture is disposed between the second lens group G₂₂ and the third lens group G₂₃. The cover glass CG is disposed between the fifth lens group G₂₅ and the imaging plane IMG. The cover glass CG is disposed as necessary and may be omitted accordingly. At the image plane IMG, the light receiving surface of a solid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₂₁ includes sequentially from the object side, a negative first lens L₂₁₁, a positive second lens L₂₁₂, a positive third lens L₂₁₃, and a positive fourth lens L₂₁₄. The first lens L₂₁₁ and the second lens L₂₁₂ are cemented.

The second lens group G₂₂ includes sequentially from the object side, a negative first lens L₂₂₁, a negative second lens L₂₂₂, a positive third lens L₂₂₃, and a negative fourth lens L₂₂₄. The first lens L₂₂₁ is a meniscus lens having a convex surface on the object side and both surfaces of the first lens L₂₂₁ are aspheric. The third lens L₂₂₃ and the fourth lens L₂₂₄ are cemented.

The third lens group G₂₃ includes sequentially from the object side, a positive first lens L₂₃₁ and a negative second lens L₂₃₂. Both surfaces of the first lens L₂₃₁ are aspheric. The second lens L₂₃₂ is a meniscus lens having a convex surface on the object side.

The fourth lens group G₂₄ includes sequentially from the object side, a positive first lens L₂₄₁ and a negative second lens L₂₄₂. The surface on the object side of the first lens L₂₄₁ is aspheric. The first lens L₂₄₁ and the second lens L₂₄₂ are cemented.

The fifth lens group G₂₅ includes sequentially from the object side, a negative first lens L₂₅₁ and a positive second lens L₂₅₂. Both surfaces of the first lens L₂₅₁ are aspheric.

The second lens group G₂₂ is moved along the optical axis from the object side toward the imaging plane IMG side, whereby the zoom lens zooms from the wide angle edge to the telephoto edge. The fourth lens group G₂₄ is moved along the optical axis, whereby the zoom lens corrects image plane variations accompanying zooming and performs focusing. The first group G₂₁ the third lens group G₂₃, and the fifth lens group G₂₅ remain stationary.

Here, various values related to the zoom lens according to second embodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to
24.0 (intermediate focal position) to 129.0 (Ft: telephoto edge)
F number = 1.6 (wide angle edge) to 3.8 (intermediate focal
position) to 4.9 (telephoto edge)
Half-angle (ω) = 38.09 (wide angle edge) to 7.07
(intermediate focal position) to 1.32 (telephoto edge)
(Lens Data)
	r1 = 261.122
	d1 = 1.00	nd1 = 1.84666	νd1 = 23.78
	r2 = 41.992
	d2 = 6.00	nd2 = 1.43700	νd2 = 95.10
	r3 = −142.792
	d3 = 0.10
	r4 = 57.592
	d4 = 3.34	nd3 = 1.61800	νd3 = 63.39
	r5 = 1461.086
	d5 = 0.10
	r6 = 31.613
	d6 = 3.50	nd4 = 1.88300	νd4 = 40.80
	r7 = 91.274
	d7 = D(7) (variable)
	r8 = 17.271 (aspheric)
	d8 = 0.70	nd5 = 1.85135	νd5 = 40.10
	r9 = 5.629 (aspheric)
	d9 = 3.82
	r10 = −11.166
	d10 = 0.50	nd6 = 1.88300	νd6 = 40.80
	r11 = 67.816
	d11 = 0.10
	r12 = 19.434
	d12 = 2.06	nd7 = 1.95906	νd7 = 17.47
	r13 = −27.282
	d13 = 0.50	nd8 = 1.88300	νd8 = 40.80
	r14 = 63.676
	d14 = D(14) (variable)
	r15 = ∞ (aperture stop)
	d15 = 0.50
	r16 = 11.267 (aspheric)
	d16 = 4.40	nd9 = 1.61881	νd9 = 63.85
	r17 = −25.469 (aspheric)
	d17 = 0.10
	r18 = 21.986
	d18 = 0.60	nd10 = 2.001	νd10 = 29.13
	r19 = 11.300
	d19 = D(19) (variable)
	r20 = 13.021 (aspheric)
	d20 = 4.18	nd11 = 1.4971	νd11 = 81.56
	r21 = −10.019
	d21 = 0.60	nd12 = 1.90366	νd12 = 31.31
	r22 = −13.773
	d22 = D(22) (variable)
	r23 = 24.019 (aspheric)
	d23 = 0.50	nd13 = 1.85135	νd13 = 40.10
	r24 = 5.699 (aspheric)
	d24 = 0.54
	r25 = 16.318
	d25 = 2.11	nd14 = 1.51633	νd14 = 64.14
	r26 = −10.039
	d26 = 1.00
	r27 = ∞
	d27 = 2.00	nd15 = 1.51633	νd15 = 64.14
	r28 = ∞
	d28 = 3.50
	r29 = ∞ (imaging plane)
Constants of the cone (k) and aspheric coefficients (A, B, C, D)
	(eighth plane)
	k = 0,
	A = −6.21082 × 10−4, B = 1.34413 × 10−5,
	C = −1.99187 × 10−7, D = 1.35410 × 10−9
	(ninth plane)
	k = −0.0060,
	A = −7.63715 × 10−4, B = −1.36437 × 10−5,
	C = 7. 63607 × 10−7, D = −2.94908 × 10−8
	(sixteenth plane)
	k = −0.2311,
	A = −6.05478 × 10−5, B = −1.25340 × 10−6,
	C = 1.67144 × 10−8, D = −8.95523 × 10−11
	(seventeenth plane)
	k = −4.7687,
	A = 6.98644 × 10−5, B = −1.72352 × 10−6,
	C = 2. 91064 × 10−8, D = −1.70266 × 10−10
	(twentieth plane)
	k = −0.4887,
	A = −7.75303 × 10−5, B = −4.64307 × 10−7,
	C = −4.68979 × 10−11, D = 2.32383 × 10−10
	(twenty-third plane)
	k = 0,
	A = −6.68416 × 10−4, B = −3.85322 × 10−5,
	C = 7.43212 × 10−7, D = 6.05435 × 10−8
	(twenty-fourth plane)
	k = −0.2788,
	A = −4.36169 × 10−4, B = −7.39966 × 10−5,
	C = 1.04310 × 10−6, D = 8.94196 × 10−8
(Zoom Data)
		wide angle	intermediate	telephoto
		edge	focal position	edge
	D(7)	0.600	19.459	27.778
	D(14)	29.021	10.161	1.843
	D(19)	9.668	4.480	13.573
	D(22)	4.508	9.697	0.604
	(Values related to conditional expression (1))
	f51 (focal length of first lens L251) = −8.889
	Y (image height) = 3.4
	|f51|/Y = 2.614
	(Values related to conditional expression (2))
	F5 (focal length of fifth lens group G25) = −51.206
	|F5/Ft| = 0.397
	(Values related to conditional expression (3))
	nd51 (refractive index of first lens L251, with respect to d-line) = 1.85135
	nd52 (refractive index of second lens L252, with respect to d-line) = 1.51633
	nd51 − nd52 = 0.335
	(Values related to conditional expression (4))
	νd12 (Abbe number of second lens L212, with respect to d-line) = 95.10
	(Values related to conditional expression (5))
	νd13 (Abbe number of third lens L213, with respect to d-line) = 63.39

FIG. 4 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the second embodiment. S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.

FIG. 5 is a cross sectional view (along the optical axis) of the zoom lens according to a third embodiment. The zoom lens includes sequentially from the object side, a first lens group G₃₁ having a positive refractive power, a second lens group G₃₂ having a negative refractive power, a third lens group G₃₃ having a positive refractive power, a fourth lens group G₃₄ having a positive refractive power, and a fifth lens group G₃₅ having a negative refractive power.

The aperture stop STP prescribing a given aperture is disposed between the second lens group G₃₂ and the third lens group G₃₃. The cover glass CG is disposed between the fifth lens group G₃₅ and the imaging plane IMG. The cover glass CG is disposed as necessary and may be omitted accordingly. At the image plane IMG, the light receiving surface of a solid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₃₁ includes sequentially from the object side, a negative first lens L₃₁₁, a positive second lens L₃₁₂, a positive third lens L₃₁₃, and a positive fourth lens L₃₁₄. The first lens L₃₁₁ and the second lens L₃₁₂ are cemented.

The second lens group G₃₂ includes sequentially from the object side, a negative first lens L₃₂₁, a negative second lens L₃₂₂, a positive third lens L₃₂₃, and a negative fourth lens L₃₂₄. The first lens L₃₂₁ is a meniscus lens having a convex surface on the object side and both surfaces of the first lens L₃₂₁ are aspheric. The third lens L₃₂₃ and the fourth lens L₃₂₄ are cemented.

The third lens group G₃₃ includes sequentially from the object side, a positive first lens L₃₃₁ and a negative second lens L₃₃₂. Both surfaces of the first lens L₃₃₁ as aspheric. The second lens L₃₃₂ is a meniscus lens having a convex surface on the object side.

The fourth lens group G₃₄ includes sequentially from the object side, a positive first lens L₃₄₁ and a negative second lens L₃₄₂. The surface on the object side of the first lens L₃₄₁ is aspheric. The first lens L₃₄₁ and the second lens L₃₄₂ are cemented.

The fifth lens group G₃₅, includes sequentially from the object side, a negative first lens L₃₅₁ and a positive second lens L₃₅₂. Both surfaces of the first lens L₃₅₁ are aspheric.

The second lens group G₃₂ is moved along the optical axis from the object side toward the imaging plane IMG side, whereby the zoom lens zooms from the wide angle edge to the telephoto edge. The fourth lens group G₃₄ is moved along the optical axis, whereby the zoom lens corrects image plane variations accompanying zooming and performs focusing. The first lens group G₃₁, the third lens group G₃₃, and the fifth lens group G₃₅ remain stationary.

Here, various values related to the zoom lens according to the third embodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to
24.0 (intermediate focal position) to 129.0 (Ft: telephoto edge)
F number = 1.6 (wide angle edge) to 3.8 (intermediate focal
position) to 4.9 (telephoto edge)
Half-angle (ω) = 37.93 (wide angle edge) to 7.09
(intermediate focal position) to 1.32 (telephoto edge)
(Lens Data)
	r1 = 143.132
	d1 = 1.00	nd1 = 1.84666	νd1 = 23.78
	r2 = 40.225
	d2 = 5.80	nd2 = 1.43700	νd2 = 95.10
	r3 = −220.562
	d3 = 0.10
	r4 = 57.824
	d4 = 3.28	nd3 = 1.59282	νd3 = 68.63
	r5 = 575.311
	d5 = 0.10
	r6 = 32.258
	d6 = 3.68	nd4 = 1.83481	νd4 = 42.72
	r7 = 106.337
	d7 = D(7) (variable)
	r8 = 53.938 (aspheric)
	d8 = 0.70	nd5 = 1.85135	νd5 = 40.10
	r9 = 6.852 (aspheric)
	d9 = 3.63
	r10 = −10.409
	d10 = 0.50	nd6 = 1.88300	νd6 = 40.80
	r11 = −119.311
	d11 = 0.10
	r12 = 32.375
	d12 = 1.99	nd7 = 1.95906	νd7 = 17.47
	r13 = −18.558
	d13 = 0.50	nd8 = 1.88300	νd8 = 40.80
	r14 = 246.052
	d14 = D(14) (variable)
	r15 = ∞ (aperture stop)
	d15 = 0.50
	r16 = 11.250 (aspheric)
	d16 = 4.50	nd9 = 1.61881	νd9 = 63.85
	r17 = −25.151 (aspheric)
	d17 = 0.14
	r18 = 25.680
	d18 = 0.70	nd10 = 2.001	νd10 = 29.13
	r19 = 12.179
	d19 = D(19) (variable)
	r20 = 12.463 (aspheric)
	d20 = 4.21	nd11 = 1.4971	νd11 = 81.56
	r21 = −10.285
	d21 = 0.60	nd12 = 1.90366	νd12 = 31.31
	r22 = −14.345
	d22 = D(22) (variable)
	r23 = 34.622 (aspheric)
	d23 = 0.50	nd13 = 1.85135	νd13 = 40.10
	r24 = 4.280 (aspheric)
	d24 = 0.11
	r25 = 5.105
	d25 = 2.54	nd14 = 1.54814	νd14 = 45.82
	r26 = −18.427
	d26 = 1.00
	r27 = ∞
	d27 = 2.00	nd15 = 1.51633	νd15 = 64.14
	r28 = ∞
	d28 = 3.50
	r29 = ∞ (imaging plane)
Constants of the cone (k) and aspheric coefficients (A, B, C, D)
	(eighth plane)
	k = 0,
	A = −1.10104 × 10−4, B = 6.86574 × 10−6,
	C = −1.80314 × 10−7, D = 1.77529 × 10−9
	(ninth plane)
	k = 0.5559,
	A = −3.93632 × 10−4, B = −6.30197 × 10−6,
	C = 4.84720 × 10−7, D = −2.99161 × 10−8
	(sixteenth plane)
	k = −0.1935,
	A = −5.34967 × 10−5, B = −1.15951 × 10−6,
	C = 1.21900 × 10−8, D = −9.39982 × 10−11
	(seventeenth plane)
	k = −6.7682,
	A = 7.38246 × 10−5, B = −1.90295 × 10−6,
	C = 2.73786 × 10−8, D = −1.67159 × 10−10
	(twentieth plane)
	k = −0.4009,
	A = −6.89337 × 10−5, B = −1.52572 × 10−6,
	C = 1.76743 × 10−8, D = 1.60421 × 10−10
	(twenty-third plane)
	k = 0,
	A = −4.81453 × 10−4, B = −1.75639 × 10−5,
	C = 1.83475 × 10−6, D = −9.28491 × 10−8
	(twenty-fourth plane)
	k = −0.2457,
	A = −4.55109 × 10−4, B = −5.44365 × 10−5,
	C = 3.09526 × 10−6, D = −2.17589 × 10−7
(Zoom Data)
		wide angle	intermediate	telephoto
		edge	focal position	edge
	D(7)	0.600	19.976	28.485
	D(14)	29.696	10.320	1.811
	D(19)	9.466	4.418	12.865
	D(22)	4.116	9.164	0.717
	(Values related to conditional expression (1))
	f51 (focal length of first lens L351) = −5.780
	Y (image height) = 3.4
	|f51|/Y = 1.7
	(Values related to conditional expression (2))
	F5 (focal length of fifth lens group G35) = −32.279
	|F5/Ft| = 0.25
	(Values related to conditional expression (3))
	nd51 (refractive index of first lens L351, with respect to d-line) = 1.85135
	nd52 (refractive index of second lens L352, with respect to d-line) = 1.54814 nd51 − nd52 = 0.303
	(Values related to conditional expression (4))
	νd12 (Abbe number of second lens L312, with respect to d-line) = 95.10
	(Values related to conditional expression (5))
	νd13 (Abbe number of third lens L313, with respect to d-line) = 68.63

FIG. 6 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the third embodiment. S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.

FIG. 7 is a cross sectional view (along the optical axis) of the zoom lens according to a fourth embodiment. The zoom lens includes sequentially from the object side, a first lens group G₄₁ having a positive refractive power, a second lens group G₄₂ having a negative refractive power, a third lens group G₄₃ having a positive refractive power, a fourth lens group G₄₄ having a positive refractive power, and a fifth lens group G₄₅ having a negative refractive power.

The aperture stop STP prescribing a given aperture is disposed between the second lens group G₄₂ and the third lens group G₄₃. The cover glass CG is disposed between the fifth lens group G₄₅ and the imaging plane IMG. The cover glass CG is disposed as necessary and may be omitted accordingly. At the image plane IMG, the light receiving surface of a solid state image sensor, such as a CCD and CMOS, is disposed.

The first lens group G₄₁ includes sequentially from the object side, a negative first lens L₄₁₁, a positive second lens L₄₁₂, a positive third lens L₄₁₃, and a positive fourth lens L₄₁₄. The first lens L₄₁₁ and the second lens L₄₁₂ are cemented.

The second lens group G₄₂ includes sequentially from the object side, a negative first lens L₄₂₁, a negative second lens L₄₂₂, a positive third lens L₄₂₃, and a negative fourth lens L₄₂₄. The first lens L₄₂₁ is a meniscus lens having a convex surface on the object side and both surfaces of the first lens L₄₂₁ are aspheric. The third lens L₄₂₃ and the fourth lens L₄₂₄ are cemented.

The third lens group G₄₃ includes sequentially from the object side, a positive first lens L₄₃₁ and a negative second lens L₄₃₂. Both surfaces of the first lens L₄₃₁ are aspheric. The second lens L₄₃₂ is a meniscus lens having a convex surface on the object side.

The fourth lens group G₄₄ includes sequentially from the object side, a positive first lens L₄₄₁ and a negative second lens L₄₄₂. The surface on the object side of the first lens L₄₄₁ is aspheric. The first lens L₄₄₁ and the second lens L₄₄₂ are cemented.

The fifth lens group G₄₅ includes sequentially from the object side, a negative first lens L₄₅₁ and a positive second lens L₄₅₂. Both surfaces of the first lens L₄₅₁ are aspheric.

The second lens group G₄₂ is moved along the optical axis from the object side toward the imaging plane IMG side, whereby the zoom lens zooms from the wide angle edge to the telephoto edge. The fourth lens group G₄₄ is moved along the optical axis, whereby the zoom lens corrects image plane variations accompanying zooming and performs focusing. The first lens group G₄₁, the third lens group G₄₃, and the fifth lens group G₄₅ remain stationary.

Here, various values related to the zoom lens according to the fourth embodiment are given.

Focal length of entire lens system = 4.3 (wide angle edge) to
24.0 (intermediate focal position) to 129.0 (Ft: telephoto edge)
F number = 1.6 (wide angle edge) to 3.8 (intermediate focal
position) to 4.9 (telephoto edge)
Half-angle (ω) = 38.01 (wide angle edge) to 7.10
(intermediate focal position) to 1.32 (telephoto edge)
(Lens Data)
	r1 = 144.159
	d1 = 1.00	nd1 = 1.84666	νd1 = 23.78
	r2 = 38.899
	d2 = 5.80	nd2 = 1.49700	νd2 = 81.60
	r3 = −273.198
	d3 = 0.10
	r4 = 52.998
	d4 = 3.31	nd3 = 1.59282	νd3 = 68.63
	r5 = 378.875
	d5 = 0.10
	r6 = 31.113
	d6 = 3.57	nd4 = 1.83481	νd4 = 42.72
	r7 = 92.838
	d7 = D(7) (variable)
	r8 = 76.499 (aspheric)
	d8 = 0.70	nd5 = 1.85135	νd5 = 40.10
	r9 = 6.041 (aspheric)
	d9 = 3.30
	r10 = −12.953
	d10 = 0.50	nd6 = 1.88300	νd6 = 40.80
	r11 = 71.416
	d11 = 0.10
	r12 = 18.115
	d12 = 1.99	nd7 = 1.94594	νd7 = 17.98
	r13 = −26.555
	d13 = 0.50	nd8 = 1.88300	νd8 = 40.80
	r14 = 95.601
	d14 = D(14) (variable)
	r15 = ∞ (aperture stop)
	d15 = 0.50
	r16 = 11.217 (aspheric)
	d16 = 4.40	nd9 = 1.61881	νd9 = 63.85
	r17 = −25.000 (aspheric)
	d17 = 0.96
	r18 = 22.880
	d18 = 0.60	nd10 = 2.001	νd10 = 29.13
	r19 = 10.741
	d19 = D(19) (variable)
	r20 = 11.970 (aspheric)
	d20 = 4.20	nd11 = 1.4971	νd11 = 81.56
	r21 = −9.300
	d21 = 0.60	nd12 = 1.90366	νd12 = 31.32
	r22 = −13.445
	d22 = D(22) (variable)
	r23 = 41.730 (aspheric)
	d23 = 0.50	nd13 = 1.85135	νd13 = 40.10
	r24 = 6.749 (aspheric)
	d24 = 0.49
	r25 = 17.244
	d25 = 2.13	nd14 = 1.56732	νd14 = 42.80
	r26 = −10.867
	d26 = 1.00
	r27 = ∞
	d27 = 2.00	nd15 = 1.51633	νd15 = 64.14
	r28 = ∞
	d28 = 3.50
	r29 = ∞ (imaging plane)
Constants of the cone (k) and aspheric coefficients (A, B, C, D)
	(eighth plane)
	k = 0,
	A = −2.65503 × 10−4, B = 1.28344 × 10−5,
	C = −3.59136 × 10−7, D = 3.83400 × 10−9
	(ninth plane)
	k = 0.3239,
	A = −5.45623 × 10−4, B = −7.61065 × 10−6,
	C = 7.83466 × 10−7, D = −5.46724 × 10−8
	(sixteenth plane)
	k = −0.1982,
	A = −5.20814 × 10−5, B = −1.30668 × 10−6,
	C = 1.67967 × 10−8, D = −1.13589 × 10−10
	(seventeenth plane)
	k = −6.0844,
	A = 7.14760 × 10−5, B = −1.84345 × 10−6,
	C = 2. 96044 × 10−8, D = −1.85685 × 10−10
	(twentieth plane)
	k = −0.2645,
	A = −5.95055 × 10−5, B = −1.16644 × 10−6,
	C = 7.95351 × 10−9, D = 3.24336 × 10−10
	(twenty-third plane)
	k = 0,
	A = −3.71965 × 10−4, B = −2.63704 × 10−5,
	C = 2.26085 × 10−6, D = −6.30326 × 10−8
	(twenty-fourth plane)
	k = 0.0775,
	A = −2.57754 × 10−4, B = −3.45586 × 10−5,
	C = 9.86053 × 10−7, D = 3.54356 × 10−10
(Zoom Data)
		wide angle	intermediate	telephoto
		edge	focal position	edge
	D(7)	0.897	19.167	27.163
	D(14)	28.094	9.824	1.828
	D(19)	10.148	4.496	14.112
	D(22)	4.564	10.216	0.600
	(Values related to conditional expression (1))
	f51 (focal length of first lens L451) = −9.520
	Y (image height) = 3.4
	|f51|/Y = 2.8
	(Values related to conditional expression (2))
	F5 (focal length of fifth lens group G45) = −90.419
	|F5/Ft| = 0.701
	(Values related to conditional expression (3))
	nd51 (refractive index of first lens L451, with respect to d-line) = 1.85135
	nd52 (refractive index of second lens L452, with respect to d-line) = 1.56732
	nd51 − nd52 = 0.284
	(Values related to conditional expression (4))
	νd12 (Abbe number of second lens L412, with respect to d-line) = 81.60
	(Values related to conditional expression (5))
	νd13 (Abbe number of third lens L413, with respect to d-line) = 68.63

FIG. 8 is a diagram of various types of aberration occurring, with respect to the d-line (λ=587.56 nm), in the zoom lens according to the fourth embodiment. S and M shown with respect to astigmatism, respectively indicate aberration at the sagittal image plane and at the meridonal image plane.

Among the values for each of the embodiments, r₁, r₂, . . . indicate radii of curvature for each lens, aperture stop surface, etc.; d₁, d₂, . . . indicate the thickness of the lenses, aperture stop, etc. or the distance between surfaces thereof; nd₁, nd₂, . . . indicate the refraction index of each lens with respect to the d-line (λ=587.56 nm); and υd₁, υd₂, . . . indicate the Abbe number of each lens with respect to the d-line (λ=587.56 nm). Lengths are indicated in units of [mm] and angles are indicated in [degrees].

Each of the aspheric surfaces above is expressed by the following equation, where Z is the depth of the aspheric surface, R is the paraxial radius of curvature, h is the height from the optical axis, and the traveling direction of light is positive.

$\begin{array}{cc}Z=\frac{y^2}{R{\left\{1+1\sqrt{1-\left(1+k\right)y/R^2}\right\}}^2}+{\mathrm{Ay}}^4+{\mathrm{By}}^6+{\mathrm{Cy}}^8+{\mathrm{Dy}}^{10}& \left[1\right]\end{array}$

Further, k is the constant of the cone, and A, B, C, and D are the fourth, the sixth, the eighth, and the tenth order aspheric coefficients, respectively.

As described, the zoom lens of each of the embodiments includes lenses having suitable aspheric surfaces and cemented lenses and by satisfying the conditional expressions above, achieves a large aperture ratio of an F number on the order of 1.6, and can implement an imaging lens that is compact and has high optical performance as well as a high zoom ratio (on the order of 30×) and that is suitable for compact imaging apparatuses equipped with a full high vision solid state image sensors.

As described, the zoom lens according to the present invention is useful for compact imaging apparatuses equipped with a solid state image sensor, such as a digital still camera and a digital video camera. In particular, the zoom lens is optimal for a surveillance camera equipped with a full high vision solid state image sensor.

According to the present invention, resolution of the optical system can be further improved.

According to the present invention, chromatic aberration particularly at the telephoto edge can be favorably corrected.

According to the present invention, spherical aberration and coma over the entire zoom range can be favorably corrected.

Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

The present document incorporates by reference the entire contents of Japanese priority document, 2012-042554 filed in Japan on Feb. 28, 2012.

Claims

1. A zoom lens comprises sequentially from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power, wherein the first lens group, the third lens group, and the fifth lens group remain stationary,the second lens group is moved along an optical axis, from the object side toward an image side, whereby zooming from a wide angle edge to a telephoto edge is performed,the fourth lens group is moved along the optical axis, whereby image plane variation accompanying zooming is corrected and focusing is performed,the fifth lens group includes sequentially from the object side, a negative first lens having at least one aspheric surface and a positive second lens, andthe zoom lens satisfies: a conditional expression (1) 1.5<|f51|/Y<3, anda conditional expression (2) 0.2<|F5/Ft|<0.8, where, f51 is a focal length of the first lens in the fifth lens group, Y is an image height for the entire optical system, F5 is a focal length of the fifth lens group, and Ft is a focal length of the entire optical system at the telephoto edge.

2. The zoom lens according to claim 1, wherein the fifth lens group includes the first lens and the second lens, andthe zoom lens satisfies a conditional expression (3) nd51−nd52>0.2, where, nd51 is a refractive index (with respect to the d-line) of the first lens in the fifth lens group and nd52 is a refractive index (with respect to the d-line) of the second lens in the fifth lens group.

3. The zoom lens according claim 1, wherein the first lens group includes sequentially from the object side, a negative first lens, a positive second lens, a positive third lens, and a positive fourth lens,the first lens and the second lens in the first lens group are cemented, andthe zoom lens satisfies: a conditional expression (4) υd12>75, anda conditional expression (5) υd13>63,where, υd12 is an Abbe number (with respect to d-line) of the second lens in the first lens group and υd13 is an Abbe number (with respect to the d-line) of the third lens in the first lens group.

4. The zoom lens according to claim 1, wherein the third lens group includes sequentially from the object side, a positive first lens having at least one aspheric surface and a negative second lens that is a meniscus lens having a convex surface on the object side.

5. The zoom lens according to claim 2, wherein the third lens group includes sequentially from the object side, a positive first lens having at least one aspheric surface and a negative second lens that is a meniscus lens having a convex surface on the object side.