JP7614741B2 - Zoom lens and imaging device - Google Patents

Description

The present invention relates to a zoom lens and an imaging device.

There is a demand for compact zoom lenses for use in imaging devices such as surveillance cameras, digital still cameras, and video cameras. Patent Document 1 discloses a two-group zoom lens that is composed of a negative lens group and a positive lens group, in that order from the object side to the image side.

JP 2002-082284 A

The zoom lens of Patent Document 1 has room for improvement in the correction of axial chromatic aberration. The present invention aims to provide a zoom lens that is advantageous in terms of, for example, compactness and correction of axial chromatic aberration.

A zoom lens according to one aspect of the present invention is a zoom lens that comprises a negative first lens group and a positive second lens group, arranged in this order from the object side to the image side, and that moves for zooming so that the distance between the first lens group and the second lens group changes. The zoom lens includes a negative plastic lens, the first lens group includes two lenses, the second lens group includes a positive plastic lens, and has an aperture stop that moves integrally with the second lens group, located closer to the image side than the first lens group. Let Nd be the refractive index of the positive plastic lens with respect to the d-line, νd be the Abbe number of the positive plastic lens based on the d-line, fw be the focal length at the wide-angle end of the zoom lens, f1 be the focal length of the first lens group, and f2 be the focal length of the second lens group.
Nd≦-0.0065νd+1.8180
1.50≦｜f1/fw｜≦2.62
1.50≦f2/fw≦2.45
The following condition is satisfied: Incidentally, an image pickup apparatus including the above-described zoom lens also constitutes another aspect of the present invention.

The present invention can provide a zoom lens that is advantageous in terms of, for example, compactness and correction of axial chromatic aberration.

FIG. 2 is a cross-sectional view of the zoom lens of the first embodiment at the wide-angle end. 5A to 5C are aberration diagrams of the zoom lens of Example 1 at the wide-angle end, at a middle zoom position, and at the telephoto end. FIG. 11 is a cross-sectional view of a zoom lens according to a second embodiment at a wide-angle end. 11A to 11C are aberration diagrams of the zoom lens of Example 2 at the wide-angle end, at a middle zoom position, and at the telephoto end. FIG. 11 is a cross-sectional view of a zoom lens according to a third embodiment at a wide-angle end. 11A to 11C are aberration diagrams of the zoom lens of Example 3 at the wide-angle end, at a middle zoom position, and at the telephoto end. FIG. 13 is a cross-sectional view of a zoom lens according to a fourth embodiment at a wide-angle end. 11A to 11C are aberration diagrams of the zoom lens of Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. FIG. 13 is a cross-sectional view of a zoom lens at a wide-angle end according to a fifth embodiment. 13A to 13C are aberration diagrams of the zoom lens of Example 5 at the wide-angle end, at a middle zoom position, and at the telephoto end. FIG. 13 is a cross-sectional view of a zoom lens at a wide-angle end according to a sixth embodiment. 13A to 13C are aberration diagrams of the zoom lens of Example 6 at the wide-angle end, at a middle zoom position, and at the telephoto end. FIG. 2 is a cross-sectional view of the zoom lens and the dome cover according to the first embodiment. FIG. 2 is a cross-sectional view of the zoom lens and the protective cover according to the first embodiment. FIG. 13 is a diagram showing a surveillance camera having a zoom lens according to any one of the first to sixth embodiments.

Below, embodiments of the present invention will be described with reference to the drawings. First, matters common to embodiments 1 to 6 described below will be described with reference to FIG. 1. In FIG. 1, the left side is the object side, and the right side is the image side.

The zoom lens of each embodiment is used as an imaging optical system in an imaging device having a solid-state imaging element that receives an optical image formed by the zoom lens. The imaging device may be covered with a dome cover or the like and used as a surveillance camera.

The zoom lens of each embodiment has, in order from the object side to the image side, a negative first lens group L1 and a positive second lens group L2, and the first and second lens groups L1 and L2 move independently of each other in the optical axis direction so that the distance between them changes during zooming. A lens group is a group of one or more lenses whose distance from the preceding and succeeding lens groups changes during zooming or focusing.

As described above, the zoom lens of each embodiment is a negative-lead type two-group zoom lens, and has a configuration suitable for wide-angle zooming by changing the spacing between the first and second lens groups L1 and L2 while making the refractive power of the first lens group L1 negative. The zoom lens of each embodiment also performs magnification change by moving the positive lens group on the image side (second lens group L2), and corrects image plane fluctuations associated with magnification change by moving the negative lens group on the object side (first lens group L1). By having only two movable lens groups, it is possible to simplify the structure of the zoom lens, which is advantageous for miniaturization. The first lens group L1 also moves for focusing from infinity to close objects.

The solid and dotted arrows below the first lens group L1 in FIG. 1 respectively indicate the movement trajectory of the first lens group L1 for correcting image plane fluctuations during zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a close distance object. Also, arrow F indicates the movement trajectory of the first lens group L1 when focusing from an object at infinity to a close distance object at the telephoto end. Note that the wide-angle end and telephoto end refer to the zoom positions when the lens group is located at both ends of the range of movement in the optical axis direction due to the zoom lens mechanism, with the wide-angle end being the widest angle of view and the telephoto end being the narrowest angle of view.

SP denotes an aperture stop. The aperture stop SP is located closer to the image side than the first lens group L1, specifically between the first lens group L1 and the second lens group L2, at the position closest to the object side of the second lens group L2, or inside the second lens group L2. The aperture stop SP may be moved integrally with the second lens group L2 during zooming, or may be stationary. This simplifies the structure of the zoom lens.

G is an optical block equivalent to an optical filter, faceplate, etc. IP is an image plane. The imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film is placed on the image plane IP.

Furthermore, the zoom lens of each embodiment satisfies the following conditions: As a result, the zoom lens is small, low-cost, and capable of correcting axial chromatic aberration well.
First, the zoom lens of each embodiment includes at least one negative plastic lens, the first lens unit L1 includes at least two lenses, and the second lens unit L2 includes at least one positive plastic lens.

Then, assuming that the refractive index of the positive plastic lens with respect to the d-line is Nd, the Abbe number of the positive plastic lens with respect to the d-line is νd, the focal length of the zoom lens at the wide-angle end is fw, and the focal length of the first lens group is f1, at least one of the at least one positive plastic lens has a refractive index of
Nd≦-0.0065νd+1.8180 (1)
1.50≦｜f1/fw｜≦2.62 (2)
The following conditions are satisfied.

When only ordinary optical glass lenses are used, the secondary spectrum of axial chromatic aberration remains in the positive direction on the image side, and it is desirable to reduce this. In response to this, a method is known in which a glass material with a high partial dispersion ratio is used for the positive lens to generate a secondary spectrum in the negative direction, thereby canceling out the lateral chromatic aberration and reducing this. If a plastic lens with a higher partial dispersion ratio than an optical glass lens is used for this positive lens, the effect of correcting axial chromatic aberration is enhanced. In each embodiment, the characteristics of this plastic lens are utilized to effectively correct axial chromatic aberration.

The plastic materials currently available on the market that can be used in optical products are primarily of two types: materials with Abbe numbers between 60 and 55, and materials with Abbe numbers between 40 and 20. In each embodiment, plastic materials with Abbe numbers between 40 and 20 in particular have a high partial dispersion ratio compared to optical glass, and by utilizing this characteristic, axial chromatic aberration can be effectively corrected.

Conditional formula (1) indicates the condition regarding the range that the optical characteristics Nd and νd of the positive plastic lens included in the second lens group L2 should take, and the use of optical characteristics within this range also allows for good correction of axial chromatic aberration. If Nd and νd exceed the range of conditional formula (1), it is not preferable because the axial chromatic aberration at the telephoto end cannot be well corrected.

Conditional formula (2) shows a condition related to the ratio of the focal length of the first lens group L to the focal length at the wide-angle end of the entire zoom lens system in order to achieve both suppression of axial chromatic aberration and size reduction by performing an appropriate power arrangement. If |f1/fw| exceeds the upper limit of conditional formula (2), the focal length of the first lens group L1 becomes too large relative to the focal length at the wide-angle end of the entire system, which makes it difficult to reduce the size of the zoom lens, which is not preferable. If |f1/fw| falls below the lower limit of conditional formula (2), the focal length of the first lens group L1 becomes too small (power is too strong) relative to the focal length at the wide-angle end of the entire system, which makes it difficult to suppress axial chromatic aberration, which is not preferable.
It is more preferable to limit the numerical range of conditional expression (2) as follows:

1.55≦｜f1/fw｜≦2.60 (2a)
It is more preferable to limit the numerical range of condition (2) as follows:

1.60≦｜f1/fw｜≦2.58 (2b)
It is preferable that the zoom lens of each embodiment satisfies the above conditional expressions (1) and (2) and also satisfies at least one of the following conditions.

When the focal length of the second lens unit L2 is f2, it is preferable to satisfy the following conditional expression (3).
1.50≦f2/fw≦2.45 (3)
Conditional formula (3) shows a condition related to the ratio of the focal length of the second lens group L2 to the focal length at the wide-angle end of the entire system in order to perform an appropriate power arrangement and achieve both suppression of axial chromatic aberration and size reduction. If f2/fw exceeds the upper limit of conditional formula (3), the focal length of the second lens group L2 becomes too large relative to the focal length at the wide-angle end of the entire system, which makes it difficult to reduce the size of the zoom lens, which is not preferable. If f2/fw falls below the lower limit of conditional formula (3), the focal length of the second lens group L2 becomes too small relative to the focal length at the wide-angle end of the entire system, which makes it difficult to suppress axial chromatic aberration, which is not preferable.

It is more preferable to limit the numerical range of condition (3) as follows:
1.52≦f2/fw≦2.44 (3a)
It is more preferable to limit the numerical range of condition (3) as follows:
1.55≦f2/fw≦2.43 (3b)
It is preferable that the aperture stop SP is disposed closer to the image side than the first lens unit L1 and moves integrally with the second lens unit L2 during zooming. By satisfying this condition, a space is created on the telephoto end side where the first lens unit L1 and the second lens unit L2 are close to each other, making it possible to reduce the size of the zoom lens and achieve even greater telephoto capabilities.

When the maximum image height on the image plane IP is Y and the total optical length of the zoom lens at the wide-angle end is TLw, it is preferable to satisfy the following conditional expression (4).

4.0≦TLw/Y≦12.0 (4)
Conditional expression (4) shows a condition regarding the ratio of the total optical length to the maximum image height in order to achieve both suppression of axial chromatic aberration and miniaturization of the zoom lens. This is the distance on the optical axis from the object-side lens surface (frontmost surface) of the lens G11 to the image plane IP. If TLw/Y exceeds the upper limit of conditional expression (4), the total optical length becomes large, and the zoom lens If TLw/Y is below the lower limit of condition (4), the total optical length becomes small, but the power of each of the first lens unit L1 and the second lens unit L2 becomes too strong. This is not preferable because it increases axial chromatic aberration.

It is more preferable to limit the numerical range of conditional expression (4) as follows:
4.2≦TLw/Y≦11.8 (4a)
It is more preferable to limit the numerical range of condition (4) as follows:
4.5≦TLw/Y≦11.5 (4b)
It is also preferable to satisfy the following condition (5):
0.60≦｜f1/f2｜≦1.30 (5)
Conditional formula (5) shows a condition related to the ratio of the focal length of the first lens group L1 to the focal length of the second lens group L2 in order to achieve both optimal power arrangement and optical performance. If |f1/f2| exceeds the upper limit of conditional formula (5), the focal length of the second lens group L2 becomes too small, which is undesirable because the fluctuation of aberrations during zooming becomes large. If |f1/f2| falls below the lower limit of conditional formula (5), the focal length of the first lens group L1 becomes too small, which is undesirable because the various aberrations increase mainly on the wide-angle side.

It is more preferable to limit the numerical range of conditional expression (5) as follows:
0.65≦|f1/f2|≦1.28 (5a)
It is more preferable to limit the numerical range of condition (5) as follows:
0.68≦|f1/f2|≦1.25 (5b)
When the total power of the at least one positive plastic lens included in the second lens group L2 is Σφp and the power of the second lens group L2 is φ2, it is preferable to satisfy the following conditional expression (6): The power of a lens is the reciprocal of the focal length of the lens, and the total power of the at least one positive plastic lens is the sum of the powers of those lenses.

0<Σφp/φ2≦1.70 (6)
Conditional expression (6) shows a condition regarding the ratio between the sum of the power of at least one positive plastic lens in the second lens unit L2 and the power of the second lens unit L2 for effective correction of longitudinal chromatic aberration. If Σφp/φ2 exceeds the upper limit of conditional expression (6), the total power of the positive plastic lenses in the second lens unit L2 becomes too large, and the axial chromatic aberration is overcorrected, which is not preferable. If /φ2 falls below the lower limit of condition (6), the total power of the positive plastic lenses in the second lens unit L2 becomes too small, resulting in insufficient correction of axial chromatic aberration, which is undesirable.

It is more preferable to limit the numerical range of condition (6) as follows:
0<Σφp/φ2≦1.68 (6a)
It is more preferable to limit the numerical range of condition (6) as follows:
0<Σφp/φ2≦1.65 (6b)
If the total power of all the plastic lenses included in the zoom lens is Σφa, then
-1.30≦Σφa/φ2≦1.30 (7)
It is preferable to satisfy the following conditional expression (7). Conditional expression (7) shows a condition related to the ratio between the sum of the powers of all the plastic lenses and the power of the second lens group L2 for suppressing defocus caused by temperature change. The sum of the powers of all the plastic lenses is the sum of the powers when the power of the negative lenses is a negative value and the power of the positive lenses is a positive value. If Σφa/φ2 exceeds the upper limit of conditional expression (7), the positive plastic lens power of all the plastic lenses becomes too large, which increases the defocus caused by temperature change, which is not preferable. If Σφa/φ2 falls below the lower limit of conditional expression (7), the power of the negative plastic lens of all the plastic lenses becomes too large, which increases the defocus caused by temperature change, which is not preferable.

It is more preferable to limit the numerical range of condition (7) as follows:
-1.25≦Σφa/φ2≦1.25 (7a)
It is more preferable to limit the numerical range of condition (7) as follows:
-1.20≦Σφa/φ2≦1.20 (7b)
Below, we will explain the specific configurations of the zoom lenses of Examples 1 to 6. In the following explanation, the order of arrangement of the lenses is from the object side to the image side, unless otherwise specified.

In the zoom lens of Example 1 shown in FIG. 1, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves to trace a convex movement locus toward the image side, and the second lens group L2 moves monotonically toward the object side. The aperture stop SP is disposed closest to the object side in the second lens group L2, and moves integrally with the second lens group L during zooming.

The first lens group L1 is composed of a negative lens G11, a negative lens G12, and a positive lens G13. E48R (manufactured by Zeon Corporation) is used as the plastic material for the negative lenses G11 and G12, which are plastic lenses.

The second lens group L2 is composed of a positive lens G21, a negative lens G22, a positive lens G23, and a negative lens G24. EP-3500 (manufactured by Mitsubishi Gas Chemical Company, Inc.) and EP-5000 (manufactured by Mitsubishi Gas Chemical Company, Inc.) are used as the plastic materials for the positive and negative plastic lenses G23 and G24, respectively. EP-3500 used in the positive lens G23 has a large partial dispersion ratio, and therefore can satisfactorily correct axial chromatic aberration. This is also true for other examples that use EP-3500.

In the zoom lens of Example 2 shown in FIG. 3, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves to trace a convex movement locus toward the image side, and the second lens group L2 moves monotonically toward the object side. The aperture stop SP is disposed closest to the object side in the second lens group L2, and moves integrally with the second lens group L during zooming.

The first lens group L1 is composed of a negative lens G11, a negative lens G12, and a positive lens G13. E48R (manufactured by Zeon Corporation) is used as the plastic material for the negative lenses G11 and G12, which are plastic lenses.

The second lens group L2 is composed of a positive lens G21, a negative lens G22, a positive lens G23, a positive lens G24, and a negative lens G25. EP-3500 (manufactured by Mitsubishi Gas Chemical Company, Inc.) and EP-5000 (manufactured by Mitsubishi Gas Chemical Company, Inc.) are used as the plastic materials for the positive lens G23 and the negative lens G25, which are plastic lenses, respectively. EP-5000 also has a large partial dispersion ratio, so it can satisfactorily correct axial chromatic aberration. This is also the case for other examples that use EP-5000.

In the zoom lens of Example 3 shown in FIG. 5, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves to trace a convex movement locus toward the image side, and the second lens group L2 moves monotonically toward the object side. The aperture stop SP is disposed closest to the object side in the second lens group L2, and moves integrally with the second lens group L during zooming.

The first lens group L1 is composed of a negative lens G11, a negative lens G12, and a positive lens G13. E48R (manufactured by Zeon Corporation) is used as the plastic material for the negative lenses G11 and G12, which are plastic lenses. EP-10000 (manufactured by Mitsubishi Gas Chemical Company, Inc.) is used as the plastic material for the positive lens G13, which is also a plastic lens.

The second lens group L2 is composed of a positive lens G21, a negative lens G22, a positive lens G23, a positive lens G24, and a negative lens G25. EP-3500 (manufactured by Mitsubishi Gas Chemical Company, Inc.) is used as the plastic material for the positive lens G23, which is a plastic lens.

In the zoom lens of Example 4 shown in FIG. 7, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves to trace a convex movement locus toward the image side, and the second lens group L2 moves monotonically toward the object side. The aperture stop SP is disposed inside the second lens group L2, and moves integrally with the second lens group L during zooming.

The first lens group L1 is composed of a negative lens G11, a negative lens G12, and a positive lens G13. E48R (manufactured by Zeon Corporation) is used as the plastic material for the negative lenses G11 and G12, which are plastic lenses.

The second lens group L2 is composed of a positive lens G21, a negative lens G22, a positive lens G23, a positive lens G24, and a negative lens G25. EP-9000 (manufactured by Mitsubishi Gas Chemical Company, Inc.) is used as the plastic material for the positive lens G23, which is a plastic lens. EP-9000 also has a large partial dispersion ratio, so it can effectively correct axial chromatic aberration.

In the zoom lens of Example 5 shown in FIG. 9, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves to trace a convex movement locus toward the image side, and the second lens group L2 moves monotonically toward the object side. The aperture stop SP is disposed between the first lens group L1 and the second lens group L2, and does not move during zooming.

The first lens group L1 is composed of a negative lens G11, a negative lens G12, a positive lens G13, and a positive lens G14. E48R (manufactured by Zeon Corporation) is used as the plastic material for the negative lenses G11 and G12, which are plastic lenses. EP-8000 (manufactured by Mitsubishi Gas Chemical Company, Inc.) is used as the plastic material for the positive lens G14, which is also a plastic lens.

The second lens group L2 is composed of a positive lens G21, a negative lens G22, a positive lens G23, a positive lens G24, and a negative lens G25. EP-5000 (manufactured by Mitsubishi Gas Chemical Co., Inc.) is used as the plastic material for the positive lens G23, which is a plastic lens.

In the zoom lens of Example 6 shown in FIG. 11, when zooming from the wide-angle end to the telephoto end, the first lens group L1 moves to trace a convex movement locus toward the image side, and the second lens group L2 moves monotonically toward the object side. The aperture stop SP is disposed closest to the object side in the second lens group L2, and moves integrally with the second lens group L during zooming.

The first lens group L1 is composed of a negative lens G11, a negative lens G12, and a positive lens G13. E48R (manufactured by Zeon Corporation) is used as the plastic material for the negative lenses G11 and G12, which are plastic lenses.

The second lens group L2 is composed of a positive lens G21, a negative lens G22, a positive lens G23, a positive lens G24, a positive lens G25, and a negative lens G26. EP-3500 (manufactured by Mitsubishi Gas Chemical Co., Inc.) is used as the plastic material for the positive lenses G23 and G24, which are plastic lenses.

2, 4, 6, 8, 10, and 12 are aberration diagrams of the zoom lenses of Examples 1 to 6 (Numerical Examples 1 to 6 described later), respectively. (A), (B), and (C) in each diagram show aberrations at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. In the spherical aberration diagrams, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line S indicates the sagittal image plane, and the dashed line M indicates the meridional image plane. The distortion aberration is shown for the d-line. In the chromatic aberration diagrams, the two-dot chain line indicates the axial chromatic aberration and lateral chromatic aberration for the g-line, and the one-dot chain line indicates the axial chromatic aberration and lateral chromatic aberration for the C-line (656.3 nm). ω is the half angle of view (°).

According to each of the embodiments described above, it is possible to realize a small zoom lens in which axial chromatic aberration is well corrected. Note that the shape and number of lenses in the zoom lens of each embodiment may be changed, or the lens group or lens may be moved in a direction perpendicular to the optical axis (including rotating about a point on the optical axis) to correct image blur caused by vibrations such as camera shake.

Below, Numerical Examples 1 to 6 corresponding to Examples 1 to 6, respectively, are shown. In each Numerical Example, ri is the radius of curvature (mm) of the ith surface from the object side, di is the lens thickness or air gap (mm) between the ith and (i+1)th surfaces, and ndi is the refractive index at the d-line of the material of the ith optical component. νdi is the Abbe number based on the d-line of the material of the ith optical component. The Abbe number νd is expressed as νd=(Nd-1)/(NF-NC), where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer line. In each Numerical Example, the two surfaces closest to the image side are flat surfaces of the optical block G.

The half angle of view (°) represents the numerical value of the half angle of view that can be photographed taking distortion into consideration. BF represents the back focus (mm). "Back focus" is the distance on the optical axis from the final surface of the zoom lens (the lens surface closest to the image) to the paraxial image plane expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the foreground surface of the zoom lens (the lens surface closest to the object) to the final surface plus the back focus, and corresponds to the total optical length in conditional formula (4).

An "*" next to a surface number means that the surface has an aspheric shape. The aspheric shape is expressed by the following formula, where X is the position in the optical axis direction, H is the height in the direction perpendicular to the optical axis, the direction of light travel is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are aspheric coefficients. "e-Z" means ×10- ^Z .

x=(h ² /R)/[1+{1-(1+K)(h/r) ² } ^1/2 ]
+A4・h ⁴ +A6・h ⁶ +A8・h ⁸ +A10・h ¹⁰ +A12・h ¹²
Moreover, values corresponding to the above-mentioned conditional expressions (1) to (7) in Numerical Examples 1 to 6 are summarized in Table 1.
[Numerical Example 1]
Unit: mm

Surface data surface number rd nd νd
1* -17.103 0.90 1.53113 55.8
2* 5.495 4.64
3* -11.578 0.60 1.53113 55.8
4* -50.153 0.20
5 18.820 1.67 1.95906 17.5
6 57.999 (variable)
7(Aperture) ∞ 0.27
8 4.572 2.79 1.49700 81.5
9 -194.363 0.82
10 -10.533 0.50 1.84666 23.8
11 50.141 0.10
12* 5.628 2.09 1.56650 37.6
13* -4.582 0.21
14* -7.941 1.50 1.63560 23.9
15* 26.067 (variable)
16 ∞ 0.50 1.52000 61.4
17 ∞ 0.43
Image plane ∞

Aspheric surface data No. 1
K = 0.00000e+000 A 4= 8.41415e-004 A 6=-9.77431e-006 A 8= 4.29052e-008

Side 2
K = 0.00000e+000 A 4= 1.37433e-004 A 6= 4.91698e-006 A 8= 1.74574e-006

Page 3
K = 0.00000e+000 A 4=-1.68036e-003 A 6= 1.30789e-004 A 8=-2.66863e-006

Side 4
K = 0.00000e+000 A 4=-1.19723e-003 A 6= 1.05878e-004 A 8=-2.56424e-006

Page 12
K = 0.00000e+000 A 4=-3.09952e-003 A 6=-1.59302e-004 A 8=-3.97563e-005

Page 13
K = 0.00000e+000 A 4= 2.98719e-003 A 6=-2.63445e-004 A 8=-1.33128e-006

Page 14
K = 0.00000e+000 A 4= 8.62376e-004 A 6= 1.75384e-004 A 8= 5.25204e-006

Page 15
K = 0.00000e+000 A 4= 6.50090e-004 A 6= 3.16410e-004 A 8= 7.69325e-006 A10=-6.78855e-006 A12= 4.60378e-007

Various data Zoom ratio 2.30
Wide Angle Mid Telephoto Focal Length 3.20 5.28 7.36
F-number 1.89 2.30 2.73
Half angle of view (°) 61.3 34.7 24.7
Image height 3.20 3.20 3.20
Lens length 33.92 28.47 27.27
BF 0.43 0.43 0.43

d6 11.38 3.88 0.62
d15 5.31 7.37 9.42
d17 0.43 0.43 0.43

Zoom lens data group Starting surface Focal length
1 1 -7.85
2 7 7.76

[Numerical Example 2]
Unit: mm

Surface data surface number rd nd νd
1* -108.249 0.90 1.53113 55.8
2* 4.848 4.88
3* -9.438 0.60 1.53113 55.8
4* 50.715 0.20
5 15.174 1.05 1.95906 17.5
6 42.130 (variable)
7(Aperture) ∞ 0.27
8 5.862 3.04 1.49700 81.5
9 -24.403 0.50
10 -9.952 0.50 1.84666 23.8
11 67.763 0.10
12* 5.735 3.00 1.56650 37.6
13* -10.616 0.57
14 -35.812 0.88 1.48749 70.2
15 -9.095 0.20
16* -903.443 1.50 1.63560 23.9
17* 9.045 (variable)
18 ∞ 0.50 1.52000 61.4
19∞0.43
Image plane ∞

Aspheric surface data No. 1
K = 0.00000e+000 A 4= 3.64378e-004 A 6=-4.10194e-006 A 8= 1.75001e-008

Side 2
K = 0.00000e+000 A 4=-9.80582e-005 A 6= 9.38316e-006 A 8= 9.77080e-009

Page 3
K = 0.00000e+000 A 4=-5.39495e-005 A 6= 1.81392e-005 A 8=-5.00878e-007

Side 4
K = 0.00000e+000 A 4= 8.87904e-005 A 6= 1.33718e-005 A 8=-6.20276e-007

Page 12
K = 0.00000e+000 A 4=-8.87183e-004 A 6=-1.47861e-005 A 8=-1.97289e-006

Page 13
K = 0.00000e+000 A 4= 2.63735e-004 A 6=-5.41552e-005 A 8= 1.29750e-006

Page 16
K = 0.00000e+000 A 4=-5.86780e-003 A 6=-1.04855e-004 A 8= 1.98712e-005

Page 17
K = 0.00000e+000 A 4=-4.70226e-003 A 6= 1.20944e-004 A 8= 7.44718e-006 A10= 1.29005e-006 A12=-1.18930e-007

Various data Zoom ratio 2.79
Wide Angle Mid Telephoto Focal Length 3.20 6.07 8.93
F-number 1.75 2.23 2.73
Half angle of view (°) 61.5 30.1 20.4
Image height 3.20 3.20 3.20
Lens length 34.89 30.83 31.56
BF 0.43 0.43 0.43

d 6 10.77 3.32 0.65
d17 5.00 8.39 11.78
d19 0.43 0.43 0.43

Zoom lens data group Starting surface Focal length
1 1 -6.53
2 7 7.72

[Numerical Example 3]
Unit: mm

Surface data surface number rd nd νd
1* -14.405 0.90 1.53113 55.8
2* 6.841 3.64
3* 11.271 0.60 1.53113 55.8
4* 5.966 0.62
5* 18.580 2.56 1.68040 18.1
6* -788.408 (variable)
7(Aperture) ∞ 0.27
8 6.681 3.35 1.49700 81.5
9 -5.366 0.21
10 -4.751 0.50 1.84666 23.8
11 -16.608 0.63
12* -30.485 1.24 1.65010 21.5
13* -5.872 0.20
14 12.707 1.31 1.49700 81.5
15 -8.138 0.20
16 20.837 1.50 1.84666 23.8
17 5.009 (variable)
18 ∞ 0.50 1.52000 61.4
19∞0.43
Image plane ∞

Aspheric surface data No. 1
K = 0.00000e+000 A 4= 1.31486e-003 A 6=-1.66968e-005 A 8= 7.56684e-008

Side 2
K = 0.00000e+000 A 4= 8.91323e-004 A 6= 1.53912e-005 A 8= 3.68484e-006

Page 3
K = 0.00000e+000 A 4=-6.25108e-003 A 6= 2.39548e-004 A 8=-2.10649e-006

Side 4
K = 0.00000e+000 A 4=-5.75647e-003 A 6= 1.09883e-004 A 8= 2.31150e-006

Page 5
K = 0.00000e+000 A 4= 2.14780e-004 A 6=-7.24394e-005 A 8= 3.16704e-006

Side 6
K = 0.00000e+000 A 4=-3.98798e-004 A 6= 1.53441e-005 A 8=-5.30628e-007

Page 12
K = 0.00000e+000 A 4=-4.17197e-003 A 6=-1.27098e-004 A 8=-5.85178e-006

Page 13
K = 0.00000e+000 A 4=-1.56198e-003 A 6=-7.76368e-005 A 8=-4.86089e-006

Various data Zoom ratio 2.00
Wide Angle Mid Telephoto Focal Length 3.26 4.88 6.51
F-number 1.89 2.23 2.56
Half angle of view (°) 60.6 37.8 27.9
Image height 3.20 3.20 3.20
Lens length 33.79 28.90 27.17
BF 0.43 0.43 0.43

d6 10.13 3.82 0.66
d17 5.00 6.43 7.85
d19 0.43 0.43 0.43

Zoom lens data group Starting surface Focal length
1 1 -8.38
2 7 7.36

[Numerical Example 4]
Unit: mm

Surface data surface number rd nd νd
1* -9.117 0.90 1.53113 55.8
2* 8.667 4.22
3* -14.611 0.60 1.53113 55.8
4* 31.944 0.20
5 23.868 1.96 1.92286 18.9
6 -92.355 (variable)
7 5.919 2.96 1.49700 81.5
8 -4.955 0.19
9 -4.352 0.50 1.84666 23.8
10 -13.110 0.45
11* -9.410 0.82 1.67070 19.3
12* -4.717 0.10
13(Aperture) ∞ 0.10
14 10.129 1.02 1.49700 81.5
15 -6.938 0.20
16 23.599 1.50 1.80518 25.4
17 4.432 (variable)
18 ∞ 0.50 1.52000 61.4
19∞0.43
Image plane ∞

Aspheric surface data No. 1
K = 0.00000e+000 A 4= 1.77384e-003 A 6=-2.11603e-005 A 8= 1.45092e-007

Side 2
K = 0.00000e+000 A 4= 9.26642e-004 A 6= 3.36285e-005 A 8= 2.67336e-006

Page 3
K = 0.00000e+000 A 4=-2.85858e-003 A 6= 1.47809e-004 A 8=-3.20067e-006

Side 4
K = 0.00000e+000 A 4=-2.04716e-003 A 6= 1.05933e-004 A 8=-1.70400e-006

Page 11
K = 0.00000e+000 A 4=-7.96855e-003 A 6=-2.92260e-004 A 8=-3.01361e-005

Page 12
K = 0.00000e+000 A 4=-3.88994e-003 A 6=-1.48722e-004 A 8=-2.13884e-005

Various data Zoom ratio 1.90
Wide Angle Mid Telephoto Focal Length 3.37 4.89 6.40
F-number 2.20 2.69 3.18
Half angle of view (°) 60.1 38.6 28.7
Image height 3.20 3.20 3.20
Lens length 30.09 26.19 24.74
BF 0.43 0.43 0.43

d 6 8.45 3.25 0.52
d17 5.00 6.29 7.58
d19 0.43 0.43 0.43

Zoom lens data group Starting surface Focal length
1 1 -8.15
2 7 6.93

[Numerical Example 5]
Unit: mm

Surface data surface number rd nd νd
1* -12.498 0.90 1.53113 55.8
2* 14.108 2.83
3* 13.710 0.60 1.53113 55.8
4* 4.806 1.36
5 -45.924 1.42 1.95906 17.5
6 -20.040 0.59
7* 33.918 1.61 1.66080 20.4
8* 58.011 (variable)
9 (Aperture) ∞ (Variable)
10 7.552 3.16 1.49700 81.5
11 -5.360 0.20
12 -4.853 0.50 1.84666 23.8
13 -14.466 0.89
14* -729.927 1.68 1.63560 23.9
15* -6.306 0.20
16 17.573 1.47 1.49700 81.5
17 -9.041 0.20
18 22.472 1.50 1.84666 23.8
19 4.995 (variable)
20∞0.501.5200061.4
21∞0.43
Image plane ∞

Aspheric surface data No. 1
K = 0.00000e+000 A 4= 1.53057e-003 A 6=-1.88282e-005 A 8= 1.05250e-007

Side 2
K = 0.00000e+000 A 4= 1.24079e-003 A 6= 1.93156e-005 A 8= 1.33929e-006

Page 3
K = 0.00000e+000 A 4=-7.21989e-003 A 6= 3.64781e-004 A 8=-6.11646e-006

Side 4
K = 0.00000e+000 A 4=-7.85188e-003 A 6= 2.62196e-004 A 8=-1.69407e-006

Side 7
K = 0.00000e+000 A 4=-4.26294e-005 A 6=-1.12793e-004 A 8= 6.99218e-006

Side 8
K = 0.00000e+000 A 4=-3.87504e-004 A 6=-6.19232e-005 A 8= 4.17202e-006

Page 14
K = 0.00000e+000 A 4=-2.59949e-003 A 6=-8.49870e-005 A 8= 3.67882e-007

Page 15
K = 0.00000e+000 A 4=-5.04581e-004 A 6=-5.42964e-005 A 8=-5.60613e-007

Various data Zoom ratio 2.00
Wide Angle Mid Telephoto Focal Length 3.31 4.96 6.61
F-number 1.89 2.20 2.62
Half angle of view (°) 58.3 37.8 27.7
Image height 3.20 3.20 3.20
Lens length 36.05 30.60 28.57
BF 0.43 0.43 0.43

d 8 7.98 2.52 0.50
d9 3.04 1.62 0.20
d19 5.00 6.42 7.84
d21 0.43 0.43 0.43

Zoom lens data group Starting surface Focal length
1 1 -8.93
2 9 ∞
3 10 7.67

[Numerical Example 6]
Unit: mm

Surface data surface number rd nd νd
1* -18.296 0.90 1.53113 55.8
2* 6.539 4.45
3* -6.129 0.60 1.53113 55.8
4* -28.399 0.46
5 16.273 0.99 1.95906 17.5
6 48.126 (variable)
7(Aperture) ∞ 0.27
8 5.053 2.72 1.49700 81.5
9 -33.807 0.29
10 -14.139 0.50 1.84666 23.8
11 82.166 0.10
12* 7.424 1.07 1.56650 37.6
13* 15.439 0.75
14* 20.794 1.20 1.56650 37.6
15* -6.238 0.20
16 -41.953 0.81 1.49700 81.5
17 -8.101 0.20
18 -8.879 1.50 1.84666 23.8
19 54.207 (variable)
20∞0.501.5200061.4
21∞0.43
Image plane ∞

Aspheric surface data No. 1
K = 0.00000e+000 A 4= 9.22437e-004 A 6=-1.05966e-005 A 8= 5.81533e-008

Side 2
K = 0.00000e+000 A 4= 3.25549e-004 A 6= 1.60308e-005 A 8= 1.07984e-006

Page 3
K = 0.00000e+000 A 4= 1.16935e-003 A 6= 3.51169e-006 A 8=-4.35443e-007

Side 4
K = 0.00000e+000 A 4= 1.49435e-003 A 6=-2.43474e-005 A 8= 6.53729e-008

Page 12
K = 0.00000e+000 A 4=-2.96481e-003 A 6=-1.64670e-004 A 8=-9.45897e-006

Page 13
K = 0.00000e+000 A 4=-3.69258e-003 A 6=-2.35156e-004 A 8= 2.94270e-006

Page 14
K = 0.00000e+000 A 4=-4.30509e-003 A 6=-2.04671e-004 A 8= 4.50940e-006

Page 15
K = 0.00000e+000 A 4=-3.36943e-004 A 6=-8.67076e-005 A 8=-4.65053e-007

Various data Zoom ratio 2.40
Wide Angle Mid Telephoto Focal Length 3.27 5.56 7.84
F-number 1.89 2.29 2.73
Half angle of view (°) 60.8 33.6 23.5
Image height 3.20 3.20 3.20
Lens length 32.68 28.78 28.63
BF 0.43 0.43 0.43

d 6 9.74 3.30 0.61
d19 5.00 7.54 10.07
d21 0.43 0.43 0.43

Zoom lens data group Starting surface Focal length
1 1 -6.79
2 7 7.53

Figure 13 shows a cross section of an imaging device using the zoom lens 16 of Example 1 together with a dome cover 15. The zoom lens may be one of other examples. The dome cover 15 is made of a plastic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC) and is formed into a dome shape with a thickness of about several millimeters. Also, Figure 14 shows a cross section of an imaging device using the zoom lens 16 of Example 1 together with a flat protective cover 17. The zoom lens may be one of other examples. When making an imaging device that assumes the use of the dome cover 15 or protective cover 17 in this way, it is desirable to design the zoom lens taking into account the influence of the focal length and material of the dome cover 15 or protective cover 17 and to correct various aberrations.

Figure 15 (A) shows an imaging device (surveillance camera) that uses any one of the zoom lenses of Examples 1 to 6 as an imaging optical system. Reference numeral 11 denotes the camera body, and reference numeral 12 denotes a solid-state imaging element such as a CCD sensor or CMOS sensor that is built into the camera body 11 and receives a subject image (optical image) formed by the zoom lens 16. Reference numeral 13 denotes a memory that records image data generated by photoelectric conversion by the solid-state imaging element 12. Reference numeral 14 denotes a network cable for transferring image data to the outside.

Figure 15 (B) shows the surveillance camera in Figure 15 (A) with a dome cover 15 attached and mounted on the ceiling.

The imaging device is not limited to a surveillance camera, but may be other imaging devices such as a video camera or a digital still camera.

The imaging device may also have a circuit that electrically corrects at least one of distortion and chromatic aberration of magnification. By having such a circuit, it is possible to tolerate a certain degree of distortion and other aberrations in the zoom lens, which in turn makes it easier to reduce the number of lenses that make up the zoom lens and make the zoom lens more compact. Furthermore, by electrically correcting chromatic aberration of magnification, it becomes easier to reduce color bleeding in the image data and improve resolution.

The above-described embodiments are merely representative examples, and various modifications and variations are possible when implementing the present invention.

L1: first lens unit L2: second lens unit SP: aperture stop

Claims (8)

A zoom lens comprising a negative first lens group and a positive second lens group, which are arranged in this order from an object side to an image side, and which moves for zooming such that a distance between the first lens group and the second lens group changes,
the zoom lens includes a negative plastic lens;
The first lens group includes two lenses,
the second lens group includes a positive plastic lens,
an aperture stop that moves integrally with the second lens group and is disposed closer to the image side than the first lens group;
The refractive index of the positive plastic lens with respect to the d-line is Nd, the Abbe number of the positive plastic lens with respect to the d-line as a reference is νd, the focal length of the zoom lens at the wide-angle end is fw, the focal length of the first lens group is f1, and the focal length of the second lens group is f2,
Nd≦-0.0065νd+1.8180
1.50≦｜f1/fw｜≦2.62
1.50≦f2/fw≦2.45
A zoom lens characterized by satisfying the following conditional expressions: Let Y be the maximum image height, and TLw be the distance on the optical axis from the lens surface closest to the object of the zoom lens at the wide-angle end to the image plane.
4.0≦TLw/Y≦12.0
2. The zoom lens according to claim 1 , wherein the following condition is satisfied: The focal length of the second lens group is f2,
0.60≦｜f1/f2｜≦1.30
3. The zoom lens according to claim 1, wherein the following condition is satisfied: The sum of the refractive powers of the one or more positive plastic lenses included in the second lens group is Σφp, and the refractive power of the second lens group is φ2,
0<Σφp/φ2≦1.70
4. The zoom lens according to claim 1, wherein the following condition is satisfied: The sum of the refractive powers of all the plastic lenses included in the zoom lens is Σφa, and the refractive power of the second lens group is φ2,
-1.30≦Σφa/φ2≦1.30
5. The zoom lens according to claim 1, which satisfies the following condition: the first lens group includes, in order from the object side to the image side, a negative plastic lens and a positive lens,
6. The zoom lens according to claim 1, wherein the second lens group includes, in order from the object side to the image side, a positive glass lens, a negative glass lens, a positive plastic lens, and a negative lens. A zoom lens comprising a negative first lens group and a positive second lens group, which are arranged in this order from an object side to an image side, and which moves for zooming such that a distance between the first lens group and the second lens group changes,
the first lens group includes, in order from the object side to the image side, a negative plastic lens and a positive lens,
the second lens group includes, in order from the object side to the image side, a positive glass lens, a negative glass lens, a positive plastic lens, and a negative lens,
The refractive index of the positive plastic lens with respect to the d-line is Nd, the Abbe number of the positive plastic lens with respect to the d-line as a reference is νd, the focal length of the zoom lens at the wide-angle end is fw, the focal length of the first lens group is f1, and the focal length of the second lens group is f2,
Nd≦-0.0065νd+1.8180
1.50≦｜f1/fw｜≦2.62
1.50≦f2/fw≦2.45
A zoom lens characterized by satisfying the following conditional expressions: A zoom lens according to any one of claims 1 to 7;
an image sensor that receives light from the zoom lens;
An imaging device comprising: