JP2006194975A - Zoom lens and imaging apparatus using the same - Google Patents

Zoom lens and imaging apparatus using the same Download PDF

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Publication number
JP2006194975A
JP2006194975A JP2005003992A JP2005003992A JP2006194975A JP 2006194975 A JP2006194975 A JP 2006194975A JP 2005003992 A JP2005003992 A JP 2005003992A JP 2005003992 A JP2005003992 A JP 2005003992A JP 2006194975 A JP2006194975 A JP 2006194975A
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lens
lens group
lt
positive
surface
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JP2005003992A
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JP2006194975A5 (en
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Kouyuki Sabe
校之 左部
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Olympus Corp
オリンパス株式会社
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Priority claimed from US11/322,564 external-priority patent/US7277233B2/en
Publication of JP2006194975A publication Critical patent/JP2006194975A/en
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Abstract

PROBLEM TO BE SOLVED: To secure a balance with optical performance while reducing the thickness at the time of collapsing, high imaging performance, a small number of components, thin on-axis thickness of each lens group, and at the time of retracting a lens barrel A zoom lens that can be made compact in size.
A first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. The zoom lens performs zooming from the telephoto end to the telephoto end. The first lens group G1 is composed of two negative lenses and one positive lens in order from the object side, and the second lens group G2 It has two positive lenses and one negative lens, and the third lens group is composed of one positive lens, and conditional expression (1) of the sum of the thicknesses on the optical axis of each lens group Satisfied.
[Selection] Figure 1

Description

  The present invention relates to a zoom lens and an image pickup apparatus using the same, and particularly suitable for electronic image pickup apparatuses such as a digital camera and a video camera that are thinned in the depth direction when retracted by devising an optical system part such as a zoom lens. The present invention relates to a zoom lens and its imaging device.

  In recent years, digital cameras have attracted attention as next-generation cameras that can replace silver salt 35 mm film cameras. Furthermore, it has come to have a number of categories in a wide range from a high-function type for business use to a portable popular type.

  In the present invention to be described later, focusing on the category of portable popular types, it is aimed to provide a technology for realizing a video camera and a digital camera with a small depth while ensuring high image quality. The biggest bottleneck in reducing the depth direction of the camera is the thickness from the most object-side surface to the imaging surface of the optical system, particularly the zoom lens system. Recently, it has become a mainstream to employ a so-called collapsible lens barrel that projects an optical system from the camera body during shooting and stores the optical system in the camera body when carried.

  In order to achieve a reduction in thickness and size, the image sensor can be made smaller. However, in order to obtain the same number of pixels, it is necessary to reduce the pixel pitch, and the lack of sensitivity must be covered by the optical system. The same is true for diffraction. Therefore, an optical system with a bright F value is required.

  Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5 disclose examples of relatively compact zoom lenses having a bright F value, a large zoom ratio of about 3 times, and a wide angle of view. There is something that was done.

However, since these zoom lenses are thick on the optical axis of each group constituting the zoom lens, even if the zoom lens is retracted, the dimension in the thickness direction of the lens barrel is not sufficiently thin, and the camera cannot be sufficiently downsized. There was a problem.
JP 2002-277740 A JP 2003-140041 A Japanese Patent Laid-Open No. 2004-4765 JP 2004-61675 A US Pat. No. 6,710,934

  The present invention has been made in view of such a situation in the prior art, and an object of the present invention is to provide a zoom lens that ensures a balance with optical performance while reducing the thickness when retracted.

  Furthermore, the zoom lens has a high F value of about 2.8, a zoom ratio of about 3 times, a wide angle of view of about 60 ° at the wide-angle end, and a high imaging performance. Accordingly, it is an object of the present invention to provide a zoom lens that can reduce the size when the lens barrel is retracted, and the axial thickness of each lens group constituting the optical system is small.

The zoom lens of the present invention that achieves the above object includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. In a zoom lens that performs zooming from the wide-angle end to the telephoto end by changing the interval of each group,
The first lens group is composed of two negative lenses and one positive lens in order from the object side.
The second lens group has two positive lenses and one negative lens,
The third lens group is composed of one positive lens,
The following conditional expression is satisfied.

(1) (Σd 1 + Σd 2 + Σd 3) / f t <0.64
Where Σd 1 is the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the first lens group,
Σd 2 : thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the second lens group,
Σd 3 : Thickness on the optical axis from the most object side lens surface to the most image side lens surface of the third lens group,
f t : focal length of the entire zoom lens system at the telephoto end,
It is.

  Below, the reason and effect | action which take the said structure in this invention are demonstrated.

  As a zoom lens suitable for an electronic imaging device, a zoom lens having a three-group configuration including a negative first lens group, a positive second lens group, and a positive third lens group is known. The present invention also employs such a three-group configuration. With such a configuration, telecentricity is improved, and light can be efficiently incident on an image pickup device such as a CCD. Further, since the back focus can be long, a space for arranging members such as an optical low-pass filter and an infrared cut filter can be secured.

  The first lens group has two negative lens elements and one positive lens in order from the object side. Since the aberration generated in the first lens group can be suppressed with the minimum configuration, there is an advantage that the total length and the retractable length do not need to be increased more than necessary.

  The second lens group has two positive lenses and one negative lens. With such a configuration, it is possible to correct spherical aberration, coma aberration, and astigmatism occurring in the second lens group.

  The third lens group has a configuration of one positive lens. Even with the configuration of only one sheet, the operation of arranging the exit pupil at an appropriate distance and the practical level of aberration correction are possible, and this is a necessary and sufficient configuration.

  At this time, it is preferable to satisfy the following conditional expression.

(1) (Σd 1 + Σd 2 + Σd 3) / f t <0.64
Where Σd 1 is the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the first lens group,
Σd 2 : thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the second lens group,
Σd 3 : Thickness on the optical axis from the most object side lens surface to the most image side lens surface of the third lens group,
f t : focal length of the entire zoom lens system at the telephoto end,
It is.

  If the upper limit of 0.64 in conditional expression (1) is exceeded, the thickness on the optical axis of each lens group constituting the zoom lens becomes too thick, and the camera can be sufficiently miniaturized when the lens barrel is retracted. Can not be.

In addition, a lower limit value is provided for this conditional expression (1),
0.30 <(Σd 1 + Σd 2 + Σd 3) / f t <0.64
It is good.

  If this lower limit of 0.30 is exceeded, the on-axis thickness and rim thickness of each lens constituting the zoom lens become too small, making processing difficult and increasing costs, or making processing impossible.

  Further, the following is better.

(1) '0.42 <(Σd 1 + Σd 2 + Σd 3) / f t <0.60
Furthermore, it is even better if the following is satisfied.

(1) "0.53 <(Σd 1 + Σd 2 + Σd 3) / f t <0.56
If the zoom lens is miniaturized by satisfying conditional expression (1), the power of each lens constituting the optical system becomes strong, so that it becomes difficult to correct aberrations and satisfy high optical performance, and manufacture of lens components. There is also a concern that the optical performance is likely to be deteriorated because of being easily affected by errors and assembly errors. In the following examples of the present invention, high optical performance has been successfully maintained by applying various devices to the optical system as described below.

  In zooming from the wide-angle end to the telephoto end, it is preferable that the first lens unit moves along a locus convex toward the image side, and the second lens unit moves only toward the object side. Thereby, the total length can be made compact while keeping the exit pupil distance appropriately.

  It is more preferable to move the third lens group by an amount different from that of the second lens group because the telecentricity can be easily adjusted.

  Further, the third lens group may be fixed. In this case, the moving mechanism of the lens group can be simplified.

  Moreover, it is preferable that the ratio of the refractive powers of the first lens group and the second lens group satisfy the following conditional expression.

(2) −1.6 <f 1 / f 2 <−1.1
Where f 1 is the focal length of the first lens group,
f 2 : focal length of the second lens group,
It is.

  If the power of the second lens unit exceeds the upper limit of -1.1 in conditional expression (2), it will be difficult to ensure telecentricity, and shading will likely occur at the corners of the shooting screen. Become. When the power of the second lens group becomes weaker beyond the lower limit of −1.6, the zooming action of the second lens group is reduced, the lens movement amount is increased, and the entire lens system is enlarged.

  The following is even better.

(2) ′ −1.5 <f 1 / f 2 <−1.2
Furthermore, it is even better if the following is satisfied.

(2) "-1.4 <f 1 / f 2 <-1.3
It is preferable to satisfy the following conditional expression for the focal length of the negative lens and the positive lens in the first lens group.

(3) 0.25 <| f 11 / f 12 | <0.60
Where f 11 is the focal length of the negative lens of the first lens group,
f 12 : focal length of the positive lens of the first lens group,
It is.

  If the upper limit of 0.60 to conditional expression (3) is exceeded, the power of the negative lens will be too weak, making it difficult to bring the front principal point of the first lens group to the image side, and the entrance pupil will tend to be deep. The ball diameter is easy to increase. If the lower limit of 0.25 is exceeded, the power of the negative lens becomes too strong, making it difficult to correct off-axis astigmatism, distortion, and lateral chromatic aberration.

  The following is even better.

(3) ′ 0.35 <| f 11 / f 12 | <0.56
Furthermore, it is even better if the following is satisfied.

(3) "0.45 <| f 11 / f 12 | <0.52
In addition, the negative lens of the first lens group may have a shape with a concave surface facing the image surface side, and an aspheric surface may be disposed on the concave surface on the image surface side. If this surface is an aspherical surface, it is effective for correcting off-axis astigmatism and distortion.

  As for the shape of the positive lens in the first lens group, it is preferable that the following conditional expression is satisfied.

(4) −0.6 <SF 12 <−0.1
Provided that SF 12 = (R 11 −R 12 ) / (R 11 + R 12 )
R 11 : Paraxial radius of curvature of the object side surface of the positive lens in the first lens group,
R 12 : Paraxial radius of curvature of the image side surface of the positive lens in the first lens group,
It is.

  If the lower limit of -0.6 of conditional expression (4) is exceeded, the manufacturing performance of the lens surface will have a greater effect on the imaging performance. It becomes difficult or the yield gets worse and the cost increases. When the upper limit of −0.1 is exceeded, the power of the positive lens becomes insufficient, and correction of off-axis astigmatism and distortion becomes insufficient.

  The following is even better.

(4) ′ −0.54 <SF 12 <−0.23
Furthermore, it is even better if the following is satisfied.

(4) ”− 0.48 <SF 12 <−0.36
As the lens configuration of the second lens group, it is preferable to employ a configuration including three lenses of a positive lens and a cemented lens of a positive lens and a negative lens in order from the object side. With such a configuration, the front principal point position of the second lens group can be brought out to the object side, so that the amount of movement of the second lens group during zooming can be reduced. Therefore, it contributes to downsizing of the lens barrel when retracted. Further, by arranging a cemented lens, axial chromatic aberration and lateral chromatic aberration can be corrected.

  Furthermore, it is preferable that the following conditional expression is satisfied for the power arrangement of the lenses constituting the second lens group.

(5) −0.90 <f 21 / f 23 <−0.15
Where f 21 is the focal length of the positive lens closest to the object side in the second lens group,
f 23 : focal length of the cemented lens of the second lens group,
It is.

  If the upper limit of -0.15 in conditional expression (5) is exceeded, the principal point of the second lens group is closer to the object side, so that the total length is shortened, but it is difficult to correct astigmatism. If the lower limit of −0.90 is exceeded, the principal point of the second lens group is closer to the image side, and the magnification of the second lens group does not increase, so the amount of movement of the first lens group and the second lens group increases. In other words, the lens barrel is likely to increase in size.

  The following is even better.

(5) ′ −0.66 <f 21 / f 23 <−0.23
Furthermore, it is even better if the following is satisfied.

(5) ”− 0.42 <f 21 / f 23 <−0.32
In the cemented lens in the second lens group, it is preferable that the positive lens to be cemented has a biconvex shape, and the cemented surface has a convex shape on the image plane side. In order to secure the rim, it is advantageous that the positive lens in the cemented lens is a meniscus-shaped positive lens and the cemented surface is convex on the object side. However, field curvature is likely to occur due to manufacturing errors in the thickness of the cemented lens. In terms of ensuring optical performance, it is preferable that the positive lens has a biconvex shape in which the cemented surface is convex toward the image surface side.

  Further, it is preferable that the following conditional expression is satisfied with respect to the radius of curvature of the cemented surface in the second lens group.

(6) 1.0 <f 23 / R cem <6.0
Where f 23 is the focal length of the cemented lens of the second lens group,
R cem : Paraxial curvature radius of the cemented surface in the cemented lens of the second lens group,
It is.

  When the lower limit of 1.0 to conditional expression (6) is exceeded, axial chromatic aberration and lateral chromatic aberration tend to be undercorrected. Exceeding the upper limit of 6.0 is not preferable because the thickness on the optical axis increases in view of securing the edge thickness of the positive lens in the cemented lens.

  The following is even better.

(6) '2.0 <f 23 / R cem <5.1
Furthermore, it is even better if the following is satisfied.

(6) "3.10 <f 23 / R cem <4.30
It is preferable to use a glass material having a refractive index of 1.75 or more to be joined. When such a glass material is used, a desired refractive power can be obtained without increasing the curvature of the lens surface, so that the amount of aberration generated can be minimized.

  Further, it is desirable that the curvature radii of the front and back surfaces are different from each other only in sign and have the same absolute value. This eliminates the trouble of discriminating the front and back during assembly, which improves assembly and eliminates the mistake of mounting the front and back, leading to improved yields and reduced costs.

  The second lens group is a group mainly responsible for zooming. In order to obtain good optical performance over the entire zooming range, it is preferable to reduce various aberrations generated in the second lens group as much as possible. For this purpose, it is desirable to arrange two or more aspheric surfaces in the second lens group.

  In particular, it is preferable that the most object-side positive lens is a double-sided aspheric lens, as shown in the examples below. If the aspheric surfaces are arranged on different lenses, the optical performance is likely to deteriorate when the lenses are decentered due to errors in the lens frame. ing. On the object side surface of the positive lens, the light beam that forms an image on the optical axis of an image pickup device such as a CCD spreads and passes through. The aspherical surface on the image side of the positive lens is effective in correcting coma and astigmatism.

  The positive lens closest to the object side in the second lens group may be an aspheric lens that satisfies the following conditional expression.

(7) −5.0 <SF 21 <−1.0
However, SF 12 = (R 21 −R 22 ) / (R 21 + R 22 )
R 21 : Paraxial radius of curvature of the object side surface of the positive lens closest to the object side in the second lens group,
R 22 : Paraxial curvature radius of the image side surface of the positive lens closest to the object side in the second lens group,
It is.

  If the upper limit of -1.0 of conditional expression (7) is exceeded, correction of coma and astigmatism due to an aspheric surface is likely to be insufficient, and it becomes difficult to ensure good optical performance in the entire zoom range. . If the lower limit of −5.0 is exceeded, the contribution of the aspheric surface to the aberration correction tends to be excessive, and the optical performance tends to be greatly deteriorated when a processing error occurs in the aspheric surface. As a result, the required processing accuracy of the aspherical surface becomes severe, so that the yield is deteriorated and the cost is increased.

  The following is even better.

(7) ′ − 3.7 <SF 21 <−1.2
Furthermore, it is even better if the following is satisfied.

(7) "-2.4 <SF 21 <-1.5
As will be described later in the embodiments of the present invention, it is preferable that the third lens group is composed of only one positive lens. The role of the third lens group in the negative, positive, and positive type zoom lenses of the configuration of the present invention is to appropriately refract off-axis light rays so that the incident angle of light rays on a light receiving surface such as a CCD surface is appropriate. It is to control the angle range so that the light beam is efficiently incident on the light receiving surface. For this purpose, only one positive lens is sufficient. Further, since the third lens group is also a place where the height of the off-axis ray passing therethrough is high, it can also play a role of correcting off-axis astigmatism and distortion, but even with only one lens, it is practical. Correction of the aberration level is possible. Therefore, it is necessary and sufficient to use only one positive lens, and it is preferable to increase the number of lenses to avoid the on-axis thickness of the lens system becoming larger than necessary.

  Further, it is preferable to perform focusing by moving the third lens group. Focusing may be performed with the first lens group, but since the lens weight is lighter when performing with the third lens group, the load on the focusing motor can be reduced. Further, when focusing is performed by moving the third lens group, the overall length does not change during focusing, and the drive motor can be arranged inside the lens frame, which is advantageous for making the lens frame compact.

  The third lens group is a place suitable for correcting off-axis astigmatism and distortion. In order to positively give a role of aberration correction, it is preferable to arrange an aspherical surface on this lens. In that case, it is preferable to satisfy the following conditional expression.

(8) 0.001 <| asp31 / f w | <0.02
Where asp31 is an aspherical deviation amount at the effective diameter of the aspherical surface disposed in the third lens group, and the aspherical deviation amount has the aspherical surface apex as the apex and the radius of curvature is the aspherical paraxial axis. It is the distance in the optical axis direction from the spherical surface to the aspherical surface as the radius of curvature,
f w : focal length of the entire zoom lens system at the wide-angle end,
It is.

  When the upper limit of 0.02 to conditional expression (8) is exceeded, the contribution of the aspherical surface of the third lens group to the astigmatism correction becomes too great, and astigmatism is corrected well when focusing on an object point at infinity. However, when the third lens unit is moved and focused on the closest object point, the fluctuation of astigmatism increases, and the off-axis optical performance tends to deteriorate. If the lower limit of 0.001 is exceeded, off-axis astigmatism and distortion will not be corrected.

  The following is even better.

(8) '0.002 <| asp31 / f w | <0.013
Furthermore, it is even better if the following is satisfied.

(8) "0.003 <| asp31 / f w | <0.005
Moreover, it is preferable that the shape of the positive lens of the third lens group satisfies the following conditional expression.

(9) −8.0 <SF 31 <0.0
However, SF 31 = (R 31 −R 32 ) / (R 31 + R 32 )
R 31 : Paraxial radius of curvature of the object side surface of the positive lens in the third lens group,
R 32 : Paraxial radius of curvature of the image side surface of the positive lens in the third lens group,
It is.

  When the lower limit of −8.0 of conditional expression (9) is exceeded, reflection occurs between the positive lens of the third lens group and an optical low-pass filter or a cover glass such as a CCD disposed on the image side of the third lens group. Light tends to cause ghosts and spot flare, which significantly deteriorates optical performance. When the upper limit of 0.0 is exceeded, it is necessary to increase the axial thickness in order to secure the lens edge thickness.

  The following is even better.

(9) ′ −5.2 <SF 31 <−0.6
Furthermore, it is even better if the following is satisfied.

(9) "-2.4 <SF 31 <-1.2
The position at which the aperture stop is disposed is preferably disposed between the first lens group and the second lens group. In this way, the entrance pupil position can be made shallow, so that the front lens diameter can be reduced, and as a result, the lens thickness on the optical axis can be reduced. Therefore, it contributes to downsizing in the thickness direction. In addition, since the exit pupil position can be set far from the image formation position, the angle of the light beam emitted to the image sensor such as a CCD can be reduced, and the occurrence of shading at the corners of the screen can be prevented. Further, it is preferable that the aperture stop is moved integrally with the second lens group at the time of zooming. Thereby, the mechanism can be simplified. In addition, a dead space at the time of retracting hardly occurs, and the F value difference between the wide-angle end and the telephoto end can be reduced.

  Further, in order from the object side, when the zoom lens is configured as a three-unit zoom lens including a first lens unit having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, the compact size when the lens barrel is retracted. This is advantageous for achieving high performance and ensuring optical performance.

  Furthermore, since the zoom lens of the present invention is advantageous for telecentricity and compactness, a zoom lens and an image sensor that is arranged on the image side and converts an image formed by the zoom lens into an electrical signal are provided. When configured as an imaging device provided, a small imaging device can be obtained.

  In any zoom lens or imaging apparatus of the present invention, it is preferable that the first lens group satisfies the following conditional expressions (10) and (11).

(10) 1.6800 <n d1 <2.3000
(11) 1.7000 <n d2 <2.3000
Where n d1 is the refractive index of the negative lens in the first lens group,
n d2 : refractive index of the positive lens in the first lens group,
It is.

  Furthermore, it is more preferable to satisfy any one of the following conditions (12), (13), (14), and (15).

(12) 30.0 <ν d2 <50.0
(13) 0.0 <n d2 −n d1 <0.5
(14) 16.0 <ν d1 −ν d2 <50.0
(15) 0.10 <Σd 1 / f t <0.50
Where ν d2 is the Abbe number of the positive lens in the first lens group,
ν d1 : Abbe number of the negative lens in the first lens group,
n d1 : refractive index of the negative lens in the first lens group,
n d2 : refractive index of the positive lens in the first lens group,
[Sigma] d 1: axial thickness from a most object side surface of the first lens group to the surface of the most image side, f t: the focal length of the zoom lens system in the telephoto end,
It is.

  Conditions (10) and (11) are preferable conditions for realizing aberration correction in the first lens group and ensuring good optical performance in the entire zoom range.

  The operation of conditional expressions (10) and (11) will be described next.

  In order to reduce the size of the zoom lens in the retracted state, it is necessary to reduce the thickness of the first lens group. For this reason, in the present invention, it is preferable to reduce the number of constituent lenses of the first lens group and to reduce the axial thickness of each lens as much as possible and to reduce the axial distance between the lens groups as much as possible. On the other hand, it becomes difficult to correct various aberrations occurring in the first lens group, particularly to correct axial chromatic aberration and lateral chromatic aberration.

  For this reason, when only the negative lens and the positive lens in the first lens group are configured, it is preferable that these lenses satisfy the conditions (10) and (11) at the same time.

  When the lower limit of 1.6800 of conditional expression (10) and 1.7000 of the lower limit of conditional expression (11) are exceeded, the curvature of the lens surface must be increased for each lens to obtain a desired refractive power. As a result, the generation of aberrations becomes large. In particular, the off-axis coma and astigmatism cannot be completely corrected, and the resolution of the captured image off-axis is insufficient. If the upper limit of 2.3,000 of these conditional expressions is exceeded, the availability and mass productivity of the glass material will deteriorate, and the cost will increase.

  Exceeding the lower limit of 30.0 of conditional expression (12), anomalous dispersion of the glass material tends to increase, and correction of the secondary spectrum of longitudinal chromatic aberration and lateral chromatic aberration becomes difficult, resulting in color blur in the photographed image. It becomes easy. Alternatively, it is necessary to increase the number of lenses constituting the zoom lens for correcting the secondary spectrum of chromatic aberration, which increases the cost and makes it impossible to make the zoom lens compact. If the upper limit of 50.0 in conditional expression (12) is exceeded, the chromatic dispersion of the positive lens becomes too small, and the chromatic aberration that occurs in the negative lens cannot be canceled out, resulting in incomplete chromatic aberration correction.

Since the height of the off-axis light beam passing through the negative lens L 11 in the first lens group passes higher than the light beam height at the positive lens L 12 , the amount of aberration generated in the negative lens L 11 is positive lens L 11. It tends to be larger than the amount of aberration canceled at 12 , and tends to remain. In particular, aberrations of off-axis principal rays such as astigmatism, distortion, and lateral chromatic aberration tend to remain. This becomes more conspicuous as the shooting angle of view becomes wider and becomes a problem. To realize the wide angle of the zoom lens becomes necessary to cancel the off-axis aberration occurring in the negative lens L 11 in the positive lens L 12, it may satisfy the conditional expression for the (13). If the lower limit of 0.0 in conditional expression (13) is exceeded, off-axis astigmatism, distortion, and lateral chromatic aberration that occur in the negative lens L 11 cannot be corrected by the positive lens L 12 , and the periphery of the screen It becomes impossible to obtain a good image up to the portion. If the upper limit of 0.5 is exceeded, combinations of glass materials compatible with conditional expressions (10) and (11) are limited, and glass materials with poor availability and mass productivity must be used. is not.

  Furthermore, it is further preferable that the following conditional expression is satisfied in any one or a plurality of conditional expressions (10), (11), (12), (13).

(10) '1.7000 <n d1 <1.9000
(11) ′ 1.8000 <n d2 <2.0000
(12) '30.5 <ν d2 <46.0
(13) ′ 0.05 <n d2 −n d1 <0.45
Furthermore, it is more preferable that the following is satisfied.

(10) "1.7200 <n d1 <1.8500
(11) "1.8500 <n d2 <1.9500
(12) "31.0 <ν d2 <42.0
(13) "0.1 <n d2 -n d1 <0.3
In zooming from the wide-angle end to the telephoto end, it is preferable that the first lens unit moves along a locus convex toward the image side, and the second lens unit moves only toward the object side. Thereby, the total length can be made compact while keeping the exit pupil distance appropriately.

  Regarding the glass material, the following conditional expression should be satisfied.

(14) 16.0 <ν d1 −ν d2 <50.0
Where ν d1 is the Abbe number of the negative lens in the first lens group,
It is.

  When the lower limit of 16.0 in conditional expression (14) is exceeded, chromatic aberration cancellation in the first lens group tends to be insufficient. If the upper limit of 50.0 is exceeded, combinations of glass materials compatible with conditional expressions (10) and (11) are limited, and glass materials with poor availability and mass productivity must be used. is not.

  The following is even better.

(14) ′ 16.8 <ν d1 −ν d2 <41.0
Furthermore, it is even better if the following is satisfied.

(14) ”17.6 <ν d1 −ν d2 <32.0
In order to employ the zoom lens of the present invention, it is preferable to satisfy the following conditional expression.

(15) 0.10 <Σd 1 / f t <0.50
However, [Sigma] d 1: axial thickness from a most object side surface of the first lens group to the surface of the most image side, f t: the focal length of the zoom lens system in the telephoto end,
It is.

  Exceeding the lower limit of 0.10 of conditional expression (15), the edge thickness and the axial thickness of the lenses constituting the first lens group cannot be sufficiently secured, making the processing difficult, and thus increasing the cost and thus making it inexpensive. A zoom lens cannot be provided. Or processing becomes impossible. If the upper limit of 0.50 is exceeded, good aberration correction can be performed without employing the configuration of the present invention.

  The following is even better.

(15) '0.16 <Σd 1 / f t <0.38
Furthermore, it is even better if the following is satisfied.

(15) "0.22 <Σd 1 / f t <0.25
In addition, you may comprise combining the component requirements mentioned above variously.

  Further, only the lower limit value or only the upper limit value of the lower-level concept conditional expression may be limited to the higher-level concept conditional expression.

  According to the present invention as described above, it is possible to obtain a zoom lens that ensures a balance with optical performance while reducing the thickness when retracted.

  In addition, the zoom lens has a high F value of about 2.8, a zoom ratio of about 3 times, a wide angle of about 60 ° at the wide angle end, and a high imaging performance. Therefore, it is possible to obtain a zoom lens that can reduce the size when the lens barrel is retracted, and the axial thickness of each lens group constituting the optical system is small.

  Examples 1 to 4 of the zoom lens according to the present invention will be described below. FIG. 1 shows lens cross sections of the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity according to the first embodiment. In addition, since the structure of Examples 2-4 is the same as that of Example 1, the same lens sectional drawing is abbreviate | omitted. In FIG. 1, the first lens group is G1, the aperture stop is S, the second lens group is G2, the third lens group is G3, and a low-pass filter is provided with a wavelength range limiting coat that limits infrared light and ultraviolet light. The parallel flat plate is indicated by F, the parallel flat plate of the cover glass of the electronic image sensor is indicated by C, and the image plane is indicated by I. In addition, you may give the multilayer film for a wavelength range restriction | limiting to the surface of the cover glass C. FIG. Further, the cover glass C may have a low-pass filter action.

  As shown in FIG. 1, the zoom lenses of Examples 1 to 4 include, in order from the object side, a first lens group G1 having a negative refractive power, an aperture stop S, and a second lens group G2 having a positive refractive power, The third lens group G3 has a positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group G1 moves along a locus that is convex toward the image plane side. Then, it is located on the object side with respect to the position of the intermediate state and slightly on the image side with respect to the position of the wide-angle end, the aperture stop S and the second lens group G2 move monotonously to the object side, and the third lens group G3 is It moves along a locus that is convex toward the object side, and is slightly closer to the image side at the telephoto end than at the wide-angle end.

  In order from the object side, the first lens group G1 includes a negative meniscus lens having a convex surface facing the object side, and a positive meniscus lens having a convex surface facing the object side. The second lens group G2 includes a biconvex positive lens and The third lens group G3 is composed of one biconvex positive lens and a biconvex positive lens and a biconcave negative lens.

  The aspherical surfaces are the image side surface of the negative meniscus lens of the first lens group G1, the surfaces on both sides of the biconvex positive lens of the single lens of the second lens group G2, and the biconvex positive lens of the single lens of the third lens group G3. Are used on four surfaces on the image side.

  In Examples 1 to 4, focusing is performed by moving the third lens group G3 in the optical axis direction.

  In all the first to fourth embodiments, focusing may be performed by moving only the first lens group G1, only the second lens group G2, or the entire zoom lens system.

Hereinafter, numerical data of each embodiment described above, but the symbols are outside the above, f is the focal length, F NO is the F-number, 2 [omega is field angle, WE denotes a wide angle end, ST intermediate state, TE is The telephoto end, r 1 , r 2 ... Is the radius of curvature of each lens surface, d 1 , d 2 ... Are the distances between the lens surfaces, n d1 , n d2 are the refractive index of the d-line of each lens, ν d1 , ν d2 ... is the Abbe number of each lens. The aspherical shape is represented by the following formula, where x is an optical axis with the light traveling direction being positive, and y is a direction orthogonal to the optical axis.

x = (y 2 / r) / [1+ {1- (K + 1) (y / r) 2 } 1/2 ]
+ A 4 y 4 + A 6 y 6 + A 8 y 8 + A 10 y 10
Here, r is a paraxial radius of curvature, K is a conical coefficient, and A 4 , A 6 , A 8 , and A 10 are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.


Example 1
r 1 = 486.879 d 1 = 1.20 n d1 = 1.74330 ν d1 = 49.33
r 2 = 6.572 (aspherical surface) d 2 = 1.84
r 3 = 11.096 d 3 = 2.64 n d2 = 1.90366 ν d2 = 31.31
r 4 = 29.983 d 4 = (variable)
r 5 = ∞ (aperture) d 5 = 0.20
r 6 = 9.565 (aspherical surface) d 6 = 2.40 n d3 = 1.58313 ν d3 = 59.46
r 7 = -32.947 (aspherical surface) d 7 = 0.10
r 8 = 10.752 d 8 = 2.31 n d4 = 1.77250 ν d4 = 49.60
r 9 = -10.752 d 9 = 0.70 n d5 = 1.64769 ν d5 = 33.79
r 10 = 5.145 d 10 = (variable)
r 11 = 15.888 d 11 = 1.74 n d6 = 1.58313 ν d6 = 59.46
r 12 = -92.317 (aspherical surface) d 12 = (variable)
r 13 = ∞ d 13 = 0.86 n d7 = 1.54771 ν d7 = 62.84
r 14 = ∞ d 14 = 0.50
r 15 = ∞ d 15 = 0.50 n d8 = 1.51633 ν d8 = 64.14
r 16 = ∞ d 16 = 0.43
r 17 = ∞ (image plane)
Aspheric coefficient 2nd surface K = -0.639
A 4 = -2.98759 × 10 -5
A 6 = 3.27427 × 10 -6
A 8 = -1.20087 × 10 -7
A 10 = 1.35884 × 10 -9
6th surface K = 0.000
A 4 = -2.50030 × 10 -4
A 6 = -5.47642 × 10 -6
A 8 = -2.75670 × 10 -7
A 10 = 7.44525 × 10 -10
Surface 7 K = 0.000
A 4 = 1.00025 × 10 -5
A 6 = -4.46990 × 10 -6
A 8 = -2.98489 × 10 -7
A 10 = 5.19077 × 10 -9
Surface 12 K = 0.000
A 4 = 9.29735 × 10 -5
A 6 = -3.43799 × 10 -6
A 8 = 5.61229 × 10 -8
A 10 = 0
Zoom data (∞)
WE ST TE
f (mm) 8.160 12.898 23.519
F NO 2.78 3.37 5.00
2ω (°) 60.6 39.1 21.5
d 4 18.95 8.79 2.56
d 10 8.51 12.48 24.73
d 12 3.93 4.69 3.27.


Example 2
r 1 = 294.078 d 1 = 1.20 n d1 = 1.74330 ν d1 = 49.33
r 2 = 6.502 (aspherical surface) d 2 = 1.80
r 3 = 10.826 d 3 = 2.57 n d2 = 1.90366 ν d2 = 31.31
r 4 = 27.909 d 4 = (variable)
r 5 = ∞ (aperture) d 5 = 0.19
r 6 = 9.136 (aspherical surface) d 6 = 2.18 n d3 = 1.58313 ν d3 = 59.46
r 7 = -39.275 (aspherical surface) d 7 = 0.10
r 8 = 10.822 d 8 = 2.50 n d4 = 1.77250 ν d4 = 49.60
r 9 = -9.099 d 9 = 0.70 n d5 = 1.64769 ν d5 = 33.79
r 10 = 5.101 d 10 = (variable)
r 11 = 15.878 d 11 = 1.67 n d6 = 1.58313 ν d6 = 59.46
r 12 = -85.491 (aspherical surface) d 12 = (variable)
r 13 = ∞ d 13 = 0.86 n d7 = 1.54771 ν d7 = 62.84
r 14 = ∞ d 14 = 0.50
r 15 = ∞ d 15 = 0.50 n d8 = 1.51633 ν d8 = 64.14
r 16 = ∞ d 16 = 0.42
r 17 = ∞ (image plane)
Aspheric coefficient 2nd surface K = -0.596
A 4 = -2.94826 × 10 -5
A 6 = 2.52126 × 10 -6
A 8 = -9.55661 × 10 -8
A 10 = 1.01269 × 10 -9
6th page K = -5.804
A 4 = 7.57126 × 10 -4
A 6 = -2.09226 × 10 -5
A 8 = 6.30687 × 10 -7
A 10 = -1.52351 × 10 -9
Surface 7 K = 0.000
A 4 = 1.12664 × 10 -4
A 6 = 5.88091 × 10 -6
A 8 = -2.73515 × 10 -7
A 10 = 2.10480 × 10 -8
Surface 12 K = 0.000
A 4 = 8.66591 × 10 -5
A 6 = -2.64058 × 10 -6
A 8 = 4.05681 × 10 -8
A 10 = 0
Zoom data (∞)
WE ST TE
f (mm) 8.160 12.848 23.520
F NO 2.79 3.36 4.99
2ω (°) 60.6 39.2 21.5
d 4 18.23 8.47 2.18
d 10 8.33 12.15 23.83
d 12 3.64 4.36 3.26.


Example 3
r 1 = 486.879 d 1 = 1.20 n d1 = 1.76802 ν d1 = 49.24
r 2 = 6.645 (aspherical surface) d 2 = 1.84
r 3 = 11.096 d 3 = 2.64 n d2 = 1.90366 ν d2 = 31.31
r 4 = 29.983 d 4 = (variable)
r 5 = ∞ (aperture) d 5 = 0.20
r 6 = 9.545 (aspherical surface) d 6 = 2.40 n d3 = 1.58313 ν d3 = 59.46
r 7 = -27.157 (aspherical surface) d 7 = 0.10
r 8 = 11.231 d 8 = 2.31 n d4 = 1.77250 ν d4 = 49.60
r 9 = -10.413 d 9 = 0.70 n d5 = 1.64769 ν d5 = 33.79
r 10 = 5.145 d 10 = (variable)
r 11 = 18.541 d 11 = 1.74 n d6 = 1.58313 ν d6 = 59.46
r 12 = -48.356 (aspherical surface) d 12 = (variable)
r 13 = ∞ d 13 = 0.86 n d7 = 1.54771 ν d7 = 62.84
r 14 = ∞ d 14 = 0.50
r 15 = ∞ d 15 = 0.50 n d8 = 1.51633 ν d8 = 64.14
r 16 = ∞ d 16 = 0.43
r 17 = ∞ (image plane)
Aspheric coefficient 2nd surface K = -0.640
A 4 = -1.93128 × 10 -5
A 6 = 3.09412 × 10 -6
A 8 = -1.14942 × 10 -7
A 10 = 1.33472 × 10 -9
6th surface K = 0.000
A 4 = -3.03396 × 10 -4
A 6 = -8.09623 × 10 -6
A 8 = -2.93773 × 10 -7
A 10 = -5.59229 × 10 -9
Surface 7 K = 0.000
A 4 = -2.34522 × 10 -5
A 6 = -7.40484 × 10 -6
A 8 = -3.02179 × 10 -7
A 10 = -2.62318 × 10 -10
Surface 12 K = 0.000
A 4 = 9.38135 × 10 -5
A 6 = -2.59439 × 10 -6
A 8 = 4.06888 × 10 -8
A 10 = 0
Zoom data (∞)
WE ST TE
f (mm) 8.160 12.898 23.517
F NO 2.80 3.40 4.99
2ω (°) 60.6 38.9 21.5
d 4 18.86 9.05 2.59
d 10 9.32 13.42 25.08
d 12 3.39 4.08 3.32.


Example 4
r 1 = 318.320 d 1 = 1.20 n d1 = 1.76802 ν d1 = 49.24
r 2 = 6.577 (aspherical surface) d 2 = 1.82
r 3 = 11.349 d 3 = 2.42 n d2 = 2.08200 ν d2 = 30.40
r 4 = 25.614 d 4 = (variable)
r 5 = ∞ (aperture) d 5 = 0.20
r 6 = 9.567 (aspherical surface) d 6 = 2.40 n d3 = 1.58313 ν d3 = 59.46
r 7 = -24.132 (aspherical surface) d 7 = 0.10
r 8 = 12.907 d 8 = 2.31 n d4 = 1.77250 ν d4 = 49.60
r 9 = -8.977 d 9 = 0.70 n d5 = 1.64769 ν d5 = 33.79
r 10 = 5.412 d 10 = (variable)
r 11 = 15.888 d 11 = 1.74 n d6 = 1.58313 ν d6 = 59.46
r 12 = -94.482 (aspherical surface) d 12 = (variable)
r 13 = ∞ d 13 = 0.86 n d7 = 1.54771 ν d7 = 62.84
r 14 = ∞ d 14 = 0.50
r 15 = ∞ d 15 = 0.50 n d8 = 1.51633 ν d8 = 64.14
r 16 = ∞ d 16 = 0.43
r 17 = ∞ (image plane)
Aspheric coefficient 2nd surface K = -0.629
A 4 = -3.38899 × 10 -5
A 6 = 3.12452 × 10 -6
A 8 = -1.21401 × 10 -7
A 10 = 1.36173 × 10 -9
6th surface K = 0.000
A 4 = -3.78307 × 10 -4
A 6 = -8.54823 × 10 -6
A 8 = -3.26150 × 10 -7
A 10 = -1.05875 × 10 -8
Surface 7 K = 0.000
A 4 = -5.94059 × 10 -5
A 6 = -8.00131 × 10 -6
A 8 = -2.99719 × 10 -7
A 10 = -4.82349 × 10 -9
Surface 12 K = 0.000
A 4 = 8.69257 × 10 -5
A 6 = -2.84130 × 10 -6
A 8 = 4.77586 × 10 -8
A 10 = 0
Zoom data (∞)
WE ST TE
f (mm) 8.160 12.899 23.519
F NO 2.80 3.39 5.04
2ω (°) 60.6 39.1 21.5
d 4 18.94 8.85 2.66
d 10 8.40 12.43 24.75
d 12 4.07 4.79 3.32.


Aberration diagrams at the time of focusing on an object point at infinity in Examples 1 to 4 are shown in FIGS. In these aberration diagrams, (a) is a wide-angle end, (b) is an intermediate state, and (c) is spherical aberration, astigmatism, distortion, and lateral chromatic aberration at a telephoto end. In each figure, “FIY” indicates the maximum image height.

  Next, the angle of view and the values of conditional expressions (1) to (9) in each of the above embodiments are shown.

Conditional Example Example 1 Example 2 Example 3 Example 4
(1) 0.550 0.540 0.550 0.540
(2) -1.353 -1.383 -1.312 -1.356
(3) -0.491 -0.491 -0.479 -0.506
(4) -0.460 -0.441 -0.460 -0.386
(5) -0.355 -0.336 -0.350 -0.410
(6) 3.404 4.231 3.514 3.279
(7) -1.818 -1.606 -2.084 -2.314
(8) 0.00344 0.00377 0.00447 0.00376
(9) -1.416 -1.456 -2.244 -1.404
(10) 1.74330 1.74330 1.76802 1.76802
(11) 1.90366 1.90366 1.90366 2.08200
(12) 31.310 31.310 31.310 30.400
(13) 0.160 0.160 0.136 0.314
(14) 18.020 18.020 17.930 18.840
(15) 0.242 0.237 0.242 0.231
.

  6 to 8 are conceptual diagrams of the configuration of the digital camera according to the present invention in which the zoom lens as described above is incorporated in the photographing optical system 41. FIG. 6 is a front perspective view showing the external appearance of the digital camera 40, FIG. 7 is a rear front view thereof, and FIG. 8 is a schematic cross-sectional view showing the configuration of the digital camera 40. However, FIGS. 6 and 8 show a state in which the photographing optical system 41 is not retracted. In this example, the digital camera 40 includes a photographing optical system 41 having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter button 45, a flash 46, a liquid crystal display monitor 47, a focal length change button 61, When the photographing optical system 41 is retracted, including the setting change switch 62, the photographing optical system 41, the finder optical system 43, and the flash 46 are covered with the cover 60 by sliding the cover 60. When the cover 60 is opened and the camera 40 is set to the photographing state, the photographing optical system 41 enters the non-collapsed state shown in FIG. Photographing is performed through the optical system 41, for example, the zoom lens of the first embodiment. An object image formed by the photographic optical system 41 is formed on the imaging surface of the CCD 49 through a low-pass filter F and a cover glass C that are provided with a wavelength band limiting coat. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the processing means 51. Further, the processing means 51 is connected to a recording means 52 so that a photographed electronic image can be recorded. The recording means 52 may be provided separately from the processing means 51, or may be configured to perform recording / writing electronically using a floppy disk, memory card, MO, or the like. Further, it may be configured as a silver salt camera in which a silver salt film is arranged in place of the CCD 49.

  Further, a finder objective optical system 53 is disposed on the finder optical path 44. The finder objective optical system 53 includes a plurality of lens groups (three groups in the figure) and two prisms, and includes a zoom optical system whose focal length changes in conjunction with the zoom lens of the photographing optical system 41. The object image formed by the finder objective optical system 53 is formed on the field frame 57 of the erecting prism 55 that is an image erecting member. Behind the erecting prism 55, an eyepiece optical system 59 for guiding the erect image to the observer eyeball E is disposed. A cover member 50 is disposed on the exit side of the eyepiece optical system 59.

  The digital camera 40 configured in this manner has the imaging optical system 41 that is extremely thin when retracted according to the present invention, and has a high zoom ratio and extremely stable imaging performance in the entire zoom range. Miniaturization and wide angle can be realized.

FIG. 2 is a lens cross-sectional view at the wide-angle end (a), the intermediate state (b), and the telephoto end (c) when focusing on an object point at infinity according to the first exemplary embodiment of the zoom lens of the present invention. FIG. 6 is an aberration diagram for Example 1 upon focusing on an object point at infinity. FIG. 6 is an aberration diagram for Example 2 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 3 upon focusing on an object point at infinity. FIG. 10 is an aberration diagram for Example 4 upon focusing on an object point at infinity. It is a front perspective view which shows the external appearance of the digital camera by this invention. FIG. 7 is a rear perspective view of the digital camera of FIG. 6. It is sectional drawing of the digital camera of FIG.

Explanation of symbols

G1 ... 1st lens group G2 ... 2nd lens group G3 ... 3rd lens group S ... Aperture stop F ... Low pass filter C ... Cover glass I ... Image plane E ... Observer eyeball 40 ... Digital camera 41 ... Shooting optical system 42 ... Optical path for photographing 43 ... finder optical system 44 ... optical path for finder 45 ... shutter button 46 ... flash 47 ... liquid crystal display monitor 49 ... CCD
DESCRIPTION OF SYMBOLS 50 ... Cover member 51 ... Processing means 52 ... Recording means 53 ... Viewfinder objective optical system 55 ... Erect prism 57 ... Field frame 59 ... Eyepiece optical system 60 ... Cover 61 ... Focal length change button 62 ... Setting change switch

Claims (12)

  1. In order from the object side to the image side, there are a first lens unit having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. In zoom lenses that perform zooming from the end to the telephoto end,
    The first lens group is composed of two negative lenses and one positive lens in order from the object side.
    The second lens group has two positive lenses and one negative lens,
    The third lens group is composed of one positive lens,
    A zoom lens satisfying the following conditional expression:
    (1) (Σd 1 + Σd 2 + Σd 3) / f t <0.64
    Where Σd 1 is the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the first lens group,
    Σd 2 : thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the second lens group,
    Σd 3 : Thickness on the optical axis from the most object side lens surface to the most image side lens surface of the third lens group,
    f t : focal length of the entire zoom lens system at the telephoto end,
    It is.
  2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
    (2) −1.6 <f 1 / f 2 <−1.1
    Where f 1 is the focal length of the first lens group,
    f 2 : focal length of the second lens group,
    It is.
  3. The zoom lens according to claim 1, wherein the first lens group satisfies the following conditional expression.
    (3) 0.25 <| f 11 / f 12 | <0.60
    Where f 11 is the focal length of the negative lens of the first lens group,
    f 12 : focal length of the positive lens of the first lens group,
    It is.
  4. The zoom lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
    (4) −0.6 <SF 12 <−0.1
    Provided that SF 12 = (R 11 −R 12 ) / (R 11 + R 12 )
    R 11 : Paraxial radius of curvature of the object side surface of the positive lens in the first lens group,
    R 12 : Paraxial radius of curvature of the image side surface of the positive lens in the first lens group,
    It is.
  5. 5. The zoom lens according to claim 1, wherein the second lens group includes a positive lens and a cemented lens of a positive lens and a negative lens in order from the object side.
  6. The zoom lens according to claim 5, wherein the second lens group satisfies the following conditional expression.
    (5) −0.90 <f 21 / f 23 <−0.15
    Where f 21 is the focal length of the positive lens closest to the object side in the second lens group,
    f 23 : focal length of the cemented lens of the second lens group,
    It is.
  7. The zoom lens according to claim 5 or 6, wherein the following conditional expression is satisfied.
    (6) 1.0 <f 23 / R cem <6.0
    Where f 23 is the focal length of the cemented lens of the second lens group,
    R cem : Paraxial curvature radius of the cemented surface in the cemented lens of the second lens group,
    It is.
  8. The zoom lens according to any one of claims 5 to 7, wherein a positive lens closest to the object side in the second lens group is an aspherical lens that satisfies the following conditional expression.
    (7) −5.0 <SF 21 <−1.0
    However, SF 12 = (R 21 −R 22 ) / (R 21 + R 22 )
    R 21 : Paraxial radius of curvature of the object side surface of the positive lens closest to the object side in the second lens group,
    R 22 : Paraxial curvature radius of the image side surface of the positive lens closest to the object side in the second lens group,
    It is.
  9. 9. The zoom lens according to claim 1, wherein the third lens group has an aspherical surface that satisfies the following conditional expression. 10.
    (8) 0.001 <| asp31 / f w | <0.02
    Where asp31 is an aspherical deviation amount at the effective diameter of the aspherical surface disposed in the third lens group, and the aspherical deviation amount has the aspherical surface apex as the apex and the radius of curvature is the aspherical paraxial axis. It is the distance in the optical axis direction from the spherical surface to the aspherical surface as the radius of curvature,
    f w : focal length of the entire zoom lens system at the wide-angle end,
    It is.
  10. The zoom lens according to any one of claims 1 to 9, wherein the positive lens of the third lens group satisfies the following condition.
    (9) −8.0 <SF 31 <0.0
    However, SF 31 = (R 31 −R 32 ) / (R 31 + R 32 )
    R 31 : Paraxial radius of curvature of the object side surface of the positive lens in the third lens group,
    R 32 : Paraxial radius of curvature of the image side surface of the positive lens in the third lens group,
    It is.
  11. The zoom lens is configured as a three-unit zoom lens including, in order from the object side, the first lens unit having the negative refractive power, the second lens group having the positive refractive power, and the third lens group having the positive refractive power. The zoom lens according to any one of claims 1 to 10.
  12. 12. An image pickup apparatus comprising: the zoom lens according to claim 1; and an image pickup element that is disposed on an image side of the zoom lens and converts an image formed by the zoom lens into an electric signal. .
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JP2007272216A (en) * 2006-03-09 2007-10-18 Matsushita Electric Ind Co Ltd Zoom lens system, imaging device and camera
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JP2010039014A (en) * 2008-08-01 2010-02-18 Nikon Corp Zoom lens, imaging apparatus and variable-magnification method
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JP2002277740A (en) * 2001-03-19 2002-09-25 Asahi Optical Co Ltd Zoom lens system
JP2004061675A (en) * 2002-07-26 2004-02-26 Canon Inc Zoom lens
JP2004333767A (en) * 2003-05-06 2004-11-25 Canon Inc Zoom lens and optical equipment having the same
JP2006078581A (en) * 2004-09-07 2006-03-23 Sony Corp Zoom lens and imaging device
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JP2007272215A (en) * 2006-03-09 2007-10-18 Matsushita Electric Ind Co Ltd Zoom lens system, imaging device and camera
JP2007272216A (en) * 2006-03-09 2007-10-18 Matsushita Electric Ind Co Ltd Zoom lens system, imaging device and camera
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US7830616B2 (en) 2008-10-02 2010-11-09 Nikon Corporation Zoom lens, optical apparatus and manufacturing method
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US8390938B2 (en) 2008-10-10 2013-03-05 Olympus Imaging Corp. Zoom lens and image pickup apparatus equipped with same
US8582211B2 (en) 2008-10-10 2013-11-12 Olympus Imaging Corp. Zoom lens and image pickup apparatus equipped with same

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