JP2009163222A - Zoom lens, and electronic imaging device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens capable of compactifying a size, capable of widening an angle, capable of making variable power high, having satisfactory image quality, and manufactured easily. <P>SOLUTION: This zoom lens is provided with the first lens group of negative power, the second lens group of positive power, the third lens group of positive power, and the fourth lens group, in this order from an object side, is constituted to narrow a space between the first lens group and the second lens group and to widen a space between the second lens group and the third lens group, when varying the power of the zoom lens from a wide-angle end to a telescopic end, and has a diaphragm moving integrally with the second lens group between the most image-side lens of the first lens group and the most image-side lens of the second lens group, and the first lens group comprises a negative lens and a positive lens, in this order from the object side, and satisfies the following conditions: 0.15&lt;&phiv;<SB>IMF</SB>/&phiv;<SB>IMR</SB>&lt;1.0, and -3.0&lt;&phiv;<SB>IPF</SB>/&phiv;<SB>IPR</SB>&lt;-1.0, where &phiv;<SB>IMF</SB>represents the power of an object-side face of the negative lens; &phiv;<SB>IMR</SB>represents the power of an image-side face of the negative lens; &phiv;<SB>IPF</SB>represents the power of the object-side face of the positive lens; and &phiv;<SB>IPR</SB>represents the power of the image-side face of the positive lens. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a zoom lens and an electronic imaging apparatus using the same.

  In recent years, digital cameras equipped with solid-state imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor) have become mainstream instead of silver salt film cameras. There are various types, from high-functional types to compact popular types.

  Among them, the compact popular type of digital camera is also requested by users who want to enjoy shooting easily. In addition to downsizing, it is easy to carry in a pocket of clothes or a bag. For convenience, the thickness has been reduced.

  Therefore, the zoom lens employed in such a compact popular type digital camera is required to be further miniaturized, and at the same time is bright and has a high zoom ratio exceeding 3 times. It is also required that the angle of view in the diagonal direction exceeds 70 °.

  Patent Documents 1 and 2 listed below are zoom lenses that can be used in compact popular digital cameras, and in order from the object side, a negative power first lens group and a positive power second lens group. And a third lens group having a positive power and a fourth lens group.

JP 2004-318107 A JP 2002-365543 A

  However, although the zoom lenses described in Patent Documents 1 and 2 are suitable for miniaturization, the zoom ratio is only about 3 times and the angle of view in the diagonal direction is only about 65 °. In order to achieve a widening or widening of the angle, there is a problem in that the size of the negative lens first lens group in the radial direction and the direction along the optical axis increases, eventually resulting in an increase in the size of the entire optical system. .

  Further, the zoom lenses described in Patent Documents 1 and 2 are the most objects among the lenses constituting the first lens group when the power of each lens is increased in order to reduce the size while achieving high zooming. Since the radius of curvature of the image-side surface of the negative power lens on the side becomes small and the difference between the center thickness and the edge thickness (change in thickness) becomes large, it becomes difficult to process the lens. There is a problem in that high-order axial coma aberration due to variations in assembling the lenses constituting the lens group increases, making it difficult to ensure good productivity and sufficient optical performance.

  The present invention has been made in view of such problems of the prior art, and the object thereof is advantageous for downsizing, wide angle, and high zooming, and the image quality of captured images is also good. A zoom lens that is easy to manufacture and an electronic imaging device using the zoom lens are provided.

In order to achieve the above object, a zoom lens of the present invention includes, in order from the object side, a first lens group having a negative power, a second lens group having a positive power, a third lens group having a positive power, and a fourth lens group. A lens group, and at the time of zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is reduced and the distance between the second lens group and the third lens group is An aperture stop that moves together with the second lens group between the most image side lens of the first lens group and the most image side lens of the second lens group; One lens group is composed of a negative power first lens disposed on the object side and a positive power second lens disposed on the image side, and satisfies the following conditional expressions (1) and (2): It is characterized by doing.
_{0.15 <φ 1MF / φ 1MR <} 1.0 ··· (1)
_{-3.0 <φ 1PF / φ 1PR <} -1.0 ··· (2)
Where φ _1MF is the power of the object side surface of the first lens having the negative power of the first lens group, φ _1MR is the power of the image side surface of the first lens having the negative power of the first lens group, and φ _1PF Is the power of the object side surface of the second lens with positive power of the first lens group, and φ _1PR is the power of the image side surface of the second lens with positive power of the first lens group.

  When the zoom lens of the present invention is configured so as to satisfy the conditional expressions (1) and (2), both surfaces of the negative lens first lens of the first lens group are aspherical surfaces. Is preferred.

  In order to achieve the above object, the zoom lens of the present invention includes, in order from the object side, a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power. A fourth lens group, and at the time of zooming from the wide-angle end to the telephoto end, an interval between the first lens group and the second lens group is narrowed, and the second lens group and the third lens group An interval between the first lens group and the most image-side lens of the first lens group; and a brightness stop that moves integrally with the second lens group between the lens and the second lens group; The first lens group includes a negative lens first lens disposed on the object side and a positive power second lens disposed on the image side, and the third lens group and the fourth lens group. However, only with a single meniscus lens with the concave surface facing the object side. Characterized in that it is configured.

In the zoom lens of the present invention, when the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side, the following conditional expression (3) Is preferably satisfied.
15 <(φ3 / φ4) <320 (3)
Here, φ ₃ is the power of the third lens group, and φ ₄ is the power of the fourth lens group.

In the zoom lens according to the present invention, when the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side, the following conditional expression (4) Is preferably satisfied.
−10 <(R _3r + R _4f ) / (R _3r −R _4f ) <0 (4)
Where R _3r is the paraxial radius of curvature of the image side surface of the meniscus lens constituting the third lens group, and R _4f is the paraxial radius of curvature of the object side surface of the meniscus lens constituting the fourth lens group. is there.

In the zoom lens of the present invention, when the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side, the following conditional expression (5) Is preferably satisfied.
1 <ds / dt <1.5 (5)
However, ds is parallel to the optical axis at the wide-angle end, and a line passing through the maximum image height position on the imaging surface intersects the image side surface of the meniscus lens constituting the third lens group and the fourth lens group. Dt is the distance from the point of intersection with the object side surface of the meniscus lens constituting the lens, dt is the image side surface of the meniscus lens constituting the third lens group at the wide angle end and the object side of the meniscus lens constituting the fourth lens group Is the distance on the optical axis from the surface of

In the zoom lens according to the present invention, it is preferable that the following conditional expression (6) is satisfied.
6 ≦ N ≦ 9 (6)
N is the total number of lenses of the zoom lens.

  In the zoom lens according to the present invention, it is preferable that the second lens group includes three or less lenses.

  In the zoom lens of the present invention, it is preferable that the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented.

  In the zoom lens of the present invention, the second lens group includes a cemented lens in which a positive power lens and a negative power lens are cemented, and the negative power lens of the cemented lens has a positive power of the cemented lens. It is preferable that the Abbe number is smaller than the lens.

In the zoom lens according to the present invention, when the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented, the following conditional expression (7 ) And (8) are preferably satisfied.
n _2pave ≧ 1.59 (7)
ν _2n ≦ 35 (8)
Here, n _2pave is the average value of the refractive indices of all the positive power lenses included in the second lens group, and ν _2n is the Abbe number of the negative power lenses included in the second lens group.

  In the zoom lens according to the present invention, when the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented, the second lens group is It is preferable that the interval between the constituting lenses is smaller than the center thickness of the negative power lens included in the second lens group.

The zoom lens according to the present invention preferably satisfies the following conditional expressions (9) and (10).
n _3ave ≧ 1.48 (9)
ν _3ave ≧ 60 (10)
However, n _3ave is the average value of the refractive indexes of all the lenses constituting the third lens group, and ν _3ave is the average value of the Abbe number of all the lenses constituting the third lens group.

  In the zoom lens according to the present invention, it is preferable that the third lens group is composed of one lens having at least one aspheric surface.

  In the zoom lens of the present invention, it is preferable that the third lens group is composed of at least one resin lens.

In the zoom lens according to the present invention, it is preferable that the fourth lens group includes a single lens and satisfies the following conditional expressions (11) and (12).
n ₄ ≧ 1.48 (11)
ν ₄ ≧ 60 (12)
Here, n ₄ is the refractive index of one lens constituting the fourth lens group, and ν ₄ is the Abbe number of one lens constituting the fourth lens group.

  In the zoom lens of the present invention, it is preferable that the fourth lens group is composed of one lens having at least one aspheric surface.

  In the zoom lens of the present invention, it is preferable that the fourth lens group is constituted by a single resin lens.

  In the zoom lens according to the present invention, it is preferable that the fourth lens group does not move during zooming.

The electronic image pickup apparatus of the present invention includes a zoom lens, an electronic image pickup device disposed in the vicinity of an image forming position of the zoom lens, an image processing unit, and a recording unit, and is obtained by the electronic image pickup device. In the electronic imaging apparatus in which the image processing means processes the changed image data to change the shape and cause the recording means to record, the zoom lens is the zoom lens according to any one of the above, and is almost infinite. The following conditional expression (13) is satisfied at the time of focusing on a far object point.
_{0.7 <y 07 / (f w} · tanω 07w) <1.5 ··· (13)
However, when the effective image pickup plane of the electronic imaging device the distance to the farthest point from the center in (imageable plane) (maximum image height) was y _10, it is represented by y ₀₇ = 0.7y _10, ω _07w is an angle with respect to an optical axis from the center of the image pickup surface direction of an object point corresponding to an image point formed at a position of y ₀₇ at the wide angle end.

  According to the present invention, it is possible to provide a zoom lens that is advantageous for downsizing, wide-angle, and high zoom ratio, good image quality of captured images, and easy to manufacture, and an electronic imaging device using the zoom lens. .

  Prior to the description of the embodiments of the zoom lens of the present invention and the electronic image pickup apparatus using the zoom lens, the effects of the configuration of the zoom lens of the present invention and the electronic image pickup apparatus using the same will be described.

  The zoom lens according to the present invention includes, as a basic configuration, in order from the object side, a first lens group having a negative power, a second lens group having a positive power, a third lens group having a positive power, and a fourth lens group. At the time of zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is reduced and the distance between the second lens group and the third lens group is increased.

  In the zoom lens of the present invention adopting such a configuration, the first lens group has negative power, so that the wide angle and the reduction in size in the radial direction are achieved, and the number of lens groups to be configured is reduced. In addition, since the number of lens groups can be reduced, the number of necessary lenses can be reduced, and as a result, the lens frame can be reduced in thickness and the cost can be reduced. The second lens group functions as a variator by changing the distance from the first lens group, and at the time of zooming from the wide-angle end to the telephoto end, it can be moved from the image side to the object side for multiplication. So as to have positive power. In addition, since the third lens group has positive power, it becomes easy to ensure performance when the total lens length is shortened, and downsizing is possible. Conventionally, aberrations such as astigmatism and field curvature generated in the second group are mainly corrected by the first lens group, but can be corrected by the fourth lens group which is the final group. Thus, it is not necessary to correct aberrations such as astigmatism and field curvature more than necessary in the first lens group, and spherical aberration and coma that increase due to high zooming can be sufficiently corrected.

  The zoom lens according to the present invention basically has a brightness that moves integrally with the second lens group between the most image side lens of the first lens group and the most image side lens of the second lens group. Has a diaphragm.

  In the zoom lens of the present invention employing such a configuration, it is easy to ensure performance at the wide-angle end while maintaining compactness. In addition, the driving mechanism can be simplified by moving the aperture stop integrally with the second lens group. In the case where the aperture stop does not move integrally with the second lens group and is configured to be closer to the object side than the above configuration at the wide angle end, the light beam height of the peripheral luminous flux in the second lens group is increased. This increases the radial size of each lens constituting the second lens group. Furthermore, since the second lens group is responsible for the main part of the imaging function of the entire lens system, the lenses constituting the second lens group are also required to have a relatively strong power. In such a position, the number of lenses must be increased in order to secure power, and it becomes difficult to make the lens frame thinner and to balance spherical aberration and coma. In addition, when the configuration is such that the aperture stop is closer to the image side than the second lens group, the height of the off-axis light beam at the wide-angle end increases, so the first lens group must be enlarged. , Widening and downsizing become difficult.

In the zoom lens according to the present invention, in addition to the basic configuration, the first lens group includes a negative power first lens disposed on the object side and a positive power second lens disposed on the image side. Therefore, the following conditional expressions (1) and (2) are satisfied.
_{0.15 <φ 1MF / φ 1MR <} 1.0 ··· (1)
_{-3.0 <φ 1PF / φ 1PR <} -1.0 ··· (2)
However, phi _{1 mF} power of the object-side surface of the first lens of negative power of the first lens group, phi _1MR the power of the image side surface of the first lens of negative power of the first lens group, phi _1PF the first The power on the object side surface of the second lens with positive power in one lens group, and φ _1PR is the power on the image side surface of the second lens with positive power in the first lens group.

  When the first lens group is composed of a negative power first lens and a positive power second lens, conventionally, most of the negative power of the first lens is concentrated on the object-side surface and the second lens By concentrating most of the positive power on the image side surface, aberrations such as spherical aberration and curvature of field were corrected. However, when the power is concentrated in such a manner, high-order spherical aberration occurs, and it is difficult to achieve high zooming. In addition, the effect of higher-order aberrations due to variations during assembly is increased, and it is difficult to ensure sufficient optical performance. Furthermore, since the power distribution of the first lens is unbalanced, the lens has a large thickness, and in order to achieve a wide angle, the lens must have a deeper spherical shape, which makes it difficult to process the lens. As a result, the design was limited.

  Therefore, the zoom lens according to the present invention is configured to satisfy the conditional expressions (1) and (2) indicating the optimum power distribution of the lenses constituting the first lens group. Since the zoom lens according to the present invention satisfies the conditional expressions (1) and (2), sufficient optical performance can be ensured even when the zoom ratio is increased to about 4 times, and good Productivity can be ensured.

  If the lower limit of conditional expression (1) is not reached, higher-order spherical aberration that occurs in the first lens of the first lens group increases, making it difficult to correct spherical aberration over the entire zoom range. In addition, the shape of the first lens of the first lens group becomes a shape with a large deviation, and the design is limited by the workability of the lens. On the other hand, if the upper limit of conditional expression (1) is exceeded, it will be difficult to correct spherical aberration and field curvature that change during zooming, and similarly it will not be possible to ensure sufficient optical performance over the entire zoom range.

In addition, it is more preferable to configure so as to satisfy one of the following conditional expressions (1) ′ and (1) ″ instead of conditional expression (1).
_{0.2 <φ 1MF / φ 1MR <} 0.8 ··· (1) '
_{0.35 <φ 1MF / φ 1MR <} 0.7 ··· (1) ''
Further, the upper limit value or lower limit value of conditional expression (1) ′ may be the upper limit value or lower limit value of conditional expression (1), (1) ″, or the upper limit value or lower limit value of conditional expression (1) ″. The value may be the upper limit value or the lower limit value of conditional expressions (1) and (1) ′.

  If the lower limit of conditional expression (2) is not reached, the power of the air lens formed between the first lens and the second lens in the first lens group becomes small, and the under field curvature that occurs as the angle of view widens. Cannot be corrected sufficiently. On the other hand, if the upper limit of conditional expression (2) is exceeded, the power of the air lens formed between the first lens and the second lens in the first lens group becomes large, and the field curvature at the wide-angle end becomes excessive. It is not possible to ensure sufficient optical performance. In addition, as the angle of view increases, the distance between the edges of the first lens and the second lens in the first lens group decreases, so the distance between these lenses increases, and the thickness along the optical axis of the first lens group increases. Increase.

In addition, it is more preferable to configure so as to satisfy one of the following conditional expressions (2) ′ and (2) ″ instead of conditional expression (2).
_{-2.5 <φ 1PF / φ 1PR <} -1.7 ··· (2) '
_{-2.0 <φ 1PF / φ 1PR <} -1.8 ··· (2) ''
Further, the upper limit value or lower limit value of conditional expression (2) ′ may be the upper limit value or lower limit value of conditional expression (2), (2) ″, or the upper limit value or lower limit value of conditional expression (2) ″. The value may be the upper limit value or the lower limit value of conditional expressions (2) and (2) ′.

  In addition to the basic configuration, the zoom lens of the present invention has both sides of the first lens with negative power of the first lens group when configured to satisfy the conditional expressions (1) and (2). An aspherical surface is preferable.

  By making both surfaces of the first lens of the first lens group aspherical, it is possible to suppress the occurrence of spherical aberration, curvature of field, and distortion.

  In the zoom lens according to the present invention, in addition to the basic configuration, the third lens group and the fourth lens group are each configured by only one meniscus lens having a concave surface facing the object side.

  In the zoom lens of the present invention adopting such a configuration, the second lens group corrects negative field curvature that occurs in the entire zoom range, and reduces the burden of field curvature correction of the first lens group. It becomes easy to take appropriate power arrangement. As a result, it becomes easy to correct aberrations that occur with widening and high zooming. Further, when the magnification is changed from the wide angle end to the telephoto end, the incident angle of the off-axis light beam on the object side surface of the third lens group and the fourth lens group becomes large, and therefore the optical path length difference between the wide angle end and the telephoto end. And the fluctuation of higher-order field curvature due to zooming in the peripheral portion can be suppressed.

In the zoom lens of the present invention, in addition to the basic configuration, when the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side, It is preferable to satisfy conditional expression (3).
15 <(φ3 / φ4) <320 (3)
Here, φ ₃ is the power of the third lens group, and φ ₄ is the power of the fourth lens group.

  Conditional expression (3) is a conditional expression that regulates the correction of the curvature of field. If the lower limit of conditional expression (3) is not reached, the field curvature and astigmatism difference will be over. If the value exceeds the upper limit, the effect of correcting the curvature of field is weakened, the burden on the first lens group is increased, an appropriate power arrangement cannot be performed, and high zooming becomes difficult.

In the zoom lens of the present invention, in addition to the basic configuration, when the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side, It is preferable to satisfy conditional expression (4).
−10 <(R _3r + R _4f ) / (R _3r −R _4f ) <0 (4)
Where R _3r is the paraxial radius of curvature of the image side surface of the meniscus lens constituting the third lens group, and R _4f is the paraxial radius of curvature of the object side surface of the meniscus lens constituting the fourth lens group. is there.

  Conditional expression (4) is a conditional expression that regulates the lens shape appropriately. When the paraxial curvature radius of the surface closest to the image side of the third lens group and the paraxial curvature radius of the surface closest to the object side of the fourth lens group are set to be within the upper and lower limits of the conditional expression (4), Since the space can be used efficiently, the zoom lens can be made compact.

In the zoom lens of the present invention, in addition to the basic configuration, when the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side, It is preferable to satisfy conditional expression (5).
1 <ds / dt <1.5 (5)
However, ds is parallel to the optical axis at the wide-angle end, and a line passing through the maximum image height position on the imaging surface intersects the image side surface of the meniscus lens constituting the third lens group and the fourth lens group. Dt is the distance from the point of intersection with the object side surface of the meniscus lens constituting the lens, dt is the image side surface of the meniscus lens constituting the third lens group at the wide angle end and the object side of the meniscus lens constituting the fourth lens group It is a space | interval on the optical axis with the surface of this.

  Conditional expression (5) is a conditional expression that regulates the lens shape appropriately. If the distance between the third lens group and the fourth lens group is configured to be within the upper and lower limits of the conditional expression (5), space can be used efficiently, so that the zoom lens has a compact configuration. Will be able to.

In the zoom lens according to the present invention, it is preferable that the following conditional expression (6) is satisfied.
6 ≦ N ≦ 9 (6)
N is the total number of lenses of the zoom lens.

  If the lower limit of conditional expression (6) is not exceeded, the power disposed in each lens group of the zoom lens can be balanced, and the occurrence of aberrations can be easily suppressed. If the upper limit of conditional expression (6) is not exceeded, the number of components can be reduced.

  In the zoom lens according to the present invention, it is preferable that the second lens group includes three or less lenses.

  By configuring the second lens group with three lenses, the entire optical system has a compact configuration.

  In the zoom lens according to the present invention, it is preferable that the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented.

  By configuring the second lens group with a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented, it is possible to easily correct aberrations when the magnification is increased and the angle is increased. Become.

  Furthermore, in the zoom lens according to the present invention, when the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented, the second lens group is: A cemented lens obtained by cementing a positive power lens and a negative power lens is provided, and the negative power lens of the cemented lens preferably has a smaller Abbe number than the positive power lens of the cemented lens.

  When the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented, the Abbe number of the negative power lens is made smaller than that of the positive power lens. This makes it easy to correct chromatic aberration and curvature of field.

In the zoom lens according to the present invention, when the second lens group includes a positive power lens and a cemented lens in which a positive power lens and a negative power lens are cemented, the following conditional expression (7 ) And (8) are preferably satisfied.
n _2pave ≧ 1.59 (7)
ν _2n ≦ 35 (8)
Here, n _2pave is the average value of the refractive indices of all the positive power lenses included in the second lens group, and ν _2n is the Abbe number of the negative power lenses included in the second lens group.

  Astigmatism is easily corrected if the lower limit of conditional expression (7) is not exceeded. If the upper limit of conditional expression (8) is not exceeded, chromatic aberration can be easily corrected.

  In the zoom lens according to the present invention, it is preferable that the distance between the lenses constituting the second lens group is smaller than the center thickness of the negative power lens included in the second lens group.

  With such a configuration, it is easy to reduce the size.

The zoom lens according to the present invention preferably satisfies the following conditional expressions (9) and (10).
n _3ave ≧ 1.48 (9)
ν _3ave ≧ 60 (10)
However, n _3ave is the average value of the refractive indexes of all the lenses constituting the third lens group, and ν _3ave is the average value of the Abbe number of all the lenses constituting the third lens group.

  In the case of a zoom lens reduced in size according to the present invention, it is difficult to correct astigmatism in the third lens group during close-up shooting. Therefore, it is desirable that the third lens group has as high a refractive index and low dispersion as possible. Therefore, if the lower limit of conditional expressions (9) and (10) is not reached, it is difficult to correct astigmatism and chromatic aberration.

Instead of the conditional expression (9), any one of the following conditional expressions (9) ′ and (9) ″ is replaced with the following conditional expressions (10) ′ and (10) ′ instead of the conditional expression (10). It is further preferable to configure so as to satisfy either of the above.
n _3ave ≧ 1.50 (9) ′
n _3ave ≧ 1.52 (9) ''
ν _3ave ≧ 58 (10) '
ν _3ave ≧ 55 (10) ''

  In the zoom lens of the present invention, it is preferable that the third lens group is composed of one lens having at least one aspheric surface.

  In the case of a zoom lens reduced in size according to the present invention, it is difficult to correct astigmatism in the third lens group during close-up shooting. Therefore, it is preferable that the third lens group is composed of lenses having one or both surfaces that are aspherical. The lens is more preferably a lens having a shape with a curvature that is stronger on the image side surface than on the object side surface.

  In the zoom lens of the present invention, it is preferable that the third lens group is composed of at least one resin lens.

  If the third lens group is composed of at least one resin lens, the cost can be reduced and lens molding is easy.

In the zoom lens of the present invention, it is preferable that the fourth lens group is composed of one lens, and satisfies the following conditional expressions (11) and (12).
n ₄ ≧ 1.48 (11)
ν ₄ ≧ 60 (12)
Here, n ₄ is the refractive index of one lens constituting the fourth lens group, and ν ₄ is the Abbe number of one lens constituting the fourth lens group.

  In the case of a zoom lens reduced in size according to the present invention, it is difficult to correct astigmatism in the fourth lens group during close-up shooting. Therefore, it is desirable that the fourth lens group has as high a refractive index and low dispersion as possible. Therefore, if the lower limit of conditional expressions (11) and (12) is not reached, it is difficult to correct astigmatism and chromatic aberration.

Instead of the conditional expression (11), any one of the following conditional expressions (11) ′ and (11) ″ is replaced with the following conditional expressions (12) ′ and (12) ′ instead of the conditional expression (12). It is further preferable to configure so as to satisfy either of the above.
n ₄ ≧ 1.50 (11) ′
n ₄ ≧ 1.52 (11) ″
ν ₄ ≧ 58 (12) ′
ν ₄ ≧ 55 (12) ''

  In the zoom lens of the present invention, it is preferable that the fourth lens group is composed of one lens having at least one aspheric surface.

  In the case of a zoom lens reduced in size according to the present invention, it is difficult to correct astigmatism in the fourth lens group during close-up shooting. Therefore, it is preferable that the four lens groups are constituted by one lens having at least one aspheric surface. The lens is more preferably a lens having a shape with a curvature that is stronger on the image side surface than on the object side surface.

  In the zoom lens of the present invention, it is preferable that the fourth lens group is composed of a single resin lens.

  If the fourth lens group is composed of at least one resin lens, the cost can be reduced and lens molding is easy.

  In the zoom lens of the present invention, it is preferable that the fourth lens group does not move during zooming.

  By preventing the fourth lens group from moving at the time of zooming, the drive unit mechanism can be simplified and the size can be easily reduced.

The electronic image pickup apparatus of the present invention includes a zoom lens, an electronic image pickup device disposed in the vicinity of an image forming position of the zoom lens, an image processing unit, and a recording unit, and is obtained by the electronic image pickup device. In the electronic imaging apparatus in which the image processing means processes the changed image data to change the shape and record it on the recording means, the zoom lens is any one of the above zoom lenses, and the object point is almost at infinity. At the time of focusing, the following conditional expression (13) is satisfied.
_{0.7 <y 07 / (f w} · tanω 07w) <1.5 ··· (13)
However, when the effective image pickup plane of the electronic imaging device the distance to the farthest point from the center in (imageable plane) (maximum image height) was y _10, it is represented by y ₀₇ = 0.7y _10, ω _07w is an angle with respect to an optical axis from the center of the image pickup surface direction of an object point corresponding to an image point formed at a position of y ₀₇ at the wide angle end.

  In the case of a zoom lens reduced in size according to the present invention, as in the present invention, astigmatism correction and barrel distortion correction tend to be in a trade-off relationship. Therefore, if the generation of distortion is allowed to some extent, the distortion of the image shape can be corrected by the image processing function of the electronic imaging apparatus. Therefore, such a correction method will be described.

For example, assume that an object at infinity is imaged by an optical system without distortion. In this case, since the image formed has no distortion, the following conditional expression (14) is satisfied.
f = y / tan ω (14)
Where y is the height of the image point from the optical axis, f is the focal length of the imaging system, ω is the angle with respect to the optical axis in the object direction corresponding to the image point connecting from the center on the imaging surface to the y position. is there.

On the other hand, when barrel distortion is allowed only when the optical system is in the vicinity of the wide-angle end, the following conditional expression (15) is satisfied.
f> y / tan ω (15)
Where y is the height of the image point from the optical axis, f is the focal length of the imaging system, ω is the angle with respect to the optical axis in the object direction corresponding to the image point connecting from the center on the imaging surface to the y position. is there.

  That is, if ω and y are constant values, the focal length f at the wide-angle end may be long, and the aberration can be corrected accordingly. The reason why the lens group corresponding to the first lens group of the zoom lens according to the present invention is generally composed of two or more components is to achieve both correction of distortion and astigmatism. However, if distortion is allowed to some extent, it is not necessary to make them compatible, and astigmatism can be easily corrected.

  Therefore, in the electronic imaging device of the present invention, the image data obtained by the electronic imaging device is electrically processed so as to correct barrel distortion by image processing means that is a signal processing system of the electronic imaging device. Processing corresponding to the shape change of the image is performed.

  In this way, the finally obtained image data is image data having a shape substantially similar to the object. Therefore, an object image may be output to a CRT or printer based on the image data.

  Conditional expression (13) defines the degree of barrel distortion at the wide-angle end. If conditional expression (13) is satisfied, astigmatism can be corrected without difficulty, and the optical system can be made thinner. Note that an image distorted in a barrel shape is photoelectrically converted by an image sensor to become image data distorted in a barrel shape. However, the image data distorted into a barrel shape is subjected to processing corresponding to the change in the shape of the image by the image processing means. In this way, even if the final image data is reproduced, the distortion is corrected and an image substantially similar to the subject shape is obtained.

  When the value exceeds the upper limit value of conditional expression (13), particularly when the value is close to 1, this corresponds to the fact that the distortion aberration is optically corrected, while it is difficult to correct astigmatism. . On the other hand, below the lower limit value of conditional expression (13), when image distortion due to distortion of the optical system is corrected by the image processing means, the stretch ratio in the radial direction of the peripheral portion of the angle of view becomes too high. As a result, the sharpness degradation at the periphery of the image becomes conspicuous.

In addition, it is more preferable to configure so as to satisfy one of the following conditional expressions (13) ′ and (13) ″ instead of conditional expression (13).
_{0.75 <y 07 / (f w} · tanω 07w) <1.3 ··· (13) '
_{0.80 <y 07 / (f w} · tanω 07w) <1.1 ··· (13) ''
Further, the upper limit value or lower limit value of conditional expression (13) ′ may be used as the upper limit value or lower limit value of conditional expressions (13), (13) ″, or the upper limit value or lower limit value of conditional expression (13) ″. The value may be the upper limit value or the lower limit value of conditional expressions (13) and (13) ′.

  Embodiments 1 to 4 of the present invention will be described below with reference to the drawings.

In the drawings, the numerals shown as subscripts in r ₁ , r ₂ ,... And d ₁ , d ₂ ,. It corresponds to 2, ... In the aberration curve diagram, ΔM in astigmatism indicates astigmatism on the meridional surface, and ΔS indicates astigmatism on the sagittal surface. The meridional plane is the plane containing the optical axis of the optical system and the principal ray (plane parallel to the paper), and the sagittal plane is the plane perpendicular to the plane containing the optical axis of the optical system and the principal ray (paper plane). Means a plane perpendicular to

In the numerical data of the lens in each of the following examples, R is a radius of curvature of each surface, D is a surface interval, Nd is a refractive index in d line, νd is an Abbe number in d line, K is a cone coefficient, A ₄ , A ₆ , A ₈ , and A ₁₀ indicate aspherical coefficients, respectively.

Each aspheric shape is expressed by the following equation using each aspheric coefficient in each embodiment. However, the coordinate in the direction along the optical axis is Z, and the coordinate in the direction perpendicular to the optical axis is Y.
Z = (Y ² / r) / [1+ {1− (1 + K) · (Y / r) ² } ^1/2 ]
+ A ₄ Y ⁴ + A ₆ Y ⁶ + A ₈ Y ⁸ + A ₁₀ Y ¹⁰ +...

  FIG. 1 is a cross-sectional view along the optical axis showing the optical configuration of the zoom lens according to the present embodiment when focusing on an object point at infinity, where (a) is a wide-angle end, (b) is an intermediate, and (c) is Each state at the telephoto end is shown. 2A and 2B are diagrams showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the zoom lens shown in FIG. 1 is focused on an object point at infinity. FIG. 2A is a wide-angle end, and FIG. , (C) show states at the telephoto end, respectively.

First, the optical configuration of the zoom lens of the present embodiment will be described with reference to FIG. The zoom lens according to the present exemplary embodiment includes, on the optical axis Lc, in order from the object side, a first lens group G _{1 having} a negative power, a second lens group G _{2 having} a positive power, a third lens group G _{3 having} a positive power, Four lens groups G ₄ are arranged. In addition, an aperture stop S is disposed between the first lens group G ₁ and the second lens group G ₂ . Incidentally, the image side of the fourth lens group G ₄ is composed of, in order from the object side, a low-pass filter LF, CCD cover glass CG, and a CCD having an imaging surface IM are arranged.

The first lens group G ₁ is, in order from the object side, a biconcave lens with both surfaces aspheric and negative power first lens L _11, and a meniscus lens with a convex surface facing the object side and positive power second lens L. It consists of _twelve .

The second lens group G ₂ is, in order from the object side, a biconvex lens having both aspheric surfaces and a positive power lens L _21, and a meniscus lens having a convex surface facing the object side, and a positive power lens L ₂₂ and the object side. It is constituted by a cemented lens of a negative power of the lens L ₂₃ located at the meniscus lens having a convex surface directed toward the.

The third lens group G ₃ is a meniscus lens that is molded of resin, has an aspheric image side surface, and has a convex surface directed to the image side, and is constituted only by a negative power lens L ₃ .

The fourth lens group G ₄ is a meniscus lens having an image-side surface that is aspheric and has a convex surface directed toward the image side, and is constituted only by a negative-power lens L ₄ .

Further, when zooming from the wide-angle end to the telephoto end, the first lens group G ₁ reciprocates on the optical axis Lc so that it first moves to the image side and then moves to the object side. The second lens group G ₂ moves along the optical axis Lc to the object side while narrowing the distance from the first lens group G ₁ together with the aperture stop S. The third lens group G ₃ reciprocates on the optical axis Lc so as to first move to the image side and then move to the object side while increasing the distance from the second lens group G ₂ . At this time, the fourth lens group G ₃ is not moved.

  Next, the structure and numerical data of the lens which comprises each optical system based on a present Example are shown. The unit is mm.

Surface data surface number Curvature radius Surface spacing Refractive index Abbe number
R D Nd νd
1 (Aspherical surface) -18.266 0.80 1.80495 40.90
2 (Aspherical surface) 8.644 1.37
3 9.690 1.27 1.92286 18.90
4 18.017 D4
5 (Aperture) ∞ 0.80
6 (Aspherical) 4.835 1.60 1.58233 59.40
7 (Aspherical surface) -15.484 0.10
8 6.661 1.12 1.78800 47.37
9 15.282 1.07 1.80518 25.42
10 3.094 D10
11 -31.473 1.89 1.53113 55.80
12 (Aspherical) -6.040 D12
13 -9.992 0.80 1.53113 55.80
14 (Aspherical) -9.837 D14
15 ∞ 0.50 1.51633 64.14
16 ∞ 0.50
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.37
19 (Imaging surface) ∞

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
RK A ₄ A ₆ A ₈ A ₁₀
1 -18.266 0.000 6.27173e-04 -8.77224e-06 6.13508e-08
2 8.644 0.991 2.94057e-04 -1.24382e-06 -1.99268e-07 -2.62692e-09
6 4.835 -0.531 -4.89810e-04 8.71213e-06 -2.15842e-06
7 -15.484 0.000 5.46267e-04 1.85378e-06 -2.19878e-06
12 -6.040 0.000 1.38066e-03 -4.48702e-05 1.46604e-06
14 -9.837 0.000 -4.56396e-04 1.08446e-04 -3.42005e-06

Various data Zoom ratio 3.88
Wide angle Medium telephoto Focal length 4.72 8.69 18.29
F number 4.65 3.73 6.05
Angle of view 83.00 44.65 21.62
Image height 3.60 3.60 3.60
Total lens length 29.52 27.65 32.98
Back focus 1.85 1.86 1.91
D4 12.35 6.07 1.32
D10 2.16 7.28 17.07
D12 2.39 1.66 1.91
D14 0.30 0.30 0.30

Zoom lens group data Group Start surface Focal length
1 1 -11.55
2 6 8.84
3 11 13.73
4 13 428.00

Data Conditional Expression (1) According to the Conditional Expression 0.15 <φ _1MF / φ _1MR <1.0: 0.473
Conditional expression _{(2) -3.0 <φ 1PF /} φ 1PR <-1.0: -1.859
Conditional expression (3) 15 <(φ3 / φ4) <320: 31.172608
Conditional expression (4) −10 <(R _3r + R _4f ) / (R _3r −R _4f ) <0: −4.057395
Conditional expression (5) 1 <ds / dt <1.5: 1.145555
Conditional expression (6) 6 ≦ N ≦ 9: 7
Conditional expression (7) n _2pave ≧ 1.59: _1.585
Conditional expression (8) ν _2n ≦ 35: 53.385
Conditional expression (9) n _3ave ≧ 1.48: 1.531
Conditional expression (10) ν _3ave ≧ 60: 55.8
Conditional expression (11) n ₄ ≧ 1.48: 1.531
Conditional expression (12) ν ₄ ≧ 60: 55.8
The conditional expression _{(13) 0.7 <y 07 /} (f w · tanω 07w) <1.5: 0.920

  3A and 3B are cross-sectional views along the optical axis showing the optical configuration of the zoom lens according to the present embodiment when focusing on an object point at infinity, where FIG. 3A is a wide angle end, FIG. 3B is an intermediate, and FIG. Each state at the telephoto end is shown. 4A and 4B are diagrams showing spherical aberration, astigmatism, distortion aberration, and lateral chromatic aberration when the zoom lens shown in FIG. 3 is focused on an object point at infinity. FIG. 4A is a wide-angle end, and FIG. , (C) show states at the telephoto end, respectively.

First, the optical configuration of the zoom lens of the present embodiment will be described with reference to FIG. The zoom lens according to the present exemplary embodiment includes, on the optical axis Lc, in order from the object side, a first lens group G _{1 having} a negative power, a second lens group G _{2 having} a positive power, a third lens group G _{3 having} a positive power, Four lens groups G ₄ are arranged. In addition, an aperture stop S is disposed between the first lens group G ₁ and the second lens group G ₂ . A flat plate-like low pass filter LF, a flat plate-like CCD cover glass CG, and a CCD having an imaging surface IM are arranged on the image side of the fourth lens group G ₄ in order from the object side.

The first lens group G ₁ is, in order from the object side, a biconcave lens with both surfaces aspheric and negative power first lens L _11, and a meniscus lens with a convex surface facing the object side and positive power second lens L. It consists of _twelve .

The second lens group G ₂ is, in order from the object side, a biconvex lens having both aspheric surfaces and a positive power lens L _21, and a meniscus lens having a convex surface facing the object side, and a positive power lens L ₂₂ and the object side. It is constituted by a cemented lens of a negative power of the lens L ₂₃ located at the meniscus lens having a convex surface directed toward the.

The third lens group G ₃ is a meniscus lens that is molded of resin, has an aspheric image side surface, and has a convex surface directed to the image side, and is constituted only by a negative power lens L ₃ .

The fourth lens group G ₄ is a meniscus lens having an image-side surface that is aspheric and has a convex surface directed toward the image side, and is constituted only by a negative-power lens L ₄ .

Further, when zooming from the wide-angle end to the telephoto end, the first lens group G ₁ reciprocates on the optical axis Lc so that it first moves to the image side and then moves to the object side. The second lens group G ₂ moves along the optical axis Lc to the object side while narrowing the distance from the first lens group G ₁ together with the aperture stop S. The third lens group G ₃ reciprocates on the optical axis Lc so as to first move to the image side and then move to the object side while increasing the distance from the second lens group G ₂ . At this time, the fourth lens group G ₃ is not moved.

  Next, the structure and numerical data of the lens which comprises each optical system based on a present Example are shown. The unit is mm.

Surface data surface number Curvature radius Surface spacing Refractive index Abbe number
R D Nd νd
1 (Aspherical surface) -20.071 0.80 1.80495 40.90
2 (Aspherical) 8.468 1.44
3 9.629 1.36 1.92286 18.90
4 17.446 D4
5 (Aperture) ∞ 0.00
6 (Aspherical) 4.896 1.53 1.58233 59.40
7 (Aspherical surface) -17.427 0.10
8 6.420 1.26 1.78800 47.37
9 14.974 0.96 1.80518 25.42
10 3.092 D10
11 -34.250 1.89 1.53113 55.80
12 (Aspherical) -6.163 D12
13 -8.132 0.80 1.52542 55.78
14 (Aspherical surface) -8.082 D14
15 ∞ 0.50 1.51633 64.14
16 ∞ 0.50
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.37
19 (Imaging surface) ∞

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
RK A ₄ A ₆ A ₈ A ₁₀
1 -20.071 0.000 5.44046e-04 -5.33453e-06 1.41179e-08
2 8.468 0.769 2.69602e-04 -3.19445e-06 2.88056e-07 -1.37906e-08
6 4.896 -0.274 -5.60755e-04 -5.91754e-06 3.57413e-06
7 -17.427 0.000 6.46385e-04 1.43732e-06 3.83621e-06
12 -6.163 0.000 1.42015e-03 -5.14081e-05 1.54981e-06
14 -8.082 0.000 -8.92351e-04 1.35650e-04 -3.80333e-06

Various data Zoom ratio 3.87
Wide angle Medium telephoto Focal length 4.77 8.57 18.44
F number 2.61 3.66 6.07
Angle of view 81.79 45.38 21.47
Image height 3.60 3.60 3.60
Total lens length 29.67 27.88 33.23
Back focus 1.85 1.87 1.89
D4 13.12 7.05 2.11
D10 2.00 6.99 17.10
D12 2.55 1.82 1.98
D14 0.30 0.30 0.30

Zoom lens group data Group Start surface Focal length
1 1 -11.70
2 6 8.94
3 11 13.83
4 13 384.02

Data Conditional Expression (1) According to the Conditional Expression 0.15 <φ _1MF / φ _1MR <1.0: 0.421
Conditional expression _{(2) -3.0 <φ 1PF /} φ 1PR <-1.0: -1.792
Conditional expression (3) 15 <(φ3 / φ4) <320: 27.776077
Conditional expression _{(4) -10 <(R 3r} + R 4f) / (R 3r -R 4f) <0: -7.257263
Conditional expression (5) 1 <ds / dt <1.5: 1.0589041
Conditional expression (6) 6 ≦ N ≦ 9: 7
Conditional expression (7) n _2pave ≧ 1.59: _1.585
Conditional expression (8) ν _2n ≦ 35: 53.385
Conditional expression (9) n _3ave ≧ 1.48: 1.531
Conditional expression (10) ν _3ave ≧ 60: 55.8
Conditional expression (11) n ₄ ≧ 1.48: 1.525
Conditional expression (12) ν ₄ ≧ 60: 55.78
The conditional expression _{(13) 0.7 <y 07 /} (f w · tanω 07w) <1.5: 0.921

  FIG. 5 is a cross-sectional view along the optical axis showing the optical configuration of the zoom lens according to the present embodiment when focusing on an object point at infinity, where (a) is the wide-angle end, (b) is the middle, and (c) is Each state at the telephoto end is shown. 6A and 6B are diagrams showing spherical aberration, astigmatism, distortion aberration, and lateral chromatic aberration when the zoom lens shown in FIG. 5 is focused on an object point at infinity. FIG. 6A is a wide-angle end, and FIG. , (C) show states at the telephoto end, respectively.

First, the optical configuration of the zoom lens of the present embodiment will be described with reference to FIG. The zoom lens according to the present exemplary embodiment includes, on the optical axis Lc, in order from the object side, a first lens group G _{1 having} a negative power, a second lens group G _{2 having} a positive power, a third lens group G _{3 having} a positive power, Four lens groups G ₄ are arranged. In addition, an aperture stop S is disposed between the first lens group G ₁ and the second lens group G ₂ . A flat plate-like low pass filter LF, a flat plate-like CCD cover glass CG, and a CCD having an imaging surface IM are arranged on the image side of the fourth lens group G ₄ in order from the object side.

The first lens group G ₁ is, in order from the object side, a biconcave lens with both surfaces aspheric and negative power first lens L _11, and a meniscus lens with a convex surface facing the object side and positive power second lens L. It consists of _twelve .

The second lens group G ₂ includes, in order from the object side, a biconvex lens having both aspheric surfaces and a positive power lens L _21, and a meniscus lens having a convex surface facing the object side and a negative power lens L _22. Has been.

The third lens group G ₃ is a meniscus lens that is molded of resin, has an aspheric image side surface, and has a convex surface directed to the image side, and is constituted only by a negative power lens L ₃ .

The fourth lens group G ₄ is a meniscus lens having an aspheric object side surface and a convex surface facing the image side, and is constituted only by a negative power lens L ₄ .

Further, when zooming from the wide-angle end to the telephoto end, the first lens group G ₁ reciprocates on the optical axis Lc so that it first moves to the image side and then moves to the object side. The second lens group G ₂ moves along the optical axis Lc to the object side while narrowing the distance from the first lens group G ₁ together with the aperture stop S. The third lens group G ₃ reciprocates on the optical axis Lc so as to first move to the image side and then move to the object side while increasing the distance from the second lens group G ₂ . At this time, the fourth lens group G ₃ is not moved.

  Next, the structure and numerical data of the lens which comprises each optical system based on a present Example are shown. The unit is mm.

Surface data surface number Curvature radius Surface spacing Refractive index Abbe number
R D Nd νd
1 (Aspherical surface) -19.567 0.80 1.80495 40.90
2 (Aspherical surface) 8.000 2.19
3 12.182 1.29 1.92286 18.90
4 27.565 D4
5 (Aperture) ∞ 0.00
6 (Aspherical) 4.526 1.69 1.58233 59.40
7 (Aspherical surface) -13.187 0.10
8 6.856 2.01 1.94595 17.98
9 3.056 D9
10 -107.403 1.66 1.53113 55.80
11 (Aspherical) -6.945 D11
12 (Aspherical surface) -10.000 0.80 1.52542 55.78
13 -9.543 D13
14 ∞ 0.50 1.51633 64.14
15 ∞ 0.50
16 ∞ 0.50 1.51633 64.14
17 ∞ 0.50
18 (Imaging surface) ∞

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
RK A ₄ A ₆ A ₈ A ₁₀
1 -19.567 0.000 5.62061e-04 -1.00515e-05 1.16591e-07
2 8.000 1.377 -7.67201e-05 -7.71670e-06 -2.51189e-07 -1.70497e-08
6 4.526 -2.585 1.78371e-03 -2.61312e-06 -9.35148e-06
7 -13.187 0.000 2.94482e-04 7.50654e-05 -1.41852e-05
11 -6.945 0.000 9.49811e-04 -3.25098e-05 1.17945e-06
12 -10.000 0.000 -2.12060e-04 -4.25320e-05 2.06801e-06 1.36129e-08

Various data Zoom ratio 3.88
Wide angle Medium telephoto Focal length 4.71 9.33 18.28
F number 2.63 3.90 6.12
Angle of view 82.60 41.87 21.82
Image height 3.60 3.60 3.60
Total lens length 29.47 27.55 33.29
Back focus 1.96 1.96 1.96
D4 12.18 5.16 1.00
D9 2.82 8.49 17.89
D11 1.97 1.40 1.90
D13 0.30 0.30 0.30

Zoom lens group data Group Start surface Focal length
1 1 -11.34
2 6 8.89
3 10 13.90
4 12 247.91

Data condition according to the above-mentioned conditional expressions _{(1) 0.15 <φ 1MF /} φ 1MR <1.0: 0.411
Conditional expression _{(2) -3.0 <φ 1PF /} φ 1PR <-1.0: -2.262
Conditional expression (3) 15 <(φ3 / φ4) <320: 17.8334033
Conditional expression (4) −10 <(R _3r + R _4f ) / (R _3r −R _4f ) <0: −5.5547386
Conditional expression (5) 1 <ds / dt <1.5: 1.0752665
Conditional expression (6) 6 ≦ N ≦ 9: 6
Conditional expression (7) n _2pave ≧ 1.59: 1.582
Conditional expression (8) v _2n ≦ 35: 59.4
Conditional expression (9) n _3ave ≧ 1.48: 1.531
Conditional expression (10) ν _3ave ≧ 60: 55.8
Conditional expression (11) n ₄ ≧ 1.48: 1.525
Conditional expression (12) ν ₄ ≧ 60: 55.78
The conditional expression _{(13) 0.7 <y 07 /} (f w · tanω 07w) <1.5: 0.932

  FIG. 7 is a cross-sectional view along the optical axis showing the optical configuration of the zoom lens according to the present embodiment when focusing on an object point at infinity, where (a) is a wide-angle end, (b) is an intermediate, and (c) is a cross-sectional view. Each state at the telephoto end is shown. 8A and 8B are diagrams showing spherical aberration, astigmatism, distortion aberration, and lateral chromatic aberration when the zoom lens shown in FIG. 7 is focused on an object point at infinity. FIG. 8A is a wide-angle end, and FIG. , (C) show states at the telephoto end, respectively.

First, the optical configuration of the zoom lens of the present embodiment will be described with reference to FIG. The zoom lens according to the present exemplary embodiment includes, on the optical axis Lc, in order from the object side, a first lens group G _{1 having} a negative power, a second lens group G _{2 having} a positive power, a third lens group G _{3 having} a positive power, Four lens groups G ₄ are arranged. In addition, an aperture stop S is disposed between the first lens group G ₁ and the second lens group G ₂ . A flat plate-like low pass filter LF, a flat plate-like CCD cover glass CG, and a CCD having an imaging surface IM are arranged on the image side of the fourth lens group G ₄ in order from the object side.

The first lens group G ₁ is, in order from the object side, a biconcave lens with both surfaces aspheric and negative power first lens L _11, and a meniscus lens with a convex surface facing the object side and positive power second lens L. It consists of _twelve .

The second lens group G ₂ is, in order from the object side, a biconvex lens having both aspheric surfaces and a positive power lens L _21, and a meniscus lens having a convex surface facing the object side, and a positive power lens L ₂₂ and the object side. It is constituted by a cemented lens of a negative power of the lens L ₂₃ located at the meniscus lens having a convex surface directed toward the.

The third lens group G ₃ is a meniscus lens that is molded of resin, has an aspheric image side surface, and has a convex surface directed to the image side, and is constituted only by a negative power lens L ₃ .

The fourth lens group G ₄ is a meniscus lens having a convex surface directed toward the image side, and includes only a positive power lens L ₄ .

Further, when zooming from the wide-angle end to the telephoto end, the first lens group G ₁ reciprocates on the optical axis Lc so that it first moves to the image side and then moves to the object side. The second lens group G ₂ moves along the optical axis Lc to the object side while narrowing the distance from the first lens group G ₁ together with the aperture stop S. The third lens group G ₃ reciprocates on the optical axis Lc so as to first move to the image side and then move to the object side while increasing the distance from the second lens group G ₂ . The fourth lens group G ₄ moves toward the image side only when zooming from the wide-angle end to the intermediate state while widening the distance from the third lens group.

  Next, the structure and numerical data of the lens which comprises each optical system based on a present Example are shown. The unit is mm.

Surface data surface number Curvature radius Surface spacing Refractive index Abbe number
R D Nd νd
1 (Aspherical surface) -18.382 0.80 1.80495 40.90
2 (Aspherical) 8.000 2.06
3 12.082 1.30 1.92286 18.90
4 28.964 D4
5 (Aperture) ∞ 0.00
6 (Aspherical) 4.600 1.71 1.58233 59.40
7 (Aspherical surface) -18.823 0.10
8 6.209 1.24 1.81600 46.62
9 11.409 0.75 1.84666 23.78
10 3.060 D10
11 -44.690 1.60 1.55402 60.71
12 (Aspherical) -6.539 D12
13 -10.000 0.80 1.52542 55.78
14 -10.230 D14
15 ∞ 0.50 1.51633 64.14
16 ∞ 0.50
17 ∞ 0.50 1.51633 64.14
18 ∞ 0.50
19 (Imaging surface) ∞

Aspheric data surface number radius of curvature cone coefficient aspheric coefficient
RK A ₄ A ₆ A ₈ A ₁₀
1 -18.382 0.000 6.00929e-04 -7.12017e-06 3.76422e-08
2 8.000 1.188 1.61098e-05 -6.02778e-06 1.59902e-07 -2.52743e-08
6 4.600 -2.062 2.11507e-03 -6.05020e-05 2.05939e-05
7 -18.823 0.000 1.34109e-03 -3.83688e-05 2.47046e-05
12 -6.539 0.000 1.08021e-03 -1.48062e-05 4.34895e-07

Various data Zoom ratio 3.88
Wide angle Medium telephoto Focal length 4.71 9.33 18.27
F number 2.62 3.87 6.09
Angle of view 82.60 42.08 21.87
Image height 3.60 3.60 3.60
Total lens length 29.35 27.50 33.29
Back focus 2.94 1.96 1.95
D4 12.05 5.08 1.00
D10 2.79 8.53 18.07
D12 1.20 1.57 1.90
D14 1.28 0.30 0.30

Zoom lens group data Group Start surface Focal length
1 1 -11.30
2 6 8.94
3 11 13.62
4 13 4266.54

Data Conditional Expression (1) According to the Conditional Expression 0.15 <φ _1MF / φ _1MR <1.0: 0.435
Conditional expression _{(2) -3.0 <φ 1PF /} φ 1PR <-1.0: -2.397
Conditional expression (3) 15 <(φ3 / φ4) <320: 313.20683
Conditional expression (4) −10 <(R _3r + R _4f ) / (R _3r −R _4f ) <0: −4.778565
Conditional expression (5) 1 <ds / dt <1.5: 1.206884
Conditional expression (6) 6 ≦ N ≦ 9: 7
Conditional expression (7) n _2pave ≧ 1.59: 1.699
Conditional expression (8) ν _2n ≦ 35: 53.01
Conditional expression (9) n _3ave ≧ 1.48: 1.554
Conditional expression (10) ν _3ave ≧ 60: 60.71
Conditional expression (11) n ₄ ≧ 1.48: 1.525
Conditional expression (12) ν ₄ ≧ 60: 55.78
The conditional expression _{(13) 0.7 <y 07 /} (f w · tanω 07w) <1.5: 0.930

  In each of the above embodiments, the aperture stop S is disposed on the object side of the second lens group. However, if the aperture stop S moves integrally with the second lens group, for example, the second lens group is configured. You may arrange | position between the lenses to perform. In each of the above embodiments, the zoom lens is configured by four lens groups. However, the present invention is not limited to such a configuration, and a lens group is further arranged on the image side of the fourth lens group. You may make it do.

  The zoom lens of the present invention may be configured as follows.

  In the zoom lens of the present invention, a flare stop may be disposed in addition to the brightness stop in order to cut unnecessary light such as ghost and flare. The flare stop is disposed at the object side of the first lens group, between the first lens group and the second lens group, between the second lens group and the third lens group, and between the third lens group and the fourth lens group. Any position between the lens group and between the fourth lens group and the imaging surface may be used. Further, the flare stop may be configured using a frame member, or may be configured using another member. Furthermore, the flare stop may be configured by printing directly on the optical member, or may be configured using a paint, an adhesive seal, or the like. Further, the shape of the flare stop may be any shape such as a circle, an ellipse, a rectangle, a polygon, or a shape surrounded by a function curve. Further, the flare stop may cut not only harmful light flux but also light flux such as coma flare around the screen.

  Further, each lens of the zoom lens of the present invention may be provided with an antireflection coating to reduce ghost and flare. In that case, in order to further effectively reduce ghost and flare, it is desirable that the antireflection coat to be applied is a multi-coat. Further, the infrared cut coat may be applied not to the low-pass filter but to the lens surface of each lens, a cover glass, or the like.

  In order to prevent the occurrence of ghosts and flares, an antireflection coating is generally applied to the air contact surface of the lens. On the other hand, the refractive index of the adhesive on the cemented surface of the cemented lens is sufficiently higher than the refractive index of air. For this reason, the cemented surface of the cemented lens often has a reflectance equivalent to or less than that of a single-layer coating from the beginning. However, if an anti-reflection coating is positively applied to the cemented surface of the cemented lens, ghosts and flares can be further reduced, and a better image can be obtained.

  In particular, recently, high refractive index glass materials with high aberration correction effects have become widespread and are widely used in camera optical systems. However, when high refractive index glass materials are used as cemented lenses, Reflection on the surface can no longer be ignored. In such a case, it is particularly effective to provide an antireflection coating on the joint surface.

The effective usage of such a bonding surface coat is disclosed in JP-A-2-27301, JP-A-2001-324676, JP-A-2005-92115, USP 7116482, and the like. Yes. As the coating material to be used, Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , HfO ₂ , relatively high refractive index, depending on the refractive index of the lens serving as the substrate and the refractive index of the adhesive, A coating material such as CeO ₂ , SnO ₂ , In ₂ O ₃ , ZnO, and Y ₂ O ₃ , a coating material such as MgF ₂ , SiO ₂ , and Al ₂ O ₃ having a relatively low refractive index is appropriately selected, and phase conditions The film thickness may be set so as to satisfy the above.

  As a matter of course, the joint surface coat may be a multi-coat as well as the coating on the air contact surface of the lens. By appropriately combining two or more layers of coating materials and film thicknesses, it is possible to further reduce the reflectance and control the spectral characteristics and angular characteristics of the reflectance. Needless to say, it is effective to coat the cemented surfaces other than the first lens group based on the same concept.

  In the case of the zoom lens according to the present invention, it is preferable that focusing for performing focus adjustment is performed in the third lens group, but any one of the first lens group, the second lens group, and the fourth lens group is used. You may carry out by a group and you may carry out by a some lens group. The focusing may be performed by moving the entire zoom lens or by moving a part of the lenses.

  In the zoom lens of the present invention, the decrease in brightness at the periphery of the image may be reduced by shifting the micro lens of the CCD. For example, the design of the CCD microlens may be changed according to the incident angle of the light beam at each image height. Further, the amount of decrease in brightness at the periphery of the image may be corrected by image processing.

  The zoom lens according to the present invention as described above can be used in a photographing apparatus, particularly a digital camera or a video camera, which performs photographing by forming an object image formed by the zoom lens on an image sensor such as a CCD. The specific example is illustrated below.

  9, FIG. 10 and FIG. 11 are conceptual diagrams showing the configuration of a digital camera using the present invention. FIG. 9 is a front perspective view showing the appearance of the digital camera, and FIG. FIG. 11 is a perspective plan view schematically showing the configuration of the digital camera. However, FIGS. 9 and 11 show the zoom lens when it is not retracted.

  The digital camera 10 includes a zoom lens 11 disposed on the photographing optical path 12, a finder optical system 13 disposed on the finder optical path 14, a shutter button 15, a flash light emitting unit 6, a liquid crystal display monitor 17, and a focal length change button. 27, a setting change switch 28, and the like. Further, when the zoom lens 11 is retracted, the cover 26 slides to cover the zoom lens 11 and the viewfinder optical system 13.

  When the cover 26 is opened and the digital camera 10 is set to the photographing state, the zoom lens 11 is in the non-collapsed state shown in FIG. In this state, when the shutter button 15 disposed on the upper part of the digital camera 10 is pressed, shooting is performed through the zoom lens 11, for example, a zoom lens as described in the first embodiment of the present invention. The object image is formed on the imaging surface of the CCD 18 that is a solid-state imaging device via the zoom lens 11, the low-pass filter LF, and the cover glass CG. Image information of the object image formed on the imaging surface of the CCD 18 is recorded in the recording unit 21 via the processing unit 20. The recorded image information can be taken out by the processing means 20 and displayed on the liquid crystal display monitor 17 provided on the back of the camera as an electronic image.

  Further, a finder objective optical system 22 is disposed on the finder optical path 14. The finder objective optical system 22 includes a plurality of lens groups (three groups in the figure) and two prisms, and the focal length changes in conjunction with the zoom lens 11. The finder objective optical system 22 forms an object image on a field frame 24 of an erecting prism 23 that is an image erecting member. An eyepiece optical system 25 that guides an erect image to the eyeball E of the observer is disposed behind the erecting prism 23. A cover member 19 is disposed on the exit side of the eyepiece optical system 25.

  In the digital camera 10 configured in this manner, the zoom lens 11 has a high zoom ratio and is small in size and can be retracted, so that good performance is ensured and the digital camera 10 is downsized. Can be realized.

FIG. 2 is a cross-sectional view along the optical axis showing the optical configuration of the zoom lens according to Example 1 of the present invention when focusing on an object point at infinity, where (a) is a wide angle end, (b) is an intermediate, and (c) is telephoto. The state at the end is shown respectively. FIG. 2 is a diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the zoom lens shown in FIG. 1 is focused on an object point at infinity, where (a) is a wide-angle end, (b) is an intermediate, and (c). Indicates the state at the telephoto end. FIG. 6 is a cross-sectional view along the optical axis showing an optical configuration when focusing on an object point at infinity of a zoom lens according to Example 2 of the present invention, where (a) is a wide angle end, (b) is an intermediate, and (c) is telephoto. The state at the end is shown respectively. FIG. 5 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the zoom lens illustrated in FIG. 4 is focused on an object point at infinity, where (a) is the wide-angle end, (b) is the middle, and (c). Indicates the state at the telephoto end. FIG. 6 is a cross-sectional view along an optical axis showing an optical configuration when focusing on an object point at infinity of a zoom lens according to Example 3 of the present invention, where (a) is a wide angle end, (b) is an intermediate, and (c) is telephoto. The state at the end is shown respectively. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the zoom lens illustrated in FIG. 5 is focused on an object point at infinity, where (a) is the wide-angle end, (b) is the middle, and (c). Indicates the state at the telephoto end. FIG. 7 is a cross-sectional view along an optical axis showing an optical configuration when focusing on an object point at infinity of a zoom lens according to Example 4 of the present invention, where (a) is a wide angle end, (b) is an intermediate, and (c) is telephoto. The state at the end is shown respectively. FIG. 8 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the zoom lens illustrated in FIG. 7 is focused on an object point at infinity, where (a) is a wide angle end, (b) is an intermediate, and (c). Indicates the state at the telephoto end. It is a front perspective view which shows the external appearance of the digital camera incorporating the zoom lens of this invention. FIG. 10 is a rear front view of the digital camera shown in FIG. 9. FIG. 10 is a perspective plan view schematically showing the configuration of the digital camera shown in FIG. 9.

Explanation of symbols

G ₁ first lens group G ₂ the second lens group G ₃ third lens group G ₄ fourth lens group _{L 11, L 12, L 21} , L 22, L 23, L 3, L 4 lenses Lc optical axis S Brightness Aperture LF Low-pass filter CG Cover glass IM Imaging surface E Eyeball of observer 10 Digital camera 11 Imaging optical system 12 Optical path for imaging 13 Viewfinder optical system 14 Optical path for viewfinder 15 Shutter button 16 Flash light emitting unit 17 Liquid crystal display monitor 18 CCD
DESCRIPTION OF SYMBOLS 19 Cover member 20 Processing means 21 Recording means 22 Viewfinder objective optical system 23 Erecting prism 24 Field frame 25 Eyepiece optical system 26 Cover 27 Focal length change button 28 Setting change switch

Claims (20)

In order from the object side, a negative power first lens group, a positive power second lens group, a positive power third lens group, and a fourth lens group,
At the time of zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is reduced and the distance between the second lens group and the third lens group is increased.
An aperture stop that moves integrally with the second lens group between the most image side lens of the first lens group and the most image side lens of the second lens group;
The first lens group is composed of a negative power first lens disposed on the object side and a positive power second lens disposed on the image side,
A zoom lens satisfying the following conditional expressions (1) and (2):
_{0.15 <φ 1MF / φ 1MR <} 1.0 ··· (1)
_{-3.0 <φ 1PF / φ 1PR <} -1.0 ··· (2)
Where φ _1MF is the power of the object side surface of the first lens having the negative power of the first lens group, φ _1MR is the power of the image side surface of the first lens having the negative power of the first lens group, and φ _1PF Is the power of the object side surface of the second lens with positive power of the first lens group, and φ _1PR is the power of the image side surface of the second lens with positive power of the first lens group.   2. The zoom lens according to claim 1, wherein both surfaces of the negative lens first lens of the first lens group are aspherical surfaces. In order from the object side, a negative power first lens group, a positive power second lens group, a positive power third lens group, and a fourth lens group,
At the time of zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the second lens group is reduced and the distance between the second lens group and the third lens group is increased.
An aperture stop that moves integrally with the second lens group between the most image side lens of the first lens group and the most image side lens of the second lens group;
The first lens group is composed of a negative power first lens disposed on the object side and a positive power second lens disposed on the image side,
The zoom lens, wherein the third lens group and the fourth lens group are each composed of only one meniscus lens having a concave surface facing the object side. The zoom lens according to claim 3, wherein the following conditional expression (3) is satisfied.
15 <(φ3 / φ4) <320 (3)
Here, φ ₃ is the power of the third lens group, and φ ₄ is the power of the fourth lens group. The zoom lens according to claim 3 or 4, wherein the following conditional expression (4) is satisfied.
−10 <(R _3r + R _4f ) / (R _3r −R _4f ) <0 (4)
Where R _3r is the paraxial radius of curvature of the image side surface of the meniscus lens constituting the third lens group, and R _4f is the paraxial radius of curvature of the object side surface of the meniscus lens constituting the fourth lens group. is there. The zoom lens according to claim 3, wherein the following conditional expression (5) is satisfied.
1 <ds / dt <1.5 (5)
However, ds is parallel to the optical axis at the wide-angle end, and a line passing through the maximum image height position on the imaging surface intersects the image side surface of the meniscus lens constituting the third lens group and the fourth lens group. Dt is the distance from the point of intersection with the object side surface of the meniscus lens constituting the lens, dt is the image side surface of the meniscus lens constituting the third lens group at the wide angle end and the object side of the meniscus lens constituting the fourth lens group Is the distance on the optical axis from the surface of The zoom lens according to claim 1, wherein the following conditional expression (6) is satisfied.
6 ≦ N ≦ 9 (6)
N is the total number of lenses of the zoom lens.   The zoom lens according to any one of claims 1 to 7, wherein the second lens group includes three or less lenses.   The said 2nd lens group is comprised by the positive lens and the cemented lens which joined the positive power lens and the negative power lens to any one of Claim 1 thru | or 8 characterized by the above-mentioned. The described zoom lens.   The second lens group includes a cemented lens obtained by cementing a positive power lens and a negative power lens, and the negative power lens of the cemented lens has an Abbe number smaller than the positive power lens of the cemented lens. The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The zoom lens according to claim 9 or 10, wherein the following conditional expressions (7) and (8) are satisfied.
n _2pave ≧ 1.59 (7)
ν _2n ≦ 35 (8)
Here, n _2pave is the average value of the refractive indices of all the positive power lenses included in the second lens group, and ν _2n is the Abbe number of the negative power lenses included in the second lens group.   The distance between lenses constituting the second lens group is smaller than a center thickness of a negative power lens included in the second lens group. Zoom lens. The zoom lens according to any one of claims 1 to 12, wherein the following conditional expressions (9) and (10) are satisfied.
n _3ave ≧ 1.48 (9)
ν _3ave ≧ 60 (10)
However, n _3ave is the average value of the refractive indexes of all the lenses constituting the third lens group, and ν _3ave is the average value of the Abbe number of all the lenses constituting the third lens group.   The zoom lens according to any one of claims 1 to 13, wherein the third lens group includes one lens having at least one aspherical surface.   The zoom lens according to any one of claims 1 to 14, wherein the third lens group includes at least one resin lens. The zoom according to any one of claims 1 to 15, wherein the fourth lens group includes one lens, and satisfies the following conditional expressions (11) and (12). lens.
n ₄ ≧ 1.48 (11)
ν ₄ ≧ 60 (12)
Here, n ₄ is the refractive index of one lens constituting the fourth lens group, and ν ₄ is the Abbe number of one lens constituting the fourth lens group.   The zoom lens according to any one of claims 1 to 16, wherein the fourth lens group includes one lens having at least one aspherical surface.   The zoom lens according to any one of claims 1 to 17, wherein the fourth lens group includes a single resin lens.   The zoom lens according to claim 1, wherein the fourth lens group does not move during zooming. A zoom lens; an electronic image sensor disposed in the vicinity of an image forming position of the zoom lens; an image processing unit; and a recording unit. The image processing unit processes image data obtained by the electronic image sensor. In the electronic imaging device that changes the shape and causes the recording means to record,
The zoom lens is the zoom lens according to any one of claims 1 to 19,
An electronic imaging apparatus characterized by satisfying the following conditional expression (13) when focusing on an object point at infinity.
_{0.7 <y 07 / (f w} · tanω 07w) <1.5 ··· (13)
However, when the distance (maximum image height) from the center to the farthest point in the effective imaging plane (in the plane where imaging is possible) of the electronic imaging element is y ₁₀ , y ₀₇ = 0.7 y ₁₀ , ω _07w is an angle with respect to the optical axis in the object direction corresponding to the image point connecting from the center on the imaging surface at the wide angle end to the position of y ₀₇ .

Images