JP2011095329A - Zoom lens and image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens that achieves miniaturization and higher performance with a simple configuration and which is in a low degree of difficulty in manufacturing. <P>SOLUTION: The zoom lens includes three groups having negative, positive and positive power in order from an object side. The first group includes a negative cemented lens formed by joining together, from the object side, a first lens comprising a negative single lens and a second lens comprising a positive single lens. The second group includes a cemented lens formed by joining together, from the object side, a third lens comprising a positive single lens and a fourth lens comprising a negative single lens, and the third group includes a fifth lens comprising a positive single lens. The zoom lens satisfies following conditional expressions (1) to (3). (1) N1d>1.55, (2) v2d<30, and (3)¾G1R1/G2R2¾<3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zoom lens and an image pickup apparatus, and more particularly to a zoom lens and an image pickup apparatus having a zoom mechanism of a digital video camera, a digital still camera or the like (hereinafter referred to as a digital camera).

  In recent years, digital cameras using an image sensor such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor have rapidly spread and become common.

  As digital cameras become more common in this way, there is a growing need for users to reduce the cost, size, and functionality of digital still cameras with integrated lenses. Against the background of such user needs, zoom lenses are known which are so-called collapsible lenses having a negative, positive, and positive three-group configuration, in which the first group and the second group are each composed only of cemented lenses (for example, (See Patent Document 1 and Patent Document 2).

JP 2005-308953 JP JP 2007-225864 JP

  By the way, in the optical system described in Patent Document 1 described above, the setting of the glass material and curvature of the negative lens and the positive lens constituting the cemented lens of the first group is required for miniaturization, thinning, and high performance. There is a problem that it cannot be said that it is sufficiently effective, and it cannot be said that downsizing, thinning, and high performance are sufficiently achieved.

  In a cemented lens in which the first group is composed of positive and negative single lenses from the object side as described in Patent Document 2 described above, the first group consists of a positive single lens and a negative single lens in order from the object side. Because the lens is composed of a cemented lens, the incident angle of the peripheral ray is sharply bent by the positive single lens in the wide-angle end state and then incident on the negative single lens.

  For this reason, the cemented lens described in Patent Document 2 has a problem that correction of aberrations such as peripheral distortion and curvature of field in the wide-angle end state is disadvantageous.

  Further, when the first group described in Patent Document 2 described above is composed of a negative single lens, the lateral chromatic aberration in the wide-angle end state and the telephoto end state generated by the negative single lens of the first group. Due to axial chromatic aberration, performance degradation occurs in both the wide-angle end state and the telephoto end state, and it is difficult to say that both miniaturization and high performance are compatible.

  The present invention has been made in consideration of the above points, and is downsized with a simple configuration. It is an object of the present invention to propose a zoom lens and an imaging apparatus with low manufacturing difficulty that can realize a reduction in thickness and performance.

In order to solve such a problem, in the zoom lens of the present invention, the first lens is composed of three negative, positive, and positive groups in order from the object side, and the first lens is a negative single lens from the object side and the positive lens. The second lens unit is composed of a negative cemented lens obtained by cementing a second lens composed of a single lens, and the second lens unit is composed of a third lens composed of a positive single lens and a cemented lens composed of a fourth lens composed of a negative single lens from the object side. And the third lens unit is composed of a fifth lens that is a positive single lens, and satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

  In this three-group type zoom lens, the first group is composed of only one cemented lens composed of a first lens having a negative power and a second lens having a positive power.

  First, in the three-group type zoom lens, the first group is not composed of a plurality of lenses, but only a cemented lens, so that performance deterioration due to eccentricity between lenses in the first group does not occur. Therefore, alignment between lenses at the time of assembling becomes unnecessary, and the manufacturing process of the alignment can be omitted and the manufacturing time can be shortened.

  That is, in the zoom lens of the three-group type, the first group is not composed of a plurality of lenses but has a single structure consisting only of cemented lenses, thereby improving performance and reducing costs compared to the case where the first group is composed of a plurality of lenses. Thinning is possible.

  Secondly, in the zoom lens of the three-group type, since the first lens group is not a plurality of lens structures but a single structure including only a cemented lens, the lens interval error in the first lens group becomes zero. As described above, the shift amount of the focus position is smaller than in the case where the first group has a plurality of lenses.

  As a result, in the zoom lens of the three-group type, the margin of the mechanical hardware configuration for adjusting the focus position by the first to third groups can be reduced, so that the whole can be further reduced in size. .

  Thirdly, in the three-group type zoom lens, the first group has a single lens configuration instead of a plurality of lens configurations, and only a cemented lens. The position of the second group can be brought closer to the principal point position of the first group as much as the second lens positioned on the image plane side does not interfere with the second group.

  Thereby, in the zoom lens of the three-group type, the action of bringing the principal point position of the first group close to the image plane can be weakened by the second group. That is, in the zoom lens of the three-group type, the second group can be constituted by only the cemented lens of the positive third lens and the negative fourth lens, thus suppressing the lens eccentricity sensitivity in the second group, and It is possible to reduce the manufacturing difficulty while realizing thinning and high performance.

  Fourth, since the zoom lens of the three-group type can be constituted not only by the first group but also by the cemented lens for the second group, the performance degradation due to the eccentricity between the lenses in the second group is obviated. Can be prevented.

  At this time, in the zoom lens of the three-group type, there is no assembly variation in the optical axis direction between the lenses in the second group, so that the amount of focus position deviation is small. As a result, in the zoom lens of the three-group type, the margin of the mechanical hardware configuration for adjusting the focus position by the first to third groups can be reduced, so that the whole can be further reduced in size. .

  Here, the conditional expressions (1) to (3) in the three-group type zoom lens are defined in order to reduce the manufacturing difficulty while realizing thinning, downsizing, and high performance. .

  Conditional expression (1) defines the refractive index of the negative first lens constituting the cemented lens of the first group with respect to the d-line, and when the lower limit is not reached, the negative power of the first group is increased. When trying to achieve miniaturization, the curvature of the negative first lens is reduced, the thickness in the optical axis direction is increased, which is disadvantageous for thinning, and correction of spherical aberration, curvature of field and distortion is also difficult. become.

  If the lower limit value of conditional expression (1) is not reached, the curvature of the negative first lens becomes small, so that it becomes difficult to join the positive second lens when molding the cemented lens, and the manufacturing difficulty increases. That is, in the zoom lens of the three-group type, the manufacturing difficulty level is reduced while realizing a reduction in thickness according to the conditional expression (1).

  Conditional expression (2) defines the Abbe number of the positive second lens that constitutes the cemented lens of the first group, and while maintaining the miniaturization, the lateral chromatic aberration in the wide-angle end state and the axis in the telephoto end state This is for correcting the upper chromatic aberration.

  If the upper limit of conditional expression (2) is exceeded, the lateral chromatic aberration in the wide-angle end state and the longitudinal chromatic aberration in the telephoto end state that occur when the negative power of the first lens in the first group is increased are corrected. Therefore, the resolution performance of the peripheral portion of the image sensor in the wide-angle end state and the central portion of the image sensor in the telephoto end state is deteriorated.

  Conditional expression (3) indicates that the radius of curvature of the second surface of the positive second lens does not become too small compared to the radius of curvature of the first surface of the negative first lens constituting the cemented lens of the first group. Is stipulated.

  When the upper limit value of the conditional expression (3) is exceeded, the radius of curvature of the second surface of the second lens in the first group becomes too small compared to the first surface of the first lens in the first group, The manufacturing difficulty of the second lens unit and the cemented lens increases, and the manufacturing cost increases. In addition, the negative power of the first lens cannot be increased sufficiently, which is disadvantageous for downsizing.

The image pickup apparatus of the present invention further includes a zoom lens and an image pickup element that converts an optical image formed by the zoom lens into an electric signal. The zoom lens includes negative, positive, and positive 3 in order from the object side. The first group is composed of a negative cemented lens in which a first lens composed of a negative single lens and a second lens composed of a positive single lens are cemented from the object side, and the second group is positive from the object side. The third lens unit is composed of a cemented lens formed by cementing a third lens composed of a single lens and a fourth lens composed of a negative single lens, and the third group is composed of a fifth lens composed of a positive single lens. Satisfy (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

  In the zoom lens of the three-group type in this image pickup apparatus, the following advantages can be obtained by configuring the first group with only one cemented lens including a first lens having a negative power and a second lens having a positive power. There is.

  First, in a three-group type zoom lens in an image pickup apparatus, performance degradation due to decentration between lenses in the first group is achieved by making the first group a single configuration with only a cemented lens instead of a plurality of lens configurations. Therefore, alignment between lenses at the time of assembling becomes unnecessary, and the manufacturing process of the alignment can be omitted, and the manufacturing time can be shortened.

  That is, in the zoom lens of the three-group type in the image pickup apparatus, the first group is not composed of a plurality of lenses but has a single structure consisting only of cemented lenses. Cost reduction and thickness reduction are possible.

  Second, in the zoom lens of the three-group type in the imaging apparatus, the lens group error in the first group becomes zero by making the first group a single configuration with only a cemented lens instead of a plurality of lens configurations. As compared with the conventional case where the first lens unit is composed of a plurality of lenses, the shift amount of the focus position is small.

  As a result, in the zoom lens of the three-group type in the image pickup apparatus, the margin of the mechanical hardware configuration for adjusting the focus position by the first group to the third group can be reduced, so that the whole is further reduced in size. be able to.

  Thirdly, in the zoom lens of the three-group type in the image pickup apparatus, the first group is not composed of a plurality of lenses but a single structure consisting of only cemented lenses, so that the first group is composed of a plurality of lenses as in the prior art. When the configuration is adopted, the position of the second group can be brought closer to the principal point position of the first group by the amount that the second lens located on the image plane side does not interfere with the second group.

  Thereby, in the zoom lens of the three-group type in the imaging apparatus, the action of bringing the principal point position of the first group close to the image plane by the second group can be weakened. That is, in the zoom lens of the three-group type, the second group can be constituted only by the cemented lens of the positive third lens and the negative fourth lens, thus suppressing the lens eccentricity sensitivity in the second group, Thinning, high performance, and easy manufacturing can be realized.

  Fourthly, in the three-group type zoom lens in the image pickup apparatus, not only the first group but also the second group can be configured by only cemented lenses, so that performance degradation due to eccentricity between lenses in the second group. Can be prevented in advance.

  At this time, in the zoom lens of the three-group type in the imaging apparatus, there is no assembly variation in the optical axis direction between the lenses in the second group, so that the amount of focus position deviation is small. As a result, in the zoom lens of the three-group type in the image pickup apparatus, the margin of the mechanical hardware configuration for adjusting the focus position by the first group to the third group can be reduced, so that the whole is further reduced in size. be able to.

  Here, the conditional expressions (1) to (3) in the three-group type zoom lens are defined in order to reduce the manufacturing difficulty while realizing thinning, downsizing, and high performance. .

  Conditional expression (1) defines the refractive index of the negative first lens constituting the cemented lens of the first group with respect to the d-line, and when the lower limit is not reached, the negative power of the first group is increased. When trying to achieve miniaturization, the curvature of the negative first lens is reduced, the thickness in the optical axis direction is increased, which is disadvantageous for thinning, and correction of spherical aberration, curvature of field and distortion is also difficult. become.

  If the lower limit value of conditional expression (1) is not reached, the curvature of the negative first lens becomes small, so that it becomes difficult to join the positive second lens when molding the cemented lens, and the manufacturing difficulty increases. In other words, the zoom lens of the three-group type in the image pickup apparatus is designed to reduce the manufacturing difficulty while realizing a reduction in thickness according to the conditional expression (1).

  Conditional expression (2) defines the Abbe number of the positive second lens that constitutes the cemented lens of the first group, and while maintaining the miniaturization, the lateral chromatic aberration in the wide-angle end state and the axis in the telephoto end state This is for correcting the upper chromatic aberration.

  If the upper limit of conditional expression (2) is exceeded, the lateral chromatic aberration in the wide-angle end state and the longitudinal chromatic aberration in the telephoto end state that occur when the negative power of the first lens in the first group is increased are corrected. Therefore, the resolution performance of the peripheral portion of the image sensor in the wide-angle end state and the central portion of the image sensor in the telephoto end state is deteriorated.

  Conditional expression (3) indicates that the radius of curvature of the second surface of the positive second lens does not become too small compared to the radius of curvature of the first surface of the negative first lens constituting the cemented lens of the first group. Is stipulated.

  When the upper limit value of the conditional expression (3) is exceeded, the radius of curvature of the second surface of the second lens in the first group becomes too small compared to the first surface of the first lens in the first group, The manufacturing difficulty of the second lens unit and the cemented lens increases, and the manufacturing cost increases. In addition, the negative power of the first lens cannot be increased sufficiently, which is disadvantageous for downsizing.

According to the zoom lens of the present invention, in order from the object side, the zoom lens includes three groups of negative, positive, and positive, and the first group includes a first lens that is a negative single lens and a positive single lens that is negative from the object side. The second lens group is composed of a negative cemented lens in which two lenses are cemented, and the second lens group is composed of a third lens composed of a positive single lens and a cemented lens composed of a fourth lens composed of a negative single lens from the object side. Consists of a fifth lens that is a positive single lens, and is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

  As a result, according to the zoom lens of the present invention, it is a simple configuration, and by setting the glass material and the curvature of the negative first lens and the positive second lens constituting the first group optimally, the manufacturing difficulty level Therefore, it is possible to realize a reduction in thickness and performance.

Further, according to the imaging apparatus of the present invention, the zoom lens includes an imaging element that converts an optical image formed by the zoom lens into an electrical signal, and the zoom lens is negative, positive, positive in order from the object side. The first group is composed of a negative cemented lens in which a first lens composed of a negative single lens and a second lens composed of a positive single lens are cemented from the object side, and the second group is constructed positively from the object side. A third lens composed of a single lens and a fourth lens composed of a negative single lens, and a third lens composed of a fifth lens composed of a positive single lens.
The following conditional expressions (1) to (3) are satisfied.
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

  Thereby, according to the imaging device of the present invention, the zoom lens has a simple configuration, and by optimally setting the glass material and curvature of the negative first lens and the positive second lens constituting the first group, The manufacturing difficulty is low as a whole, and thinning and high performance can be realized.

FIG. 3 is a schematic cross-sectional view illustrating a configuration of a zoom lens according to a first numerical example. It is a rough-line sectional drawing which shows the lens group arrangement | positioning of a 1st numerical example. It is a characteristic curve figure which shows the various aberrations of a 1st numerical example. It is a rough-line sectional drawing which shows the structure of the zoom lens of a 2nd numerical example. It is an approximate line sectional view showing lens group arrangement of the 2nd numerical example. It is a characteristic curve figure which shows the various aberrations of the 2nd numerical example. It is a rough-line sectional drawing which shows the structure of the zoom lens of a 3rd numerical example. It is a rough-line sectional view showing the lens group arrangement of the third numerical example. It is a characteristic curve figure which shows the various aberrations of the 3rd numerical example. 1 is a schematic block diagram illustrating a configuration of a digital still camera equipped with an imaging apparatus of the present invention.

Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an embodiment) will be described. The description will be given in the following order.
1. Embodiment 2. FIG. Numerical examples corresponding to the embodiments (first numerical example to third numerical example)
3. 3. Imaging device and digital still camera Other embodiments

<1. Embodiment>
In the zoom lens of the three-group type according to the embodiment of the present invention, the first lens is composed of three negative, positive, and positive groups in order from the object side, and the first lens is a positive single lens from the object side and the positive lens. A cemented lens composed of a negative cemented lens obtained by cementing a second lens composed of a single lens, and a second lens composed of a third lens composed of a positive single lens and a fourth lens composed of a negative single lens from the object side. And the third group is composed of a fifth lens that is a positive single lens, and is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

  In this three-group type zoom lens, the first group is composed of only one cemented lens composed of a first lens having a negative power and a second lens having a positive power.

  First, in the three-group type zoom lens, the first group is not composed of a plurality of lenses, but only a cemented lens, so that performance deterioration due to eccentricity between lenses in the first group does not occur. Therefore, alignment between lenses at the time of assembling becomes unnecessary, and the manufacturing process of the alignment can be omitted and the manufacturing time can be shortened.

  That is, in the zoom lens of the three-group type, the first group is not composed of a plurality of lenses but has a single structure consisting only of cemented lenses, thereby improving performance and reducing costs compared to the case where the first group is composed of a plurality of lenses. It is possible to reduce the thickness.

  Secondly, in the zoom lens of the three-group type, since the first lens group is not a plurality of lens structures but a single structure including only a cemented lens, the lens interval error in the first lens group becomes zero. As described above, the shift amount of the focus position is smaller than in the case where the first group has a plurality of lenses.

  As a result, in the zoom lens of the three-group type, the margin of the mechanical hardware configuration for adjusting the focus position by the first to third groups can be reduced, so that the whole can be further reduced in size. .

  Thirdly, in the three-group type zoom lens, the first group has a single lens configuration instead of a plurality of lens configurations, and only a cemented lens. The position of the second group can be brought closer to the principal point position of the first group as much as the second lens positioned on the image plane side does not interfere with the second group.

  Thereby, in the zoom lens of the three-group type, the action of bringing the principal point position of the first group close to the image plane can be weakened by the second group. That is, in the zoom lens of the three-group type, the second group can be constituted by only the cemented lens of the positive third lens and the negative fourth lens, thus suppressing the lens eccentricity sensitivity in the second group, and It is possible to reduce the manufacturing difficulty while realizing thinning and high performance.

  Fourth, since the zoom lens of the three-group type can be constituted not only by the first group but also by the cemented lens for the second group, the performance degradation due to the eccentricity between the lenses in the second group is obviated. Can be prevented.

  At this time, in the zoom lens of the three-group type, there is no assembly variation in the optical axis direction between the lenses in the second group, so that the amount of focus position deviation is small. As a result, in the zoom lens of the three-group type, the margin of the mechanical hardware configuration for adjusting the focus position by the first to third groups can be reduced, so that the whole can be further reduced in size. .

  Here, the conditional expressions (1) to (3) in the three-group type zoom lens are defined in order to reduce the manufacturing difficulty while realizing thinning, downsizing, and high performance. .

  Conditional expression (1) defines the refractive index of the negative first lens constituting the cemented lens of the first group with respect to the d-line, and when the lower limit is not reached, the negative power of the first group is increased. When trying to achieve miniaturization, the curvature of the negative first lens is reduced, the thickness in the optical axis direction is increased, which is disadvantageous for thinning, and correction of spherical aberration, curvature of field and distortion is also difficult. become.

  If the lower limit value of conditional expression (1) is not reached, the curvature of the negative first lens becomes small, so that it becomes difficult to join the positive second lens when molding the cemented lens, and the manufacturing difficulty increases. That is, in the zoom lens of the three-group type, the manufacturing difficulty level is reduced while realizing a reduction in thickness according to the conditional expression (1).

  Conditional expression (2) defines the Abbe number of the positive second lens that constitutes the cemented lens of the first group, and while maintaining the miniaturization, the lateral chromatic aberration in the wide-angle end state and the axis in the telephoto end state This is for correcting the upper chromatic aberration.

  If the upper limit of conditional expression (2) is exceeded, the lateral chromatic aberration in the wide-angle end state and the longitudinal chromatic aberration in the telephoto end state that occur when the negative power of the first lens in the first group is increased are corrected. Therefore, the resolution performance of the peripheral portion of the image sensor in the wide-angle end state and the central portion of the image sensor in the telephoto end state is deteriorated. Incidentally, in the conditional expression (2), if the upper limit value is set to 27, the effect is further enhanced.

  Conditional expression (3) indicates that the radius of curvature of the second surface of the positive second lens does not become too small compared to the radius of curvature of the first surface of the negative first lens constituting the cemented lens of the first group. Is stipulated.

  When the upper limit value of the conditional expression (3) is exceeded, the radius of curvature of the second surface of the second lens in the first group becomes too small compared to the first surface of the first lens in the first group, The manufacturing difficulty of the second lens unit and the cemented lens increases, and the manufacturing cost increases. In addition, the negative power of the first lens cannot be increased sufficiently, which is disadvantageous for downsizing. Incidentally, even in the conditional expression (3), if the upper limit value is set to 1.7, the effect is further enhanced.

Subsequently, in the zoom lens of the third group type of the present invention, the curvature of the surface closest to the object side and the curvature of the surface closest to the image plane in the cemented lens of the first group are expressed by the following conditional expressions (4) and (5). It is configured to satisfy.
(4) G1R1 / fw <−2.2
(5) G2R2 / fw> 3
However,
fw: The focal length in the wide-angle end state.

  Conditional expression (4) defines the radius of curvature of the most object-side surface of the first lens in the first group cemented lens, and conditional expression (5) is the second in the first group cemented lens. It defines the radius of curvature of the surface closest to the image plane of the lens.

  If the upper limit value of the conditional expression (4) is exceeded, the radius of curvature of the most object side surface of the first lens in the first group cemented lens becomes too small, and the most object side surface of the first lens. The protrusion in the optical axis direction of the lens end with respect to the apex becomes large, which is disadvantageous for thinning.

  When the lower limit of conditional expression (5) is not reached, the radius of curvature of the surface closest to the image plane of the second lens in the cemented lens of the first group becomes too small with respect to the focal length in the wide-angle end state. The manufacturing difficulty of the second single lens and the cemented lens increases, and the manufacturing cost increases.

  At this time, the radius of curvature of the image surface side surface of the second lens in the cemented lens of the first group becomes too small, so that the optical axis of the lens end with respect to the surface vertex of the image surface side of the second lens. Since the protrusion in the direction becomes large and interferes, it is difficult to sufficiently shorten the interval between the first group and the second group.

  As a result, in the three-group type zoom lens, the principal point position of the first group cannot be brought close to the image plane by the second group, so that it is particularly difficult to correct spherical aberration and curvature of field.

Next, the zoom lens of the third group type according to the present invention is configured such that at least one surface of the first group closest to the object side or the image surface side has a spherical shape and satisfies the following conditional expression (6). ing.
(6) | G1R1 / G2R2 | <1.4

  Here, the conditional expression (6) is similar to the conditional expression (3) described above in the positive second lens compared to the radius of curvature of the first surface in the negative first lens constituting the cemented lens of the first group. This is defined so that the radius of curvature of the second surface does not become too small.

  When exceeding the upper limit value of the conditional expression (6), if it is attempted to have a sufficient negative power in the first group, the first surface or the positive second in the negative first lens constituting the cemented lens of the first group. The radius of curvature of the second surface of the lens becomes too small.

  At this time, in the zoom lens of the three-group type, an aspherical surface formed on at least one surface on the most object side or the most image surface side of the first group is corrected for distortion aberration, field curvature, coma aberration, etc. in the wide-angle end state. It becomes difficult only with the shape, and the deterioration of the optical performance in the peripheral portion particularly in the wide-angle end state becomes remarkable.

  In the case of a three-group type zoom lens, when one of the negative first lens and the positive second lens constituting the cemented lens of the first group is a spherical lens in order to reduce the cost, aberration correction is required. It is better to make the positive second lens spherical.

  The reason is that the positive second lens on the image plane side is closer to the optical axis in the wide-angle end state than the negative first lens on the object side, and the positive second lens. It can be mentioned that the radius of curvature is large because the lens is weaker than the negative first lens.

  When the refractive index of the first lens is low as in the prior art document 1, when trying to increase the negative power of the first group, the first surface or the positive surface of the negative first lens constituting the cemented lens of the first group is positive. Unless both surfaces of the second surface of the second lens are aspherical, it becomes difficult to correct distortion aberration, curvature of field, spherical aberration, coma aberration, and the like in the wide-angle end state.

  Therefore, in the zoom lens of the three-group type, not only the cost is reduced by making one of the first lens and the second lens constituting the cemented lens of the first group spherical, but also the required accuracy of the cemented lens. Therefore, the cost of the cemented lens can be reduced.

  Further, in the zoom lens of the three-group type according to the present invention, the cemented lens of the first group is composed of a composite aspherical lens composed of a first lens made of a negative glass lens and a second lens made of a positive resin lens. It is characterized by being.

  As described above, the zoom lens of the three-group type constitutes the cemented lens of the first group by molding using a resin. Therefore, compared with the case where the glass lenses are cemented with each other, the second lens made of the resin is used. The thickness of the periphery of the lens can be made much thinner than in the case of a glass lens.

Furthermore, in the zoom lens of the third group type according to the present invention, the distance from the aperture stop of the second group to the vertex of the lens surface of the fourth lens disposed closest to the image plane in the second group is expressed by the following conditional expression ( 7) is satisfied.
(7) L / (fw * ft) ^1/2 <0.25
However,
ft: focal length in the telephoto end state L: a fourth lens disposed closest to the image plane of the second group from the aperture stop disposed in the second group
The distance to the apex of the lens surface.

  This conditional expression (7) defines the distance from the aperture stop to the lens surface apex of the fourth lens disposed closest to the image plane in the second group, and specifies that this distance is not too long. It is.

  When the upper limit value of conditional expression (7) is exceeded, the incident angle of the peripheral ray to the fourth lens disposed closest to the image plane in the second group particularly in the wide-angle end state becomes large, and coma aberration occurs. Resolution performance deteriorates.

<2. Numerical Example Corresponding to Embodiment>
Next, numerical examples in which specific numerical values are applied to the three-group type zoom lens of the present invention will be described below with reference to the drawings and diagrams. Here, in each numerical example, the aspherical surface is expressed by the following equation (1).

x = cy ² / (1+ (1- (1 + k) c ² y ² ) ^1/2 ) + Ay ⁴ + By ⁶ +
...... (1)

  Here, y is the height from the optical axis, x is the sag amount, c is the curvature, k is the conic constant, and A, B,... Are aspherical coefficients.

[2-1. First numerical example]
In FIG. 1, reference numeral 1 denotes a zoom lens according to a first numerical example corresponding to the first embodiment as a whole, and in order from the object side, a negative first group G1, a positive second group G2, and a positive first group. It is formed by a three-group configuration of three groups G3.

  FIG. 2 shows the lens group arrangement in the first numerical example when the zoom lens 1 is in the wide-angle end state (WIDE), the intermediate focal length state (MID), and the telephoto end state (TELE).

  The first group G1 is a cemented lens L12 composed of a first lens L1 made of a negative glass aspheric lens and a second lens L2 made of a positive glass aspheric lens, and has a negative power as a whole. is doing.

  The second group G2 includes a cemented lens L34 in which a third lens L3 that is a positive aspheric lens and a fourth lens L4 that is a negative aspheric lens are cemented, and an aperture stop S is located on the object side of the second group G2. Is arranged. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 includes a fifth lens L5 made of a positive single lens. In the zoom lens 1, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are disposed between the third group G3 and the image plane IMG.

  Tables 1 to 5 below list the specification values of the first numerical example corresponding to the first embodiment. Here, f in the specification table in the first numerical example is a focal length, FNO is an F number, ω is a half angle of view, and a refractive index is a value with respect to the d-line (wavelength 587.6 nm). In Table 1, the curvature radius ∞ means a plane.

The first surface, the third surface, the fifth surface, the seventh surface, the eighth surface, and the ninth surface are aspherical, and the aspherical coefficients are as shown in Table 3. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, the variable interval when the lens position state changes in the zoom lens 1 of the first numerical example is shown in Table 4 below. In the zoom lens 1, the first group G1, the second group G2, and the third group G3 are all movable, and zooming is realized mainly by changing the interval between the first group G1 and the second group G2. In addition, by moving the third group G3 to absorb the focal position variation at each angle of view, high performance can be ensured while maintaining miniaturization.

  Table 5 below shows values corresponding to the conditional expressions in the zoom lens 1 of the first numerical example.

  Next, FIG. 3 is a diagram showing various aberrations in the infinite focus state in the first numerical example. FIG. 3A is a wide-angle end state (ω = 30.06 degrees), and FIG. FIG. 3C shows various aberrations in the telephoto end state (ω = 12.74 degrees), respectively, in the focal length state (ω = 19.15 degrees).

  3A to 3C, the spherical aberration corresponds to the C-line with a wavelength of 656.3 nm, the D-line with a wavelength of 587.6 nm, and the G-line with a wavelength of 435.8 nm, and the solid line in the field curvature diagram is The sagittal image plane and the broken line indicate the meridional image plane, and the distortion corresponds to the D-line having a wavelength of 587.6 nm.

  3A to 3C, the zoom lens 1 of the first numerical example corrects various aberrations in spite of being made thinner and smaller, and has excellent imaging. It turns out that it has performance.

[2-2. Second numerical example]
In FIG. 4, reference numeral 2 denotes a zoom lens according to a second numerical example corresponding to the first embodiment as a whole, and in order from the object side, a negative first group G1, a positive second group G2, and a positive first group. It consists of 3 groups of 3 groups G3.

  FIG. 5 shows the lens group arrangement in the second numerical example when the zoom lens 2 is in the wide-angle end state (WIDE), the intermediate focal length state (MID), and the telephoto end state (TELE).

  The first group G1 is a cemented lens L12 composed of a first lens L1 made of a negative glass aspheric lens and a second lens L2 made of a positive glass spherical lens, and has negative power as a whole. ing.

  The second group G2 includes a cemented lens L34 in which a third lens L3 that is a positive aspheric lens and a fourth lens L4 that is a negative aspheric lens are cemented, and an aperture stop S is located on the object side of the second group G2. Is arranged. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 includes a fifth lens L5 made of a positive single lens. In the zoom lens 2, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are arranged between the third group G3 and the image plane IMG.

  Tables 6 to 10 below show specification values of the second numerical example corresponding to the first embodiment. Here, f in the specification table in the second numerical example represents the focal length, FNO represents the F number, ω represents the half angle of view, and the refractive index is a value with respect to the d-line (wavelength 587.6 nm). In Table 1, the curvature radius ∞ means a plane.

The first surface, the fifth surface, the seventh surface, the eighth surface, and the ninth surface have aspherical shapes, and the aspherical coefficients are as shown in Table 8. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, the variable interval when the lens position state changes in the zoom lens 2 of the second numerical example is shown in Table 9 below. In the zoom lens 2, all of the first group G1, the second group G2, and the third group G3 are movable, and the zooming is realized mainly by changing the interval between the first group G1 and the second group G2. In addition, by moving the third group G3 to absorb the focal position variation at each angle of view, high performance can be ensured while maintaining miniaturization.

  Table 10 below shows values corresponding to the conditional expressions in the zoom lens 2 of the second numerical example.

  Next, FIG. 6 is a diagram showing various aberrations in the infinite focus state in the second numerical example. FIG. 6A is a wide-angle end state (ω = 30.26 degrees), and FIG. FIG. 6C shows various aberrations in the telephoto end state (ω = 12.96 degrees), respectively, in the focal length state (ω = 19.36 degrees).

  6A to 6C, the spherical aberration corresponds to a C-line with a wavelength of 656.3 nm, a D-line with a wavelength of 587.6 nm, and a G-line with a wavelength of 435.8 nm, and the solid line in the field curvature diagram is The sagittal image plane and the broken line indicate the meridional image plane, and the distortion corresponds to the D-line having a wavelength of 587.6 nm.

  6A to 6C, the zoom lens 2 of the second numerical example corrects various aberrations in spite of being made thinner and smaller, and has excellent imaging. It turns out that it has performance.

[2-3. Third numerical example]
In FIG. 7, reference numeral 3 denotes a zoom lens according to a third numerical example corresponding to the first embodiment as a whole, and in order from the object side, a negative first group G1, a positive second group G2, and a positive first group. It consists of 3 groups of 3 groups G3.

  FIG. 8 shows the lens group arrangement when the zoom lens 3 is in the wide-angle end state (WIDE), the intermediate focal length state (MID), and the telephoto end state (TELE) in the third numerical example.

  The first group G1 is a cemented lens L12 composed of a composite aspherical lens in which a first lens L1 composed of a negative glass aspherical lens and a second lens L2 composed of a positive resin are cemented. Has power.

  The second group G2 includes a third lens L3 that is a positive aspheric lens and a cemented lens L34 that is a cemented fourth lens L4 that is a negative aspheric lens, and the aperture stop S is an object of the second group G2. Arranged on the side. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 includes a fifth lens L5 made of a positive single lens. In the zoom lens 3, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are disposed between the third group G3 and the image plane IMG.

  Tables 11 to 15 below list specification values of the third numerical value example corresponding to the first embodiment. Here, f in the specification table in the third numerical example represents the focal length, FNO represents the F number, ω represents the half angle of view, and the refractive index is a value with respect to the d-line (wavelength 587.6 nm). In Table 1, the curvature radius ∞ means a plane.

The first surface, the third surface, the fifth surface, the seventh surface, the eighth surface, and the ninth surface are aspherical, and the aspherical coefficients are as shown in Table 13. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, the variable interval when the lens position state changes in the zoom lens 3 of the third numerical example is shown in Table 14 below. In the zoom lens 3, all of the first group G1, the second group G2, and the third group G3 are movable, and the zooming is realized mainly by changing the interval between the first group G1 and the second group G2. In addition, by moving the third group G3 to absorb the focal position variation at each angle of view, high performance can be ensured while maintaining miniaturization.

  Table 15 below shows values corresponding to the conditional expressions in the zoom lens 3 of the third numerical example.

  FIG. 9 is a diagram showing various aberrations in the infinitely focused state of the third numerical example. FIG. 9A is a wide-angle end state (ω = 29.89 degrees), and FIG. FIG. 9C shows various aberrations in the telephoto end state (ω = 12.71 degrees), respectively, at the focal length state (ω = 19.02 degrees).

  9A to 9C, the spherical aberration corresponds to the C-line with a wavelength of 656.3 nm, the D-line with a wavelength of 587.6 nm, and the G-line with a wavelength of 435.8 nm, and the solid line in the field curvature diagram is The sagittal image plane and the broken line indicate the meridional image plane, and the distortion corresponds to the D-line having a wavelength of 587.6 nm.

  9A to 9C, the zoom lens 3 according to the third numerical example corrects various aberrations in spite of being thinned and miniaturized, and has excellent imaging. It turns out that it has performance.

  As described above, according to the first to third numerical examples corresponding to the embodiments, in the zoom lenses 1 to 3, the focal length Wf in the wide-angle end state is 28 mm to 38 mm (35 mm film equivalent), Low-cost and high-capacity imaging system with a zoom ratio of about 2 to 4 times, FNO in the wide-angle end state of about 2.5 to 3.5, and FNO in the telephoto end state of about 5 to 6.5 It is made to be able to realize.

<3. Imaging device and digital still camera>
[3-1. Configuration of imaging device]
Next, the imaging device of the present invention will be described. This imaging apparatus is, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary) for converting an optical image formed by the zoom lens 1 (or 2, 3) shown in the embodiment of the present invention into an electrical signal. (Metal Oxide Semiconductor) sensor and other image sensor.

The zoom lens 1 (or 2, 3) is composed of three groups of negative, positive, and positive in order from the object side, and the first lens G1 is a positive single lens from the object side and a positive lens L1. Consists of a negative cemented lens L12 cemented with a second lens L2 composed of a single lens, and the second lens unit G2 cements a third lens L3 composed of a positive single lens and a fourth lens L4 composed of a negative single lens from the object side. The third lens group G3 includes a fifth lens L5 that is a positive single lens, and is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

  In this three-group type zoom lens 1 (or 2, 3), only one cemented lens L12 including a first lens L1 having a negative power and a second lens L2 having a positive power is used as the first group G1. The configuration has the following merits.

  First, in the zoom lens 1 (or 2, 3) of the three-group type, the first lens group G1 is not composed of a plurality of lenses, but has a single configuration of only the cemented lens L12, so that the lenses in the first lens group G1 Since there is no performance deterioration due to the eccentricity between the lenses, alignment between the lenses at the time of assembling becomes unnecessary, and the manufacturing process of the alignment can be omitted and the manufacturing time can be shortened.

  That is, in the zoom lens 1 (or 2, 3) of the three-group type, the first group G1 has a single lens configuration by forming the first lens group G1 only with a cemented lens L12 instead of a plurality of lens lenses. Rather than doing so, it is possible to improve performance, reduce costs and reduce thickness.

  Secondly, in the zoom lens 1 (or 2, 3) of the three-group type, the first lens group G1 is not composed of a plurality of lenses but has a single structure consisting only of the cemented lens L12. Since the distance error is 0, the amount of shift in the focus position is smaller than in the conventional case where the first group G1 has a plurality of lenses.

  Thereby, in the zoom lens 1 (or 2, 3) of the three group type, the margin of the mechanical hardware configuration for adjusting the focus position by the first group G1 to the third group G3 can be reduced. The whole can be further reduced in size.

  Thirdly, in the zoom lens 1 of the three-group type (or 2, 3), the first group G1 is not a plurality of lens configurations but a single configuration of only the cemented lens L12. When the group G1 has a plurality of lenses, the second lens L2 positioned on the image plane side does not get in the way of the second group G2, and the position of the second group G2 is further increased. The point position can be approached.

  Thereby, in the zoom lens 1 (or 2, 3) of the three-group type, the action of bringing the principal point position of the first group G1 closer to the image plane by the second group G2 can be weakened. That is, in the three-group type zoom lens 1 (or 2, 3), the second group G2 can be configured only by the cemented lens L34 of the positive third lens L3 and the negative fourth lens L4. The lens eccentricity sensitivity in G2 can be suppressed, and the manufacturing difficulty can be lowered while realizing a reduction in thickness and performance.

  Fourthly, in the zoom lens 1 (or 2, 3) of the third group type, not only the first group G1 but also the second group G2 can be constituted by only the cemented lens L34. It is possible to prevent deterioration in performance due to eccentricity between lenses.

  At this time, in the three-group type zoom lens 1 (or 2, 3), there is no assembly variation in the optical axis direction between the lenses in the second lens group G2, so that the amount of focus position deviation is small. Thereby, in the zoom lens 1 (or 2, 3) of the three group type, the margin of the mechanical hardware configuration for adjusting the focus position by the first group G1 to the third group G3 can be reduced. The whole can be further reduced in size.

  Here, the conditional expressions (1) to (3) in the three-group type zoom lens 1 (or 2, 3) are intended to reduce the manufacturing difficulty while realizing a reduction in thickness, size, and performance. It is stipulated in.

  Conditional expression (1) defines the refractive index with respect to the d-line of the negative first lens L1 constituting the cemented lens L12 of the first group G1, and when the lower limit is not reached, the negative value of the first group G1 is negative. When attempting to reduce the size by increasing the power, the curvature of the negative first lens L1 is reduced, the thickness in the optical axis direction is increased, which is disadvantageous for the reduction in thickness, and spherical aberration, field curvature, and distortion. Aberration correction is also difficult.

  When the lower limit of conditional expression (1) is not reached, the curvature of the negative first lens L1 becomes small, so that it becomes difficult to join the positive second lens L2 when the cemented lens L12 is molded, and the manufacturing difficulty increases. End up. That is, the zoom lens 1 (or 2, 3) of the three-group type is designed to reduce the manufacturing difficulty while realizing a reduction in thickness by the conditional expression (1).

  Conditional expression (2) prescribes the Abbe number of the positive second lens L2 constituting the cemented lens L12 of the first group G1, and maintains the miniaturization, the chromatic aberration of magnification in the wide-angle end state, and the telephoto end. This is for correcting the axial chromatic aberration in the state.

  If the upper limit of conditional expression (2) is exceeded, the lateral chromatic aberration in the wide-angle end state and the longitudinal chromatic aberration in the telephoto end state that occur when the negative power of the first lens L1 in the first group G1 is increased. It cannot be corrected, and the resolution performance of the peripheral portion of the image sensor in the wide-angle end state and the center portion of the image sensor in the telephoto end state is deteriorated. Incidentally, in the conditional expression (2), if the upper limit value is set to 27, the effect is further enhanced.

  Conditional expression (3) indicates that the radius of curvature of the second surface of the positive second lens L2 is smaller than the radius of curvature of the first surface of the negative first lens L1 constituting the cemented lens L12 of the first group G1. It prescribes not to become too much.

  When the upper limit value of conditional expression (3) is exceeded, the radius of curvature of the second surface of the second lens L2 of the first group G1 is too small compared to the first surface of the first lens L1 of the first group G1. As a result, the manufacturing difficulty of the single second lens L2 and the cemented lens L12 increases, and the manufacturing cost increases. In addition, the negative power of the first lens L1 cannot be sufficiently increased, which is disadvantageous for downsizing. Incidentally, even in the conditional expression (3), if the upper limit value is set to 1.7, the effect is further enhanced.

Subsequently, in the third group type zoom lens 1 (or 2, 3), the curvature of the surface closest to the object side and the curvature of the surface closest to the image plane in the cemented lens L12 of the first group G1 are expressed by the following conditional expressions ( 4) and (5) are satisfied.
(4) G1R1 / fw <−2.2
(5) G2R2 / fw> 3
However,
fw: The focal length in the wide-angle end state.

  Conditional expression (4) defines the radius of curvature of the most object side surface of the first lens L1 in the cemented lens L12 of the first group G1, and conditional expression (5) is the cemented lens of the first group G1. This defines the radius of curvature of the surface closest to the image plane of the second lens L2 in the lens L12.

  When the upper limit value of the conditional expression (4) is exceeded, the radius of curvature of the most object side surface of the first lens L1 in the cemented lens L12 of the first group G1 becomes too small, and the most object of the first lens L1. The protrusion in the optical axis direction of the lens end with respect to the surface apex on the side becomes large, which is disadvantageous for thinning.

  When the lower limit of conditional expression (5) is not reached, the radius of curvature of the surface closest to the image plane of the second lens L2 in the cemented lens L12 of the first group G1 becomes smaller than the focal length fw in the wide-angle end state. Therefore, the manufacturing difficulty of the second lens L2 single product and the cemented lens L12 increases, and the manufacturing cost increases.

  At this time, the radius of curvature of the image surface side surface of the second lens L2 in the cemented lens L12 of the first group G1 becomes too small, and the end of the lens relative to the surface vertex of the image surface side of the second lens L2 becomes smaller. Since the protrusion in the optical axis direction becomes large and interferes, it is difficult to sufficiently shorten the distance between the first group G1 and the second group G2.

  As a result, in the zoom lens 1 (or 2, 3) of the third group type, the principal point position of the first group G1 cannot be brought close to the image plane IMG by the second group G2, and thus spherical aberration and curvature of field are particularly important. Correction becomes difficult.

Next, in the three-group type zoom lens 1 (or 2, 3), at least one surface closest to the object side or the image surface side of the first group G1 is spherical, and the following conditional expression (6) is satisfied. Is configured to do.
(6) | G1R1 / G2R2 | <1.4

  Here, the conditional expression (6) is positive as compared with the above-described conditional expression (3), compared to the curvature radius of the first surface of the negative first lens L1 constituting the cemented lens L12 of the first group G1. This is defined so that the radius of curvature of the second surface of the two lens L2 does not become too small.

  When exceeding the upper limit value of the conditional expression (6), if the first group G1 is to have sufficient negative power, the first surface in the negative first lens L1 constituting the cemented lens L12 of the first group G1 or The radius of curvature of the second surface of the positive second lens L2 becomes too small.

  At this time, in the zoom lens 1 (or 2, 3) of the three-group type, correction for distortion aberration, field curvature, coma aberration, etc. in the wide-angle end state is performed at least on the most object side or the most image plane side of the first group G1. It becomes difficult only with the aspherical shape formed on one surface, and the deterioration of the optical performance in the peripheral portion particularly in the wide-angle end state becomes remarkable.

  In the three-group type zoom lens 1 (or 2, 3), for the purpose of cost reduction, whichever of the negative first lens L1 and the positive second lens L2 constituting the cemented lens L12 of the first group G1 is selected. In the case of using a spherical lens, it is better to make the positive second lens L2 spherical in terms of aberration correction.

  The reason is that the positive second lens L2 on the image plane side is closer to the optical axis in the wide-angle end state than the negative first lens L1 on the object side, and is positive. Since the power of the second lens L2 is weaker than that of the negative first lens L1, the radius of curvature is large.

  When the refractive index of the first lens L1 is low as in the prior art document 1, if an attempt is made to increase the negative power of the first group G1, the first lens L1 in the negative first lens L1 constituting the cemented lens L12 of the first group G1 will be described. Unless both the first surface and the second surface of the positive second lens L2 are aspherical, it is difficult to correct distortion aberration, curvature of field, spherical aberration, coma aberration, and the like in the wide-angle end state.

  Accordingly, in the zoom lens 1 (or 2, 3) of the three-group type, either the first lens L1 or the second lens L2 constituting the cemented lens L12 of the first group G1 is aspherical. In addition to reducing the cost, the required accuracy of bonding is also reduced, so that the cost of the cemented lens L12 can be reduced.

  Further, in the three-group type zoom lens 1 (or 2, 3), the cemented lens L12 of the first group G1 is based on the first lens L1 made of a negative glass lens and the second lens L2 made of a positive resin lens. It is characterized by comprising a composite aspheric lens.

  As described above, the zoom lens 1 (or 2, 3) of the three-group type constitutes the cemented lens L12 of the first group G1 by molding using a resin. In comparison, the thickness of the periphery of the second lens L2 made of the resin can be made much thinner than in the case of a glass lens.

Further, in the zoom lens 1 (or 2, 3) of the third group type, the distance from the aperture stop S of the second group G1 to the vertex of the lens surface of the fourth lens L4 arranged closest to the image plane of the second group G2. Is configured to satisfy the following conditional expression (7).
(7) L / (fw * ft) ^1/2 <0.25
However,
ft: focal length in the telephoto end state L: a fourth lens disposed closest to the image plane of the second group from the aperture stop disposed in the second group
The distance to the apex of the lens surface.

  This conditional expression (7) defines the distance from the aperture stop S to the apex of the lens surface of the fourth lens L4 arranged closest to the image plane in the second group G2, and this distance is not too long. It prescribes.

  When the upper limit value of the conditional expression (7) is exceeded, the incident angle of the peripheral ray on the fourth lens L4 arranged closest to the image plane of the second group G2 particularly in the wide-angle end state becomes large, and coma aberration occurs. This degrades the resolution performance.

[3-2. Configuration of digital still camera]
As shown in FIG. 10, a digital still camera 100 equipped with the above-described imaging device includes a camera block 15 that assumes an imaging function as an imaging device, an analog-to-digital conversion process for an image signal captured by the camera block 15, and the like. And a camera signal processing unit 20 for performing the signal processing.

  The digital still camera 100 performs writing / reading to / from the image processing unit 30 that performs recording / playback processing of image signals, an LCD (Liquid Crystal Display) 40 that displays captured images and the like, and a memory card 51. A reader / writer 50.

  In addition, the digital still camera 100 includes a CPU (Central Processing Unit) 60 that controls the entire camera, an input unit 70 for operation input by the user, and lens drive control that controls driving of the lenses in the camera block 15. Part 80.

  The camera block 15 has a configuration in which an optical system including the zoom lens 1 (or 2, 3) is combined with an image sensor 16 formed of, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. Have.

  The camera signal processing unit 20 performs signal processing such as conversion processing of an output signal from the image sensor 16 into a digital signal, noise removal, image quality correction, and conversion processing into a luminance / color difference signal.

  The image processing unit 30 performs compression encoding / decompression decoding processing of image signals based on a predetermined image data format, conversion processing of data specifications such as resolution, and the like.

  The memory card 51 is composed of a detachable semiconductor memory. The reader / writer 50 writes the image data encoded by the image processing unit 30 to the memory card 51 and reads the image data recorded on the memory card 51.

  The CPU 60 controls each circuit block in the digital still camera 100 in an integrated manner, and controls each circuit block based on an instruction input signal or the like from the input unit 70.

  The input unit 70 includes, for example, a shutter release button for performing a shutter operation, a selection switch for selecting an operation mode, and the like, and outputs an instruction input signal according to an operation by a user to the CPU 60.

  The lens drive control unit 80 controls a motor (not shown) that drives the lens group in the zoom lens 1 (or 2, 3) based on a control signal from the CPU 60.

  Next, the operation of the digital still camera 100 will be briefly described. When the digital still camera 100 is in a shooting standby state, the image signal captured by the camera block 15 is output to the LCD 40 via the camera signal processing unit 20 and displayed as a camera through image under the control of the CPU 60. Has been made.

  In the digital still camera 100, when an instruction input signal for zooming is input from the input unit 70, the CPU 60 outputs a control signal to the lens drive control unit 80, and zooms based on the control of the lens drive control unit 80. A predetermined lens group in the lens 1 (or 2, 3) is moved.

  The digital still camera 100 outputs a captured image signal from the camera signal processing unit 20 to the image processing unit 30 when a shutter (not shown) of the camera block 15 is released by an instruction input signal from the input unit 70.

  In the image processing unit 30, the image signal supplied from the camera signal processing unit 20 is subjected to predetermined compression coding, and then converted into digital data of a predetermined data format, which is converted into a memory card 51 via the reader / writer 50. It is made to write in.

  In focusing, for example, when the shutter release button is half-pressed or fully pressed for recording, the lens drive control unit 80 drives the zoom lens 1 (or 2, 3) based on a control signal from the CPU 60. This is done by controlling.

  When reproducing the image data recorded on the memory card 51, the CPU 60 reads the image data from the memory card 51 by the reader / writer 50 in response to an operation on the input unit 70, and decompresses and decodes it by the image processing unit 30. This is output to the LCD 40.

  The LCD 40 is configured to display a reproduced image based on the image data that has been decompressed and decoded by the image processing unit 30.

  Incidentally, in this embodiment, the case where the imaging apparatus of the present invention is applied to a digital still camera has been described. However, the present invention can also be applied to other imaging apparatuses such as a digital video camera.

<4. Other embodiments>
In addition, the specific shapes, structures, and numerical values of the respective parts shown in the embodiment and the first numerical example to the third numerical example described above are only examples of the implementation performed in carrying out the present invention. However, the technical scope of the present invention should not be construed in a limited manner.

  In the above-described embodiment, the case where the imaging apparatus is mounted on the digital still camera 100 is shown as an example. However, the object on which the imaging device is mounted is not limited to this, and is widely applied to various other electronic devices such as a digital video camera, a mobile phone, a personal computer with a camera mounted thereon, and a PDA with a camera incorporated therein. can do.

  1, 2, 3, ... Zoom lens, 15 ... Camera block, 16 ... Imaging device, 30 ... Image processing unit, 40 ... LCD, 50 ... Reader / writer, 51 ... Memory card, 60 ... CPU , 70... Input unit, 80... Lens drive control unit.

Claims (6)

A negative cemented lens composed of three negative, positive, and positive groups in order from the object side, in which the first lens unit is joined from the object side by a first lens that is a negative single lens and a second lens that is a positive single lens. The second group is composed of a cemented lens formed by cementing a third lens that is a positive single lens and a fourth lens that is a negative single lens from the object side, and the third group is a fifth lens that is a positive single lens. Consisting of lenses,
A zoom lens that satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index v2d for negative d-line constituting the first group cemented lens v2d: Abbe number G1R of the positive second lens constituting the first group cemented lens: Negative constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the first lens: the radius of curvature of the second surface of the positive second lens constituting the cemented lens of the first group. The zoom lens
The zoom lens according to claim 1, wherein the following conditional expressions (4) and (5) are satisfied.
(4) G1R1 / fw> −2.2
(5) G2R2 / fw> 3
However,
fw: focal length in the wide-angle end state. In the zoom lens, at least one surface closest to the object side or the image surface side of the first group is spherical.
The zoom lens according to claim 1, wherein the following conditional expression (6) is satisfied.
(6) | G1R1 / G2R2 | <1.4 In the zoom lens, the cemented lens of the first group is composed of a composite aspherical lens including the first lens made of a negative glass lens and the second lens made of a positive resin lens. Item 4. The zoom lens according to Item 1. The zoom lens has a distance from the aperture stop of the second group to the apex of the lens surface of the fourth lens arranged closest to the image plane of the second group,
The zoom lens according to claim 1, wherein the following conditional expression (7) is satisfied.
(7) L / (fw * ft) ^1/2 <0.25
However,
ft: Focal length L in the telephoto end state: The above-mentioned second lens unit disposed closest to the image plane of the second lens unit from the aperture stop arranged in the second lens unit
The distance to the apex of the four lens surfaces. A zoom lens, and an image sensor that converts an optical image formed by the zoom lens into an electrical signal;
The zoom lens
A negative cemented lens composed of three negative, positive, and positive groups in order from the object side, in which the first lens unit is joined from the object side by a first lens that is a negative single lens and a second lens that is a positive single lens. The second group is composed of a cemented lens formed by cementing a third lens that is a positive single lens and a fourth lens that is a negative single lens from the object side, and the third group is a fifth lens that is a positive single lens. Consisting of lenses,
An imaging apparatus that satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) | G1R1 / G2R2 | <3
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number G1R1: positive second lens constituting the first group cemented lens The radius of curvature G2R2 of the first surface of the negative first lens to be configured is the radius of curvature of the second surface of the positive second lens that constitutes the cemented lens of the first group.

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