JP2011095328A - Zoom lens and image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens that achieves smaller thickness 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, from the object side, a third lens comprising a positive single lens and a cemented lens formed by joining together a fourth lens comprising a positive single lens and a fifth lens comprising a negative signal lens, and the third group includes a sixth 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) f21/fw>1. <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, there is known an optical system that is thinned by a so-called collapsible lens having a negative, positive, and positive three-group configuration (see, for example, Patent Document 1 and Patent Document 2).

JP 2005-308953 JP JP 2008-233161 A

  By the way, in the optical system described in Patent Document 1 described above, the second lens group is composed only of a cemented lens composed of negative and positive single lenses. There has been a problem that the axial chromatic aberration, the spherical aberration in the end state, and the field curvature change due to the object distance variation in the telephoto end state become large.

  Further, in the optical system described in Patent Document 2 described above, the second lens unit is composed of a positive single lens and a cemented lens of positive and negative single lenses, so that spherical aberration in the telephoto end state, It is possible to suppress a change in field curvature due to a change in object distance in the telephoto end state.

  However, in this case, since the power of the positive single lens closest to the object side in the second group is large, the decentering sensitivity of the lenses in the second group is increased, and the accuracy required for assembly is increased, and an alignment process is added. There is a problem that the manufacturing process becomes complicated. Further, since each group is movable, there is a problem that the mechanical hardware configuration becomes complicated.

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

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 formed by cementing a second lens composed of a single lens, and the second lens unit includes a third lens composed of a positive single lens from the object side, a fourth lens composed of a positive single lens, and a negative single lens. The third lens unit is composed of a sixth lens composed of a positive single lens, and satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second 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, when the second group is composed of a positive third lens and a cemented lens of a positive fourth lens and a negative fifth lens, the power of the positive third lens is increased. Even if it is smaller than the conventional one, high performance can be realized, thus reducing the lens eccentricity sensitivity in the second lens group and reducing the manufacturing difficulty while realizing thinning and high performance. Can do.

  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 a reduction in thickness and 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) defines the ratio between the focal length of the wide-angle end state and the focal length of the positive third lens closest to the object side in the second lens group. The power of the third lens is weakened.

  If the lower limit value of conditional expression (3) is not reached, the power of the positive third lens closest to the object side in the second group becomes too strong compared to the focal length in the wide-angle end state, and the second group. The decentering sensitivity of the positive third lens and the cemented lens composed of the positive fourth lens and the negative fifth lens is increased, and the assembly accuracy of the second group is increased. For this reason, in the zoom lens of the three-group type, the performance is reduced or the manufacturing difficulty level is increased.

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. A sixth lens composed of a third lens composed of a single lens, a cemented lens formed by cementing a fourth lens composed of a positive single lens and a fifth lens composed of a negative single lens, and the third lens group consisting of a positive single lens. And is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second 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, when the second group is composed of a positive third lens and a cemented lens of a positive fourth lens and a negative fifth lens, the power of the positive third lens is increased. Even if it is smaller than the conventional one, it is possible to achieve high performance, thus suppressing the lens eccentricity sensitivity in the second lens group and reducing the manufacturing difficulty while realizing thinning and high performance. it can.

  Here, the conditional expressions (1) to (3) in the three-group type zoom lens in the image pickup apparatus are defined in order to reduce the manufacturing difficulty while realizing thinning 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 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 level 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) defines the ratio between the focal length of the wide-angle end state and the focal length of the positive third lens closest to the object side in the second lens group. The power of the third lens is weakened.

  If the lower limit value of conditional expression (3) is not reached, the power of the positive third lens closest to the object side in the second group becomes too strong compared to the focal length in the wide-angle end state, and the second group. The decentering sensitivity of the positive third lens and the cemented lens composed of the positive fourth lens and the negative fifth lens is increased, and the assembly accuracy of the second group is increased. For this reason, in the zoom lens of the three-group type, the performance is reduced or the manufacturing difficulty level is increased.

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. A third lens composed of a negative cemented lens in which two lenses are cemented, the second group being a positive single lens from the object side, a fourth lens being a positive single lens, and a fifth lens being a negative single lens. The sixth lens unit is composed of a cemented cemented lens and the third lens unit 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) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group.

  Thus, according to the zoom lens of the present invention, the configuration is simple, the manufacturing difficulty is low as a whole, and a reduction in thickness and performance can be realized.

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, a cemented lens formed by cementing a fourth lens composed of a positive single lens and a fifth lens composed of a negative single lens, and the third group is a sixth lens composed of a positive single lens. The lens is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group.

  Thus, according to the imaging apparatus of the present invention, the zoom lens has a simple configuration, the manufacturing difficulty is low as a whole, and a reduction in thickness and 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 corresponding to the first embodiment. FIG. 3 is a schematic cross-sectional view showing a lens group arrangement of a first numerical example corresponding to the first embodiment. It is a characteristic curve figure which shows the various aberrations of the 1st numerical example corresponding to 1st Embodiment. It is a rough sectional drawing which shows the structure of the zoom lens of the 2nd numerical example corresponding to 1st Embodiment. It is a rough sectional drawing showing lens group arrangement of the 2nd numerical example corresponding to the 1st embodiment. It is a characteristic curve figure which shows the various aberrations of the 2nd numerical example corresponding to 1st Embodiment. It is a rough-line sectional drawing which shows the structure of the zoom lens of the 3rd numerical example corresponding to 1st Embodiment. FIG. 6 is a schematic cross-sectional view showing a lens group arrangement of a third numerical example corresponding to the first embodiment. It is a characteristic curve figure which shows the various aberrations of the 3rd numerical example corresponding to 1st Embodiment. It is a rough-line sectional drawing which shows the structure of the zoom lens of the 4th numerical example corresponding to 1st Embodiment. FIG. 6 is a schematic cross-sectional view showing a lens group arrangement of a fourth numerical example corresponding to the first embodiment. It is a characteristic curve figure which shows the various aberrations of the 4th numerical example corresponding to 1st Embodiment. It is a rough-line sectional drawing which shows the structure of the zoom lens of the 1st numerical example corresponding to 2nd Embodiment. FIG. 6 is a schematic cross-sectional view showing a lens group arrangement of a first numerical example corresponding to the second embodiment. It is a characteristic curve figure which shows the various aberrations of the 1st numerical example corresponding to 2nd Embodiment. FIG. 6 is a schematic cross-sectional view showing a configuration of a zoom lens according to a second numerical example corresponding to the second embodiment. FIG. 6 is a schematic cross-sectional view showing a lens group arrangement of a second numerical example corresponding to the second embodiment. It is a characteristic curve figure which shows the various aberrations of the 2nd numerical example corresponding to 2nd Embodiment. It is a rough-line sectional drawing which shows the structure of the zoom lens of the 3rd numerical example corresponding to 2nd Embodiment. FIG. 6 is a schematic cross-sectional view showing a lens group arrangement of a third numerical example corresponding to the second embodiment. It is a characteristic curve figure which shows the various aberrations of the 3rd numerical example corresponding to 2nd Embodiment. 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. First embodiment (3-group type zoom lens)
2. Numerical examples corresponding to the first embodiment (first numerical example to fourth numerical example)
3. Second Embodiment (4-group zoom lens)
4). Numerical examples corresponding to the second embodiment (first numerical example to third numerical example)
5. 5. Imaging device and digital still camera Other embodiments

<1. First Embodiment>
In the three-group type zoom lens according to the first embodiment of the present invention, the zoom lens includes three groups of negative, positive, and positive in order from the object side, and the first group is a negative single lens from the object side. The second lens unit is composed of a negative cemented lens obtained by cementing a lens and a second lens composed of a positive single lens, and the second lens unit is composed of a positive single lens from the object side, a fourth lens composed of a positive single lens, and a negative lens. The third lens unit is composed of a sixth lens composed of a positive single lens, and the following conditional expressions (1) to (3) are satisfied. Has been.
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second 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, when the second group is composed of a positive third lens and a cemented lens of a positive fourth lens and a negative fifth lens, the power of the positive third lens is increased. Higher performance can be achieved even if it is smaller than the conventional one, thus reducing the lens eccentricity sensitivity in the second lens group and reducing the manufacturing difficulty while realizing a thinner and higher performance. Can do.

  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 a reduction in thickness and 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 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 level increases. . That is, in the zoom lens of the three-group type, the manufacturing difficulty level is lowered 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.

In the case of a three-group type zoom lens, if the following conditional expression (2) ′ is satisfied instead of conditional expression (2), the correction effect (achromatic effect) for lateral chromatic aberration and axial chromatic aberration can be further increased. it can.
(2) ′ v2d <26.5

  Conditional expression (3) defines the ratio between the focal length of the wide-angle end state and the focal length of the positive third lens closest to the object side in the second lens group. The power of the third lens is weakened.

  If the lower limit value of conditional expression (3) is not reached, the power of the positive third lens closest to the object side in the second group becomes too strong compared to the focal length in the wide-angle end state, and the second group. The decentering sensitivity of the positive third lens and the cemented lens composed of the positive fourth lens and the negative fifth lens is increased, and the assembly accuracy of the second group is increased. For this reason, in the zoom lens of the three-group type, the performance is reduced or the manufacturing difficulty level is increased.

In the case of a zoom lens of the 3 group type, if the following conditional expression (3) ′ is satisfied instead of the conditional expression (3), the eccentricity sensitivity in the second group is further reduced, and the manufacturing difficulty is further reduced. It becomes possible to do.
(3) 'f21 / fw> 1.5

Subsequently, in the zoom lens of the third group type according to the present invention, at least one surface closest to the object side or the image surface side in the cemented lens of the first group and the positive third lens closest to the object side of the second group. At least one surface has an aspherical shape, and is configured to satisfy the following conditional expression (4).
(4) f21 / f2> 1
However,
f2: The focal length of the second group.

  In the zoom lens of the three-group type, at least one surface on the most object side or the most image surface side in the first-group cemented lens is aspherical, so that coma aberration and astigmatism in the peripheral portion particularly in the wide-angle end state are achieved. Aberration and distortion can be suppressed.

  Further, in the zoom lens of the third group type, it occurs when the negative power of the first group is increased by making at least one surface of the cemented lens of the first group closest to the object side or the image surface side to be aspherical. Since various aberrations can be corrected, deterioration of optical performance can be suppressed.

  At this time, in the zoom lens of the three group type, the same zoom ratio can be obtained even if the moving distance between the first group and the second group is shortened by increasing the negative power of the first group. Accordingly, the optical total length can be shortened and the size can be further reduced.

  Further, in the zoom lens of the three-group type, at least one surface of the positive third lens closest to the object side in the second group is formed into an aspheric shape, so that the telephoto side due to spherical aberration, astigmatism, and object distance fluctuation is obtained. Fluctuations in the field curvature in the image can be suppressed, and thus the resolution performance can be further improved.

  Conditional expression (4) defines the ratio between the focal length of the entire second group and the focal length of the positive third lens closest to the object in the second group, and the power of the entire second group. In contrast, the power of the third lens is weakened.

  When the lower limit of conditional expression (4) is not reached, the focal length of the positive third lens closest to the object side in the second group becomes shorter than the focal length of the second group, that is, the entire second group. The power of the third lens becomes too strong with respect to the power of.

  At this time, in the zoom lens of the three-group type, the decentration sensitivity between the positive third lens closest to the object side in the second group and the cemented lens including the positive fourth lens and the negative fifth lens is increased. Since the assembly accuracy of the second group is increased, the performance is degraded or the manufacturing difficulty level is increased.

Incidentally, in the case of a three-group type zoom lens, when the following conditional expression (4) ′ is satisfied instead of conditional expression (4), the eccentricity sensitivity in the second group is further reduced, and the manufacturing difficulty level is further reduced. It becomes possible to do.
(4) 'f21 / f2> 1.3

  Next, in the zoom lens of the third group type according to the present invention, at least one surface closest to the object side or most image surface side in the cemented lens of the first group has an aspherical shape, and the positive lens located closest to the object side of the second group. Both surfaces of the third lens have a spherical shape, and at least one surface closest to the object side or the image surface side of the cemented lens of the second group has an aspherical shape.

  In the zoom lens of the three-group type, at least one surface closest to the object side or the image surface side of the cemented lens of the first group has an aspherical shape, and both surfaces of the positive third lens closest to the object side of the second group. Is made spherical, and at least one surface closest to the object side or most image side of the second group cemented lens is aspherical, so that coma, astigmatism and distortion in the peripheral portion at the wide-angle end state are obtained. In addition, it is possible to reduce the manufacturing difficulty while suppressing spherical aberration and coma in the telephoto end state.

Further, in the zoom lens of the third group type according to the present invention, the curvature of the surface closest to the object side in the cemented lens of the first group satisfies the following conditional expression (5).
(5) -1> G1R1 / fw> -3.3
However,
G1R1: The radius of curvature of the surface closest to the object side in the cemented lens of the first group.

  Conditional expression (5) defines the radius of curvature of the most object-side surface in the first group cemented lens.

  If the lower limit value of conditional expression (5) is not reached, it is necessary to reduce the radius of curvature of the cemented surface of the cemented lens of the first group in order to increase the negative power of the first group. The curvature radius of the cemented surface of the positive second lens constituting the cemented lens also needs to be reduced, and the manufacturing difficulty of the negative first lens and the positive second lens constituting the cemented lens increases. Resulting in.

  On the other hand, when the upper limit value of conditional expression (5) is exceeded, the radius of curvature of the object side surface of the cemented lens of the first group becomes too small, and in particular, it becomes difficult to correct distortion and curvature of field. .

  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.

<2. Numerical Example Corresponding to First 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 spherical lens and a second lens L2 made of a positive glass aspheric lens, and has negative power as a whole. ing.

  The second group G2 includes a third lens L3 that is a positive double-sided aspheric lens, and a cemented lens L45 in which a fourth lens L4 that is a positive single lens and a fifth lens L5 that is a negative single lens are cemented. The aperture stop S is disposed on the object side of the second group G2. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 includes a sixth lens L6 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 third surface, the fifth surface, the sixth surface, the tenth surface, and the eleventh 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 = 28.58 degrees), and FIG. The focal length state (ω = 18.16 degrees) and FIG. 3C show various aberrations in the telephoto end state (ω = 12.16 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 thinned, and has excellent imaging performance. You can see that

[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 third lens L3 made of a positive double-sided spherical lens, and a cemented lens L45 in which a fourth lens L4 made of a positive aspheric lens and a fifth lens L5 made of a negative spherical lens are cemented. The aperture stop S is disposed on the object side of the second group. The aperture stop S may be disposed on the image plane side of the second group.

  The third group G3 includes a sixth lens L6 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 third surface, the seventh surface, the tenth surface, and the eleventh surface are aspherical, 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 the wide-angle end state (ω = 28.19 degrees), and FIG. FIG. 6C shows various aberrations in the telephoto end state (ω = 11.93 degrees), respectively, in the focal length state (ω = 18.11 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 thinned, and has excellent imaging performance. You can see that

[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, a cemented lens L45 in which a fourth lens L4 that is a positive spherical lens, and a fifth lens L5 that is a negative spherical lens are cemented together. An aperture stop S is disposed on the object side of the second group G2. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 includes a sixth lens L6 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 sixth surface, the tenth surface, and the eleventh 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.

  Next, FIG. 9 is a diagram of various aberrations in the infinite focus state in the third numerical example, FIG. 9A is a wide-angle end state (ω = 28.91 degrees), and FIG. FIG. 9C shows various aberrations in the telephoto end state (ω = 9.32 degrees), respectively, at the focal length state (ω = 17.67 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 of the third numerical example corrects various aberrations in spite of being thinned, and has excellent imaging performance. You can see that

[2-4. Fourth numerical example]
In FIG. 10, reference numeral 4 denotes a zoom lens according to a fourth 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. 11 shows the lens group arrangement in the fourth numerical example when the zoom lens 4 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 composite aspherical lens in which a first lens L1 composed of a negative glass spherical lens and a second lens L2 composed of a positive resin aspherical lens are cemented. Has negative power.

  The second group G2 includes a third lens L3 that is a positive double-sided aspheric lens, and a cemented lens L45 in which a positive fourth lens L4 and a negative fifth lens L5 are cemented, and the aperture stop S is the second group. Arranged on the image plane side of G2. The aperture stop S may be disposed on the object side of the second group G2.

  The third group G3 includes a sixth lens L6 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 16 to 20 below show specification values of the fourth numerical example corresponding to the first embodiment. Here, f in the specification table in the fourth 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 a d-line (wavelength 587.6 nm). In Table 1, the curvature radius ∞ means a plane.

The third surface, the fourth surface, the fifth surface, the eleventh surface, and the twelfth surface are aspherical, and the aspherical coefficients are as shown in Table 18. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, the variable interval when the lens position state changes in the zoom lens 4 of the fourth numerical example is shown in Table 19 below. In the zoom lens 4, 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 20 below shows values corresponding to the conditional expressions in the zoom lens 4 of the fourth numerical example.

  Next, FIG. 12 is a diagram showing various aberrations in the infinite focus state in the fourth numerical example. FIG. 12A is the wide-angle end state (ω = 28.18 degrees), and FIG. In the focal length state (ω = 17.46 degrees), FIG. 12C shows various aberrations in the telephoto end state (ω = 11.87 degrees).

  12A to 12C, 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.

  12A to 12C, the zoom lens 4 of the fourth numerical example corrects various aberrations in spite of being thinned, and has excellent imaging performance. You can see that

  Thus, according to the first to fourth numerical examples corresponding to the first embodiment, in the zoom lenses 1 to 4, the focal length Wf in the wide-angle end state is 28 mm to 38 mm (35 mm film equivalent). ), The zoom ratio is about 2 to 4 times, the FNO in the wide-angle end state is about 2.5 to 3.5, and the FNO in the telephoto end state is about 5 to 6.5. The image pickup system can be realized.

<3. Second Embodiment>
The four-group type zoom lens according to the second embodiment of the present invention includes four groups of negative, positive, positive, and negative in order from the object side, and the first group is a negative single lens from the object side. A third lens composed of a negative cemented lens obtained by cementing a first lens and a second lens composed of a positive single lens, and a second lens composed of a positive single lens from the object side and a fourth lens composed of a positive single lens And a cemented lens obtained by cementing a fifth lens that is a negative single lens, a seventh group that is composed of a sixth lens that is a positive single lens, and a fourth group that has a fixed distance from the imaging surface. The lens is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group.

  In this four-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 a four-group type zoom lens, the first group is not composed of a plurality of lenses but has a single structure consisting of only cemented lenses, so that performance degradation 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 four-group type zoom lens, the first group is not a plurality of lenses, but only a cemented lens, thereby improving performance and reducing costs compared to the first group having a plurality of lenses. Thinning is possible.

  Secondly, in the four-group type zoom lens, since the first lens unit is not a plurality of lens units but a single unit composed of only cemented lenses, the lens interval error in the first unit 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 four-group type zoom lens, 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 can be further reduced in size. .

  Thirdly, in a four-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.

  As a result, in a four-group type zoom lens, the second group can weaken the action of bringing the principal point position of the first group closer to the image plane. That is, in a four-group type zoom lens, when the second group is composed of a positive third lens and a cemented lens of a positive fourth lens and a negative fifth lens, the power of the positive third lens is increased. Higher performance can be achieved even if it is smaller than the conventional one, thus reducing the lens eccentricity sensitivity in the second lens group and reducing the manufacturing difficulty while realizing a thinner and higher performance. Can do.

  Here, the conditional expressions (1) to (3) in the four-group type zoom lens are defined in order to achieve a reduction in manufacturing difficulty while realizing thinning 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 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 level 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.

In the case of a four-group type zoom lens, if the following conditional expression (2) ′ is satisfied instead of conditional expression (2), the correction effect (achromatic effect) for lateral chromatic aberration and axial chromatic aberration can be further increased. it can.
(2) ′ v2d <26.5

  Conditional expression (3) defines the ratio between the focal length of the wide-angle end state and the focal length of the positive third lens closest to the object side in the second lens group. The power of the third lens is weakened.

  If the lower limit value of conditional expression (3) is not reached, the power of the positive third lens closest to the object side in the second group becomes too strong compared to the focal length in the wide-angle end state, and the second group. The decentering sensitivity of the positive third lens and the cemented lens composed of the positive fourth lens and the negative fifth lens is increased, and the assembly accuracy of the second group is increased. For this reason, in a four-group type zoom lens, the performance is lowered or the manufacturing difficulty level is raised.

In the case of a four-group type zoom lens, if the following conditional expression (3) ′ is satisfied instead of conditional expression (3), the eccentricity sensitivity in the second group is further reduced, and the manufacturing difficulty level is further reduced. It becomes possible to do.
(3) 'f21 / fw> 1.5

Subsequently, in the four-group type zoom lens of the present invention, at least one surface closest to the object side or the image surface side in the cemented lens of the first group and the positive third lens closest to the object side of the second group. At least one surface has an aspherical shape, and is configured to satisfy the following conditional expression (4).
(4) f21 / f2> 1
However,
f2: The focal length of the second group.

  In this four-group type zoom lens, at least one surface closest to the object side or the most image plane side in the first lens group cemented lens is aspherical, so that coma aberration and astigmatism in the peripheral portion particularly in the wide-angle end state are achieved. Aberration and distortion can be suppressed.

  Further, in the case of a 4-group type zoom lens, when at least one surface closest to the object side or the image surface side of the cemented lens of the first group is aspherical, the negative power of the first group is increased. Since various aberrations can be corrected, deterioration of optical performance can be suppressed.

  At this time, in the zoom lens of the four group type, the same zoom ratio can be obtained even if the moving distance between the first group and the second group is shortened by increasing the negative power of the first group. Accordingly, the optical total length can be shortened and the size can be further reduced.

  Further, in the zoom lens of the four-group type, at least one surface of the positive third lens closest to the object side in the second group is formed into an aspheric shape, so that the telephoto side due to spherical aberration, astigmatism, and object distance fluctuation is obtained. Fluctuations in the field curvature in the image can be suppressed, and thus the resolution performance can be further improved.

  Conditional expression (4) defines the ratio between the focal length of the entire second group and the focal length of the positive third lens closest to the object in the second group, and the power of the entire second group. In contrast, the power of the third lens is weakened.

  When the lower limit of conditional expression (4) is not reached, the focal length of the positive third lens closest to the object side in the second group becomes shorter than the focal length of the second group, that is, the entire second group. The power of the third lens becomes too strong with respect to the power.

  At this time, in the four-group type zoom lens, the eccentricity sensitivity between the positive third lens closest to the object side in the second group and the cemented lens including the positive fourth lens and the negative fifth lens is increased. Since the assembly accuracy of the second group is increased, the performance is degraded or the manufacturing difficulty level is increased.

Incidentally, in the case of a four-group type zoom lens, if the following conditional expression (4) ′ is satisfied instead of conditional expression (4), the eccentricity sensitivity in the second group is further reduced, and the manufacturing difficulty level is further reduced. It becomes possible to do.
(4) 'f21 / f2> 1.3

  In the four-group type zoom lens, the fourth group has a negative power, so that the optical performance can be improved even for a short-distance object in the telephoto end state.

  Next, in the four-group type zoom lens of the present invention, at least one surface closest to the object side or most image surface side of the first lens group cemented lens has an aspherical shape, and the positive lens located closest to the object side in the second lens group. Both surfaces of the third lens have a spherical shape, and at least one surface closest to the object side or the image surface side of the second group cemented lens has an aspherical shape.

  In this four-group type zoom lens, at least one surface closest to the object side or most image surface side of the cemented lens of the first group is aspherical, and both surfaces of the positive third lens closest to the object side of the second group are used. Is made spherical, and at least one surface closest to the object side or most image side of the second group cemented lens is aspherical, so that coma, astigmatism and distortion in the peripheral portion at the wide-angle end state are obtained. In addition, it is possible to reduce the manufacturing difficulty while suppressing spherical aberration and coma in the telephoto end state.

In the four-group type zoom lens of the present invention, the curvature of the surface closest to the object side in the cemented lens of the first group satisfies the following conditional expression (5).
(5) -1> G1R1 / fw> -3.3
However,
G1R1: The radius of curvature of the surface closest to the object side in the cemented lens of the first group.

  Conditional expression (5) defines the radius of curvature of the most object-side surface in the first group cemented lens.

  If the lower limit value of conditional expression (5) is not reached, it is necessary to reduce the radius of curvature of the cemented surface of the cemented lens of the first group in order to increase the negative power of the first group. The curvature radius of the cemented surface of the positive second lens constituting the cemented lens also needs to be reduced, and the manufacturing difficulty of the negative first lens and the positive second lens constituting the cemented lens increases. Resulting in.

  On the other hand, when the upper limit value of conditional expression (5) is exceeded, the radius of curvature of the object side surface of the cemented lens of the first group becomes too small, and in particular, it becomes difficult to correct distortion and curvature of field. .

Furthermore, in the four-group type zoom lens of the present invention, the seventh lens in the fourth group has a negative power and satisfies the following conditional expression (6).
(6) f1 / f4 <0.9
However,
f1: focal length of first group f4: focal length of fourth group

  Conditional expression (6) defines the power of the fourth group with respect to the power of the first group, and takes into account that the seventh lens of the fourth group is disposed at the closest location to the image sensor serving as a heat source. When the fourth lens in the fourth group is made of a resin lens, the radius of curvature is moderated to prevent performance deterioration due to thermal deformation.

  When the lower limit value of conditional expression (6) is not reached, the negative power of the fourth group becomes too strong, so that it is necessary to increase the positive power of the second group and the third group. In order to secure the edge thickness of the sixth lens, it is necessary to further increase the center thickness, which is disadvantageous for thinning when retracted.

Incidentally, in the case of a four-group type zoom lens, if the following conditional expression (6) ′ is satisfied instead of conditional expression (6), performance degradation at the time of temperature / humidity change is suppressed, which is further advantageous for thinning. .
(6) ′ f1 / f4 <0.6

  Furthermore, in the four-group type zoom lens of the present invention, the third group and the fourth group are formed of resin lenses, so that it is possible to provide a low-cost imaging device as compared to the case of using glass lenses.

  Here, in the four-group type zoom lens, the third group and the fourth group are made of resin lenses having positive and negative powers, respectively, so that the focus position fluctuation at the time of temperature / humidity change is changed to the third group and the fourth group. Therefore, it is possible to provide a high-performance imaging device at a low cost.

  Further, in the four-group type zoom lens of 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, since the zoom lens of the four-group type constitutes the first group cemented lens by molding using a resin, the second lens made of the resin is used as compared with the case where the glass lenses are respectively cemented. The thickness of the periphery of the lens can be made much thinner than in the case of a glass lens.

  In the zoom lens of the four-group type, the effect of correcting the field curvature is improved by the fourth group, and the mechanical structure can be simplified by fixing the fourth group. Further, in the four-group type zoom lens, by adding the fourth group, the optical total length can be shortened compared with the three-group type by the amount that the power of the first group to the third group can be increased. .

<4. Numerical Example Corresponding to Second Embodiment>
Next, numerical examples in which specific numerical values are applied to the four-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 above-described equation (1).

[4-1. First numerical example]
In FIG. 13, reference numeral 11 denotes a zoom lens according to a first numerical example corresponding to the second 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 the third group G3 and the negative fourth group configuration.

  FIG. 14 shows the lens group arrangement in the first numerical example when the zoom lens 11 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 third lens L3 that is a positive double-sided aspheric lens, and a cemented lens L45 in which a fourth lens L4 that is a positive single lens and a fifth lens L5 that is a negative single lens are cemented. The aperture stop S is disposed on the object side of the second group G2. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 is composed of a sixth lens L6 composed of a positive single lens, and the fourth group G4 is composed of a seventh lens L7 composed of a negative single lens having a fixed distance from the image plane IMG. ing.

  In the zoom lens 11, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are disposed between the fourth group G4 and the image plane IMG.

  Table 21 to Table 25 below show specification values of the second numerical example corresponding to the second 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 sixth surface, the tenth surface, the eleventh surface, the twelfth surface, and the thirteenth surface are aspherical, and the aspherical coefficients are as shown in Table 23. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, the variable interval when the lens position state changes in the zoom lens 11 of the first numerical example is shown in Table 24 below. In the zoom lens 11, the first group G1, the second group G2, and the third group G3 are movable, and the distance from the image plane IMG is fixed in the fourth group.

  In the zoom lens 11, zooming is realized mainly by changing the distance between the first group G1 and the second group G2, and the third group G3 is moved to absorb the focal position variation at each angle of view. Thus, high performance can be ensured while maintaining miniaturization.

  Table 25 below shows values corresponding to the conditional expressions in the zoom lens 11 of the first numerical example.

  FIG. 15 is a graph showing various aberrations in the infinite focus state in the first numerical example. FIG. 15A is the wide-angle end state (ω = 29.36 degrees), and FIG. The focal length state (ω = 18.68 degrees) and FIG. 15C show various aberrations in the telephoto end state (ω = 12.40 degrees).

  In FIGS. 15A to 15C, the spherical aberration corresponds to the C-line having a wavelength of 656.3 nm, the D-line having a wavelength of 587.6 nm, and the G-line having 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.

  15A to 15C, the zoom lens 11 of the first numerical example corrects various aberrations in spite of being thinned, and has excellent imaging performance. You can see that

[4-2. Second numerical example]
In FIG. 16, reference numeral 12 denotes a zoom lens according to a second numerical example corresponding to the second 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 the third group G3 and the negative fourth group configuration.

  FIG. 17 shows the lens group arrangement when the zoom lens 12 in the second numerical example 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 composite aspherical lens composed of a first lens L1 composed of a negative glass spherical lens and a second lens L2 composed of a positive resin aspherical lens. Has negative power.

  The second group G2 includes a third lens L3 that is a positive double-sided aspheric lens, and a cemented lens L45 in which a fourth lens L4 that is a positive single lens and a fifth lens L5 that is a negative single lens are cemented. The aperture stop S is disposed on the object side of the second group G2. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 is composed of a sixth lens L6 made of a positive resin lens, and the fourth group G4 is made of a seventh lens L7 made of a negative resin lens having a fixed distance from the image plane IMG. ing.

  In the zoom lens 12, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are disposed between the fourth group G4 and the image plane IMG.

  Tables 26 to 30 below show specification values of the second numerical example corresponding to the second 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 third surface, the fifth surface, the sixth surface, the tenth surface, the eleventh surface, the twelfth surface, and the thirteenth surface are aspherical, and the aspherical coefficients are as shown in Table 28. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, in Table 29 below, variable intervals when the lens position state changes in the zoom lens 12 of the second numerical example are shown. In the zoom lens 12, the first group G1, the second group G2, and the third group G3 are movable, and the distance from the image plane IMG is fixed to the fourth group G4.

  In the zoom lens 12, zooming is realized mainly by changing the distance between the first group G1 and the second group G2, and the third group G3 is moved to absorb the focal position variation at each angle of view. Thus, high performance can be ensured while maintaining miniaturization.

  Table 30 below shows values corresponding to the conditional expressions in the zoom lens 12 of the second numerical example.

  Next, FIG. 18 is a diagram showing various aberrations in the infinite focus state in the second numerical example, FIG. 18A is the wide-angle end state (ω = 29.36 degrees), and FIG. FIG. 18C shows various aberrations in the telephoto end state (ω = 12.47 degrees), respectively, in the focal length state (ω = 18.68 degrees).

  18A to 18C, 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.

  18A to 18C, the zoom lens 12 of the second numerical example corrects various aberrations in spite of being thinned, and has excellent imaging performance. You can see that

[4-3. Third numerical example]
In FIG. 19, reference numeral 13 denotes a zoom lens according to a third numerical example corresponding to the second 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 the third group G3 and the negative fourth group configuration.

  FIG. 20 shows the lens group arrangement in the third numerical example when the zoom lens 13 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 including a first lens L1 made of a negative glass spherical lens and a second lens L2 made of a positive resin lens, and has a negative power as a whole. .

  The second group G2 includes a third lens L3 that is a positive aspheric lens, a cemented lens L45 in which a fourth lens L4 that is a positive single lens, and a fifth lens L5 that is a negative single lens are cemented. An aperture stop S is disposed on the object side of the second group G2. The aperture stop S may be disposed on the image plane side of the second group G2.

  The third group G3 is composed of a sixth lens L6 made of a positive resin lens, and the fourth group G4 is made of a seventh lens L7 made of a negative resin lens having a fixed distance from the image plane IMG. ing.

  In the zoom lens 13, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are disposed between the fourth group G4 and the image plane IMG.

  Table 31 to Table 35 below show specification values of the third numerical value example corresponding to the second 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 fifth surface, the sixth surface, the tenth surface, the eleventh surface, the twelfth surface, and the thirteenth surface are aspherical, and the aspherical coefficients are as shown in Table 33. For example, 0.26029E-05 means 0.26029 × 10 ⁻⁵ .

  Subsequently, the variable interval when the lens position state changes in the zoom lens 13 of the third numerical example is shown in Table 34 below. In the zoom lens 13, the first group G1, the second group G2, and the third group G3 are movable, and the distance from the image plane IMG is fixed in the fourth group.

  In the zoom lens 13, zooming is realized mainly by changing the distance between the first group G1 and the second group G2, and the third group G3 is moved to absorb the focal position variation at each angle of view. Thus, high performance can be ensured while maintaining miniaturization.

  Table 35 below shows values corresponding to the conditional expressions in the zoom lens 13 of the third numerical example.

  Next, FIG. 21 is a diagram of various aberrations in the infinite focus state in the third numerical example. FIG. 21A is a wide-angle end state (ω = 28.4 degrees), and FIG. FIG. 21C shows various aberrations in the telephoto end state (ω = 11.93 degrees), respectively, in the focal length state (ω = 18.11 degrees).

  21A to 21C, 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.

  From the aberration diagrams in FIGS. 21A to 21C, the zoom lens 13 of the third numerical example corrects various aberrations in spite of being thinned, and has excellent imaging performance. You can see that

<5. Imaging device and digital still camera>
[5-1. Configuration of imaging device]
Next, the imaging device of the present invention will be described. This imaging apparatus includes the zoom lens 1 (or 2, 3, 4) shown in the numerical example in the first embodiment, and the zoom lens 11 (or 12) shown in the numerical example in the second embodiment. 13) for converting the optical image formed by 13) into an electrical signal, for example, an image pickup device such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor.

The zoom lens 1 (or 2, 3, 4) is composed of three negative, positive, and positive groups in order from the object side, and the first lens G1 is a first lens L1 that is a negative single lens from the object side. The third lens L3 is composed of a negative cemented lens L12 obtained by cementing the second lens L2 composed of a positive single lens, and the second lens group G2 is composed of a positive single lens from the object side, and a fourth lens composed of a positive single lens. L4 and a cemented lens L45 cemented with a fifth lens L5 composed of a negative single lens, and a third group composed of a sixth lens L6 composed of a positive single lens. The following conditional expressions (1) to (3) It is configured to satisfy.
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group.

  In this three-group type zoom lens 1 (or 2, 3, 4), the first lens group G1 is a cemented lens L12 consisting of a first lens L1 having a negative power and a second lens L2 having a positive power. The configuration with only one sheet has the following advantages.

  First, in the zoom lens 1 of the three-group type (or 2, 3, 4), the first group G1 has a single configuration of only the cemented lens L12 instead of a plurality of lens configurations. Therefore, there is no need for alignment between lenses at the time of assembly, so that the manufacturing process of the alignment can be omitted and the manufacturing time can be shortened.

  That is, in the zoom lens 1 of the three-group type (or 2, 3, 4), the first group G1 is not composed of a plurality of lenses but a single configuration consisting only of the cemented lens L12, so that the first group G1 is composed of a plurality of lenses. It is possible to improve performance, reduce costs, and reduce the thickness as compared with the configuration.

  Secondly, in the zoom lens 1 of the three-group type (or 2, 3, 4), the first group G1 has a single configuration of only the cemented lens L12 instead of a plurality of lens configurations, whereby the first group G1. Since the lens interval error at is 0, the amount of shift in the focus position is smaller than in the conventional case where the first lens unit G1 has a plurality of lenses.

  As a result, in the zoom lens 1 of the three-group type (or 2, 3, 4), the margin of mechanical hardware configuration for adjusting the focus position by the first group G1 to the third group G3 can be reduced. Therefore, the whole can be further downsized.

  Thirdly, in the three-group type zoom lens 1 (or 2, 3, 4), 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. When the first lens group G1 has a plurality of lens configurations, the position of the second lens group G2 is further increased as much as the second lens L2 located on the image plane side does not interfere with the second lens group G2. It is possible to approach the principal point position.

  Thereby, in the three-group type zoom lens 1 (or 2, 3, 4), the second group G2 can weaken the action of bringing the principal point position of the first group G1 closer to the image plane IMG. That is, in the three-group type zoom lens 1 (or 2, 3, 4), the second group G2 is composed of the positive third lens L3 and the cemented lens L45 of the positive fourth lens L4 and the negative fifth lens L5. In the case of being configured, it is possible to achieve high performance even if the power of the positive third lens L3 is made smaller than before, thus suppressing the lens eccentricity sensitivity in the second group G2, and reducing the thickness. While realizing high performance, the manufacturing difficulty can be reduced.

  Here, the conditional expressions (1) to (3) in the zoom lens 1 of the three-group type (or 2, 3, 4) are for reducing the manufacturing difficulty while realizing a reduction in thickness and performance. It is specified.

  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 value 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 molding the cemented lens L12, and the manufacturing difficulty increases. Resulting in. That is, the zoom lens 1 (or 2, 3, 4) of the three-group type is designed to reduce the manufacturing difficulty while realizing thinning 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.

In the case of a three-group type zoom lens, if the following conditional expression (2) ′ is satisfied instead of conditional expression (2), the correction effect (achromatic effect) for lateral chromatic aberration and axial chromatic aberration can be further increased. it can.
(2) ′ v2d <26.5

  Conditional expression (3) defines the ratio between the focal length of the wide-angle end state and the focal length of the positive third lens L3 closest to the object side in the second group G2, and thus the second group G2 The power of the positive third lens L3 is weakened.

  If the lower limit value of conditional expression (3) is not reached, the power of the positive third lens L3 closest to the object side in the second group G2 becomes too strong compared to the focal length fw in the wide-angle end state. The decentering sensitivity of the positive third lens L3 in the second group G2 and the cemented lens L45 including the positive fourth lens L4 and the negative fifth lens L5 is increased, and the assembly accuracy of the second group G2 is increased. End up. For this reason, in the three-group type zoom lens 1 (or 2, 3, 4), the performance is deteriorated or the manufacturing difficulty is increased.

In the case of the zoom lens of the third group type, if the following conditional expression (3) ′ is satisfied instead of the conditional expression (3), the eccentricity sensitivity in the second group G2 is further reduced, and the manufacturing difficulty level is further increased. It can be reduced.
(3) 'f21 / fw> 1.5

Subsequently, in the third group type zoom lens 1 (or 2, 3, 4), at least one surface closest to the object side or the most image surface side in the cemented lens L12 of the first group G1 and the most object of the second group G2. At least one surface of the positive third lens L3 on the side has an aspherical shape, and is configured to satisfy the following conditional expression (4).
(4) f21 / f2> 1
However,
f2: The focal length of the second group.

  In this three-group type zoom lens, at least one surface on the most object side or the most image surface side in the cemented lens L12 of the first group G1 is aspherical, so that coma aberration in the peripheral portion particularly in the wide-angle end state is reduced. Astigmatism and distortion can be suppressed.

  In the third group type zoom lens 1 (or 2, 3, 4), the cemented lens L12 of the first group G1 has at least one surface on the most object side or the most image side to be aspherical. Since various aberrations that occur when the negative power of the group is increased can be corrected, deterioration of optical performance can be suppressed.

  In this case, in the zoom lens of the three group type, the same zoom ratio can be obtained even if the moving distance between the first group G1 and the second group G2 is shortened by increasing the negative power of the first group G1. Therefore, it is possible to further reduce the size by shortening the optical total length accordingly.

  Further, in the zoom lens 1 (or 2, 3, 4) of the third group type, by making at least one surface of the positive third lens L3 closest to the object side of the second group G2 into an aspheric shape, spherical aberration / Variations in field curvature on the telephoto side due to astigmatism and object distance variations can be suppressed, and thus the resolution performance can be further improved.

  Conditional expression (4) defines the ratio between the focal length f2 of the entire second group G2 and the focal length f21 of the positive third lens L3 closest to the object side in the second group G2. The power of the third lens L3 is weakened with respect to the power of the entire second group G2.

  When the lower limit value of conditional expression (4) is not reached, the focal length f21 of the positive third lens L3 closest to the object side in the second group G2 becomes shorter than the focal length f2 of the second group G2, That is, the power of the third lens L3 becomes too strong with respect to the power of the entire second group G2.

Incidentally, in the case of a three-group type zoom lens, when the following conditional expression (4) ′ is satisfied instead of conditional expression (4), the eccentricity sensitivity in the second group is further reduced, and the manufacturing difficulty level is further reduced. It becomes possible to do.
(4) 'f21 / f2> 1.3

  At this time, in the third group type zoom lens 1 (or 2, 3, 4), the positive third lens L3 closest to the object side of the second group G2, the positive fourth lens L4, and the negative fifth lens L5. The decentering sensitivity with the cemented lens L45 made of this increases, and the assembly accuracy of the second lens group G2 increases, leading to a decrease in performance or an increase in manufacturing difficulty.

  Next, in the zoom lens 1 (or 2, 3, 4) of the third group type, at least one surface closest to the object side or the most image side in the cemented lens of the first group G1 is aspherical, and the second group Both surfaces of the positive third lens L3 closest to the object side of G2 have a spherical shape, and at least one surface on the most object side or the most image side of the cemented lens L45 of the second group G2 has an aspheric shape.

  In the three-group type zoom lens 1 (or 2, 3, 4), at least one surface closest to the object side or the image surface side in the cemented lens L12 of the first group G1 is aspherical, Both surfaces of the positive third lens L3 closest to the object side have a spherical shape, and at least one surface on the most object side or the most image side of the cemented lens L45 of the second group G2 has an aspheric shape. It is possible to reduce the manufacturing difficulty while suppressing the coma aberration, astigmatism and distortion in the peripheral portion in the end state, and the spherical aberration and coma aberration in the telephoto end state.

In the zoom lens 1 (or 2, 3, 4) of the third group type of the present invention, the curvature of the surface closest to the object side in the cemented lens L12 of the first group G1 satisfies the following conditional expression (5). .
(5) -1> G1R1 / fw> -3.3
However,
G1R1: The radius of curvature of the surface closest to the object side in the cemented lens of the first group.

  Conditional expression (5) defines the radius of curvature of the most object-side surface of the cemented lens L12 of the first group G1.

  If the lower limit of conditional expression (5) is not reached, it is necessary to reduce the radius of curvature of the cemented surface of the cemented lens L12 of the first group G1 in order to increase the negative power of the first group G1, so that Accordingly, it is necessary to reduce the radius of curvature of the cemented surface of the positive second lens L2 constituting the cemented lens L12, and the negative first lens L1 and the positive second lens constituting the cemented lens L12. The manufacturing difficulty of the lens L2 will increase.

  On the other hand, when the value exceeds the upper limit value of the conditional expression (5), the radius of curvature of the object side surface of the cemented lens L12 of the first group G1 becomes too small, and in particular, it becomes difficult to correct distortion and curvature of field. End up.

  Further, in the three-group type zoom lens 1 (or 2, 3, 4), the cemented lens L12 of the first group G1 includes a first lens L1 made of a negative glass lens and a 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, 4) of the three-group type uses a resin lens instead of a glass lens for the second lens L2 constituting the cemented lens L12 of the first group G1. As a result, the thickness of the peripheral portion of the second lens L2 made of the resin lens can be made much thinner than that of the glass lens.

In addition, the zoom lens 11 (or 12, 13) is configured by four groups of negative, positive, positive, and negative in order from the object side, and the first lens L1 in which the first group G1 is a negative single lens from the object side. And a negative cemented lens L12 obtained by cementing a second lens L2 that is a positive single lens, and a second lens group G3 that is a positive single lens from the object side, and a fourth lens that is a positive single lens. The lens L4 and a cemented lens L45 that is a negative single lens cemented with a fifth lens L5. The third group G3 is composed of a sixth lens L6 that is a positive single lens, and the fourth group G4 is separated from the imaging surface. The seventh lens L7 has a fixed distance, and is configured to satisfy the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group.

  In the four-group type zoom lens 11 (or 12, 13), only one cemented lens L12 including a first lens L1 having negative power and a second lens L2 having positive power is used as the first group G1. The configuration has the following merits.

  First, in the four-group type zoom lens 11 (or 12, 13), the first group G1 is not a plurality of lenses, but only a cemented lens L12, so that the lenses in the first 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 11 (or 12, 13) of the four-group type, the first group G1 is composed of a plurality of lenses instead of a plurality of lenses, so that the first group G1 is composed of a plurality of lenses. Rather than doing so, it is possible to improve performance, reduce costs and reduce thickness.

  Secondly, in the zoom lens 11 (or 12, 13) of the four-group type, the first group G1 is not composed of a plurality of lenses but has a single structure consisting of only 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.

  As a result, in the four-group type zoom lens 11 (or 12, 13), 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 11 (or 12, 13) of the four-group type, the first group G1 is not a plurality of lens configurations but a single configuration of only the cemented lens L12, so that the first 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.

  Accordingly, in the four-group type zoom lens 11 (or 12, 13), the second group G2 can weaken the action of bringing the principal point position of the first group G1 closer to the image plane. That is, in the four-group type zoom lens 11 (or 12, 13), the second group G2 includes a positive third lens L3, and a cemented lens L45 of the positive fourth lens L4 and the negative fifth lens L5. In this case, even if the power of the positive third lens L3 is smaller than that of the conventional lens, high performance can be realized, thus reducing the lens eccentricity sensitivity in the second group G2, while reducing the thickness and performance. It is possible to reduce the manufacturing difficulty level while realizing the realization.

  Here, the conditional expressions (1) to (3) in the four-group type zoom lens 11 (or 12, 13) are defined in order to achieve a reduction in manufacturing difficulty while realizing thinning and high performance. Is.

  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 value 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 molding the cemented lens L12, and the manufacturing difficulty increases. Resulting in. That is, in the four-group type zoom lens 11 (or 12, 13, and 14), the conditional expression (1) realizes a reduction in thickness while reducing the manufacturing difficulty.

  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.

In the four-group type zoom lens 11 (or 12, 13), if the following conditional expression (2) ′ is satisfied instead of the conditional expression (2), the correction effect (achromaticity) on the lateral chromatic aberration and the axial chromatic aberration is satisfied. Effect) can be further increased.
(2) ′ v2d <26.5

  Conditional expression (3) defines the ratio between the focal length fw in the wide-angle end state and the focal length f21 of the positive third lens L3 closest to the object side in the second group G2, and thereby the second The power of the positive third lens L3 in the group G2 is weakened.

  If the lower limit value of conditional expression (3) is not reached, the power of the positive third lens L3 closest to the object side in the second group G2 becomes too strong compared to the focal length fw in the wide-angle end state. The decentering sensitivity of the positive third lens L3 in the second group G2 and the cemented lens L45 including the positive fourth lens L4 and the negative fifth lens L5 is increased, and the assembly accuracy of the second group G2 is increased. End up. For this reason, in the four-group type zoom lens 11 (or 12, 13, 14), the performance is deteriorated or the manufacturing difficulty is increased.

In addition, in the four-group type zoom lens 11 (or 12, 13), when the following conditional expression (3) ′ is satisfied instead of the conditional expression (3), the eccentricity sensitivity in the second group G2 is much lower. Thus, the manufacturing difficulty can be further reduced.
(3) 'f21 / fw> 1.5

Subsequently, in the fourth group type zoom lens 11 (or 12, 13), the cemented lens L12 of the first group G1 has at least one surface closest to the object side or the image surface side and the most object side of the second group G2. At least one surface of a certain positive third lens L3 has an aspherical shape, and is configured to satisfy the following conditional expression (4).
(4) f21 / f2> 1
However,
f2: The focal length of the second group.

  In this four-group type zoom lens 11 (or 12, 13), at least one surface closest to the object side or the most image surface side in the cemented lens L12 of the first group G1 is aspherical, so that the wide-angle end state is particularly achieved. The coma aberration, astigmatism, and distortion of the peripheral part in can be suppressed.

  In the four-group type zoom lens 11 (or 12, 13), at least one surface closest to the object side or the image surface side in the cemented lens L12 of the first group G1 is aspherical, so that the first group G1 is used. Since the various aberrations that occur when the negative power is increased can be corrected, it is possible to suppress the deterioration of the optical performance.

  At this time, in the four-group type zoom lens 11 (or 12, 13), the negative power of the first group G1 is increased so that the movement distance between the first group G1 and the second group G2 is shortened. Since the zoom ratio can be obtained, the total optical length can be shortened by that amount, and the size can be further reduced.

  Further, in the zoom lens 11 (or 12, 13) of the four-group type, at least one surface of the positive third lens L3 closest to the object side in the second group G2 is aspherical, so that spherical aberration / astigmatism is achieved. It is possible to suppress the field curvature variation on the telephoto end side due to the aberration and the object distance variation, thereby further improving the resolution performance.

  Conditional expression (4) defines the ratio between the focal length f2 of the entire second group G2 and the focal length f21 of the positive third lens L3 closest to the object side in the second group G2. The power of the third lens L3 is weakened with respect to the power of the entire second group G2.

  When the lower limit value of conditional expression (4) is not reached, the focal length f21 of the positive third lens L3 closest to the object side in the second group G2 becomes shorter than the focal length f2 of the second group G2, That is, the power of the third lens L3 becomes too strong with respect to the power of the entire second group G2.

  At this time, the zoom lens 11 (or 12, 13) of the four group type includes a positive third lens L3 closest to the object side of the second group G2, a positive fourth lens L4, and a negative fifth lens L5. The sensitivity to decentering with the cemented lens L45 is increased, and the assembly accuracy of the second group G2 is increased, resulting in a decrease in performance or an increase in manufacturing difficulty.

Incidentally, in the four-group type zoom lens 11 (or 12, 13), when the following conditional expression (4) ′ is satisfied instead of the conditional expression (4), the eccentricity sensitivity in the second group G2 is much lower. Thus, the manufacturing difficulty can be further reduced.
(4) 'f21 / f2> 1.3

  In the fourth group type zoom lens 11 (or 12, 13), the fourth group G4 is set to have a negative power, so that the optical performance can be improved even for a short distance object in the telephoto end state. Has been made.

  Next, in the zoom lens 11 (or 12, 13) of the fourth group type according to the present invention, at least one surface on the most object side or the most image side in the cemented lens L12 of the first group G1 has an aspherical shape. Both surfaces of the positive third lens L3 closest to the object side in the second group G2 have a spherical shape, and at least one surface on the most object side or the most image side of the cemented lens L45 in the second group G2 has an aspheric shape. is there.

  In the four-group type zoom lens 11 (or 12, 13), at least one surface closest to the object side or the most image surface side in the cemented lens L12 of the first group G1 is aspherical, and the most object of the second group G2 is used. A wide-angle end state is achieved by making both surfaces of the positive third lens L3 on the side spherical, and making at least one surface closest to the object side or image side of the cemented lens L45 of the second group G2 aspherical. The manufacturing difficulty can be reduced while suppressing the coma aberration, astigmatism / distortion aberration, and the spherical aberration and coma aberration in the telephoto end state.

In the four-group type zoom lens 11 (or 12, 13), the curvature of the surface closest to the object side in the cemented lens L12 of the first group G1 satisfies the following conditional expression (5).
(5) -1> G1R1 / fw> -3.3
However,
G1R1: The radius of curvature of the surface closest to the object side in the cemented lens of the first group.

  Conditional expression (5) defines the radius of curvature of the most object-side surface of the cemented lens L12 of the first group G1.

  If the lower limit of conditional expression (5) is not reached, it is necessary to reduce the radius of curvature of the cemented surface of the cemented lens L12 of the first group G1 in order to increase the negative power of the first group G1, so that Accordingly, it is necessary to reduce the radius of curvature of the cemented surface of the positive second lens L2 constituting the cemented lens L12, and the negative first lens L1 and the positive second lens constituting the cemented lens L12. The manufacturing difficulty of the lens L2 will increase.

  On the other hand, when the value exceeds the upper limit value of the conditional expression (5), the radius of curvature of the object side surface of the cemented lens L12 of the first group G1 becomes too small, and in particular, it becomes difficult to correct distortion and curvature of field. End up.

Furthermore, in the four-group type zoom lens 11 (or 12, 13), the seventh lens L7 of the fourth group G4 has negative power, and satisfies the following conditional expression (6).
(6) f1 / f4 <0.9
However,
f1: focal length of first group f4: focal length of fourth group

  Conditional expression (6) prescribes the power of the fourth group G4 with respect to the power of the first group G1, and the seventh lens L7 of the fourth group G4 is disposed at a position closest to the image sensor serving as a heat source. In view of this, when the seventh lens L7 of the fourth group G4 is formed of a resin lens, the radius of curvature is made gentle to prevent performance deterioration due to thermal deformation.

  When the lower limit value of conditional expression (6) is not reached, the negative power of the fourth group G4 becomes too strong, so that it is necessary to increase the positive power of the second group G2 and the third group G3. In order to secure the edge thickness in the positive sixth lens L6 of the group G3, the center thickness must be further increased, which is disadvantageous for thinning at the time of collapse.

Incidentally, in the four-group type zoom lens 11 (or 12, 13), when the following conditional expression (6) ′ is satisfied instead of the conditional expression (6), the performance deterioration at the time of temperature / humidity change is suppressed, and the thin lens is thin. This will be even more advantageous.
(6) ′ f1 / f4 <0.6

  Further, in the four-group type zoom lens 11 (or 12, 13), the third group G3 and the fourth group G4 are made of resin lenses, thereby providing a low-cost imaging device as compared with the case of using glass lenses. can do.

  Here, in the four-group type zoom lens 11 (or 12, 13), the third lens group G3 and the fourth lens group G4 are made of resin lenses having negative and positive powers, respectively, so that the focus position at the time of temperature and humidity changes. Since the fluctuation can be canceled by the third group G3 and the fourth group G4, it is possible to provide a high-performance imaging apparatus at a low cost.

  Further, in the four-group type zoom lens 11 (or 12, 13), 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 four-group zoom lens 11 (or 12, 13) uses a resin lens instead of a glass lens for the second lens L2 constituting the cemented lens L12 of the first group G1. Thus, the thickness of the peripheral portion of the second lens L2 made of the resin lens can be made much thinner than that of the glass lens.

  In the fourth group type zoom lens 11 (or 12, 13), the fourth group G4 improves the field curvature correction effect, and the fourth group G4 is fixed, thereby simplifying the mechanical structure. can do. Further, in the zoom lens 11 (or 12, 13) of the four group type, the optical total length is increased by 3 to the extent that the power of the first group G3 to the third group G3 can be increased by adding the fourth group G4. It can be shorter than the group type.

[5-2. Configuration of digital still camera]
As shown in FIG. 22, 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 includes an optical system including the zoom lens 1 (or 2, 3, 4) and the zoom lens 11 (or 12, 13), and a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, for example. Etc., and an image pickup device 16 made up of the above.

  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 includes a motor (not shown) that drives the zoom lens 1 (or 2, 3, 4) and the lens group in the zoom lens 11 (or 12, 13) based on a control signal from the CPU 60. It is made to control.

  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, 4) or the zoom lens 11 (or 12, 13) 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 the focusing, for example, when the shutter release button is half-pressed or fully pressed for recording, the lens drive control unit 80 controls the zoom lens 1 (or 2, 3, 4) based on a control signal from the CPU 60. Alternatively, the zoom lens 11 (or 12, 13) is driven and controlled.

  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.

<6. Other embodiments>
In addition, the specific shapes, structures, and numerical values of the respective parts shown in the first and second embodiments and the first numerical example to the seventh numerical example described above are specific examples of implementation in carrying out the present invention. These are merely examples, and the technical scope of the present invention should not be construed in a limited way.

  In the above-described second embodiment, the case where the fourth group G4 having negative power is used has been described. However, the present invention is not limited to this, and the fourth group G4 having a positive power may be used.

  In the second embodiment described above, an IR cut filter CF and a seal glass SG for protecting the image plane IMG are arranged between the fourth group G4 and the image plane IMG. Stated. However, the present invention is not limited to this, and only the IR cut filter CF may be disposed between the fourth group G4 and the image plane IMG by making the fourth group G4 also serve as a sealing glass. good.

  Further, in the above-described embodiment, the case where the imaging device is mounted on the digital still camera 100, for example, is shown as an example. However, the target on which the imaging device is mounted is not limited to this. The present invention can be widely applied to various other electronic devices such as a telephone, a personal computer equipped with a camera, and a PDA incorporating a camera.

  1, 2, 3, 4, 11, 12, 13 ... zoom lens, 15 ... camera block, 16 ... image sensor, 30 ... image processing unit, 40 ... LCD, 50 ... reader / writer, 51 ... ... Memory card, 60 ... CPU, 70 ... Input section, 80 ... Lens drive control section.

Claims (14)

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 lens unit is composed of a third lens composed of a positive single lens from the object side, a cemented lens formed by cementing a fourth lens composed of a positive single lens and a fifth lens composed of a negative single lens, The third group consists of a sixth lens consisting of a positive single lens,
A zoom lens that satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group. In the zoom lens, at least one surface on the most object side or the most image side in the cemented lens of the first group and at least one surface of the positive third lens located on the most object side in the second group are not. The zoom lens according to claim 1, wherein the zoom lens has a spherical shape and satisfies the following conditional expression (4).
(4) f21 / f2> 1
However,
f2: The focal length of the second group. In the zoom lens, at least one surface closest to the object side or the image surface side of the cemented lens of the first group has an aspherical shape, and both surfaces of the positive third lens located closest to the object side of the second group. The zoom lens according to claim 1, wherein is a spherical shape, and at least one surface closest to the object side or the image surface side of the cemented lens of the second group is an aspherical shape. The zoom lens has a curvature of a surface closest to the object side in the cemented lens of the first group,
The zoom lens according to claim 1, wherein the following conditional expression (5) is satisfied.
(5) -1> G1R1 / fw> -3.3
However,
G1R1: The radius of curvature of the surface closest to the object side in the cemented lens of the first group. 2. The zoom lens according to claim 1, wherein 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. 4. The zoom lens according to 4. 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 lens unit is composed of a third lens composed of a positive single lens from the object side, a cemented lens formed by cementing a fourth lens composed of a positive single lens and a fifth lens composed of a negative single lens, The third group consists of a sixth lens consisting of a positive single lens,
An imaging apparatus that satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group. In order from the object side, it is composed of four groups of negative, positive, positive, negative, or positive, and the first lens unit is joined from the object side to the first lens that is a negative single lens and the second lens that is a positive single lens. A cemented lens composed of a negative cemented lens, a third lens composed of a positive single lens from the object side, a fourth lens composed of a positive single lens, and a fifth lens composed of a negative single lens; The third group consists of a sixth lens consisting of a positive single lens, and the fourth group consists of a seventh lens consisting of a single lens with a fixed distance from the imaging surface,
A zoom lens that satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group. In the zoom lens, at least one surface on the most object side or the most image side in the cemented lens of the first group and at least one surface of the positive third lens located on the most object side in the second group are not. The zoom lens according to claim 7, which has a spherical shape and satisfies the following conditional expression (4).
(4) f21 / f2> 1
However,
f2: The focal length of the second group. In the zoom lens, at least one surface closest to the object side or the image surface side of the cemented lens of the first group has an aspherical shape, and both surfaces of the positive third lens located closest to the object side of the second group. The zoom lens according to claim 7, wherein is a spherical shape, and at least one surface closest to the object side or the image surface side of the cemented lens of the second group is an aspherical shape. 10. The zoom lens according to claim 7, wherein the curvature of the most object-side surface of the cemented lens of the first group satisfies the following conditional expression (5).
(5) -1> G1R1 / fw> -3.3
However,
G1R1: The radius of curvature of the surface closest to the object side in the cemented lens of the first group. In the zoom lens, the fourth group has a negative power,
The zoom lens according to claim 7, wherein the following conditional expression (6) is satisfied.
(6) f1 / f4 <0.9
However,
f1: focal length of first group f4: focal length of fourth group 12. The zoom lens according to claim 7, wherein the sixth lens constituting the third group and the seventh lens constituting the fourth group are made of resin. 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. The zoom lens according to 12. A zoom lens, and an image sensor that converts an optical image formed by the zoom lens into an electrical signal;
The zoom lens
In order from the object side, it is composed of four groups of negative, positive, positive, negative, or positive, and the first lens unit is joined from the object side to the first lens that is a negative single lens and the second lens that is a positive single lens. A cemented lens composed of a negative cemented lens, a third lens composed of a positive single lens from the object side, a fourth lens composed of a positive single lens, and a fifth lens composed of a negative single lens; The third group consists of a sixth lens consisting of a positive single lens, and the fourth group consists of a seventh lens consisting of a single lens with a fixed distance from the imaging surface,
An imaging apparatus that satisfies the following conditional expressions (1) to (3).
(1) N1d> 1.55
(2) v2d <30
(3) f21 / fw> 1
However,
N1d: Refractive index with respect to d-line of the negative first lens constituting the first group cemented lens v2d: Abbe number fw of the positive second lens constituting the first group cemented lens fw: Focal length f21 in the wide-angle end state : The focal length of the positive third lens closest to the object in the second group.

Images