JP2008158418A - Zoom lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens satisfying a high variable power ratio, high performance and miniaturization, and an imaging apparatus using the zoom lens. <P>SOLUTION: The zoom lens has four lens groups having positive, negative, positive and positive power. The second lens group is a variable power group and the fourth lens group is a compensating group. Assuming that f1 is the focal length of the first lens group, fw is the focal length of the entire system in a wide angle end state, ft is the focal length of the entire system in a telephoto end state, f3 is the focal length of the third lens group, r22 is the radius of curvature of the image-side lens surface of a negative lens L21 arranged in the second lens group, r3a is the radius of curvature of a lens surface positioned nearest to the object side in the third lens group (r3a>0), and r3b is the radius of curvature of a lens surface positioned nearest to the image side in the third lens group (r3b<0), the zoom lens satisfies conditional expressions: (1) 1.8<f1/(fw×ft)<SP>1/2</SP><2.2, (2) 0.9<f3/(fw×ft)<SP>1/2</SP><1.2, (3) 1.1<r22/fw<1.3 and (4) -0.8<(r3a+r3b)/(r3a-r3b)<0.5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a novel zoom lens and an imaging apparatus. Specifically, the present invention relates to a zoom lens having a zoom ratio as high as nearly 20 times and an imaging apparatus using the zoom lens.

  In recent years, in the field of lens-integrated cameras, user needs for zoom lenses having a high zoom ratio are increasing. This is because, unlike a single-lens reflex camera, lenses cannot be exchanged, and therefore, if the zoom ratio is low, various shooting scenes cannot be handled.

  To date, zoom lenses that have achieved a high zoom ratio include those described in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5, for example.

  In the zoom lens described in Patent Document 1, the second lens group is constituted by a cemented lens of a negative lens, a negative lens, and a positive lens.

  In the zoom lens described in Patent Document 2, the third lens group is composed of a biconvex positive lens and a meniscus negative lens with a concave surface facing the image side.

Japanese Patent Laid-Open No. 2004-240151 JP 2001-116997 A JP 2001-91830 A JP 2000-267005 A JP 2004-333769 A

  However, with a conventional zoom lens, it has been difficult to achieve all of high zoom magnification, high image quality, and miniaturization.

  The zoom lens described in Patent Document 1 has a large amount of change in the lateral magnification of the second lens group accompanying a change in the lens position state, and sufficient performance cannot be achieved with a three-lens configuration.

  In the zoom lens described in Patent Document 2, since the negative lens arranged closest to the image side of the third lens group has a concave surface facing the image side, performance deterioration due to mutual eccentricity of the positive lens and the negative lens However, it was difficult to achieve a stable optical quality due to manufacturing errors and the like.

  In the zoom lens described in Patent Document 3, since the positive refractive power of the first lens group is weak, the total lens length is large and it is not suitable for miniaturization.

  In the zoom lens described in Patent Document 4, the positive refractive power by the third lens group is weak, and there is a problem in shortening the total lens length.

  In the zoom lens described in Patent Document 5, the positive refractive power of the first lens group is extremely strong, and there is a problem in improving the performance.

  The present invention has been made in view of the above-described problems, and provides a zoom lens capable of satisfying a high zoom ratio, high performance, and downsizing, and an imaging device using the zoom lens. This is the issue.

A zoom lens according to an embodiment of the present invention has a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power, which are sequentially located from the object side to the image plane side. The third lens group has a fourth lens group having a positive refractive power, and when the lens position changes from the wide-angle end state to the telephoto end state, the second lens group moves to the image side, and The fourth lens group is moved so as to compensate for the fluctuation of the image plane position accompanying the movement of the second lens group, and an aperture stop is disposed between the second lens group and the third lens group. The second lens group includes four meniscus negative lens L21, negative lens L22, positive lens L23, and negative lens L24 having a concave surface facing the image side. The third lens group includes at least one positive lens. Consists of a lens and a negative lens Together to satisfy the following condition (1) to 4.
(1) 1.8 <f1 / (fw · ft) ^1/2 <2.2
(2) 0.9 <f3 / (fw · ft) ^1/2 <1.2
(3) 1.1 <r22 / fw <1.3
(4) -0.8 <(r3a + r3b) / (r3a-r3b) <0.5
However,
f1: Focal length fw of the first lens group fw: Focal length of the entire system in the wide-angle end state ft: Focal length of the entire system in the telephoto end state f3: Focal length r22 of the third lens group: Arranged in the second lens group Radius of curvature r3a of the image side lens surface of the negative lens L21: radius of curvature of the lens surface located closest to the object side in the third lens group (r3a> 0)
r3b: The radius of curvature (r3b <0) of the lens surface located closest to the image side in the third lens unit.

An image pickup apparatus according to an embodiment of the present invention includes a zoom lens and an image pickup element that converts an optical image formed by the zoom lens into an electrical signal, and the zoom lens sequentially moves from an object side to an image plane side. A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, When the lens position state changes from the wide-angle end state to the telephoto end state, the second lens group moves to the image side, and the variation of the image plane position accompanying the movement of the second lens group is compensated for. A fourth lens group moves, an aperture stop is disposed between the second lens group and the third lens group, and the second lens group has a meniscus negative lens L21 having a concave surface facing the image side, Negative lens L22, positive lens L23, negative lens It is constituted by four's L24, the third lens group with constituted by at least respective one or more positive lens and the negative lens satisfies the following conditional expressions (1) to (4).
(1) 1.8 <f1 / (fw · ft) ^1/2 <2.2
(2) 0.9 <f3 / (fw · ft) ^1/2 <1.2
(3) 1.1 <r22 / fw <1.3
(4) -0.8 <(r3a + r3b) / (r3a-r3b) <0.5
However,
f1: Focal length fw of the first lens group fw: Focal length of the entire system in the wide-angle end state ft: Focal length of the entire system in the telephoto end state f3: Focal length r22 of the third lens group: Arranged in the second lens group Radius of curvature r3a of the image side lens surface of the negative lens L21: radius of curvature of the lens surface located closest to the object side in the third lens group (r3a> 0)
r3b: The radius of curvature (r3b <0) of the lens surface located closest to the image side in the third lens unit.

  According to the present invention, it is possible to satisfy high zoom ratio, high performance, and downsizing.

  The best mode for carrying out the zoom lens and the imaging apparatus of the present invention will be described below with reference to the drawings.

  First, the zoom lens of the present invention will be described.

The zoom lens according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, which are sequentially positioned from the object side to the image plane side. A fourth lens group having a positive refractive power, and when the lens position changes from the wide-angle end state to the telephoto end state, the second lens group moves to the image side, and the second lens group The fourth lens group is moved so as to compensate for fluctuations in the image plane position accompanying the movement, an aperture stop is disposed between the second lens group and the third lens group, and the second lens group is The lens is composed of four meniscus negative lenses L21, negative lenses L22, positive lenses L23, and negative lenses L24 having a concave surface facing the image side. The third lens group includes at least one positive lens and one negative lens. As well as the following conditions (1) to satisfy the (4).
(1) 1.8 <f1 / (fw · ft) ^1/2 <2.2
(2) 0.9 <f3 / (fw · ft) ^1/2 <1.2
(3) 1.1 <r22 / fw <1.3
(4) -0.8 <(r3a + r3b) / (r3a-r3b) <0.5
However,
f1: Focal length fw of the first lens group fw: Focal length of the entire system in the wide-angle end state ft: Focal length of the entire system in the telephoto end state f3: Focal length r22 of the third lens group: Arranged in the second lens group Radius of curvature r3a of the image side lens surface of the negative lens L21: radius of curvature of the lens surface located closest to the object side in the third lens group (r3a> 0)
r3b: The radius of curvature (r3b <0) of the lens surface located closest to the image side in the third lens unit.

In the zoom lens according to the present invention, a high zoom ratio is achieved by focusing on the following five points on the basis of a configuration in which four groups of positive, negative, positive and positive are composed of two groups as a variable power group and four groups as a compensate group. High performance and downsizing were achieved.
1) An aperture stop is disposed between the second lens group and the third lens group. 2) The focal length of the first lens group is appropriately set. 3) The second lens group is sequentially positioned from the object side. Consists of four meniscus negative lens L21, negative lens L22, positive lens L23, and negative lens L24 with a concave surface facing the lens, and devise the shape of the negative lens L21. 4) The focal length of the third lens group is appropriate. 5) The third lens group is composed of at least one positive lens and at least one negative lens, and the shape of the third lens group is devised. In general, it is desirable that the aperture stop be disposed near the center of the optical system. The zoom lens according to the present invention is also disposed between the second lens group and the third lens group.

  In order to achieve both high zoom ratio and high performance, at least one movable lens group is arranged on each of the object side and the image side of the aperture stop. It is important to positively change the off-axis light beam passing through.

  In the zoom lens according to the present invention, by arranging an aperture stop between the second lens group and the third lens group, the second lens group disposed on the object side and the fourth lens group disposed on the image side are provided. It becomes a movable lens group. The off-axis light beam passing through the second lens group passes away from the optical axis in the wide-angle end state, and approaches the optical axis when the lens position state changes to the telephoto end state. By utilizing this, fluctuations in off-axis aberration that occur when the lens position changes are corrected well. Further, the off-axis light beam passing through the fourth lens group also changes its distance from the optical axis as the fourth lens group moves in accordance with the change in the lens position state. It is possible to satisfactorily correct the fluctuation of off-axis aberration that occurs in

  The first lens group is disposed closest to the object side, and the off-axis light beam passes through a position away from the optical axis. Further, since the total lens length is greatly affected by the refractive power, it is desirable to set the refractive power appropriately.

  When the refractive power of the first lens group becomes strong, it is suitable for shortening the total lens length, but in the telephoto end state, the aberration due to the first lens group is further magnified by the second lens group, so that various aberrations are magnified. As a result, the optical performance is degraded.

  Conversely, when the refractive power of the first lens group is weakened, the total lens length is increased.

  Conditional expression (1) defines conditions for setting the focal length of the first lens group within an appropriate range.

  If the upper limit value of conditional expression (1) is exceeded, the overall length of the lens increases, making it difficult to reduce the size.

  If the lower limit value of conditional expression (1) is not reached, the off-axis light beam that passes through the first lens group is separated from the optical axis, which causes an increase in the lens diameter. Further, in the wide-angle end state, coma aberration is greatly generated in the peripheral portion of the screen, and it becomes impossible to sufficiently achieve high performance.

  The third lens group has a function of converging the light beam diverged by the second lens group.

  Generally, in a positive / negative / positive / positive four-group zoom lens, since there is no negative lens group on the image side from the aperture stop, it is important to correct distortion in the wide-angle end state. In a conventional zoom lens, the third lens group is composed of a negative subgroup having a negative refractive power and a positive subgroup having a positive refractive power arranged on the image side thereof (hereinafter referred to as “negative positive structure”). ), However, the light beam diverged by the second lens group is further diverged by the negative subgroup, so that it is necessary to increase the number of lenses in order to satisfactorily correct the negative spherical aberration generated by the third lens group alone. In addition, since the negative subgroup is arranged in the vicinity of the aperture stop, the effect on the correction of distortion is weak.

  Further, in another conventional zoom lens, the third lens group is configured by a positive subgroup having a positive refractive power and a negative subgroup having a negative refractive power arranged on the image side thereof (hereinafter referred to as “positive / negative structure”). However, since the negative subgroup expands the image formed by the positive subgroup, the optical performance is greatly deteriorated due to the mutual eccentricity between the positive subgroup and the negative subgroup, and the optical stability is stable due to manufacturing errors. It was difficult to ensure performance.

  Therefore, in the zoom lens of the present invention, by devising the configuration of the second lens group, negative distortion generated by the second lens group is suppressed, and the distortion aberration correction burden in the third lens group is reduced. Yes.

  Specifically, the second lens group is configured by four lenses, a meniscus negative lens L21, a negative lens L22, a positive lens L23, and a negative lens L24, which are located in order from the object side and have a concave surface facing the image side. Yes.

  The negative lens L21 mainly corrects off-axis aberrations, and the three lenses arranged on the image side, the negative lens L22, the positive lens L23, and the negative lens L24 have a triplet configuration, thereby correcting axial aberrations. And the correction of off-axis aberrations.

  Compared to the conventionally known three-lens configuration of the negative lens, negative lens, and positive lens, which is the configuration of the second lens group, the four-lens configuration of the negative lens and the triplet is changed from the three-lens configuration of the negative lens and the doublet. As a result, both on-axis aberration and off-axis aberration can be corrected better. As a result, it is possible to more favorably correct the variation of the on-axis aberration caused by the change in the lateral magnification of the second lens group, to improve the performance, and to generate negative in the wide-angle end state. Generation of distortion can be suppressed.

  Conditional expression (3) defines the radius of curvature of the image side lens surface of the negative lens L21 disposed in the second lens group.

  As described above, the negative lens L21 mainly corrects off-axis aberrations. However, if the upper limit value of the conditional expression (3) is exceeded, a large amount of internal coma aberration occurs in the wide-angle end state, resulting in high performance. It will not be possible to achieve sufficient conversion.

  Conversely, if the lower limit value of conditional expression (3) is not reached, higher-order field curvature occurs at the peripheral edge of the screen in the wide-angle end state, so that high performance is achieved over the entire screen. Will not be able to.

  Since it is no longer necessary to correct negative distortion occurring in the wide-angle end state of the third lens group, the zoom lens of the present invention does not require the third lens group to adopt a positive / negative structure or a negative / positive structure. As a result, the third lens group is composed of at least one positive lens and one negative lens, and the lens surface closest to the object side of the third lens group has a convex surface facing the object side, and the lens closest to the image side. Since the convex surface can be directed to the image side, it is possible to reduce the influence of assembling errors and the like at the time of manufacture and to ensure stable optical quality.

  Further, in the zoom lens according to the present invention, the third lens group does not have to have a positive / negative structure or a negative / positive structure, so that the refractive power of the third lens group can be increased positively, and the total lens length can be shortened. Became possible. In addition, it is possible to achieve higher performance by configuring the third lens group with a cemented lens of a positive lens and a negative lens and a positive lens arranged on the image side thereof.

  By configuring the third lens group with at least one positive lens and at least one negative lens and increasing the positive refractive power, it is possible to satisfactorily correct on-axis aberrations generated by the third lens group alone. High performance can be achieved.

  Conditional expression (2) defines the focal length of the third lens group.

If the upper limit value of conditional expression (2) is exceeded, the total lens length will increase, making it difficult to reduce the size. If the lower limit value of conditional expression (2) is not reached, the axial light beam that exits the third lens group In other words, since the lateral magnification of the fourth lens group approaches 0 to 1, the movement of the fourth lens group necessary to compensate for the fluctuation of the image plane position accompanying the movement of the second lens group. The amount is too large. As a result, the drive mechanism for moving the fourth lens group becomes complicated, and a sufficient space needs to be widened on the object side and the image side of the fourth lens group, so that the total lens length cannot be shortened sufficiently. .

  The conditional expression (4) is a conditional expression that defines the shape of the third lens group.

  When the upper limit of conditional expression (4) is exceeded, that is, when the radius of curvature of the object side lens surface becomes loose, the off-axis light beam that passes through the lens surface closest to the image side of the third lens group is separated from the optical axis. As a result, a large amount of coma occurs at the periphery of the screen in the wide-angle end state, so that high performance cannot be achieved sufficiently.

  If the lower limit of conditional expression (4) is not reached, the negative on-axis aberration generated on the lens surface closest to the object side in the third lens group becomes too large, and sufficient performance cannot be achieved. End up.

In the zoom lens according to an embodiment of the present invention, the aperture stop is at a fixed position in the optical axis direction regardless of the lens position state, and Ds is a length along the optical axis from the aperture stop to the image plane. , TL is the total lens length, and it is desirable to satisfy the following conditional expression (5).
(5) 0.35 <Ds / TL <0.45
By fixing the aperture stop in the optical axis direction regardless of the lens position state, a drive mechanism for moving the aperture stop can be omitted, and space saving can be achieved.

  Conditional expression (5) is a conditional expression that defines the position of the aperture stop.

  If the upper limit value of conditional expression (5) is exceeded, the position of the aperture stop is closer to the object side, so the movement stroke of the second lens group is reduced, and in order to obtain a predetermined zoom ratio, Refractive power must be increased, and it becomes difficult to satisfactorily correct fluctuations in off-axis aberrations accompanying changes in the lens position.

  When the lower limit value of conditional expression (5) is not reached, the position of the aperture stop is closer to the image plane side, so that the angle formed by the principal ray emitted from the lens system with respect to the optical axis becomes large. Along with this, the angle formed by the principal ray at the aperture stop position and the optical axis also increases, so the off-axis light beam passing through the first lens group or the second lens group also moves away from the optical axis, causing an increase in the lens diameter. Therefore, further downsizing cannot be achieved.

In the zoom lens according to the embodiment of the present invention, it is desirable to satisfy the following conditional expression (6) in order to shorten the total lens length and to better correct the optical performance in the telephoto end state.
(6) 0.4 <f1 / ft <0.5
Conditional expression (6) is a conditional expression that defines the focal length of the first lens group.

  When the lower limit of conditional expression (6) is not reached, negative spherical aberration that occurs in the first lens group alone increases, and at the same time, various aberrations that occur in the first lens group are greatly magnified after the second lens group. End up. As a result, the negative spherical aberration that occurs in the telephoto end state cannot be sufficiently corrected, and high performance cannot be achieved sufficiently.

  If the upper limit of conditional expression (6) is exceeded, it is not preferable to achieve a predetermined zoom ratio because the total lens length increases.

  In the zoom lens according to the embodiment of the present invention, it is desirable that the positive lens L23 and the negative lens L24 are cemented in the second lens group.

  As a result, it is possible to reduce the influence of assembly errors at the time of manufacture and to ensure stable optical performance.

  When a lens is incorporated in the lens chamber, there is always a backlash in the radial direction, and the lens is eccentric due to the backlash. When a plurality of lenses are inserted in a stacked manner, the amount of eccentricity changes due to the influence of the eccentricity of the previously incorporated lens, so that it is difficult to incorporate each lens in a stable state.

  Since the second lens group has a zooming function and is composed of a large number of four, in order to reduce the influence of assembly errors during manufacturing and obtain stable optical quality, mutual decentering of each lens is required. I want to incorporate it in the lens room with reduced pressure. By using the positive lens L23 and the negative lens L24 as a cemented lens, decentering elements can be reduced and stable optical quality can be obtained.

In the zoom lens according to an embodiment of the present invention, in order to satisfactorily correct the coma aberration generated in the wide-angle end state and improve the performance, N2 is the four lenses constituting the second lens group. It is desirable to satisfy the following conditional expression (7) as the average refractive index for the d-line. .
(7) 1.8 <N2
In the zoom lens according to the embodiment of the present invention, in order to further improve the performance, the first lens group is located in order from the object side, and is a cemented lens of a negative lens L11 and a positive lens L12, a positive lens. It is desirable that the lens is composed of four lenses, L13 and positive lens L14.

  In the first lens group, since the axial light beam is incident with a wide light beam diameter particularly in the telephoto end state, negative spherical aberration is likely to occur. In addition, since off-axis light flux is incident away from the optical axis, off-axis aberration is likely to occur.

  Therefore, by arranging a cemented lens of the negative lens L11 and the positive lens L12 on the most object side of the first lens group, it is possible to satisfactorily correct negative spherical aberration and axial chromatic aberration. In addition, the light beam emitted from the first lens group becomes a convergent light beam. If this converging action is performed with a single positive lens, a large amount of negative spherical aberration occurs in the telephoto end state, thereby achieving high performance. I can't. Therefore, by performing the convergence action with two positive lenses L13 and L14, negative spherical aberration can be corrected and high optical performance can be realized.

  In the zoom lens according to an embodiment of the present invention, in order to satisfactorily correct variations in various aberrations accompanying changes in the subject position, the fourth lens group is positioned in order from the object side, and a convex surface is provided on the object side. It is desirable that the lens is composed of a positive lens directed toward the surface and a negative lens having a concave surface directed toward the image side.

  With the doublet configuration, it is possible to correct off-axis aberrations and on-axis aberrations at the same time, and it is possible to satisfactorily correct variations in various aberrations that occur when the subject position changes.

  In the zoom lens according to an embodiment of the present invention, it is desirable to use a glass material with high anomalous dispersion for the first lens group in order to better suppress the occurrence of chromatic aberration.

  In particular, among the lenses constituting the first lens group, the positive lens L12 in the cemented lens of the negative lens L11 and the positive lens L12 is made of a glass material having a high anomalous dispersion, so that it occurs at the center of the screen in the telephoto end state. The secondary dispersion can be corrected well.

  In the zoom lens according to the embodiment of the present invention, it is desirable to dispose a fifth lens group including a negative lens and a positive lens on the image side of the fourth lens group.

  Thereby, it is possible to satisfactorily correct the negative distortion in the wide-angle end state, and to further improve the performance by moving the exit pupil away from the optical axis.

  In the zoom lens according to an embodiment of the present invention, it is desirable to use an aspheric lens.

  Thereby, higher optical performance can be realized. In particular, by introducing an aspheric lens into the third lens group, it is possible to further improve the central performance. Further, by using an aspheric lens for the second lens group, it is possible to satisfactorily correct coma variation due to the angle of view that occurs in the wide-angle end state.

  Furthermore, it goes without saying that higher optical performance can be obtained by using a plurality of aspheric surfaces.

  In the zoom lens according to an embodiment of the present invention, a low-pass filter is disposed on the image side of the lens system to prevent the occurrence of moire fringes, or an infrared cut filter is disposed according to the spectral sensitivity characteristics of the light receiving element. It is desirable.

  Next, specific embodiments of the zoom lens of the present invention and numerical examples in which specific numerical values are applied to the embodiments will be described with reference to the drawings and tables.

  In each embodiment, an aspherical surface is introduced, and the aspherical shape is defined by the following equation (1).

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

  FIG. 1 shows the refractive power distribution of the zoom lenses 1 and 2 according to the first and second embodiments of the present invention. The first lens group having positive refractive power in order from the object side. G1, second lens group G2 having negative refractive power, third lens group G3 having positive refractive power, fourth lens group G4 having positive refractive power, and fifth lens group G5 having positive refractive power The first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed in the optical axis direction during zooming from the wide-angle end state to the telephoto end state, and the second lens group G2 Moves to the image side, and the fourth lens group G4 once moves to the object side and then moves to the image side.

  FIG. 2 is a diagram showing a lens configuration of the zoom lens 1 according to the first embodiment of the present invention. The first lens group G1, which is located in order from the object side to the image side, is a cemented lens of a negative meniscus lens L11 having a convex surface facing the object side and a positive lens L12 having a convex surface facing the object side, and a convex surface facing the object side And a positive lens L14 having a convex surface on the object side. The second lens group G2 includes a meniscus negative lens L21 having a concave surface facing the image side, a biconcave negative lens L22, and a positive lens L23 having a convex surface facing the object side, which are positioned in order from the object side to the image side. It is constituted by a cemented lens with a negative lens L24 having a concave surface facing the image side. The third lens group G3 is located in order from the object side to the image side, and includes a meniscus positive lens L31 having a convex surface on the object side and an aspheric surface on the object side, and a meniscus negative lens L32 having a concave surface on the image side. And a biconvex positive lens L33. The fourth lens group G4 includes a positive lens L41 that is biconvex and has an aspheric surface on the object side, and a meniscus negative lens L42 that has a concave surface on the object side. The fifth lens group G5 includes a biconcave negative lens L51 and a biconvex positive lens L52, which are sequentially positioned from the object side to the image side. The aperture stop S is located close to the object side of the third lens group G3, and is fixed in the optical axis direction upon zooming from the wide-angle end state to the telephoto end state. Further, a filter FL such as an infrared cut filter or a low-pass filter is disposed between the fifth lens group G5 and the image plane IMG.

  Table 1 below lists values of specifications of Numerical Example 1 in which specific numerical values are applied to the zoom lens 1 according to the first embodiment. In Table 1 and the following specification table, “surface number” indicates the i-th surface counted from the object side, and “curvature radius” represents the curvature radius of the i-th surface counted from the object side. “Surface spacing” indicates the axial top surface spacing between the i-th surface and the (i + 1) -th surface counted from the object side, and “refractive index” indicates the d-line of the glass material having the i-th surface on the object side. The “Abbe number” indicates the Abbe number with respect to the d-line of the glass material having the i-th surface on the object side. And regarding the radius of curvature, “0” indicates that the surface is a flat surface, and regarding the surface interval, “(Di)” indicates that the surface interval is a variable interval.

In the zoom lens 1, the object side surface (16th surface) of the meniscus positive lens L31 in the third lens group G3 and the object side surface (21st surface) of the biconvex positive lens L41 in the fourth lens group G4 are shown. It is composed of an aspherical surface. Therefore, Table 2 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients A, B, C, and D together with the conic constant κ in the numerical example 1. In Table 2 and the following table showing aspherical coefficients, “E-i” represents an exponential expression with a base of 10, that is, “10- ⁱ ”. For example, “0.12345E-05” represents “ 0.12345 × 10 ⁻⁵ ”.

  In zoom lens 1, when zooming from the wide-angle end state to the telephoto end state, the surface distance D7 between the first lens group G1 and the second lens group G2, the second lens group G2 and the third lens group G3 (opening) The surface distance D14 between the diaphragm S), the surface distance D20 between the third lens group G3 and the fourth lens group G4, and the surface distance D24 between the fourth lens group G4 and the fifth lens group G5 are changed. To do. Therefore, the respective values in the wide-angle end state (f = 1.000), the intermediate focal length state (f = 7.025), and the telephoto end state (f = 18.808) of the distance between the surfaces in Numerical Example 1 are focused. Table 3 shows the distance f, F number FNO, and angle of view 2ω.

  Table 4 shows values corresponding to the conditional expressions (1) to (7) in the numerical value example 1.

  FIGS. 3 to 5 show various aberration diagrams in the infinite focus state of Numerical Example 1, FIG. 3 is a wide-angle end state (f = 1.000), and FIG. 4 is an intermediate focal length state (f = 7.025) and FIG. 5 are graphs showing various aberrations in the telephoto end state (f = 18.808).

  3 to 5, the solid line in the spherical aberration diagram indicates spherical aberration, the solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the lateral aberration diagram, A represents the angle of view, and y represents the image height.

  From the aberration diagrams, it is clear that Numerical Example 1 has excellent image forming performance with various aberrations corrected well.

  FIG. 6 is a diagram showing a lens configuration of the zoom lens 2 according to the second embodiment of the present invention. The first lens group G1, which is located in order from the object side to the image side, is a cemented lens of a negative meniscus lens L11 having a convex surface facing the object side and a positive lens L12 having a convex surface facing the object side, and a convex surface facing the object side And a positive lens L14 having a convex surface on the object side. The second lens group G2 includes a meniscus negative lens L21 having a concave surface facing the image side, a biconcave negative lens L22, and a positive lens L23 having a convex surface facing the object side, which are positioned in order from the object side to the image side. It is constituted by a cemented lens with a negative lens L24 having a concave surface facing the image side. The third lens group G3 is composed of a cemented lens of a positive lens L31 having a biconvex shape and an aspheric surface on the object side, and a meniscus negative lens L32 having a convex surface on the object side, which are sequentially positioned from the object side to the image side. Composed. The fourth lens group G4 is formed by a cemented lens of a positive lens L41 having a biconvex shape and an aspheric surface on the object side, and a meniscus negative lens L42 having a concave surface on the object side, which are sequentially positioned from the object side to the image side. Composed. The fifth lens group G5 is composed of a meniscus negative lens L51 having a concave surface facing the image side, which is positioned in order from the object side to the image side, and a positive lens L52 having a biconvex shape and an aspheric surface on the object side. The aperture stop S is located close to the object side of the third lens group G3, and is fixed in the optical axis direction upon zooming from the wide-angle end state to the telephoto end state. Further, a filter FL such as an infrared cut filter or a low-pass filter is disposed between the fifth lens group G5 and the image plane IMG.

  Table 5 below lists values of specifications of Numerical Example 2 in which specific numerical values are applied to the zoom lens 2 according to the second embodiment.

  In the zoom lens 2, the object side surface (16th surface) of the biconvex positive lens L31 in the third lens group G3, and the object side surface (19th surface) of the biconvex positive lens L41 in the fourth lens group G4. The object side surface (the 24th surface) of the biconvex positive lens L52 in the fifth lens group G5 is an aspherical surface. Therefore, Table 6 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients A, B, C, and D together with the conic constant κ in the numerical example 2.

  When the zoom lens 2 is zoomed from the wide-angle end state to the telephoto end state, the surface distance D7 between the first lens group G1 and the second lens group G2, the second lens group G2 and the third lens group G3 (opening) The surface distance D14 between the diaphragm S), the surface distance D18 between the third lens group G3 and the fourth lens group G4, and the surface distance D21 between the fourth lens group G4 and the fifth lens group G5 are changed. To do. Accordingly, the respective values in the wide-angle end state (f = 1.000), the intermediate focal length state (f = 8.675), and the telephoto end state (f = 18.810) of the distance between the surfaces in Numerical Example 2 are focused. Table 7 shows the distance f, F number FNO, and angle of view 2ω.

  Table 8 shows values corresponding to the conditional expressions (1) to (7) in Numerical Example 2.

  FIGS. 7 to 9 show various aberration diagrams of the numerical example 2 in the infinite focus state, FIG. 7 is the wide-angle end state (f = 1.000), and FIG. 8 is the intermediate focal length state (f = 8.675) and FIG. 9 are graphs showing various aberrations in the telephoto end state (f = 18.810).

  7 to 9, the solid line in the spherical aberration diagram indicates the spherical aberration, the solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the lateral aberration diagram, A represents the angle of view, and y represents the image height.

  From each aberration diagram, it is clear that Numerical Example 2 has excellent imaging performance with various aberrations corrected well.

  FIG. 10 shows the refractive power distribution of the zoom lens 3 according to the third embodiment of the present invention. In order from the object side, the first lens group G1 having a positive refractive power and the first lens group G having a negative refractive power. The second lens group G2, the third lens group G3 having a positive refractive power, and the fourth lens group G4 having a positive refractive power are arranged to form a first lens upon zooming from the wide-angle end state to the telephoto end state. The lens group G1 and the third lens group G3 are fixed in the optical axis direction, the second lens group G2 moves to the image side, and the fourth lens group G4 once moves to the object side and then moves to the image side.

  FIG. 11 is a diagram showing a lens configuration of the zoom lens 3 according to the third embodiment of the present invention. The first lens group G1, which is located in order from the object side to the image side, is a cemented lens of a negative meniscus lens L11 having a convex surface facing the object side and a positive lens L12 having a convex surface facing the object side, and a convex surface facing the object side And a positive lens L14 having a convex surface on the object side. The second lens group G2 includes a meniscus negative lens L21 having a concave surface facing the image side, a biconcave negative lens L22, and a positive lens L23 having a convex surface facing the object side, which are positioned in order from the object side to the image side. It is constituted by a cemented lens with a negative lens L24 having a concave surface facing the image side. The third lens group G3 is located in order from the object side to the image side, and includes a meniscus positive lens L31 having a convex surface on the object side and an aspheric surface on the object side, and a meniscus negative lens L32 having a concave surface on the image side. And a biconvex positive lens L33. The fourth lens group G4 includes a positive lens L41 that is biconvex and has an aspheric surface on the object side, and a meniscus negative lens L42 that has a concave surface on the object side. The aperture stop S is located close to the object side of the third lens group G3, and is fixed in the optical axis direction upon zooming from the wide-angle end state to the telephoto end state. Further, a filter FL such as an infrared cut filter or a low-pass filter is disposed between the fourth lens group G4 and the image plane IMG.

  Table 9 below presents values of specifications of Numerical Example 3 in which specific numerical values are applied to the zoom lens 3 according to the third embodiment.

  In the zoom lens 3, the object side surface (16th surface) of the meniscus positive lens L31 in the third lens group G3 and the object side surface (21st surface) of the biconvex positive lens L41 in the fourth lens group G4 are shown. It is composed of an aspherical surface. Therefore, Table 10 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients A, B, C, and D together with the conic constant κ in the numerical example 3.

  In zoom lens 1, when zooming from the wide-angle end state to the telephoto end state, the surface distance D7 between the first lens group G1 and the second lens group G2, the second lens group G2 and the third lens group G3 (opening) The surface distance D14 between the diaphragm S), the surface distance D20 between the third lens group G3 and the fourth lens group G4, and the surface distance D24 between the fourth lens group G4 and the filter FL change. Therefore, the respective values in the wide-angle end state (f = 1.000), the intermediate focal length state (f = 6.084), and the telephoto end state (f = 18.806) of the distance between the surfaces in Numerical Example 3 are focused. Table 11 shows the distance f, F number FNO, and angle of view 2ω.

  Table 12 shows values corresponding to the conditional expressions (1) to (7) in Numerical Example 3.

  FIGS. 12 to 14 show various aberration diagrams of the numerical example 3 in the infinite focus state, FIG. 12 is a wide-angle end state (f = 1.000), and FIG. 13 is an intermediate focal length state (f = 6.084) and FIG. 14 are graphs showing various aberrations in the telephoto end state (f = 18.806).

  In each aberration diagram of FIGS. 12 to 14, the solid line in the spherical aberration diagram indicates the spherical aberration, the solid line in the astigmatism diagram indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the lateral aberration diagram, A represents the angle of view, and y represents the image height.

  From each aberration diagram, it is clear that Numerical Example 3 has excellent imaging performance with various aberrations corrected well.

  Next, the imaging apparatus of the present invention will be described.

The imaging apparatus of the present invention includes a zoom lens and an imaging element that converts an optical image formed by the zoom lens into an electrical signal, and the zoom lens is located in order from the object side to the image plane side, It has a first lens group having a refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. When the lens position state changes to the end state, the second lens group moves to the image side, and the fourth lens group is arranged to compensate for the fluctuation of the image plane position accompanying the movement of the second lens group. An aperture stop is disposed between the second lens group and the third lens group. The second lens group has a meniscus negative lens L21, a negative lens L22, a positive lens with a concave surface facing the image side. Four lenses, L23 and negative lens L24 Ri is configured, the third lens group with constituted by at least respective one or more positive lens and the negative lens satisfies the following conditional expressions (1) to (4).
(1) 1.8 <f1 / (fw · ft) ^1/2 <2.2
(2) 0.9 <f3 / (fw · ft) ^1/2 <1.2
(3) 1.1 <r22 / fw <1.3
(4) -0.8 <(r3a + r3b) / (r3a-r3b) <0.5
However,
f1: Focal length fw of the first lens group fw: Focal length of the entire system in the wide-angle end state ft: Focal length of the entire system in the telephoto end state f3: Focal length r22 of the third lens group: Arranged in the second lens group Radius of curvature r3a of the image side lens surface of the negative lens L21: radius of curvature of the lens surface located closest to the object side in the third lens group (r3a> 0)
r3b: The radius of curvature (r3b <0) of the lens surface located closest to the image side in the third lens unit.

  FIG. 15 is a block diagram showing a configuration example of an embodiment embodying the imaging apparatus of the present invention. In the illustrated embodiment, the present invention is applied to a digital still camera.

  The digital still camera 100 includes a lens block 10 having an imaging function, a camera signal processing unit 20 that performs signal processing such as analog-digital conversion of a captured image signal, and an image processing unit 30 that performs recording / reproduction processing of the image signal. An LCD (Liquid Crystal Display) 40 for displaying captured images and the like, an R / W (reader / writer) 50 for writing to and reading from the memory card 51, and a CPU (Central Processing Unit) for controlling the entire apparatus ) 60, an input unit 70 for an operation input by the user, and a lens drive control unit 80 for controlling driving of the lenses in the lens block 10.

  The lens block 10 includes an optical system including a zoom lens 11 to which the present invention is applied, an imaging element 12 such as a CCD, and the like. The camera signal processing unit 20 performs signal processing such as conversion of an output signal from the image sensor 12 into a digital signal, noise removal, image quality correction, and conversion into a luminance / color difference signal. The image processing unit 30 performs compression encoding / decompression decoding processing of an image signal based on a predetermined image data format, conversion processing of data specifications such as resolution, and the like. As the zoom lens 11, the zoom lenses 1 to 3 of the present invention and numerical examples 1 to 3 of the present invention can be used, and the zoom lens 11 is implemented according to a mode other than the above-described embodiment and numerical examples. The zoom lens of the present invention can also be used.

  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 is a control processing unit that controls each circuit block in the digital still camera, 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 mode selection switch for selecting an operation mode, and the like, and outputs an instruction input signal corresponding to an operation by the user to the CPU 60. The lens drive control unit 80 controls a motor (not shown) that drives the lens in the zoom lens 11 based on a control signal from the CPU 60.

  The operation of the digital still camera 100 will be briefly described below.

  In the shooting standby state, under the control of the CPU 60, the image signal captured by the lens block 10 is output to the LCD 40 via the camera signal processing unit 20 and displayed as a camera through image. 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 the zoom lens 11 in the zoom lens 11 is controlled based on the control of the lens drive control unit 80. A predetermined lens is moved.

  When a shutter (not shown) of the lens block 10 is released by an instruction input signal from the input unit 70, the captured image signal is output from the camera signal processing unit 20 to the image processing unit 30 and subjected to compression coding processing. Is converted into digital data of the data format. The converted data is output to the reader / writer 50 and written to the memory card 51.

  Note that focusing is performed by the lens drive control unit 80 based on a control signal from the CPU 60 when the shutter release button is half-pressed or when the shutter release button is fully pressed for recording. This is done by moving the lens.

  When reproducing the image data recorded on the memory card 51, predetermined image data is read from the memory card 51 by the reader / writer 50 in response to an operation by the input unit 70, and decompressed by the image processing unit 30. After the decoding process, the reproduced image signal is output to the LCD 40. As a result, a reproduced image is displayed.

  In the above-described embodiment, the case where the imaging apparatus of the present invention is applied to a digital still camera has been described. For example, a camera unit built in a PC (Personal Computer), a PDA (Personal Digital Assistant), or the like is used. It is also possible to apply to an imaging device or the like.

  In addition, the shapes and numerical values of the respective parts shown in the respective embodiments and numerical examples are merely examples of specific embodiments for carrying out the present invention, and the technology of the present invention is thereby limited. The scope should not be interpreted in a limited way.

It is a figure which shows refractive power arrangement | positioning of 1st and 2nd embodiment of the zoom lens of this invention. It is a figure which shows the lens structure of 1st Embodiment of this invention zoom lens. FIG. 4 and FIG. 5 show aberration diagrams of Numerical Example 1 in which specific numerical values are applied to the first embodiment. This diagram shows spherical aberration, astigmatism, distortion, and lateral aberration in the wide-angle end state. Is. It shows spherical aberration, astigmatism, distortion, and lateral aberration in the intermediate focal length state. It shows spherical aberration, astigmatism, distortion, and lateral aberration in the telephoto end state. It is a figure which shows the lens structure of 2nd Embodiment of this invention zoom lens. FIG. 8 and FIG. 9 show aberration diagrams of Numerical Example 2 in which specific numerical values are applied to the second embodiment. This drawing shows spherical aberration, astigmatism, distortion, and lateral aberration in the wide-angle end state. Is. It shows spherical aberration, astigmatism, distortion, and lateral aberration in the intermediate focal length state. It shows spherical aberration, astigmatism, distortion, and lateral aberration in the telephoto end state. It is a figure which shows refractive power arrangement | positioning of 3rd Embodiment of this invention zoom lens. It is a figure which shows the lens structure of 3rd Embodiment of this invention zoom lens. 13 and 14 show aberration diagrams of Numerical Example 3 in which specific numerical values are applied to the third embodiment. This drawing shows spherical aberration, astigmatism, distortion, and lateral aberration in the wide-angle end state. Is. It shows spherical aberration, astigmatism, distortion, and lateral aberration in the intermediate focal length state. It shows spherical aberration, astigmatism, distortion, and lateral aberration in the telephoto end state. 1 is a circuit block diagram of an embodiment in which the imaging apparatus of the present invention is applied to a digital still camera.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Zoom lens, G1 ... 1st lens group, G2 ... 2nd lens group, G3 ... 3rd lens group, G4 ... 4th lens group, G5 ... 5th lens group, 2 ... Zoom lens, G1 ... 1st lens Group, G2 ... second lens group, G3 ... third lens group, G4 ... fourth lens group, G5 ... fifth lens group, 3 ... zoom lens, G1 ... first lens group, G2 ... second lens group, G3 ... 3rd lens group, G4 ... 4th lens group, 100 ... Digital still camera (imaging device), 11 ... Zoom lens, 12 ... Imaging element

Claims (6)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power, which are sequentially positioned from the object side to the image plane side. Having a fourth lens group;
When the lens position state changes from the wide-angle end state to the telephoto end state, the second lens group moves to the image side, and the variation of the image plane position accompanying the movement of the second lens group is compensated for. The fourth lens group moves,
An aperture stop is disposed between the second lens group and the third lens group;
The second lens group includes four meniscus negative lenses L21, a negative lens L22, a positive lens L23, and a negative lens L24 having a concave surface facing the image side.
The third lens group includes at least one positive lens and one negative lens, respectively, and satisfies the following conditional expressions (1) to (4).
(1) 1.8 <f1 / (fw · ft) ^1/2 <2.2
(2) 0.9 <f3 / (fw · ft) ^1/2 <1.2
(3) 1.1 <r22 / fw <1.3
(4) -0.8 <(r3a + r3b) / (r3a-r3b) <0.5
However,
f1: Focal length fw of the first lens group fw: Focal length of the entire system in the wide-angle end state ft: Focal length of the entire system in the telephoto end state f3: Focal length r22 of the third lens group: Arranged in the second lens group Radius of curvature r3a of the image side lens surface of the negative lens L21: radius of curvature of the lens surface located closest to the object side in the third lens group (r3a> 0)
r3b: The radius of curvature (r3b <0) of the lens surface located closest to the image side in the third lens unit. Regardless of the lens position state, the aperture stop is at a fixed position in the optical axis direction,
The zoom lens according to claim 1, wherein the following conditional expression (5) is satisfied.
(5) 0.35 <Ds / TL <0.45
However,
Ds: Length along the optical axis from the aperture stop to the image plane TL: Total lens length. The zoom lens according to claim 1, wherein the following conditional expression (6) is satisfied.
(6) 0.4 <f1 / ft <0.5 A zoom lens according to the second lens group, wherein a positive lens L23 and a negative lens L24 are cemented. The zoom lens according to claim 4, wherein the following conditional expression (7) is satisfied.
(7) 1.8 <N2
However,
N2: The average refractive index with respect to the d-line (wavelength = 587.6 nm (nanometer)) of the four lenses constituting the second lens group. An imaging apparatus comprising a zoom lens and an image sensor that converts an optical image formed by the zoom lens into an electrical signal,
The zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, which are positioned in order from the object side to the image plane side. A fourth lens group having a refractive power of
When the lens position state changes from the wide-angle end state to the telephoto end state, the second lens group moves to the image side, and the variation of the image plane position accompanying the movement of the second lens group is compensated for. The fourth lens group moves,
An aperture stop is disposed between the second lens group and the third lens group;
The second lens group includes four meniscus negative lenses L21, a negative lens L22, a positive lens L23, and a negative lens L24 having a concave surface facing the image side.
The third lens group includes at least one positive lens and one negative lens, respectively, and satisfies the following conditional expressions (1) to (4).
(1) 1.8 <f1 / (fw · ft) ^1/2 <2.2
(2) 0.9 <f3 / (fw · ft) ^1/2 <1.2
(3) 1.1 <r22 / fw <1.3
(4) -0.8 <(r3a + r3b) / (r3a-r3b) <0.5
However,
f1: Focal length fw of the first lens group fw: Focal length of the entire system in the wide-angle end state ft: Focal length of the entire system in the telephoto end state f3: Focal length r22 of the third lens group: Arranged in the second lens group Radius of curvature r3a of the image side lens surface of the negative lens L21: radius of curvature of the lens surface located closest to the object side in the third lens group (r3a> 0)
r3b: The radius of curvature (r3b <0) of the lens surface located closest to the image side in the third lens unit.

Images