JP2008015433A - Zoom lens and optical apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens having a wide angle of view and a high variable power ratio, made compact and having high image-forming performance. <P>SOLUTION: The zoom lens has a first lens group G1 having negative refractive power, an aperture stop S, a second lens group G2 having positive refractive power and a third lens group G3 having positive refractive power in order from an object side along an optical axis. When varying power from a wide angle end state W to a telephoto end state T, at least the first lens group and the second lens group move. The first lens group comprises a negative meniscus lens turning its convex surface to the object side and a positive lens in order from the object side, and at least the surface of the negative meniscus lens on an image surface side is aspherical, and at least one surface of the positive lens is aspherical. The second lens group comprises a first positive lens, a second positive lens, a negative lens and a third positive lens in order from the object side, and at least the surface of the first positive lens on the object side is aspherical. The third lens group comprises one positive lens. The zoom lens satisfies a predetermined condition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a zoom lens suitable for an optical apparatus using a solid-state imaging device or the like, and an optical apparatus having the same.

  2. Description of the Related Art In recent years, imaging devices such as digital still cameras and digital video cameras that use solid-state imaging devices have been rapidly increasing in performance and size. In these photographing apparatuses, a zoom lens is generally used as an imaging lens, and the photographer can easily perform photographing at an angle of view optimum for photographing conditions.

  Among these zoom lenses, especially those mounted on small cameras have a zoom ratio of about 3 times, and most of them have a lens group having negative refractive power arranged on the most object side. There has been proposed a negative leading zoom lens in which one or more lens groups having positive refractive power are arranged on the image plane side (see, for example, Patent Document 1).

  The reason why the negative leading type is widely used is that a zoom ratio of about 3 times can be obtained and a relatively good aberration correction can be achieved even with a simple configuration composed of about 2 to 4 lens groups. Because. In addition, since the entrance pupil position can be moved to the object side, it is advantageous in that the diameter of the lens group closest to the object side can be reduced and the exit pupil position can be sufficiently distant from the image sensor. .

Further, since the negative leading zoom lens has a reverse telephoto type refractive power arrangement as a whole, it has characteristics suitable for widening the angle of view compared to the positive leading zoom lens. Therefore, in order to provide a zoom lens that has an angle of view that can support full-scale wide-angle shooting and that has optical performance that is compatible with imaging devices that are becoming more sophisticated year by year, the negative leading zoom lens type should be adopted. Is reasonable. On top of this, the refractive power arrangement of each lens group constituting the zoom lens, the lens configuration in each lens group, the position of the aspherical surface, the glass material of each lens, etc. are appropriately selected, and good aberrations even for a wide angle of view It is necessary to realize the correction.
JP 2004-37700 A

  However, the negative leading zoom lens tends to be longer in total length than the focal length, and there is a problem that aberration correction becomes extremely difficult if it is forced to be compact.

  The present invention has been made in view of the above problems, and provides a zoom lens that has a wide angle of view and a high zoom ratio, achieves compact and high imaging performance, and an optical apparatus having the zoom lens. Let it be an issue.

In order to solve the above problems, the present invention includes, in order from the object side along the optical axis, a first lens group having a negative refractive power, an aperture stop, and a second lens group having a positive refractive power; A third lens group having a positive refractive power, and the distance between the first lens group and the second lens group decreases upon zooming from the wide-angle end state to the telephoto end state, and the second lens At least the first lens group and the second lens group move along the optical axis so that the distance between the group and the third lens group increases, and the first lens group is an object along the optical axis. In order from the side, a negative meniscus lens having a convex surface facing the object side and a positive lens, at least the image plane side surface of the negative meniscus lens is an aspheric surface, and at least one surface of the positive lens is an aspheric surface The second lens group includes a first lens unit sequentially from the object side along the optical axis. A lens, a second positive lens, a negative lens, and a third positive lens. At least the object-side surface of the first positive lens is an aspherical surface, and the third lens group is composed of one positive lens. A zoom lens characterized by satisfying the conditions is provided.
1.13 <| f1 | / (fw × ft) ^1/2 <1.35
Where f1 is the focal length of the first lens group, fw is the focal length of the entire zoom lens system in the wide-angle end state, and ft is the focal length of the entire zoom lens system in the telephoto end state.

  The present invention also provides an optical device having the zoom lens.

In addition, the present invention has a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and a positive refractive power in order from the object side along the optical axis. A third lens group, and the first lens group includes, in order from the object side along the optical axis, a negative meniscus lens having a convex surface facing the object side, and a positive lens, and at least an image of the negative meniscus lens. The surface-side surface is an aspheric surface, at least one surface of the positive lens is an aspheric surface, and the second lens group includes, in order from the object side along the optical axis, a first positive lens, a second positive lens, The first lens is composed of a negative lens and a third positive lens. At least the object side surface of the first positive lens is an aspherical surface, and the third lens group is composed of one positive lens. In zooming from the state to the telephoto end state, the first lens group and the second lens group At least the first lens group and the second lens group are moved along the optical axis so that the distance between the second lens group and the third lens group is increased. A scaling method characterized by the above is provided.
1.13 <| f1 | / (fw × ft) ^1/2 <1.35
Where f1 is the focal length of the first lens group, fw is the focal length of the entire zoom lens system in the wide-angle end state, and ft is the focal length of the entire zoom lens system in the telephoto end state.

  According to the present invention, it is possible to provide a zoom lens that has a wide angle of view and a high zoom ratio, achieves compact and high imaging performance, and an optical apparatus having the zoom lens.

  Embodiments of the present invention will be described below.

  1A and 1B show an electronic still camera equipped with a zoom lens according to an embodiment to be described later. FIG. 1A shows a front view and FIG. 1B shows a rear view. FIG. 2 is a cross-sectional view taken along the line A-A ′ of FIG.

  1 and 2, in the electronic still camera 1 according to the embodiment, when a power button (not shown) is pressed, a shutter (not shown) of the photographing lens 2 is opened and light from a subject (not shown) is collected by the photographing lens 2. The light is emitted and imaged on an image sensor C (for example, CCD or CMOS) disposed on the image plane I. The subject image formed on the image sensor C is displayed on the liquid crystal monitor 3 disposed behind the electronic still camera 1. The photographer determines the composition of the subject image while looking at the liquid crystal monitor 3, and then presses the release button 4 to photograph the subject image with the image sensor C, and records and saves it in a memory (not shown).

  The photographing lens 2 includes a zoom lens 2 according to an embodiment described later. The electronic still camera 1 also zooms the auxiliary light emitting unit 5 that emits auxiliary light when the subject is dark and the zoom lens 2 that is the photographing lens 2 from the wide-angle end state (W) to the telephoto end state (T). A wide (W) -tele (T) button 6 and a function button 7 used for setting various conditions of the electronic still camera 1 are arranged.

  In this way, an electronic still camera 1 including a zoom lens 2 according to an embodiment described later is configured.

  Next, the zoom lens according to the embodiment will be described.

  First, the basic structure of the zoom lens according to the embodiment will be described. The zoom lens according to the embodiment includes, in order from the object side along the optical axis, a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and positive refraction. A zoom lens of a negative leading type having a third lens group having power. The second lens group is a zoom unit and a master lens group, and the first lens group is a compensator group. The third lens group is fixed or moved during zooming, the exit pupil position of the entire zoom lens system is optimized with respect to the image sensor, and the remaining aberration that cannot be corrected by the first lens group and the second lens group. Perform the correction.

  Next, the configuration of the first lens group will be described. The first lens group is preferably composed of two lenses, a negative meniscus lens having a convex surface directed toward the object side and a positive lens in order from the object side along the optical axis. With this configuration, it is possible to correct lower coma, astigmatism, and distortion in the wide-angle end state, and spherical aberration and lower coma in the telephoto end state. Further, since the entrance pupil moves toward the object side, the principal ray height passing through the negative meniscus lens is reduced, and the outer diameter of the negative meniscus lens can be reduced.

  Further, it is desirable that at least the image side surface of the negative meniscus lens surface included in the first lens group is aspherical. The aspherical surface can not only satisfactorily correct distortion at the wide-angle end state, but also can increase the refractive power of the entire first lens unit, and can make the entire zoom lens compact.

  In addition, it is desirable that at least one of the positive lens surfaces included in the first lens group is aspherical. By making the lens aspherical, downward coma, astigmatism, field curvature, lateral chromatic aberration, and spherical aberration in the telephoto end state at the wide-angle end state can be corrected more favorably.

  Next, the configuration of the second lens group will be described. Since the negative leading zoom lens has a reverse telephoto type refractive power arrangement as a whole, it has a characteristic that negative distortion and lateral chromatic aberration are likely to occur. Therefore, it is desirable to adopt a lens type with a high degree of freedom in correcting these aberrations for the second lens group.

  The lens type that satisfies this condition with the simplest configuration is a triplet composed of three lenses, positive, negative, and positive. The triplet can control distortion aberration and lateral chromatic aberration relatively freely by appropriately selecting the refractive power distribution and dispersion of each lens.

  However, when the second lens group made of triplets is arranged behind the first lens group having negative refractive power as in the zoom lens of the embodiment, the second lens group is diverged by the first lens group. Since the light beam is incident, it is difficult to correct the spherical aberration. In order to improve the ability to correct the negative distortion generated in the first lens group, the entire second lens group needs to have a telephoto refractive power arrangement. Since the strong refractive power concentrates on the positive lens located on the side, it is more difficult to correct spherical aberration. In order to correct spherical aberration satisfactorily, it is necessary to weaken the refractive power of the second lens group as a whole. However, as the back focus of the second lens group increases, the entire zoom lens becomes larger. Therefore, when the second lens group is composed of triplets, it is difficult to achieve both compactness and high performance of the entire zoom lens.

  For the above reason, in the zoom lens according to the embodiment, the positive lens located closest to the object side of the triplet is divided into two, and the first positive lens and the second positive lens are sequentially arranged from the object side along the optical axis. It is desirable that the second lens group is composed of four lenses, a negative lens and a third positive lens. With this configuration, it is possible to satisfactorily correct the spherical aberration of the second lens group. In addition, since the telephoto refractive power arrangement in the second lens group and the refractive power of the entire second lens group can be increased, the back focus of the second lens group can be shortened and the entire zoom lens can be made compact. Is possible.

  Further, it is desirable that at least the object side surface of the lens surfaces of the first positive lens included in the second lens group is aspherical. Aspherical surface not only makes it possible to correct spherical aberration generated in the second lens group even better, but also increases the telephoto refractive power arrangement in the second lens group and the refractive power of the entire second lens group. Therefore, the zoom lens can be made compact. It is also possible to correct the spherical aberration and the coma aberration more satisfactorily by making both surfaces of the lens surface of the first positive lens of the second lens group aspherical.

  In addition, it is desirable that the second positive lens and the negative lens of the second lens group are cemented. By joining, it is possible to prevent a decrease in optical performance such as coma due to decentering between the second positive lens and the negative lens.

  The third lens group is preferably composed of one positive lens. Constructing the third lens group with a single lens is not only advantageous from the viewpoint of cost, but can also reduce the thickness when retracted.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (1).
(1) 1.13 <| f1 | / (fw × ft) ^1/2 <1.35
Where f1 is the focal length of the first lens group, fw is the focal length of the entire zoom lens system in the wide-angle end state, and ft is the focal length of the entire zoom lens system in the far-end state.

  Conditional expression (1) defines an appropriate range of the focal length of the first lens group for performing good aberration correction while keeping the entire length of the zoom lens compact.

  If the lower limit value of conditional expression (1) is not reached, the back focus of the second lens group increases in the telephoto end state, and the overall length of the zoom lens becomes significantly long. Further, it is not preferable to correct the lower coma aberration and distortion in the wide-angle end state because it becomes difficult to correct spherical aberration and lower coma aberration in the telephoto end state. Furthermore, since the longitudinal magnification of the second lens group in the telephoto end state increases, the spherical aberration in the telephoto end state is likely to deteriorate significantly due to manufacturing errors of the first lens group, which is not preferable from the viewpoint of productivity.

  If the upper limit of conditional expression (1) is exceeded, it is necessary to increase the air gap between the first lens group and the second lens group in the wide-angle end state in order to ensure the amount of movement of the second lens group necessary for zooming. Occurs. For this reason, the overall length in the wide-angle end state is remarkably increased, and the outer diameter of the negative meniscus lens positioned closest to the object side in the first lens group is increased. In addition, it is difficult to ensure the distance between the first lens group and the second lens group in the telephoto end state. In order to secure this distance, it is necessary to remarkably increase the telephoto refractive power arrangement in the second lens group, but it is difficult to correct the upper coma aberration in the intermediate focal length state. Further, since the spherical aberration in the telephoto end state is likely to be significantly deteriorated due to the manufacturing error of the second lens group, it is not preferable from the viewpoint of productivity.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (1) to 1.17. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (1) to 1.20. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (1) to 1.33. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (1) to 1.30.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (2).
(2) 0.90 <| f1 | / f2 <1.15
Here, f2 is the focal length of the second lens group.

  Since the focal length f1 of the first lens group is already defined by the conditional expression (1), the conditional expression (2) substantially defines the focal length f2 of the second lens group. If the lower limit value of conditional expression (2) is not reached, the back focus of the second lens group increases in the telephoto end state, and not only the total length of the zoom lens becomes remarkably long, but also it is difficult to correct lateral chromatic aberration in the telephoto end state. Therefore, it is not preferable. If the upper limit of conditional expression (2) is exceeded, correction of astigmatism in the wide-angle end state is not preferable because it becomes difficult to correct upper coma in the intermediate focal length state.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (2) to 0.93. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (2) to 0.95. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (2) to 1.12. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (2) to 1.10.

  In the zoom lens according to the embodiment, it is desirable that focusing from an object at infinity to an object at finite distance is performed by moving the third lens group. When the third lens group is used for focusing from an object at infinity to an object at a finite distance, there is a feature that a change in chief ray height in the first lens group accompanying focusing is small in the wide-angle end state. Accordingly, it is possible to prevent a reduction in the amount of light at the periphery of the screen, which is likely to occur when shooting a close-distance object in the wide-angle end state. In the zoom lens according to the embodiment, focusing by moving the first lens group is also possible in principle, but the principal ray height that passes through the first lens group at the time of photographing a very close distance object in the wide-angle end state is high. Therefore, the amount of light at the periphery of the screen is significantly reduced due to the scuffing when shooting an object at a close distance. In order to prevent this, it is necessary to increase the outer diameter of the first lens group, but this is not preferable because it becomes difficult to correct coma aberration in the wide-angle end state.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (3).
(3) -0.40 <(Rb + Ra) / (Rb-Ra) <1.30
However, Ra is the radius of curvature of the object side surface of the positive lens of the third lens group, and Rb is the radius of curvature of the image side surface of the positive lens of the third lens group.

    Conditional expression (3) defines an appropriate range for the shape of the positive lens of the third lens group. If the lower limit value of conditional expression (3) is not satisfied, it is difficult to correct the field curvature and astigmatism in the telephoto end state at the time of shooting an object at a close distance. If the upper limit of conditional expression (3) is exceeded, it is not preferable because correction of lateral chromatic aberration and distortion in the wide-angle end state becomes difficult to correct downward coma in the telephoto end state.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (3) to −0.10. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (3) to 0.00. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (3) to 1.00. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit value of conditional expression (3) to 0.80.

It is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (4).
(4) 80.0 <ν31 <95.0
Where ν31 is the Abbe number with respect to the d-line (λ = 587.6 nm) of the material of the positive lens of the third lens group.

  Conditional expression (4) defines an appropriate range for the Abbe number of the positive lens in the third lens group. The third lens group has positive refracting power and a large principal ray height, and thus tends to generate negative lateral chromatic aberration. Therefore, it is necessary to use a low dispersion glass material for the third lens group to reduce the occurrence of lateral chromatic aberration. If the lower limit of conditional expression (4) is not reached, it is difficult to correct lateral chromatic aberration in the telephoto end state, and the variation in lateral chromatic aberration associated with the focusing described above is not preferable. If the upper limit of conditional expression (4) is exceeded, it is necessary to use fluorite for the positive lens with currently available lens materials, but it is extremely difficult to guarantee the shape accuracy of the refracting surface using an inexpensive processing method. Therefore, it is not preferable. Also, the Petzval sum becomes positive, and it becomes impossible to correct curvature of field and specific point aberration at the same time.

  In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (4) to 92.0.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (5).
(5) 1.81 <n23
However, n23 is the refractive index with respect to d line ((lambda) = 587.6nm) of the material of the negative lens of a 2nd lens group.

  Conditional expression (5) defines an appropriate range of the refractive index of the negative lens of the second lens group. The image side surface of the negative lens in the second lens group plays a role of correcting spherical aberration, upper coma aberration, astigmatism, field curvature, and distortion in the second lens group. When the refractive index of the negative lens is extremely low, the radius of curvature of the image side of the negative lens becomes too small, so that it is difficult to correct astigmatism, field curvature, and upper coma. Therefore, it is preferable to use a glass material having a high refractive index for the negative lens and loosen the radius of curvature of the image side surface. When the lower limit value of conditional expression (5) is not reached, correction of field curvature and astigmatism in the wide-angle end state is not preferable because it becomes difficult to correct upper coma in the intermediate focal length state and the telephoto end state.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.85. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (5) to 1.90.

It is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (6).
(6) 23.9 <ν23 <34.0
Where ν23 is the Abbe number with respect to the d-line (λ = 587.6 nm) of the material of the negative lens of the second lens group.

  Conditional expression (6) defines an appropriate range of the Abbe number of the negative lens in the second lens group. If the lower limit of conditional expression (6) is not reached, lateral chromatic aberration in the telephoto end state will be overcorrected, which is not preferable. If the upper limit of conditional expression (6) is exceeded, it will be necessary to remarkably increase the refractive power of the negative lens in order to correct axial chromatic aberration, and correction of the difference in spherical aberration depending on the wavelength from the wide-angle end state to the intermediate focal length state Is not preferable because it becomes difficult.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (6) to 24.1. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (6) to 24.7. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (6) to 33.0. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (6) to 32.0.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (7).
(7) 1.45 <n24 <1.65
Here, n24 is the refractive index with respect to the d-line (λ = 587.6 nm) of the material of the third positive lens.

  Conditional expression (7) defines an appropriate range of the refractive index of the third positive lens of the second lens group. The third positive lens plays a role of adjusting the balance of higher-order aberrations by generating spherical aberration, upper coma aberration, and astigmatism aberration opposite to those of the negative lens. Also, there is an effect of correcting the spherical aberration fluctuation due to the zooming in the second lens group. Therefore, it is necessary to increase the radius of curvature of each lens surface by using a glass material having a low refractive index for the third positive lens to generate an appropriate amount of aberration. If the lower limit value of conditional expression (7) is not reached, the Petzval sum becomes significantly positive, which makes it difficult to simultaneously correct astigmatism and field curvature in the telephoto end state. Exceeding the upper limit of conditional expression (7) is not preferable because the field curvature in the wide-angle end state increases.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (7) to 1.48. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (7) to 1.51. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (7) to 1.63. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (7) to 1.61.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (8).
(8) 1.27 <| fL11 | / fw <1.46
Here, fL11 is the focal length of the negative meniscus lens, and fw is the focal length of the entire zoom lens system in the wide-angle end state.

  Conditional expression (8) defines an appropriate range for the focal length of the negative meniscus lens included in the first lens group. When the lower limit value of conditional expression (8) is not reached, the focal length of the negative meniscus lens becomes too small, so that correction of astigmatism and field curvature in the wide-angle end state is correct, and downward coma aberration in the telephoto end state is corrected. Since it becomes difficult, it is not preferable. Exceeding the upper limit of conditional expression (8) is not preferable because the outer diameter of the negative meniscus lens is increased, making it difficult to reduce the size of the lens, and increasing fluctuations in coma due to zooming.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (8) to 1.29. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (8) to 1.30. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (8) to 1.43. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (8) to 1.41.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (9).
(9) 1.78 <n11
However, n11 is the refractive index with respect to d line ((lambda) = 587.6nm) of the material of a negative meniscus lens.

  Conditional expression (9) defines an appropriate range of the refractive index of the negative meniscus lens. If the lower limit value of conditional expression (9) is not reached, the radius of curvature of the negative meniscus lens on the image side becomes excessively small, making it difficult to correct downward coma, astigmatism, and field curvature at the wide-angle end. This is not preferable. Moreover, since it is difficult to process the refractive surface of the negative meniscus lens, it is not preferable from the viewpoint of productivity.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (9) to 1.79. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (9) to 1.80.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (10).
(10) 35.0 <ν11
Here, ν11 is an Abbe number with respect to the d-line (λ = 587.6 nm) of the material of the negative meniscus lens.

  Conditional expression (10) defines an appropriate range of the refractive index of the negative meniscus lens. If the lower limit of conditional expression (10) is not reached, correction of lateral chromatic aberration in the wide-angle end state becomes difficult, which is not preferable. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (10) to 36.5.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (11).
(11) 1.84 <n12
However, n12 is a refractive index with respect to d line ((lambda) = 587.6nm) of the material of the positive lens of a 1st lens group.

  Conditional expression (11) defines an appropriate range of the refractive index of the positive lens of the first lens group. If the lower limit value of conditional expression (11) is not reached, it is not preferable to correct downward coma and astigmatism in the wide-angle end state because it becomes difficult to correct spherical aberration in the telephoto end state. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (11) to 1.86. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (11) to 1.90.

In addition, it is desirable that the zoom lens according to the embodiment satisfies the following conditional expression (12).
(12) ν12 <25.0
Where ν12 is the Abbe number with respect to the d-line (λ = 587.6 nm) of the material of the positive lens of the first lens group.

  Conditional expression (12) defines an appropriate range of the Abbe number of the positive lens in the first lens group. Exceeding the upper limit of conditional expression (12) is not preferable because it becomes difficult to correct lateral chromatic aberration in the wide-angle end state. In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (12) to 23.5. In order to further secure the effect of the embodiment, it is more preferable to set the upper limit of conditional expression (12) to 22.5.

  In the zoom lens according to the embodiment, it is preferable that at least one surface of the positive lens in the third lens group is an aspherical surface. Astigmatism and curvature of field can be corrected more satisfactorily by aspherical at least one of the lens surfaces included in the third lens group.

  The zoom lens according to the embodiment includes, in order from the object side along the optical axis, a first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and a positive lens. The first lens group includes a negative meniscus lens having a convex surface directed toward the object side in order from the object side along the optical axis, and a positive lens, and the negative meniscus lens. At least the surface on the image plane side is an aspheric surface, at least one surface of the positive lens is an aspheric surface, and the second lens group includes a first positive lens and a second positive lens in order from the object side along the optical axis. , A negative lens, and a third positive lens. At least the object-side surface of the first positive lens is an aspherical surface, and the third lens group is composed of one positive lens, satisfying the above conditional expression (1). During zooming from the wide-angle end state to the telephoto end state, the first lens group and the second lens unit A zooming method that moves at least the first lens group and the second lens group along the optical axis is desirable so that the distance between the lens group and the second lens group is increased. . By adopting such a zooming method, the drive mechanism can be simplified and the entire length of the zoom lens can be shortened.

  In the zoom lens according to the embodiment, out of the lens groups constituting the zoom lens, the entire lens group or a part of the lens group may be moved in a direction substantially perpendicular to the optical axis. it can. Thereby, it is possible to move the image on the image plane, and it is possible to realize a so-called anti-vibration lens.

(Example)
Examples of the zoom lens according to the embodiment will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 3 is a diagram illustrating a lens configuration of the zoom lens according to the first example. In FIG. 3, the zoom lens according to the first example includes, in order from the object side along the optical axis, a first lens group G1 having a negative refractive power, an aperture stop S, and a second lens having a positive refractive power. It consists of a lens group G2 and a third lens group G3 having a positive refractive power, and the distance between the first lens group G1 and the second lens group G2 decreases upon zooming from the wide-angle end state W to the telephoto end state T. Then, the first lens group G1 and the second lens group G2 move along the optical axis so that the distance between the second lens group G2 and the third lens group G3 increases, and the third lens group G3 is fixed. It is a configuration.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side, and the negative meniscus lens L11. The lens surface on the image plane I side and the lens surface on the object side of the positive meniscus lens L12 are aspheric.

  The second lens group G2 includes, in order from the object side along the optical axis, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex lens. And a lens surface on the object side of the positive meniscus lens L21 is an aspherical surface. The positive lens L22 and the negative lens L23 are cemented.

  The third lens group G3 includes only one biconvex positive lens L31, and focusing from an infinite object to a finite distance object is performed by moving the third lens group G3 along the optical axis.

  The aperture stop S is disposed closer to the object side than the most object-side positive meniscus lens L21 in the second lens group G2, and is integrated with the second lens group G2 upon zooming from the wide-angle end state W to the telephoto end state T. Move on.

  The filter group FL disposed between the third lens group G3 and the image plane I is composed of a low-pass filter, an infrared cut filter, and the like.

  Table 1 below provides values of specifications of the zoom lens according to the first example. In [Overall Specifications], f represents a focal length, FNO represents an F number, 2ω represents an angle of view (unit: degree), and Ymax represents a maximum image height. In [lens specifications], the first column is the lens surface number when counted from the object side, the second column r is the radius of curvature of the lens surface, the third column d is the distance on the optical axis of the lens surface, and the fourth The column ν indicates the Abbe number with respect to the d-line (λ = 587.6 nm), and the fifth column n indicates the refractive index with respect to the d-line (λ = 587.6 nm). In addition, * attached | subjected to the left of the 1st column shows that the lens surface is an aspherical surface, and B.f. shows a back focus. Note that the refractive index of air n = 1.000 000 is omitted, and “∞” in the radius of curvature r column indicates a plane.

The aspherical surface of [Aspherical data] is the distance along the optical axis from the tangential plane of each vertex of the aspheric surface to each aspherical surface at the height y (sag amount). Is S (y), the radius of curvature of the reference sphere (paraxial radius of curvature) is R, the conic constant is κ, and the nth-order aspherical coefficient is Cn, it is expressed by the following equation. “En” (n is an integer) in the aspherical data column indicates “× 10 ⁻ⁿ ”.
S (y) = (y ² / R) / {1+ (1-κy ² / R ² ) ^1/2 }
+ C4y ⁴ + C6y ⁶ + C8y ⁸ + C10y ¹⁰
[Variable interval data] includes the focal length f, magnification β, distance D0 from the object to the lens surface closest to the object, and values of each variable interval in the wide-angle end state, intermediate focal length state, and telephoto end state. Respectively. In [Conditional Expression Corresponding Value], the corresponding value of each conditional expression is shown.

  In all the following specification values, “mm” is generally used as the focal length f, radius of curvature r, surface interval d and other lengths, etc. unless otherwise specified, but the optical system is proportional. Even if it is enlarged or proportionally reduced, the same optical performance can be obtained. Further, the unit is not limited to “mm”, and other appropriate units may be used. Further, the explanation of these symbols is the same in the other embodiments, and the explanation is omitted.

(Table 1)
[Overall specifications]
f = 4.76-16.70
FNO = 2.90-5.70
2ω = 78.0 ° ~ 24.4 °
Ymax = 3.60

[Lens specifications]
rd ν n
1) 59.4349 1.2000 42.71 1.820800
* 2) 4.8923 2.7000
* 3) 11.4092 1.7500 21.15 1.906800
4) 27.6941 (d4)

5) ∞ 0.4000 Aperture S
* 6) 5.6257 1.7000 53.22 1.693500
7) 434.2250 0.2000
8) 8.4733 1.5000 54.66 1.729160
9) -35.8220 0.5000 31.31 1.903660
10) 4.1845 0.6000
11) 18.2960 1.3500 60.69 1.563840
12) -18.0872 (d12)

13) 16.2248 1.6000 82.56 1.497820
14) -44.6093 (d14)

15) ∞ 0.5000 70.70 1.544400
16) ∞ 0.5000
17) ∞ 0.5000 64.12 1.516800
18) ∞ (Bf)


[Aspherical data]
(Second side)
κ = 0.1443
C4 = 2.54480E-04
C6 = 3.19110E-06
C8 = -9.28700E-08
C10 = 1.38360E-09

(Third side)
κ = 1.4326
C4 = 3.65748E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 3.17534E-10

(Sixth surface)
κ = 0.4246
C4 = -3.32103E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

[Variable interval data]
At infinity focus Wide-angle end state Intermediate focal length state Telephoto end state
f 4.76 8.90 16.70
D0 ∞ ∞ ∞
d4 16.80729 7.18190 2.01278
d12 4.94164 10.07570 19.74873
d14 2.61334 2.61334 2.61334

At close focus (shooting distance 300mm)
Wide-angle end state Intermediate focal length state Telephoto end state β -0.01777 -0.03247 -0.05932
D0 259.614 264.105 259.601
d4 16.80729 7.18190 2.01278
d12 4.72486 9.36464 17.56809
d14 2.83012 3.32439 4.79398

[Values for conditional expressions]
(1) | f1 | / (fw × ft) ^1/2 = 1.27280
(2) | f1 | / f2 = 1.02677
(3) (Rb + Ra) / (Rb−Ra) = 0.46659
(4) ν31 = 82.56
(5) n23 = 1.90336
(6) ν23 = 31.31
(7) n24 = 1.56384
(8) | fL11 | /fw=1.37818
(9) n11 = 1.8208
(10) ν11 = 42.71
(11) n12 = 1.9068
(12) ν12 = 21.15

  4A to 4C are graphs showing various aberrations when the zoom lens according to Example 1 is in focus at infinity. FIG. 4A shows a wide-angle end state, and FIG. 4B shows an intermediate focal length state. , (C) show the telephoto end state, respectively. FIGS. 5A to 5C are graphs showing various aberrations when the zoom lens according to Example 1 is in close focus (shooting distance 300 mm). FIG. 5A shows the wide-angle end state. ) Shows the intermediate focal length state, and (c) shows the telephoto end state.

  In each aberration diagram, FNO is an F number, Y is an image height, A is a half angle of view (unit: degree), and H0 is an object height at close-up shooting. In each aberration diagram, d is d-line (λ = 587.6 nm), g is g-line (λ = 435.8 nm), C is C-line (λ = 656.3 nm), and F is F-line (λ = 486.1 nm). Each aberration curve is shown. Further, in the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In addition, in the various aberration diagrams of the following examples, the same reference numerals as in this example are used, and the following description is omitted.

  From each aberration diagram, it can be seen that the zoom lens according to the first example has excellent optical performance with various aberrations corrected well in each focal length state from the wide-angle end state W to the telephoto end state T.

(Second embodiment)
FIG. 6 is a diagram illustrating a lens configuration of a zoom lens according to the second example. In FIG. 6, the zoom lens according to the second example includes, in order from the object side along the optical axis, a first lens group G1 having a negative refractive power, an aperture stop S, and a second lens having a positive refractive power. It consists of a lens group G2 and a third lens group G3 having a positive refractive power, and the distance between the first lens group G1 and the second lens group G2 decreases upon zooming from the wide-angle end state W to the telephoto end state T. Then, the first lens group G1 and the second lens group G2 move along the optical axis so that the distance between the second lens group G2 and the third lens group G3 increases, and the third lens group G3 is fixed. It is a configuration.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side, and the negative meniscus lens L11. The lens surface on the image plane I side and the lens surface on the object side of the positive meniscus lens L12 are aspheric.

  The second lens group G2 includes, in order from the object side along the optical axis, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex lens. And a lens surface on the object side of the positive meniscus lens L21 is an aspherical surface. The positive lens L22 and the negative lens L23 are cemented.

  The third lens group G3 includes only one biconvex positive lens L31, and focusing from an infinite object to a finite distance object is performed by moving the third lens group G3 along the optical axis.

  The aperture stop S is disposed closer to the object side than the most object-side positive meniscus lens L21 in the second lens group G2, and is integrated with the second lens group G2 upon zooming from the wide-angle end state W to the telephoto end state T. Move on.

  The filter group FL disposed between the third lens group G3 and the image plane I is composed of a low-pass filter, an infrared cut filter, and the like.

  Table 2 below shows values of specifications of the zoom lens according to the second example.

(Table 2)
[Overall specifications]
f = 4.76-18.10
FNO = 2.88 ~ 6.01
2ω = 78.0 ° ~ 22.6 °
Ymax = 3.60

[Lens specifications]
rd ν n
1) 63.7103 1.2000 40.10 1.851350
* 2) 5.0195 2.6000
* 3) 11.8387 1.7000 20.65 2.001700
4) 28.3593 (d4)

5) ∞ 0.4000 Aperture S
* 6) 5.3648 1.7000 49.23 1.768020
7) 68.9818 0.2500
8) 10.0698 1.4000 40.77 1.883000
9) -41.8100 0.5000 28.27 2.003300
10) 4.0184 0.6000
11) 10.7159 1.3500 58.89 1.518230
12) -21.3817 (d12)

13) 16.0470 1.6000 91.20 1.456000
14) -39.4872 (d14)

15) ∞ 0.5000 70.70 1.544400
16) ∞ 0.5000
17) ∞ 0.5000 64.12 1.516800
18) ∞ (Bf)


[Aspherical data]
(Second side)
κ = 0.1382
C4 = 2.20415E-04
C6 = 2.31914E-06
C8 = -2.59007E-08
C10 = -3.06152E-10

(Third side)
κ = 1.8204
C4 = -1.10636E-06
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

(Sixth surface)
κ = 0.4653
C4 = -1.64571E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

[Variable interval data]
At infinity focus Wide-angle end state Intermediate focal length state Telephoto end state
f 4.76 9.10 18.10
D0 ∞ ∞ ∞
d4 17.69964 7.60129 2.09408
d12 4.67613 10.00077 21.04266
d14 2.69182 2.69182 2.69182

At close focus (shooting distance 300mm)
Wide-angle end state Intermediate focal length state Telephoto end state β -0.01781 -0.03324 -0.06415
D0 259.4687 264.2426 258.7078
d4 17.69964 7.60129 2.09408
d12 4.45448 9.24322 18.49283
d14 2.91347 3.44938 5.24165

[Values for conditional expressions]
(1) | f1 | / (fw × ft) ^1/2 = 1.23572
(2) | f1 | /f2=1.03147
(3) (Rb + Ra) / (Rb-Ra) = 0.42209
(4) ν31 = 91.20
(5) n23 = 2.00330
(6) ν23 = 28.27
(7) n24 = 1.51823
(8) | fL11 | /fw=1.35733
(9) n11 = 1.85135
(10) ν11 = 40.10
(11) n12 = 2.0017
(12) ν12 = 20.65

  FIGS. 7A to 7C are graphs showing various aberrations when the zoom lens according to Example 2 is in focus at infinity. FIG. 7A shows the wide-angle end state, and FIG. 7B shows the intermediate focal length state. , (C) show the telephoto end state, respectively. FIGS. 8A to 8C are graphs showing various aberrations when the zoom lens according to Example 2 is in close focus (shooting distance 300 mm). FIG. 8A shows a wide-angle end state. ) Shows the intermediate focal length state, and (c) shows the telephoto end state.

From each aberration diagram, it can be seen that the zoom lens according to the second example has excellent optical performance with various aberrations corrected well in each focal length state from the wide-angle end state W to the telephoto end state T.
(Third embodiment)
FIG. 9 is a diagram illustrating a lens configuration of a zoom lens according to the third example. In FIG. 9, the zoom lens according to the third example, in order from the object side along the optical axis, a first lens group G1 having a negative refractive power, an aperture stop S, and a second lens having a positive refractive power. It consists of a lens group G2 and a third lens group G3 having a positive refractive power, and the distance between the first lens group G1 and the second lens group G2 decreases upon zooming from the wide-angle end state W to the telephoto end state T. Then, the first lens group G1 and the second lens group G2 move along the optical axis so that the distance between the second lens group G2 and the third lens group G3 increases, and the third lens group G3 is fixed. It is a configuration.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side, and the negative meniscus lens L11. The lens surface on the image plane I side and the lens surface on the object side of the positive meniscus lens L12 are aspheric.

  The second lens group G2 includes, in order from the object side along the optical axis, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex lens. And a lens surface on the object side of the positive meniscus lens L21 is an aspherical surface. The positive lens L22 and the negative lens L23 are cemented.

  The third lens group G3 includes only one biconvex positive lens L31, and focusing from an infinite object to a finite distance object is performed by moving the third lens group G3 along the optical axis.

  The aperture stop S is disposed closer to the object side than the most object-side positive meniscus lens L21 in the second lens group G2, and is integrated with the second lens group G2 upon zooming from the wide-angle end state W to the telephoto end state T. Move on.

  The filter group FL disposed between the third lens group G3 and the image plane I is composed of a low-pass filter, an infrared cut filter, and the like.

  Table 3 below provides values of specifications of the zoom lens according to the third example.

(Table 3)
[Overall specifications]
f = 4.76-18.10
FNO = 2.88 ～ 6.00
2ω = 78.0 ° ~ 22.5 °
Ymax = 3.60

[Lens specifications]
rd ν n
1) 63.7103 1.2000 40.10 1.851350
* 2) 4.9410 2.5500
* 3) 11.3234 1.7000 20.65 2.001700
4) 26.8995 (d4)

5) ∞ 0.4000 Aperture S
* 6) 5.4166 1.7000 49.23 1.768020
7) 74.7735 0.2500
8) 10.1503 1.4000 40.77 1.883000
9) -32.7150 0.5000 28.27 2.003300
10) 4.0517 0.6000
11) 10.0545 1.3500 58.89 1.518230
12) -23.3863 (d12)

13) 12.6597 1.6000 82.56 1.497820
14) -1698.2972 (d14)

15) ∞ 0.5000 70.70 1.544400
16) ∞ 0.5000
17) ∞ 0.5000 64.12 1.516800
18) ∞ (Bf)


[Aspherical data]
(Second side)
κ = 0.1115
C4 = 1.71490E-04
C6 = 3.13470E-06
C8 = -4.04849E-08
C10 = 3.30092E-10

(Third side)
κ = 1.8204
C4 = -5.01431E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

(Sixth surface)
κ = 0.4587
C4 = -6.12214E-07
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

[Variable interval data]
At infinity focus Wide-angle end state Intermediate focal length state Telephoto end state
f 4.76 9.10 18.10
D0 ∞ ∞ ∞
d4 17.69915 7.60080 2.09360
d12 5.01514 10.33978 21.38167
d14 2.41966 2.41966 2.41966

At close focus (shooting distance 300mm)
Wide-angle end state Intermediate focal length state Telephoto end state β -0.01781 -0.03324 -0.06416
D0 259.4524 264.2262 258.6915
d4 17.69915 7.60080 2.09360
d12 4.79346 9.58214 18.83159
d14 2.64134 3.17730 4.96974

[Values for conditional expressions]
(1) | f1 | / (fw × ft) ^1/2 = 1.23572
(2) | f1 | /f2=1.03147
(3) (Rb + Ra) / (Rb-Ra) = 0.98520
(4) ν31 = 82.56
(5) n23 = 2.00330
(6) ν23 = 28.27
(7) n24 = 1.51823
(8) | fL11 | /fw=1.33430
(9) n11 = 1.85135
(10) ν11 = 40.10
(11) n12 = 2.0017
(12) ν12 = 20.65

  FIGS. 10A to 10C are graphs showing various aberrations of the zoom lens according to the third example at the time of focusing on infinity, in which FIG. 10A shows the wide-angle end state, and FIG. 10B shows the intermediate focal length state. , (C) show the telephoto end state, respectively. FIGS. 11A to 11C are graphs showing various aberrations when the zoom lens according to Example 3 is in close focus (shooting distance 300 mm). FIG. 11A shows the wide-angle end state. ) Shows the intermediate focal length state, and (c) shows the telephoto end state.

  From each aberration diagram, it can be seen that the zoom lens according to the third example has excellent optical performance with various aberrations corrected well in each focal length state from the wide-angle end state W to the telephoto end state T.

(Fourth embodiment)
FIG. 12 is a diagram illustrating a lens configuration of a zoom lens according to the fourth example. In FIG. 4, the zoom lens according to the fourth example, in order from the object side along the optical axis, a first lens group G1 having a negative refractive power, an aperture stop S, and a second lens having a positive refractive power. It consists of a lens group G2 and a third lens group G3 having a positive refractive power, and the distance between the first lens group G1 and the second lens group G2 decreases upon zooming from the wide-angle end state W to the telephoto end state T. Then, the first lens group G1 and the second lens group G2 move along the optical axis so that the distance between the second lens group G2 and the third lens group G3 increases, and the third lens group G3 is fixed. It is a configuration.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side, and the negative meniscus lens L11. The lens surface on the image plane I side and the lens surface on the object side of the positive meniscus lens L12 are aspheric.

  The second lens group G2 includes, in order from the object side along the optical axis, a biconvex positive lens L21, a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex positive lens. The lens surface on the object side of the positive lens L21 is an aspherical surface. The positive lens L22 and the negative lens L23 are cemented.

  The third lens group G3 includes only one biconvex positive lens L31, and focusing from an infinite object to a finite distance object is performed by moving the third lens group G3 along the optical axis. The lens surface on the image plane I side of the positive lens L31 is an aspherical surface.

  The aperture stop S is disposed on the object side of the positive lens L21 closest to the object side of the second lens group G2, and is integrated with the second lens group G2 upon zooming from the wide-angle end state W to the telephoto end state T. Move to.

  The filter group FL disposed between the third lens group G3 and the image plane I is composed of a low-pass filter, an infrared cut filter, and the like.

  Table 4 below shows values of specifications of the zoom lens according to the fourth example.

(Table 4)
[Overall specifications]
f = 4.76-16.36
FNO = 2.91-5.66
2ω = 78.0 ° ~ 24.8 °
Ymax = 3.60

[Lens specifications]
rd ν n
1) 63.5029 1.2000 42.71 1.820800
* 2) 4.9962 2.6500
* 3) 11.2634 1.7000 21.15 1.906800
4) 25.5063 (d4)

5) ∞ 0.4000 Aperture S
* 6) 5.3877 1.7000 53.22 1.693500
7) -372.6356 0.1000
8) 9.3666 1.6000 54.66 1.729160
9) -22.1915 0.5000 32.35 1.850 260
10) 3.9838 0.6000
11) 16.0927 1.3500 70.45 1.487490
12) -16.9870 (d12)

13) 25.2496 1.6000 82.56 1.497820
* 14) -20.6725 (d14)

15) ∞ 0.5000 70.70 1.544400
16) ∞ 0.5000
17) ∞ 0.5000 64.12 1.516800
18) ∞ (Bf)


[Aspherical data]
(Second side)
κ = 0.1570
C4 = 2.61512E-04
C6 = 4.99441E-06
C8 = -1.14151E-07
C10 = 1.26897E-09

(Third side)
κ = 1.7289
C4 = 2.61910E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

(Sixth surface)
κ = 0.4203
C4 = -8.88971E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

(14th page)
κ = 11.3000
C4 = 2.96872E-04
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

[Variable interval data]
At infinity focus Wide-angle end state Intermediate focal length state Telephoto end state
f 4.76 8.80 16.36
D0 ∞ ∞ ∞
d4 16.37003 7.12796 2.09604
d12 4.58584 9.45798 18.57517
d14 2.61349 2.61349 2.61349

At close focus (shooting distance 300mm)
Wide-angle end state Intermediate focal length state Telephoto end state β -0.01770 -0.03197 -0.05775
D0 260.9548 265.3248 261.2395
d4 16.37003 7.12796 2.09604
d12 4.36520 8.75212 16.46072
d14 2.83413 3.31935 4.72794

[Values for conditional expressions]
(1) | f1 | / (fw × ft) ^1/2 = 1.27711
(2) | f1 | / f2 = 1.04837
(3) (Rb + Ra) / (Rb-Ra) = -0.09967
(4) ν31 = 82.56
(5) n23 = 1.85026
(6) ν23 = 32.35
(7) n24 = 1.48749
(8) | fL11 | /fw=1.40092
(9) n11 = 1.82080
(10) ν11 = 42.71
(11) n12 = 1.90680
(12) ν12 = 21.15

  FIGS. 13A to 13C are graphs showing various aberrations when the zoom lens according to Example 4 is in focus at infinity. FIG. 13A shows the wide-angle end state, and FIG. 13B shows the intermediate focal length state. , (C) show the telephoto end state, respectively. FIGS. 14A to 14C are graphs showing various aberrations when the zoom lens according to Example 4 is in close focus (shooting distance 300 mm). FIG. 14A shows a wide-angle end state, and FIG. ) Shows the intermediate focal length state, and (c) shows the telephoto end state.

  From each aberration diagram, it can be seen that the zoom lens according to the fourth example has excellent optical performance with various aberrations corrected well in each focal length state from the wide-angle end state W to the telephoto end state T.

(5th Example)
FIG. 15 is a diagram illustrating a lens configuration of a zoom lens according to a fifth example. In FIG. 15, the zoom lens according to the fifth example, in order from the object side along the optical axis, a first lens group G1 having a negative refractive power, an aperture stop S, and a second lens having a positive refractive power. It consists of a lens group G2 and a third lens group G3 having a positive refractive power, and the distance between the first lens group G1 and the second lens group G2 decreases upon zooming from the wide-angle end state W to the telephoto end state T. Then, the first lens group G1 and the second lens group G2 move along the optical axis so that the distance between the second lens group G2 and the third lens group G3 increases, and the third lens group G3 is fixed. It is a configuration.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side, and the negative meniscus lens L11. The lens surface on the image plane I side and the lens surface on the object side of the positive meniscus lens L12 are aspheric.

  The second lens group G2 includes, in order from the object side along the optical axis, a biconvex positive lens L21, a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex positive lens. The lens surface on the object side of the positive lens L21 is an aspherical surface. The positive lens L22 and the negative lens L23 are cemented.

  The third lens group G3 includes only one biconvex positive lens L31, and focusing from an infinite object to a finite distance object is performed by moving the third lens group G3 along the optical axis. The lens surface on the object side of the positive lens L31 is an aspherical surface.

  The aperture stop S is disposed on the object side of the positive lens L21 closest to the object side of the second lens group G2, and is integrated with the second lens group G2 upon zooming from the wide-angle end state W to the telephoto end state T. Move to.

  The filter group FL disposed between the third lens group G3 and the image plane I is composed of a low-pass filter, an infrared cut filter, and the like.

  Table 5 below shows values of specifications of the zoom lens according to the fifth example.

(Table 5)
[Overall specifications]
f = 4.76-16.36
FNO = 2.81-5.61
2ω = 77.9 ° ~ 24.3 °
Ymax = 3.60

[Lens specifications]
rd ν n
1) 58.7466 1.2000 42.71 1.820800
* 2) 4.7777 2.5500
* 3) 9.3701 1.7000 21.15 1.906800
4) 18.2634 (d4)

5) ∞ 0.4000 Aperture S
* 6) 5.1454 1.7500 49.23 1.768020
7) -256.1792 0.1000
8) 9.1887 1.4500 46.63 1.816000
9) -21.8558 0.5000 28.27 2.003300
10) 3.7694 0.6000
11) 11.9047 1.3500 40.75 1.581440
12) -25.9856 (d12)

* 13) 13.6227 1.6500 82.56 1.497820
14) -62.8104 (d14)

15) ∞ 0.5000 70.70 1.544400
16) ∞ 0.5000
17) ∞ 0.5000 64.12 1.516800
18) ∞ (Bf)


[Aspherical data]
(Second side)
κ = 0.1126
C4 = 1.44197E-04
C6 = 7.28792E-06
C8 = -2.82949E-07
C10 = 5.84984E-09

(Third side)
κ = 1.0581
C4 = -4.98121E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 4.09320E-10

(Sixth surface)
κ = -0.4243
C4 = 7.22190E-04
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

(13th page)
κ = 3.5963
C4 = -1.83530E-04
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

[Variable interval data]
At infinity focus Wide-angle end state Intermediate focal length state Telephoto end state
f 4.76 8.90 16.70
D0 ∞ ∞ ∞
d4 15.48655 6.71169 1.99948
d12 5.03906 9.74240 18.60376
d14 1.58820 1.58820 1.58820

At close focus (shooting distance 300mm)
Wide-angle end state Intermediate focal length state Telephoto end state β -0.01759 -0.03208 -0.05814
D0 262.6133 266.6849 262.5358
d4 15.48655 6.71169 1.99948
d12 4.79532 8.95602 16.28281
d14 1.83193 2.37457 3.90914

[Values for conditional expressions]
(1) | f1 | / (fw × ft) ^1/2 = 1.22254
(2) | f1 | / f2 = 1.07921
(3) (Rb + Ra) / (Rb-Ra) = 0.64351
(4) ν31 = 82.56
(5) n23 = 2.00330
(6) ν23 = 28.27
(7) n24 = 1.58144
(8) | fL11 | /fw=1.34459
(9) n11 = 1.82080
(10) ν11 = 42.71
(11) n12 = 1.90680
(12) ν12 = 21.15

  FIGS. 16A to 16C are graphs showing various aberrations when the zoom lens according to Example 5 is in focus at infinity. FIG. 16A shows a wide-angle end state, and FIG. 16B shows an intermediate focal length state. , (C) show the telephoto end state, respectively. FIGS. 17A to 17C are graphs showing various aberrations when the zoom lens according to Example 5 is in close focus (shooting distance 300 mm). FIG. 17A shows the wide-angle end state. ) Shows the intermediate focal length state, and (c) shows the telephoto end state.

  From each aberration diagram, it can be seen that the zoom lens according to the fifth example has excellent optical performance with various aberrations corrected well in each focal length state from the wide-angle end state W to the telephoto end state T.

(Sixth embodiment)
FIG. 18 is a diagram illustrating a lens configuration of a zoom lens according to the sixth example. In FIG. 18, the zoom lens according to the sixth example, in order from the object side along the optical axis, the first lens group G1 having negative refractive power, the aperture stop S, and the second lens having positive refractive power. It consists of a lens group G2 and a third lens group G3 having a positive refractive power, and the distance between the first lens group G1 and the second lens group G2 decreases upon zooming from the wide-angle end state W to the telephoto end state T. Then, the first lens group G1 and the second lens group G2 move along the optical axis so that the distance between the second lens group G2 and the third lens group G3 increases, and the third lens group G3 is fixed. It is a configuration.

  The first lens group G1 includes, in order from the object side along the optical axis, a negative meniscus lens L11 having a convex surface facing the object side, and a positive meniscus lens L12 having a convex surface facing the object side, and the negative meniscus lens L11. The lens surface on the image plane I side and the lens surface on the object side of the positive meniscus lens L12 are aspheric.

  The second lens group G2 includes, in order from the object side along the optical axis, a positive meniscus lens L21 having a convex surface directed toward the object side, a biconvex positive lens L22, a biconcave negative lens L23, and a biconvex lens. And a lens surface on the object side of the positive meniscus lens L21 is an aspherical surface. The positive lens L22 and the negative lens L23 are cemented.

  The third lens group G3 includes only one biconvex positive lens L31, and focusing from an infinite object to a finite distance object is performed by moving the third lens group G3 along the optical axis.

  The aperture stop S is disposed closer to the object side than the most object-side positive meniscus lens L21 in the second lens group G2, and is integrated with the second lens group G2 upon zooming from the wide-angle end state W to the telephoto end state T. Move on.

  The filter group FL disposed between the third lens group G3 and the image plane I is composed of a low-pass filter, an infrared cut filter, and the like.

  Table 6 below provides values of specifications of the zoom lens according to the sixth example.

(Table 6)
[Overall specifications]
f = 4.76-18.10
FNO = 2.81-5.86
2ω = 78.0 ° ~ 22.5 °
Ymax = 3.60

[Lens specifications]
rd ν n
1) 63.7103 1.2000 40.10 1.851350
* 2) 5.0336 2.6000
* 3) 12.0022 1.7000 20.65 2.001700
4) 29.1296 (d4)

5) ∞ 0.4000 Aperture S
* 6) 5.3670 1.7000 49.23 1.768020
7) 51.6511 0.2500
8) 10.6299 1.4000 40.77 1.883000
9) -48.4773 0.5000 28.27 2.003300
10) 4.1293 0.6000
11) 10.5950 1.3500 58.89 1.518230
12) -17.1353 (d12)

13) 15.2568 1.6000 91.20 1.456000
14) -49.7131 (d14)

15) ∞ 0.5000 70.70 1.544400
16) ∞ 0.5000
17) ∞ 0.5000 64.12 1.516800
18) ∞ (Bf)


[Aspherical data]
(Second side)
κ = 0.1425
C4 = 2.32509E-04
C6 = 1.99685E-06
C8 = -1.89887E-08
C10 = -4.95183E-10

(Third side)
κ = 1.8204
C4 = 1.33499E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00

(Sixth surface)
κ = 0.5029
C4 = -3.59472E-05
C6 = 0.00000E + 00
C8 = 0.00000E + 00
C10 = 0.00000E + 00


[Variable interval data]
At infinity focus Wide-angle end state Intermediate focal length state Telephoto end state
f 4.76 9.10 18.10
D0 ∞ ∞ ∞
d4 17.49779 7.48523 1.98487
d12 4.87325 10.46086 21.50924
d14 2.61892 2.33707 1.89850

At close focus (shooting distance 300mm)
Wide-angle end state Intermediate focal length state Telephoto end state β -0.01781 -0.03319 -0.06355
D0 259.5143 264.2213 259.1118
d4 17.49779 7.48523 1.98487
d12 4.64811 9.65989 18.72514
d14 2.84405 3.13804 4.68261

[Values for conditional expressions]
(1) | f1 | / (fw × ft) ^1/2 = 1.23713
(2) | f1 | /f2=1.03186
(3) (Rb + Ra) / (Rb−Ra) = 0.53034
(4) ν31 = 91.20
(5) n23 = 2.00330
(6) ν23 = 28.27
(7) n24 = 1.51823
(8) | fL11 | /fw=1.36147
(9) n11 = 1.82080
(10) ν11 = 42.71
(11) n12 = 1.90680
(12) ν12 = 21.15

  FIGS. 19A to 19C are graphs showing various aberrations when the zoom lens according to Example 6 is focused at infinity. FIG. 19A shows a wide-angle end state, and FIG. 19B shows an intermediate focal length state. , (C) show the telephoto end state, respectively. FIGS. 20A to 20C are graphs showing various aberrations when the zoom lens according to Example 6 is in close focus (shooting distance 300 mm). FIG. 20A shows the wide-angle end state. ) Shows the intermediate focal length state, and (c) shows the telephoto end state.

  From each aberration diagram, it can be seen that the zoom lens according to the sixth example has excellent optical performance with various aberrations corrected well in each focal length state from the wide-angle end state W to the telephoto end state T.

  As described above, according to the zoom lens according to the embodiment, the zoom lens as a whole has a high zoom ratio of about 3 to 4 times, including a field angle exceeding 70 degrees in the wide angle end state, and is compact. In addition, it is possible to realize a zoom lens having excellent optical performance and suitable for a digital still camera or a video camera.

  The contents described below can be appropriately adopted as long as the optical performance is not impaired.

  In the embodiment, the three-group configuration is shown, but the present invention can also be applied to other group configurations such as the fourth group or the fifth group.

  Moreover, it is good also as an in-focus lens group which moves a single lens or a some lens group, or a partial lens evaluation to an optical axis direction, and focuses from an infinite object to a short distance object. The focusing lens group can also be applied to autofocus, and is also suitable for driving a motor for autofocus (such as an ultrasonic motor). In particular, the first or third lens group is preferably a focusing lens group.

  Alternatively, the lens group or the partial lens group may be vibrated in a direction perpendicular to the optical axis so as to correct an image blur caused by camera shake. In particular, the second lens group is preferably an anti-vibration lens group.

  The lens surface may be an aspherical surface. The aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface in which a glass is formed into an aspherical shape, or a composite aspherical surface in which a resin is formed in an aspherical shape on the glass surface.

  Further, each lens surface is provided with an antireflection film having a high transmittance over a wide wavelength range, and flare and ghost can be reduced to achieve high optical performance with high contrast.

  In addition, in order to explain the present invention in an easy-to-understand manner, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

1 shows an electronic still camera equipped with a lens system according to an embodiment, where (a) shows a front view and (b) shows a rear view. FIG. 2 shows a cross-sectional view taken along line A-A ′ of FIG. It is a figure which shows the lens structure of the zoom lens concerning 1st Example. FIG. 4 is a diagram illustrating various aberrations of the zoom lens according to the first example when focusing on infinity, where (a) shows a wide-angle end state, (b) shows an intermediate focal length state, and (c) shows a telephoto end state. . FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to the first example when focusing on a close range (shooting distance: 300 mm), where (a) is a wide-angle end state, (b) is an intermediate focal length state, and (c) is telephoto. Each end state is shown. It is a figure which shows the lens structure of the zoom lens concerning 2nd Example. FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to Example 2 when focusing on infinity, where (a) shows a wide-angle end state, (b) shows an intermediate focal length state, and (c) shows a telephoto end state. . FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to Example 2 when focusing on a close range (shooting distance: 300 mm), (a) showing a wide-angle end state, (b) showing an intermediate focal length state, and (c) showing telephoto. Each end state is shown. It is a figure which shows the lens structure of the zoom lens concerning 3rd Example. FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to Example 3 at the time of focusing on infinity, where (a) shows the wide-angle end state, (b) shows the intermediate focal length state, and (c) shows the telephoto end state. . FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to Example 3 when focusing on a close range (shooting distance: 300 mm), (a) showing a wide-angle end state, (b) showing an intermediate focal length state, and (c) showing telephoto. Each end state is shown. It is a figure which shows the lens structure of the zoom lens concerning 4th Example. FIG. 7A is a diagram illustrating various aberrations of the zoom lens according to Example 4 at the time of focusing on infinity, where (a) illustrates a wide-angle end state, (b) illustrates an intermediate focal length state, and (c) illustrates a telephoto end state. . FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to Example 4 when focusing on a close range (shooting distance: 300 mm), where (a) is a wide-angle end state, (b) is an intermediate focal length state, and (c) is telephoto. Each end state is shown. It is a figure which shows the lens structure of the zoom lens concerning 5th Example. FIG. 9A is a diagram illustrating various aberrations of the zoom lens according to Example 5 at the time of focusing on infinity, where (a) shows the wide-angle end state, (b) shows the intermediate focal length state, and (c) shows the telephoto end state. . FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to Example 5 when focusing on a close range (shooting distance: 300 mm), (a) showing a wide-angle end state, (b) showing an intermediate focal length state, and (c) showing telephoto. Each end state is shown. It is a figure which shows the lens structure of the zoom lens concerning 6th Example. FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to Example 6 at the time of focusing on infinity, where (a) shows a wide-angle end state, (b) shows an intermediate focal length state, and (c) shows a telephoto end state. . FIG. 10 is a diagram illustrating various aberrations of the zoom lens according to Example 6 when focusing on a close range (shooting distance: 300 mm), (a) showing a wide-angle end state, (b) showing an intermediate focal length state, and (c) showing telephoto. Each end state is shown.

Explanation of symbols

1 Electronic still camera 2 Imaging lens (zoom lens)
3 LCD Monitor 4 Release Button 5 Auxiliary Light Issuing Unit 6 Wide (W) -Tele (T) Button 7 Function Button C Image Sensor G1 First Lens Group G2 Second Lens Group G3 Third Lens Group FL Filter Group S Aperture I Image plane

Claims (13)

A first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side along the optical axis. Have
During zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group is decreased, and the distance between the second lens group and the third lens group is increased. , At least the first lens group and the second lens group move along the optical axis,
The first lens group includes, in order from the object side along the optical axis, a negative meniscus lens having a convex surface directed toward the object side, and a positive lens, and at least the surface on the image plane side of the negative meniscus lens is an aspherical surface. , At least one surface of the positive lens is an aspheric surface,
The second lens group includes, in order from the object side along the optical axis, a first positive lens, a second positive lens, a negative lens, and a third positive lens, and at least the object-side surface of the first positive lens is non-surface. Is spherical,
The third lens group is composed of one positive lens,
A zoom lens satisfying the following conditions:
1.13 <| f1 | / (fw × ft) ^1/2 <1.35
However,
f1: the focal length of the first lens group,
fw: focal length of the entire zoom lens system in the wide-angle end state;
ft: focal length of the entire zoom lens system in the telephoto end state, The zoom lens according to claim 1, wherein the following condition is satisfied.
0.90 <| f1 | / f2 <1.15
However,
f2: focal length of the second lens group,   The zoom lens according to claim 1 or 2, wherein focusing from an object at infinity to an object at a finite distance is performed by moving the third lens group. The zoom lens according to any one of claims 1 to 3, wherein the following condition is satisfied.
−0.40 <(Rb + Ra) / (Rb−Ra) <1.30
However,
Ra: radius of curvature of the object side surface of the positive lens in the third lens group,
Rb: radius of curvature of the image side surface of the positive lens in the third lens group The zoom lens according to claim 1, wherein the following condition is satisfied.
80.0 <ν31 <95.0
However,
ν31: Abbe number with respect to d-line (λ = 587.6 nm) of the material of the positive lens of the third lens group The zoom lens according to claim 1, wherein the following condition is satisfied.
1.81 <n23
23.9 <ν23 <34.0
However,
n23: refractive index with respect to d-line (λ = 587.6 nm) of the material of the negative lens of the second lens group,
ν23: Abbe number with respect to d-line (λ = 587.6 nm) of the material of the negative lens of the second lens group The zoom lens according to claim 1, wherein the following condition is satisfied.
1.45 <n24 <1.65
However,
n24: Refractive index with respect to d-line (λ = 587.6 nm) of the material of the third positive lens The zoom lens according to any one of claims 1 to 7, wherein the following condition is satisfied.
1.27 <| fL11 | / fw <1.46
However,
fL11: focal length of the negative meniscus lens,
fw: focal length of the entire zoom lens system in the wide-angle end state The zoom lens according to claim 1, wherein the following condition is satisfied.
1.78 <n11
35.0 <ν11
However,
n11: Refractive index for the d-line (λ = 587.6 nm) of the material of the negative meniscus lens ν11: Abbe number of the material of the negative meniscus lens for the d-line (λ = 587.6 nm) The zoom lens according to claim 1, wherein the following condition is satisfied.
1.84 <n12
ν12 <25.0
However,
n12: refractive index with respect to d-line (λ = 587.6 nm) of the material of the positive lens of the first lens group,
ν12: Abbe number with respect to d-line (λ = 587.6 nm) of the material of the positive lens of the first lens group   The zoom lens according to claim 1, wherein at least one surface of the positive lens of the third lens group is an aspherical surface.   An optical apparatus comprising the zoom lens according to claim 1. A first lens group having a negative refractive power, an aperture stop, a second lens group having a positive refractive power, and a third lens group having a positive refractive power in order from the object side along the optical axis. Have
The first lens group includes, in order from the object side along the optical axis, a negative meniscus lens having a convex surface directed toward the object side, and a positive lens, and at least the surface on the image plane side of the negative meniscus lens is an aspherical surface. , At least one surface of the positive lens is an aspheric surface,
The second lens group includes, in order from the object side along the optical axis, a first positive lens, a second positive lens, a negative lens, and a third positive lens, and at least the object-side surface of the first positive lens is non-surface. Is spherical,
The third lens group consists of one positive lens and satisfies the following conditions:
During zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group is decreased, and the distance between the second lens group and the third lens group is increased. A zooming method characterized by moving at least the first lens group and the second lens group along an optical axis.
1.13 <| f1 | / (fw × ft) ^1/2 <1.35
However,
f1: the focal length of the first lens group,
fw: focal length of the entire zoom lens system in the wide-angle end state;
ft: focal length of the entire zoom lens system in the telephoto end state.

Images