# Patent

## Title
Zoom lens, imaging optical apparatus, and digital device

## Abstract

A zoom lens includes, in an order from an object side, four groups of a positive group, a negative group, a positive group, and a negative group. For varying magnification from a wide-angle end to a telephoto end, the first group is configured to be moved toward the object side, the second group is configured to be moved toward an image side, the third group is configured to be moved toward the object side, and the fourth group is configured to be moved toward the object side, and conditional equations of −0.63<f2/f1<−0.25, −10<f2/y′max <−3, and 6<f1/y′max<20 (f1: the focal distance of the first group; f2: the focal distance of the second group; y′max: the maximum image height) are satisfied.

## Background
The entire disclosure of Japanese Patent Application No. 2013-187968 filed on Sep. 11, 2013 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
Embodiments of the present invention relate to zoom lenses, imaging optical apparatuses, and digital devices. For example, the embodiments relate to, of imaging optical systems having variable power, a zoom lens that is optimal for a telephotographing system with a viewing angle (2ω) at a telephoto end of less than 15°. The embodiments also relate to an imaging optical apparatus that is configured to output a picture of a photographing subject captured by the zoom lens and an image sensor in the form of electrical signals, and a digital device with an image input function, such as a digital camera, installed with the imaging optical apparatus.
2. Description of the Related Art
JP 08-086962 A, JP 2012-027261 A, and JP 2013-037105 A have been proposed for a telephotographing zoom lens suitable for an imaging optical system.
Recently, demand for compact and lightweight lenses including an interchangeable lens has become stronger with respect to digital single lens reflex cameras, especially in the mirrorless field. Generally, of a zoom lens with a viewing angle at a telephoto end of less than 15°, the entire length tends to be longer. In addition, forcibly shortening the entire length involves increasing of the powers of lens groups, and this could magnify deterioration in performance due to manufacturing error.
The zoom lens described in JP 08-086962 A is not fully responsive to today's demand for compact and lightweight lenses. JP 2012-027261 A and JP 2013-037105 A disclose zoom lenses for a compact design. However, as a result of reduction in size, the powers of first and second groups are increased, which enhances deterioration in performance in case where the lens groups are decentered from the designed conditions.
SUMMARY OF THE INVENTION
Embodiments of the present invention have been made in view of the foregoing circumstances, and an object of the embodiments of the present invention is to provide a zoom lens, even with a viewing angle at a telephoto end of less than 15°, that is operable with favorable optical performance in the entire zoom range while being reduced in size and having higher produceability, as well as an imaging optical apparatus and a digital device that include the lens.
To achieve the above object, according to an aspect, a zoom lens reflecting one aspect of the present invention includes: a plurality of lens groups arranged at inter-group spacings along an optical axis between an object side and an image side, the zoom lens being configured such that magnification is varied by change of the inter-group spacings to be caused by movement of the lens groups along the optical axis,
the lens groups including, in an order from the object side, a first group of positive power, a second group of negative power, a third group of positive power, and a fourth group of negative power, wherein
for varying magnification from a wide-angle end to a telephoto end, the first group is configured to be moved toward the object side, the second group is configured to be moved toward the image side, the third group is configured to be moved toward the object side, and the fourth group is configured to be moved toward the object side, and
the following conditional equations (1) to (3) are satisfied:

−0.63<f2/f1<−0.25  (1);

−10<f2/y′max<−3  (2); and

6<f1/y′max<20  (3),

where

    f1 represents the focal distance of the first group,
    f2 represents the focal distance of the second group, and
    y′max represents the maximum image height.


In the zoom lens of Item. 1, where an inter-lens group spacing is an inter-lens spacing t satisfying a conditional equation (0):0.14<t/y′max of inter-lens spacings t in the third group, the third group preferably includes, from the order from the object side, a positive lens group, a negative lens group, and a positive lens group, and the following conditional equation (4) is satisfied:

−0.7<f3n/f3<−0.4  (4),

where

    f3 represents the focal distance of the third group, and
    f3n represents the focal distance of the negative lens group in the third group,


the positive lens group on the object side in the third group preferably includes lenses from, calculation of t/y′max being performed in an order from a lens having the strongest negative power in the third group toward the object side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14 up to a lens closest to the object side in the third group,
the negative lens group in the third group preferably includes a negative lens having the strongest power in the third group, and includes lenses from a lens that is next by one to the image side from, calculation of t/y′max being performed in the order from the negative lens toward the object side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14 up to a lens that is next by one to the object side from, calculation of t/y′max being performed in an order from the negative lens toward the image side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14, and
the positive lens group on the image side in the third group preferably includes lenses from, calculation of t/y′max being performed in the order from the lens having the strongest negative power in the third group toward the image side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14 up to a lens closest to the image side in the third group.
In the zoom lens of Item. 1, where an inter-group spacing is an inter-lens spacing t satisfying a conditional equation (0):0.14<t/y′max of inter-lens spacings t in the second group, the second group preferably includes, from the order from the object side, a negative group and a positive group, the positive group having at least one cemented lens.
In the zoom lens of Item. 3, the negative group of the second group preferably includes a negative meniscus lens having a convex surface as a surface on the object side, and the positive group of the second group preferably includes a lens having a convex surface as a surface on the object side and a lens having a concave surface as a surface on the image side.
In the zoom lens of Item. 1, for focusing from the infinity to a proximate object, the fourth group is preferably configured to be moved toward the image side along the optical axis.
In the zoom lens of Item. 1, the fourth group preferably has at least a positive lens and a negative lens.
In the zoom lens of Item. 1, any one of the positive lens groups in the third group preferably has at least two positive lenses.
According to another aspect, an imaging optical apparatus reflecting one aspect of the present invention includes:
the zoom lens of Item. 1; and
an image sensor having a photoreceiving surface, the image sensor being configured to convert an optical image formed on the photoreceiving surface into electrical signals, wherein
the zoom lens is arranged such that an optical image of a photographing subject is adapted to be formed on the photoreceiving surface of the image sensor.
According to another aspect, a digital device reflecting one aspect of the present invention includes the imaging optical apparatus of Item. 8, the imaging optical apparatus providing at least one function of still image photographing or moving picture shooting of a photographing subject.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given byway of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein:
FIG. 1 is an optical composition diagram of a first embodiment (Example 1);
FIG. 2 is an optical composition diagram of a second embodiment (Example 2);
FIG. 3 is an optical composition diagram of a third embodiment (Example 3);
FIG. 4 is an optical composition diagram of a fourth embodiment (Example 4);
FIG. 5 is an optical composition diagram of a fifth embodiment (Example 5);
FIG. 6 is an optical composition diagram of a sixth embodiment (Example 6);
FIG. 7 is an optical composition diagram of a seventh embodiment (Example 7);
FIG. 8 is an optical composition diagram of an eighth embodiment (Example 8);
FIG. 9 is an optical composition diagram of a ninth embodiment (Example 9);
FIG. 10 is an optical composition diagram of a tenth embodiment (Example 10);
FIG. 11 is an optical composition diagram of an eleventh embodiment (Example 11);
FIGS. 12A-I are aberration diagrams corresponding to Example 1;
FIGS. 13A-I are aberration diagrams corresponding to Example 2;
FIGS. 14A-I are aberration diagrams corresponding to Example 3;
FIGS. 15A-I are aberration diagrams corresponding to Example 4;
FIGS. 16A-I are aberration diagrams corresponding to Example 5;
FIGS. 17A-I are aberration diagrams corresponding to Example 6;
FIGS. 18A-I are aberration diagrams corresponding to Example 7;
FIGS. 19A-I are aberration diagrams corresponding to Example 8;
FIGS. 20A-I are aberration diagrams corresponding to Example 9;
FIGS. 21A-I are aberration diagrams corresponding to Example 10;
FIGS. 22A-I are aberration diagrams corresponding to Example 11; and
FIG. 23 is a schematic diagram depicting an exemplary configuration of a digital device installed with a zoom lens.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.
Description is given below of a zoom lens, an imaging optical apparatus, and a digital device according to embodiments of the present invention. A zoom lens according to an embodiment of the present invention is configured such that magnification is varied by change of inter-group spacings to be caused by movement of a plurality of lens groups along the optical axis. The zoom lens includes, in the order from the object side, a first group of positive power, a second group of negative power, a third group of positive power, and a fourth group of negative power (the power indicates the amount defined by the reciprocal of the focal distance). The zoom lens is configured such that, in varying magnification from a wide-angle end to a telephoto end, the first group is moved toward the object side, the second group is moved toward the image side, the third group is moved toward the object side, and the fourth group is moved toward the object side, in such a way as to satisfy the following conditional equations (1) to (3):

−0.63<f2/f1<−0.25  (1);

−10<f2/y′max<−3  (2);

6<f1/y′max<20  (3),

where

    f1: the focal distance of the first group;
    f2: the focal distance of the second group; and
    y′max: the maximum image height.


For the above-described zoom configuration, a positive group-preceding configuration is adopted so as to achieve favorable optical performance and compact size of the telephotographing zoom lens. Further, the power arrangement is such that the second group is negative and the third group is positive; thus, the lens back is secured with a retrofocusing power arrangement at the wide-angle end. In the meanwhile, the spacing between the second group and the third group is set shorter to reduce the retrofocusing power at the telephoto end, such that a compact full length is achieved.
The conditional equation (1) is for appropriately setting the focal distances of the first group and the second group. Below the lower limit of the conditional equation (1), the power of the negative second group is too weak against the positive first group, making it difficult to correct spherical aberration, coma aberration, and field curvature that could occur in the first group. Above the upper limit of the conditional equation (1), power shortage of the first group is likely, causing increase in amount of movement of the first group in varying magnification and thus making it difficult to shorten the full length. Hence, improvement in optical performance and shortening of the full length are achieved in a well-balanced manner by satisfying the conditional equation (1).
The conditional equation (2) is for appropriately setting the focal distance of the second group. Below the lower limit of the conditional equation (2), the focal distance of the second group is too long, making it difficult to shorten the full length due to an increased amount of movement of the second group in varying magnification. Above the upper limit of the conditional equation (2), the power of the second group is too strong, thus enhancing deterioration in performance in the event of decentering due to manufacturing error. Further, high-order spherical aberration or coma aberration which could occur in the second group is enhanced. Hence, improvement in optical performance and shortening of the full length are achieved in a well-balanced manner by satisfying the conditional equation (2).
The conditional equation (3) is for appropriately setting the focal distance of the first group. Below the lower limit of the conditional equation (3), the focal distance of the first group is too long, making it difficult to shorten the entire length due to an increased amount of movement of the first group in varying magnification. Above the upper limit of the conditional equation (3), the power of the first group is too strong, thus enhancing deterioration in performance in the event of decentering due to manufacturing error. Further, high-order spherical aberration or coma aberration which could occur in the first group is magnified. Hence, improvement in optical performance and shortening of the full length are achieved in a well-balanced manner by satisfying the conditional equation (3).
The above characteristic configuration allows for achievement of a zoom lens, even with a viewing angle (2ω) at a telephoto end of less than 15°, with a compact design and higher produceability while having favorable optical performance in the entire zoon range, as well as an imaging optical apparatus including the lens. The zoom lens or the image optical apparatus is applicable to a digital device, e.g., a digital camera, thus adding a high-performance image input function to the digital device in a compact manner. This contributes to reduction in size and cost, improvement in performance, and sophistication of functions, to name a few, of the digital device. For example, since the zoom lens according to an embodiment of the present invention is suitably used as an interchangeable lens for a digital camera or a video camera, a lightweight and compact interchangeable lens with higher portability is achieved. Description is given below of conditions and other factors for obtaining such effects in a well-balanced manner and also for achieving, for example, still higher optical performance and reduction in size.
The following conditional equation (1a) is further preferably satisfied:

−0.58<f2/f1<−0.30  (1a)

This conditional equation (1a) defines a further preferred conditional range in the conditional range defined by the conditional equation (1) based on, for example, the above aspects. Hence, the conditional equation (1a) is preferably satisfied to increase the above effects.
The following conditional equation (2a) is further preferably satisfied:

−8<f2/y′max<−3.4  (2a)

This conditional equation (2a) defines a further preferred conditional range in the conditional range defined by the conditional equation (2) based on, for example, the above aspects. Hence, the conditional equation (2a) is preferably satisfied to increase the above effects.
The following conditional equation (3a) is further preferably satisfied:

8<f1/y′max<18  (3a)

This conditional equation (3a) defines a further preferred conditional range in the conditional range defined by the conditional equation (3) based on, for example, the above aspects. Hence, the conditional equation (3a) is preferably satisfied to increase the above effects.
Where the inter-lens group spacing is an inter-lens spacing t satisfying a conditional equation (0):0.14<t/y′max of inter-lens spacings t in the third group, the third group preferably includes, from the order from the object side, a positive lens group, a negative lens group, and a positive lens group, and the following conditional equation (4) is preferably satisfied:

−0.7<f3n/f3<−0.4  (4),

where

    f3: the focal distance of the third group, and
    f3n: the focal distance of the negative lens group in the third group.


The positive lens group on the object side in the third group includes lenses from, when calculation of t/y′max is performed in the order from the lens having the strongest negative power in the third group toward the object side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14 up to the lens closest to the object side in the third group.
The negative lens group in the third group includes a negative lens having the strongest power in the third group, and includes lenses from a lens that is next by one to the image side from, when calculation of t/y′max is performed in the order from the negative lens toward the object side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14 up to a lens that is next by one to the object side from, when calculation of t/y′max is performed in the order from the negative lens toward the image side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14.
The positive lens group on the image side in the third group includes lenses from, when calculation of t/y′max is performed in the order from the lens having the strongest negative power in the third group toward the image side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14 up to the lens closest to the image side in the third group.
The conditional equation (4) is for appropriately setting the focal distance in the third group. Below the lower limit of the conditional equation (4), the negative power in the third group is insufficient, causing increase of the Petzval sum and thus insufficient correction of field curvature. Above the upper limit of the conditional equation (4), the negative power in the third group is excessive, which relatively increases the power of the positive lens group, thus resulting in enhanced fluctuation in spherical aberration or coma aberration due to change in incident light in varying magnification. Further, deterioration in performance due to manufacturing error is also increased. Hence, improvement in optical performance is achieved in a well-balanced manner by satisfying the conditional equation (4).
The following conditional equation (4a) is further preferably satisfied.

−0.68<f3n/f3<−0.45  (4a)

This conditional equation (4a) defines a further preferred conditional range in the conditional range defined by the conditional equation (4) based on, for example, the above aspects. Hence, the conditional equation (4a) is preferably satisfied to increase the above effects.
Where the inter-group spacing is an inter-lens spacing t satisfying the conditional equation (0):0.14<t/y′max of inter-lens spacings t in the second group, the second group preferably includes, from the order from the object side, a negative group and a positive group, and the positive group preferably has at least one cemented lens. Fluctuation in chromatic aberration in varying magnification is effectively suppressed by this configuration.
The second group preferably includes, as described above, in the order from the object side, a negative group and a positive group, and the following conditional equation (5) is preferably further satisfied:

0.4<f2n/f2<1.4  (5),

where

    f2: the focal distance of the second group, and
    f2n: the focal distance of the negative group in the second group.


The conditional equation (5) defines the focal distance of the negative group in the second group. Below the lower limit of the conditional equation (5), the focal distance of the negative group is too short, thus enhancing deterioration in performance due to, for example, manufacturing error such as decentering of a lens. Above the upper limit of the conditional equation (5), the negative power in the second group is insufficient, resulting in unsatisfactory correction of chromatic aberration in the second group and thus increased fluctuation in chromatic aberration in varying magnification. Further, the Petzval sum is increased, making it difficult to correct the field property. Hence, improvement in optical performance is achieved in a well-balanced manner by satisfying the conditional equation (5).
The following conditional equation (5a) is further preferably satisfied:

0.47<f2n/f2<1.18  (5a)

This conditional equation (5a) defines a further preferred conditional range in the conditional range defined by the conditional equation (5) based on, for example, the above aspects. Hence, the conditional equation (5a) is preferably satisfied to increase the above effects.
The negative group of the second group preferably includes a negative meniscus lens having a convex surface as a surface on the object side, and the positive group of the second group preferably includes a lens having a convex surface as a surface on the object side and a lens having a concave surface as a surface on the image side. As above, having a negative meniscus lens as a lens on the object side of the second group allows for prevention of extreme enlargement of the incident angle of incident light that changes while magnification is varied, and thus coma aberration on the surface on the object side is suppressed. Further, having a convex shape as a surface on the object side of the positive group in the second group allows for cancellation of negative spherical aberration that has occurred in the convex lens on the object side in the negative group, and enlargement of the lens is prevented by the effect of convergence. Having a concave surface shape of the surface on the image side of the lens closest to the image side facilitates correction of coma aberration or zooming chromatic aberration that could occur in the positive group of the second group.
For focusing from the infinity to a proximate object, the fourth group is preferably configured to be moved toward the image side along the optical axis. In this manner, the focusing group is easily reduced in weight and size. As a result, rapid focusing and downsizing of the entire lens camera cone are achieved.
The fourth group preferably has at least a positive lens and a negative lens. In this manner, fluctuation in on-axis chromatic aberration and zooming chromatic aberration in varying magnification is suppressed. Further, where the fourth group is the focusing group, fluctuation in on-axis chromatic aberration and zooming chromatic aberration is also suppressed, which could occur in focusing to a proximate object.
Any one of the positive lens groups in the third group preferably has at least two positive lenses. This allows for suppression of deterioration in performance which could happen by inhibiting a single lens from having extremely strong positive power.
The zoom lens according to an embodiment of the present invention is suitably used as an imaging lens of a digital device with an image input function, such as a lens-interchangeable digital camera. Combining such a zoom lens with, for example, an image sensor allows for configuration of an image optical apparatus operable to optically capture a picture of a photographing subject and to output the picture in the form of electrical signals. The imaging optical apparatus is a principal constituent optical device of a camera to be used for taking still images or shooting moving pictures of a photographing subject; for example, the apparatus includes, in the order from the object (i.e., the photographing subject) side, a zoom lens for forming an optical image of the object, and an image sensor for converting the optical image formed by the zoom lens into electrical signals. The zoom lens with the above-described features is arranged in such a manner as to form an optical image of the photographing subject on the photoreceiving surface (i.e., the imaging surface) of the image sensor, such that an imaging optical apparatus with higher performance besides a reduced size and cost and a digital device including the apparatus are achieved.
Exemplary digital devices with an image input function include digital cameras, video cameras, surveillance cameras, in-vehicle cameras, and cameras for video conference. Also included are personal computers, portable digital devices such as cell phones, smart phones, and mobile computers, peripheral devices for these devices such as scanners and printers, and other types of digital devices with a built-in or attached camera function. As can be seen from these examples, not only a camera is configurable by using the imaging optical apparatus, but also a camera function is attachable by installing the imaging optical apparatus in various devices. For example, a digital device with an image input function, such as a cell phone with a camera, is configurable.
FIG. 23 depicts a schematic configuration example of a digital device DU in the form of a schematic profile to exemplify the digital device with an image input function. An imaging optical apparatus LU installed in the digital device DU depicted in FIG. 23 includes, in the order from the object (i.e., the photographing subject) side, a zoom lens ZL (AX: optical axis) configured to form an optical image (image surface) IM of an object in variable magnification, a plane parallel plate PT (corresponding to, for example, a cover glass of an image sensor SR; an optical filter such as an optical low-pass filter or an infrared cutoff filter disposed as needed), and the image sensor SR configured to convert the optical image IM that is formed by the zoom lens ZL on a photoreceiving surface (imaging surface) SS into electrical signals. In case where the imaging optical apparatus LU is used to configure the digital device DU with an image input function, the imaging optical apparatus LU is typically positioned inside the body, while any mode is adoptable as needed to implement a camera function. For example, a unitized imaging optical apparatus LU is configurable so as to be detachable or rotatable with respect to the main body of the digital device DU.
The zoom lens ZL is a four-component zoom lens including, in the order from the object side, a positive lens group, a negative lens group, a positive lens group, and a negative lens group. Varying of magnification, i.e., zooming, from a wide-angle end to a telephoto end is performed by changing the spacings between the groups (inter-group spacings). For varying the magnification from the wide-angle end to the telephoto end, the first group is configured to be moved toward the object side, the second group is configured to be moved toward the image side, the third group is configured to be moved toward the object side, and the fourth group is configured to be moved toward the object side. A solid-state image sensor such as a CCD (Charge Coupled Device) image sensor having a plurality of pixels or a CMOS (Complementary Metal-Oxide Semiconductor) image sensor is usable for the image sensor SR. The zoom lens ZL is positioned such that the optical image IM of a photographing subject is formed on the photoreceiving surface SS serving as a photoelectric converter of the image sensor SR; thus, the optical image IM formed by the zoom lens ZL is converted by the image sensor SR into electrical signals.
The digital device DU includes, in addition to the imaging optical apparatus LU, a signal processor 1, a controller 2, a memory 3, an operation unit 4, and a display unit 5. Signals generated at the image sensor SR are subjected to, for example, predetermined digital image processing and image compression processing at the signal processor 1 as needed, so as to be recorded as digital picture signals on the memory 3 (e.g., a semiconductor memory or an optical disk), or depending on the circumstances, to be transmitted to another device through a cable or in the converted form of, for example, infrared signals (e.g., a communication function of a cell phone). The controller 2 includes a microcomputer and intensively performs control of functions such as a photographing function including a still image photographing function and a moving picture shooting function and an image replay function; and control of lens moving mechanism for, for example, zooming, focusing, and image stabilization. For example, the controller 2 performs control over the imaging optical apparatus LU so as to perform at least one of still image photographing or moving picture shooting of a photographing subject. The display unit 5 includes a display such as a liquid crystal monitor and is configured to perform image display by using image signals converted by the image sensor SR or image information recorded on the memory 3. The operation unit 4 includes an operation member including an operation button such as a release button and an operation dial such as a photographing mode dial, and is configured to transmit to the controller 2 information that the operator inputs through an operation.
The specific optical composition of the zoom lens ZL is described here in further detail in connection with first to eleventh embodiments. FIGS. 1 to 11 are optical composition diagrams corresponding to each of the zoom lenses ZL that configure the first to eleventh embodiments, and the figures depict lens arrangements and lens shapes at a wide-angle end (W) and a telephoto end (T) in optical profile. These zoom lenses ZL each include, in the order from the object side, a first group Gr1 of positive power, a second group Gr2 of negative power, a third group Gr3 of positive power, and a fourth group Gr4 of negative power.
The arrows m1, m2, m3, and m4 in the optical composition diagrams (FIGS. 1 to 11) schematically represent the movement of the first group Gr1, the second group Gr2, the third group Gr3, and the fourth group Gr4, respectively, in zooming from the wide-angle end (W) to the telephoto end (T). In this manner, the zoom lenses ZL are configured to perform the variable magnification process, i.e., zooming, from the wide-angle end (W) to the telephoto end (T) by changing the inter-group spacings on the axis. In varying magnification, the first group Gr1, the second group Gr2, the third group Gr3, and the fourth group Gr4 are each moved relative to the image surface IM. A diaphragm (aperture diaphragm) ST is located on the object side of the third group Gr3 and is moved together with the third group Gr3 when magnification is varied. For varying magnification from the wide-angle end (W) to the telephoto end (T), the spacing between the first group Gr1 and the second group Gr2 is increased, the spacing between the second group Gr2 and the third group Gr3 is decreased, the spacing between the third group Gr3 and the fourth group Gr4 is decreased, and the spacing between the fourth group Gr4 and the image surface IM is increased. In focusing, the fourth group Gr4 is moved along the optical axis AX. In other words, the fourth group Gr4 is a focusing group, and is moved toward the image surface IM side as indicated by the arrows mF in focusing from the infinity to an object at a short distance.
In the first to fifth and eighth to eleventh embodiments, the second group Gr2 includes, in the order from the object side, a negative group Gr2A and a positive group Gr2B. More specifically, the second group Gr2 includes, in the order from the object side, the negative group Gr2A and the positive group Gr2B that has at least one cemented lens, where the inter-group spacing is an inter-lens spacing t satisfying the conditional equation (0):0.14<t/y′max of the inter-lens spacings t in the second group Gr2.
In the first to eleventh embodiments, the third group Gr3 includes, in the order from the object side, a positive lens group Gr3A, a negative lens group Gr3B, and a positive lens group Gr3C. More specifically, the third group Gr3 includes, in the order from the object side, the positive lens group Gr3A, the negative lens group Gr3B, and the positive lens group Gr3C, where the inter-group spacing is an inter-lens spacing t satisfying the conditional equation (0):0.14<t/y′max of the inter-lens spacings t in the third group Gr3. It is to be noted that the positive lens group Gr3A on the object side in the third group Gr3 includes lenses from, when calculation of t/y′max is performed in the order from the lens having the strongest negative power in the third group Gr3 toward the object side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14 up to the lens closest to the object side in the third group Gr3. The negative lens group Gr3B in the third group Gr3 includes a negative lens with the strongest power in the third group Gr3, and includes lenses from the lens that is next by one to the image side from, when calculation of t/y′max is performed in the order from the aforementioned negative lens toward the object side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14 up to the lens that is next by one to the object side from, when calculation of t/y′max is performed in the order from the aforementioned negative lens toward the image side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14. Further, the positive lens group Gr3C on the image side in the third group Gr3 includes lenses from, when calculation of t/y′max is performed in the order from the lens with the strongest negative power in the third group Gr3 toward the image side, the first lens having an inter-lens spacing t with the adjacent lens of or larger than t/y′max=0.14 up to the lens closest to the image side in the third group Gr3.
The groups in the first embodiment (FIG. 1) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes one biconcave negative lens; the positive lens group Gr3C includes a positive meniscus lens that is convex on the image side and a biconvex positive lens; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the second embodiment (FIG. 2) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes two biconvex positive lenses; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the third embodiment (FIG. 3) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes two biconvex positive lenses; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the fourth embodiment (FIG. 4) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes two biconvex positive lenses; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the fifth embodiment (FIG. 5) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes two biconvex positive lenses; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the sixth embodiment (FIG. 6) are configured as follows in the order from the object side: The first group Gr1 includes a cemented lens comprised of a negative meniscus lens that is concave on the image side and a biconvex positive lens, and a positive meniscus lens that is convex on the object side. The second group Gr2 includes a negative meniscus lens that is concave on the image side, a biconvex positive lens, and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes one biconvex positive lens; the negative lens group Gr3B includes one biconcave negative lens; the positive lens group Gr3C includes a positive meniscus lens that is convex on the image side and a biconvex positive lens; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a plano-concave negative lens with the concave surface oriented to the object side.
The groups in the seventh embodiment (FIG. 7) are configured as follows in the order from the object side: The first group Gr1 includes a cemented lens comprised of a negative meniscus lens that is concave on the image side and a biconvex positive lens, and a positive meniscus lens that is convex on the object side. The second group Gr2 includes a biconvex positive lens, a biconcave negative lens, and a positive meniscus lens that is convex on the object side. In the third group Gr3, the positive lens group Gr3A includes one biconvex positive lens; the negative lens group Gr3B includes one biconcave negative lens; the positive lens group Gr3C includes a positive meniscus lens that is convex on the image side and a biconvex positive lens; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the eighth embodiment (FIG. 8) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes a biconvex positive lens and a positive meniscus lens that is convex on the image side; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the ninth embodiment (FIG. 9) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes two biconvex positive lenses; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes two biconvex positive lenses; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the tenth embodiment (FIG. 10) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes a biconvex positive lens and a positive meniscus lens that is convex on the object side; the negative lens group Gr3B includes a biconcave negative lens and a positive meniscus lens that is convex on the object side; the positive lens group Gr3C includes a biconvex positive lens and a positive meniscus lens that is convex on the image side; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
The groups in the eleventh embodiment (FIG. 11) are configured as follows in the order from the object side: The first group Gr1 includes one cemented lens comprised of a negative meniscus lens that is concave on the image side and a positive meniscus lens that is convex on the object side. In the second group Gr2, the negative group Gr2A includes a negative meniscus lens that is concave on the image side, and the positive group Gr2B includes a cemented lens comprised of a biconvex positive lens and a biconcave negative lens. In the third group Gr3, the positive lens group Gr3A includes two biconvex positive lenses; the negative lens group Gr3B includes one cemented lens of a biconcave negative lens and a negative meniscus lens that is concave on the image side; the positive lens group Gr3C includes a positive meniscus lens that is convex on the image side and a biconvex positive lens; and the diaphragm ST is positioned on the object side of the third group Gr3. The fourth group Gr4 includes a positive meniscus lens that is convex on the image side and a biconcave negative lens.
EXAMPLES
The configurations and so forth of zoom lenses to which embodiments of the present invention are applied are described below further specifically with reference to, for example, construction data of Examples. Examples 1 to 11 (EX1 to EX11) illustrated herein are numerical examples corresponding to the foregoing first to eleventh embodiments, respectively, and the optical composition diagrams (FIGS. 1 to 11) representing the first to eleventh embodiments depict, for example, the lens arrangements and the lens shape optical paths of the corresponding Examples 1 to 11.
In the construction data of Examples, surface number i, radius of curvature r (mm), on-axis surface spacing d (mm), refractive index nd with respect to d-line (wavelength of 587.56 nm), Abbe number vd with respect to d-line, and t/y′max (t: inter-lens spacing; y′max: maximum image height) are presented as surface data sequentially from the left column. Zoom ratio (variable magnification ratio) is presented as various data; for the focal distance states W, M, and T, focal distance of the whole system (Fl, mm), F-number (Fno.), half field angle (ω, °), image height (y′max, mm), lens full length (TL, mm), back focal distance (BF, mm), and variable surface spacing (di, i: surface number, mm) are presented; the respective focal distances of the lens groups Gr1, Gr2, Gr3, and Gr4 (f1, f2, f3, f4; mm) are presented as zoom lens group data. It is to be noted that regarding back focal distance BF, the distance from the last optical surface of the system to the paraxial image plane is indicated by the air conversion length; and lens full length TL is the distance from the front optical surface to the last optical surface of the system added with back focal distance BF. Further, TABLE 1 shows corresponding values of the conditional equations with respect to each Example, and TABLE 2 shows focal distances of sub-groups of the second group Gr2 and the third group Gr3 (the negative group Gr2A and the positive group Gr2B; the positive lens group Gr3A, the negative lens group Gr3B, and the positive lens group Gr3C) with respect to each Example.
FIGS. 12A to 22I are aberration diagrams (longitudinal aberration diagrams in the focused state at the infinity) corresponding to Examples 1 to 11 (EX1 to EX11), respectively; FIGS. 12A to 12C, 13A to 13C, 14A to 14C, 15A to 15C, 16A to 16C, 17A to 17C, 18A to 18C, 19A to 19C, 20A to 20C, 21A to 21C, and 22A to 22C indicate various types of aberration at the wide-angle end W, FIGS. 12D to 12F, 13D to 13F, 14D to 14F, 15D to 15F, 16D to 16F, 17D to 17F, 18D to 18F, 19D to 19F, 20D to 20F, 21D to 21F, and 22D to 22F indicate various types of aberration in the middle focal distance state M, and FIGS. 12G to 12I, 13G to 13I, 14G to 14I, 15G to 15I, 16G to 16I, 17G to 17I, 18G to 18I, 19G to 19I, 20G to 20I, 21G to 21I, and 22G to 22I indicate various types of aberration at the telephoto end T. In FIGS. 12A to 22I, FIGS. 12A, 12D, and 12G, FIGS. 13A, 13D, and 13G, FIGS. 14A, 14D, and 14G, FIGS. 15A, 15D, and 15G, FIGS. 16A, 16D, and 16G, FIGS. 17A, 17D, and 17G, FIGS. 18A, 18D, and 18G, FIGS. 19A, 19D, and 19G, FIGS. 20A, 20D, and 20G, FIGS. 21A, 21D, and 21G, and FIGS. 22A, 22D, and 22G are spherical aberration diagrams, FIGS. 12B, 12E, and 12H, FIGS. 13B, 13E, and 13H, FIGS. 14B, 14E, and 14H, FIGS. 15B, 15E, and 15H, FIGS. 16B, 16E, and 16H, FIGS. 17B, 17E, and 17H, FIGS. 18B, 18E, and 18H, FIGS. 19B, 19E, and 19H, FIGS. 20B, 20E, and 20H, FIGS. 21B, 21E, and 21H, and FIGS. 22B, 22E, and 22H are astigmatism diagrams, and FIGS. 12C, 12F, and 12I, FIGS. 13C, 13F, and 13I, FIGS. 14C, 14F, and 14I, FIGS. 15C, 15F, and 15I, FIGS. 16C, 16F, and 16I, FIGS. 17C, 17F, and 17I, FIGS. 18C, 18F, and 18I, FIGS. 19C, 19F, and 19I, FIGS. 20C, 20F, and 20I, FIGS. 21C, 21F, and 21I, and FIGS. 22C, 22F, and 22I are distortion aberration diagrams.
The spherical aberration diagrams represent the amount of spherical aberration with respect to d-line (wavelength of 587.56 nm) indicated by the solid line, the amount of spherical aberration with respect to c-line (wavelength of 656.28 nm) indicated by the alternate long and short dash line, and the amount of spherical aberration with respect to g-line (wavelength of 435.84 nm) indicated by the broken line, byway of the amount of displacement from the paraxial image plane in the direction of optical axis AX (unit: mm). The vertical axis represents the value given by standardizing the incident height to the pupil by the maximum height, i.e., the relative pupil height. In the astigmatism diagrams, the broken line T indicates the tangential surface with respect to d-line, and the solid line S indicates the sagittal surface with respect to d-line, by way of the amount of displacement (unit: mm) from the paraxial image plane in the direction of optical axis AX, and the vertical axis indicates the image height (IMG HT, unit: mm). In the distortion aberration diagrams, the horizontal axis indicates the distortion with respect to d-line (unit: %), and the vertical axis indicates the image height (IMG HT, unit: mm). It is to be noted that the maximum value of the image height IMG HT, i.e., the maximum image height y′max, corresponds to half the diagonal length of the photoreceiving surface SS of the image sensor SR, i.e., the diagonal image height.
Example 1










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
52.594
2.000
1.91082
35.25


 2
38.917
8.000
1.48749
70.44


 3
3987.708
variable


 4
114.892
1.800
1.83481
42.72


 5
24.059
8.256


0.581


 6
30.650
5.920
1.75211
25.05


 7
−239.193
1.500
1.90366
31.31


 8
66.130
variable


 9 (stop)
infinity
1.500


10
55.226
2.684
1.49700
81.61


11
−73.572
0.500


0.035


12
28.604
2.398
1.48749
70.44


13
90.512
5.675


0.400


14
−38.120
1.200
1.75520
27.53


15
39.367
6.496


0.457


16
−129.595
2.319
1.83481
42.72


17
−33.266
0.500


0.035


18
56.051
2.822
1.49700
81.61


19
−52.149
variable


20
−56.079
2.559
1.59270
35.45


21
−25.922
4.884


0.344


22
−21.437
1.000
1.69680
55.46


23
175.162
variable


image
infinity










Various data


zoom ratio 2.34













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
56.291
82.189
131.888



Fno.
3.600
5.000
5.700



ω
14.158
9.802
6.145



y′max
14.200
14.200
14.200



TL
126.570
147.320
171.425



BF
19.998
29.428
45.204



d3
11.368
34.676
58.494



d8
17.164
10.996
3.714



d19
16.028
10.208
2.000



d23
19.998
29.428
45.204











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
153.340



2 (4-8)
−68.640



 3 (9-19)
38.128



 4 (20-23)
−45.045










Example 2










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
54.338
0.800
1.91082
35.25


 2
41.692
6.141
1.48749
70.44


 3
326.381
variable


 4
76.160
8.000
1.83481
42.72


 5
23.754
6.290


0.443


 6
24.330
5.021
1.71736
29.50


 7
−46.443
0.750
1.91082
35.25


 8
44.274
variable


 9 (stop)
infinity
0.500


10
51.945
2.860
1.61800
63.39


11
−57.434
0.500


0.035


12
24.363
2.915
1.49700
81.61


13
1218.203
2.805


0.198


14
−35.047
3.000
1.80610
33.27


15
22.929
0.500


0.035


16
20.232
2.065
1.75211
25.05


17
23.858
4.414


0.311


18
280.602
2.432
1.56883
56.04


19
−33.764
0.500


0.035


20
111.142
2.710
1.49700
81.61


21
−29.808
variable


22
−31.037
1.500
1.84666
23.78


23
−25.072
8.535


0.601


24
−20.378
1.500
1.69680
55.46


25
163.742
variable


image
infinity










Various data


zoom ratio 2.35













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
56.220
81.350
131.864



Fno.
3.600
5.000
5.700



ω
14.175
9.901
6.146



y′max
14.200
14.200
14.200



TL
126.554
146.014
171.395



BF
18.274
24.437
35.429



d3
12.534
37.460
66.355



d8
22.609
13.615
3.874



d21
9.400
6.766
2.000



d25
18.274
24.437
35.429











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
190.927



2 (4-8)
−60.371



 3 (9-21)
33.463



 4 (22-25)
−33.575










Example 3










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
81.789
0.800
1.91082
35.25


 2
54.987
5.249
1.59282
68.62


 3
1823.892
variable


 4
67.524
4.000
1.88100
40.14


 5
24.159
5.572


0.392


 6
25.059
6.296
1.71736
29.50


 7
−47.307
0.800
1.91082
35.25


 8
49.645
variable


 9 (stop)
infinity
0.500


0.035


10
40.953
2.799
1.61800
63.39


11
−93.443
0.500


0.035


12
23.973
2.886
1.49700
81.61


13
484.941
2.843


0.200


14
−34.451
1.000
1.91082
35.25


15
24.535
0.500


0.035


16
19.593
3.000
1.59270
35.45


17
22.979
3.627


0.255


18
89.392
2.995
1.56883
56.04


19
−26.384
0.500


0.035


20
80.806
2.594
1.49700
81.61


21
−38.634
variable


22
−47.419
2.000
1.84666
23.78


23
−30.030
7.964


0.561


24
−20.001
1.500
1.80420
46.50


25
83.863
variable


image
infinity










Various data


zoom ratio 2.38













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
55.292
81.144
131.839



Fno.
3.600
5.000
5.700



ω
14.403
9.926
6.147



y′max
14.200
14.200
14.200



TL
126.573
148.861
171.374



BF
18.673
24.288
34.650



d3
15.082
43.710
71.894



d8
25.843
16.261
4.103



d21
9.049
6.677
2.802



d25
18.673
24.288
34.650











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
197.538



2 (4-8)
−67.386



 3 (9-21)
32.684



 4 (22-25)
−27.955










Example 4










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
86.267
0.800
1.91082
35.25


 2
57.555
5.943
1.59282
68.62


 3
3533.975
variable


 4
101.769
2.864
1.88100
40.14


 5
25.667
3.445


0.243


 6
26.780
5.906
1.71736
29.50


 7
−47.864
0.800
1.91082
35.25


 8
70.765
variable


 9 (stop)
infinity
0.500


0.035


10
41.891
2.767
1.61800
63.39


11
−112.549
0.500


0.035


12
24.470
2.936
1.49700
81.61


13
259.464
2.913


0.205


14
−41.000
2.211
1.91082
35.25


15
29.191
0.500


0.035


16
22.454
3.000
1.59270
35.45


17
24.912
3.262


0.230


18
411.011
3.010
1.56883
56.04


19
−28.246
0.500


0.035


20
49.984
3.280
1.49700
81.61


21
−44.137
variable


22
−47.018
2.111
1.84666
23.78


23
−28.709
6.953


0.490


24
−19.799
1.879
1.80420
46.50


25
80.619
variable


image
infinity










Various data


zoom ratio 2.91













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
45.258
81.615
131.828



Fno.
3.600
5.000
5.700



ω
17.419
9.870
6.148



y′max
14.200
14.200
14.200



TL
126.607
157.909
171.372



BF
18.001
24.120
34.873



d3
2.000
50.168
73.242



d8
41.457
20.803
3.686



d21
9.067
6.737
3.491



d25
18.001
24.120
34.873











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
204.346



2 (4-8)
−69.389



3 (9-21)
33.303



4 (22-25)
−28.121










Example 5










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
78.094
1.443
1.91082
35.25


 2
53.711
5.722
1.59282
68.62


 3
482.027
variable


 4
72.908
8.000
1.88100
40.14


 5
28.331
6.600


0.465


 6
29.223
4.454
1.71736
29.50


 7
−68.017
0.850
1.91082
35.25


 8
54.825
variable


 9 (stop)
infinity
0.500


10
41.155
3.050
1.61800
63.39


11
−82.487
0.500


0.035


12
24.926
2.843
1.49700
81.61


13
121.090
3.437


0.242


14
−46.297
3.000
1.91082
35.25


15
25.663
0.500


0.035


16
20.843
3.000
1.59270
35.45


17
23.850
4.548


0.320


18
2108.708
2.685
1.56883
56.04


19
−33.791
0.500


0.035


20
63.273
3.287
1.49700
81.61


21
−35.863
variable


22
−54.512
2.075
1.84666
23.78


23
−32.244
7.519


0.530


24
−22.097
1.286
1.80420
46.50


25
89.199
variable


image
infinity










Various data


zoom ratio 2.34













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
56.291
82.194
131.858



Fno.
3.600
5.000
5.700



ω
14.158
9.802
6.147



y′max
14.200
14.200
14.200



TL
131.566
150.445
171.391



BF
18.335
24.455
35.471



d3
2.000
32.478
64.411



d8
36.033
21.125
3.710



d21
9.400
6.589
2.000



d25
18.335
24.455
35.471











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
217.327



2 (4-8)
−86.804



3 (9-21)
37.578



4 (22-25)
−31.903










Example 6










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity





 1
87.114
2.000
1.90366
31.31



 2
58.247
7.955
1.48749
70.44



 3
−631.679 
0.500


0.035


 4
54.073
3.911
1.49700
81.61



 5
78.305
variable





 6
73.423
2.000
1.91082
35.25



 7
23.155
8.942


0.630


 8
27.644
6.396
1.75211
25.05



 9
−109.054
2.057


0.145


10
−84.718
1.500
1.90366
31.31



11
49.046
variable





12
infinity
1.000





(stop)







13
34.924
3.293
1.65844
50.85



14
−112.002
7.423


0.523


15
−26.188
1.500
1.75211
25.05



16
54.970
2.719


0.191


17
−161.997
2.967
1.88100
40.14



18
−29.542
0.500


0.035


19
46.941
3.444
1.48749
70.44



20
−48.949
variable





21
−71.577
2.259
1.84666
23.78



22
−30.446
4.243


0.299


23
−24.432
1.000
1.91082
35.25



24
infinity
variable





image
infinity










Various data


zoom ratio 2.66











Wide Angle (W)
Middle (M) 
Telephoto(T)





Fl
50.191
82.201
133.658


Fno.
3.600
5.000
5.700


ω
15.797
9.801
6.064


y′max
14.200
14.200
14.200


TL
126.686
149.291 
171.406


BF
20.104
31.997 
47.573


d5
2.000
29.277 
52.923


d11
20.257
11.050
3.293


d20
18.718
11.360
2.010


d24
20.104
31.997
47.573










Zoom lens group data








Group (Surface) 
Focal Distance





1 (1-5) 
142.286


2 (6-11) 
−53.222


3 (12-20)
36.030


4 (21-24)
−53.066









Example 7










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
112.364
2.000
1.90366
31.31


 2
68.521
6.960
1.48749
70.44


 3
−396.071
0.500


0.035


 4
57.744
4.049
1.48749
70.44


 5
95.514
variable


 6
133.121
2.958
1.75211
25.05


 7
−259.882
3.671


0.259


 8
−150.203
2.000
1.91082
35.25


 9
22.922
3.823


0.269


10
26.727
3.075
1.84666
23.78


11
53.574
variable


12 (stop)
infinity
1.000


0.070


13
35.433
3.075
1.74400
44.72


14
−262.568
9.272


0.653


15
−26.498
1.500
1.75211
25.05


16
50.961
2.736


0.193


17
−262.356
4.000
1.83481
42.72


18
−28.864
0.500


0.035


19
46.137
3.665
1.48749
70.44


20
−51.405
variable


21
−90.946
3.430
1.80518
25.46


22
−27.819
2.617


0.184


23
−23.855
2.000
1.91082
35.25


24
2642.274
variable


image
infinity










Various data


zoom ratio 2.67













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
50.066
82.212
133.704



Fno.
3.600
5.000
5.700



ω
15.835
9.800
6.062



y′max
14.200
14.200
14.200



TL
126.633
150.628
171.401



BF
20.266
27.657
38.954



d5
2.377
36.573
65.310



d11
22.685
11.093
2.308



d20
18.475
12.475
2.000



d24
20.266
27.657
38.954











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-5)
150.106



2 (6-11)
−55.563



3 (12-20)
36.748



4 (21-24)
−60.500










Example 8










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
58.099
3.000
1.90366
31.31


 2
44.172
5.676
1.48749
70.44


 3
419.930
variable


 4
167.066
2.880
1.83481
42.72


 5
24.848
3.573


0.252


 6
24.577
5.884
1.71736
29.50


 7
−30.391
0.800
1.91082
35.25


 8
58.724
variable


 9 (stop)
infinity
0.500


0.035


10
50.466
3.073
1.61800
63.39


11
−44.801
0.500


0.035


12
21.456
2.951
1.49700
81.61


13
179.022
2.949


0.208


14
−33.660
1.000
1.80610
33.27


15
17.859
0.500


0.035


16
17.279
2.538
1.75211
25.05


17
22.223
2.847


0.200


18
95.144
2.693
1.56883
56.04


19
−29.863
4.544


0.320


20
−224.787
2.632
1.49700
81.61


21
−23.612
variable


22
−32.541
1.500
1.84666
23.78


23
−25.718
7.867


0.554


24
−20.162
1.500
1.56883
56.04


25
69.014
variable


image
infinity










Various data


zoom ratio 2.45













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
53.735
81.043
131.835



Fno.
3.600
5.000
5.700



ω
14.803
9.938
6.148



y′max
14.200
14.200
14.200



TL
126.597
145.420
171.460



BF
18.495
24.705
35.854



d3
18.186
42.849
70.285



d8
21.875
11.712
3.657



d21
8.634
6.747
2.257



d25
18.495
24.705
35.854











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
190.159



2 (4-8)
−49.764



3 (9-21)
32.942



4 (22-25)
−36.228










Example 9










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
60.186
3.000
1.90366
31.31


 2
45.423
7.610
1.48749
70.44


 3
390.006
variable


 4
157.714
2.261
1.83481
42.72


 5
22.136
2.130


0.150


 6
23.154
6.870
1.71736
29.50


 7
−41.845
0.800
1.90366
31.31


 8
83.087
variable


 9 (stop)
infinity
0.500


0.035


10
38.674
2.901
1.61800
63.39


11
−85.684
0.500


0.035


12
26.542
2.849
1.49700
81.61


13
−909.204
2.732


0.192


14
−35.446
1.000
1.80610
33.27


15
21.657
0.500


0.035


16
21.149
4.748
1.75211
25.05


17
28.777
2.747


0.193


18
228.781
2.390
1.56883
56.04


19
−35.301
0.500


0.035


20
114.574
2.662
1.48749
70.44


21
−29.803
variable


22
−26.050
1.500
1.84666
23.78


23
−21.677
7.589


0.534


24
−17.518
1.500
1.56883
56.04


25
90.196
variable


image
infinity










Various data


zoom ratio 2.45













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
53.749
80.792
131.803



Fno.
3.600
5.000
5.700



ω
14.799
9.968
6.149



y′max
14.200
14.200
14.200



TL
126.543
147.814
171.306



BF
18.246
24.330
35.306



d3
13.687
43.272
72.656



d8
28.118
16.128
3.519



d21
9.201
6.794
2.535



d25
18.246
24.330
35.306











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
204.604



2 (4-8)
−64.420



3 (9-21)
33.036



4 (22-25)
−33.196










Example 10










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
57.374
2.398
1.90366
31.31


 2
43.949
5.769
1.48749
70.44


 3
442.074
variable


 4
134.904
1.800
1.83481
42.72


 5
23.544
3.776


0.266


 6
23.105
6.140
1.71736
29.50


 7
−28.716
0.800
1.91082
35.25


 8
50.818
variable


 9 (stop)
infinity
0.500


0.035


10
39.963
3.303
1.61800
63.39


11
−43.642
0.500


0.035


12
23.464
2.901
1.49700
81.61


13
551.601
2.889


0.203


14
−30.458
1.000
1.80610
33.27


15
17.314
0.692


0.049


16
16.985
2.977
1.75211
25.05


17
21.289
3.038


0.214


18
109.585
2.584
1.56883
56.04


19
−31.368
4.487


0.316


20
−412.603
2.774
1.49700
81.61


21
−22.103
variable


22
−31.806
1.500
1.84666
23.78


23
−25.401
8.180


0.576


24
−20.331
1.500
1.56883
56.04


25
72.603
variable


image
infinity










Various data


zoom ratio 2.45













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
53.721
81.141
131.801



Fno.
3.600
5.000
5.700



ω
14.806
9.926
6.149



y′max
14.200
14.200
14.200



TL
126.580
145.505
171.466



BF
18.587
24.751
35.920



d3
19.555
43.541
70.070



d8
20.427
10.959
3.773



d21
8.506
6.748
2.197



d25
18.587
24.751
35.920











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
184.654



2 (4-8)
−46.380



3 (9-21)
32.983



4 (22-25)
−36.869










Example 11










Unit: mm







Surface data












i
r
d
nd
vd
t/y′max





object
infinity
infinity


 1
59.751
3.000
1.90366
31.31


 2
45.505
5.574
1.48749
70.44


 3
421.746
variable


 4
141.932
4.000
1.83481
42.72


 5
25.452
4.167


0.293


 6
25.346
6.015
1.71736
29.50


 7
−33.196
0.800
1.91082
35.25


 8
56.651
variable


 9 (stop)
infinity
0.500


0.035


10
62.503
2.764
1.58913
61.25


11
−55.625
0.500


0.035


12
22.046
3.835
1.49700
81.61


13
−249.261
3.173


0.223


14
−40.392
2.234
1.80610
33.27


15
32.072
3.000
1.75211
25.05


16
28.727
5.483


0.386


17
−235.712
2.261
1.56883
56.04


18
−32.505
0.500


0.035


19
61.766
2.660
1.48749
70.44


20
−39.873
variable


21
−29.703
1.500
1.84666
23.78


22
−23.565
7.206


0.507


23
−18.879
1.171
1.56883
56.04


24
86.167
variable


image
infinity










Various data


zoom ratio 2.45













Wide Angle (W)
Middle (M)
Telephoto (T)







Fl
53.745
80.992
131.885



Fno.
3.600
5.000
5.700



ω
14.800
9.944
6.145



y′max
14.200
14.200
14.200



TL
126.585
144.753
171.488



BF
18.586
24.800
35.979



d3
16.816
41.712
70.486



d8
22.273
11.155
2.435



d20
8.568
6.744
2.246



d24
18.586
24.800
35.979











Zoom lens group data










Group (Surface)
Focal Distance







1 (1-3)
196.288



2 (4-8)
−52.255



3 (9-20)
33.012



4 (21-24)
−36.708






















TABLE 1





Corresponding







value of


conditional
(1)
(2)
(3)
(4)
(5)


equation
f2/f1
f2/y′max
f1/y′max
f3n/f3
f2n/f2







Example 1
−0.45
−4.83
10.80
−0.67
0.54


Example 2
−0.32
−4.25
13.44
−0.55
0.74


Example 3
−0.34
−4.75
13.91
−0.50
0.66


Example 4
−0.34
−4.88
14.39
−0.57
0.57


Example 5
−0.40
−6.11
15.31
−0.50
0.66


Example 6
−0.37
−3.75
10.02
−0.65
—


Example 7
−0.37
−3.91
10.57
−0.63
—


Example 8
−0.26
−3.50
13.39
−0.50
0.71


Example 9
−0.31
−4.53
14.41
−0.58
0.48


Example 10
−0.25
−3.26
13.00
−0.46
0.74


Example 11
−0.27
−3.68
13.82
−0.61
0.72


















TABLE 2









Focal distance













Gr2A
Gr2B
Gr3A
Gr3B
Gr3C



(Negative)
(Positive)
(Positive)
(Negative)
(Positive)
















Example 1
−36.78
85.59
36.63
−25.48
27.22


Example 2
−44.44
140.99
23.92
−18.45
25.64


Example 3
−44.63
114.38
24.63
−16.40
22.01


Example 4
−39.66
86.50
26.32
−18.99
24.03


Example 5
−57.42
153.97
26.43
−18.63
26.42


Example 6
—
—
40.80
−23.40
22.68


Example 7
—
—
42.15
−22.99
22.21


Example 8
−35.29
103.53
21.91
−16.47
24.69


Example 9
−31.08
56.56
24.13
−19.14
26.17


Example 10
−34.42
107.28
20.57
−15.21
24.31


Example 11
−37.74
114.55
22.98
−20.21
28.83









According to the above embodiments of the present invention, a zoom lens and an imaging optical apparatus are achieved, which zoom lens is reduced in size even with a viewing angle (2ω) at a telephoto end of less than 15° and has higher produceability while being operable with favorable optical performance in the entire zoom range. The zoom lens or the imaging optical apparatus is applicable to a digital device, e.g., a digital camera, thus adding a high-performance image input function to the digital device in a compact manner.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by terms of the appended claims.

## Claims

1. A zoom lens comprising a plurality of lens groups arranged at inter-group spacings along an optical axis between an object side and an image side, the zoom lens being configured such that magnification is varied by change of the inter-group spacings to be caused by movement of the lens groups along the optical axis,
the lens groups comprising, in an order from the object side, a first group of positive power, a second group of negative power, a third group of positive power, and a fourth group of negative power, wherein
for varying magnification from a wide-angle end to a telephoto end, the first group is configured to be moved toward the object side, the second group is configured to be moved toward the image side, the third group is configured to be moved toward the object side, and the fourth group is configured to be moved toward the object side, and
the following conditional equations (1) to (3) are satisfied:


−0.63<f2/f1<−0.25  (1);



−10<f2/y′max<−3  (2); and



6<f1/y′max<20  (3),



where
f1 represents the focal distance of the first group,
f2 represents the focal distance of the second group, and
y′max represents the maximum image height; and
where an inter-lens group spacing is an inter-lens spacing t satisfying a conditional equation (0): 0.14<t/y′max of inter-lens spacings t in the third group, the third group comprises, from the order from the object side, a positive lens group, a negative lens group, and a positive lens group, and the following conditional equation (4) is satisfied:


−0.7 <f3n/f3 <−0.4  (4),



where
f3 represents the focal distance of the third group, and
f3 n represents the focal distance of the negative lens group in the third group,
the positive lens group on the object side in the third group comprises lenses from, calculation of t/y′max being performed in an order from a lens having the strongest negative power in the third group toward the object side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14 up to a lens closest to the object side in the third group,
the negative lens group in the third group includes a negative lens having the strongest power in the third group, and comprises lenses from a lens that is next by one to the image side from, calculation of t/y′max being performed in the order from the negative lens toward the object side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14 up to a lens that is next by one to the object side from, calculation of t/y′max being performed in an order from the negative lens toward the image side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14, and
the positive lens group on the image side in the third group comprises lenses from, calculation of t/y′max being performed in the order from the lens having the strongest negative power in the third group toward the image side, a first lens having an inter-lens spacing t with an adjacent lens of or larger than t/y′max=0.14 up to a lens closest to the image side in the third group.

2. The zoom lens according to claim 1, wherein, for focusing from the infinity to a proximate object, the fourth group is configured to be moved toward the image side along the optical axis.

3. The zoom lens according to claim 1, wherein the fourth group has at least a positive lens and a negative lens.

4. The zoom lens according to claim 1, wherein any one of the positive lens groups in the third group has at least two positive lenses.

5. An imaging optical apparatus comprising:
the zoom lens of claim 1; and
an image sensor having a photoreceiving surface, the image sensor being configured to convert an optical image formed on the photoreceiving surface into electrical signals, wherein
the zoom lens is arranged such that an optical image of a photographing subject is adapted to be formed on the photoreceiving surface of the image sensor.

6. A digital device comprising the imaging optical apparatus of claim 5, the imaging optical apparatus providing at least one function of still image photographing or moving picture shooting of a photographing subject.

7. A zoom lens comprising a plurality of lens groups arranged at inter-group spacings along an optical axis between an object side and an image side, the zoom lens being configured such that magnification is varied by change of the inter-group spacings to be caused by movement of the lens groups along the optical axis,
the lens groups comprising, in an order from the object side, a first group of positive power, a second group of negative power, a third group of positive power, and a fourth group of negative power, wherein
for varying magnification from a wide-angle end to a telephoto end, the first group is configured to be moved toward the object side, the second group is configured to be moved toward the image side, the third group is configured to be moved toward the object side, and the fourth group is configured to be moved toward the object side, and
the following conditional equations (1) to (3) are satisfied:


−0.63<f2/f1<−0.25  (1);



−10<f2/y′max<−3  (2); and



6<f1/y′max<20  (3),



where
f1 represents the focal distance of the first group,
f2 represents the focal distance of the second group, and
y′max represents the maximum image height; and
where an inter-group spacing is an inter-lens spacing t satisfying a conditional equation (0): 0.14<t/y′max of inter-lens spacings t in the second group, the second group comprises, from the order from the object side, a negative group and a positive group, the positive group having at least one cemented lens.

8. The zoom lens according to claim 7, wherein the negative group of the second group comprises a negative meniscus lens having a convex surface as a surface on the object side, and the positive group of the second group comprises a lens having a convex surface as a surface on the object side and a lens having a concave surface as a surface on the image side.

9. The zoom lens according to claim 7, wherein, for focusing from the infinity to a proximate object, the fourth group is configured to be moved toward the image side along the optical axis.

10. The zoom lens according to claim 7, wherein the fourth group has at least a positive lens and a negative lens.

11. An imaging optical apparatus comprising:
the zoom lens of claim 7; and
an image sensor having a photoreceiving surface, the image sensor being configured to convert an optical image formed on the photoreceiving surface into electrical signals, wherein
the zoom lens is arranged such that an optical image of a photographing subject is adapted to be formed on the photoreceiving surface of the image sensor.

12. A digital device comprising the imaging optical apparatus of claim 11, the imaging optical apparatus providing at least one function of still image photographing or moving picture shooting of a photographing subject.