# Patent

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

## Abstract

A positive-negative-positive-positive-positive zoom lens changes magnification by moving each of a first group to a fourth group so as to alter the interval between each group. The third group comprises first and second lens components, at least one of which has an aspheric surface, and the first lens component is a positive-negative-positive cemented lens in sequence from the object side. The zoom lens satisfies the conditional expressions, 7<β2t/β2w<10, 5<β3t/β3w<12, 0.7<(β2t/β2w)/(β3t/β3w)<1.65) (where: β2t is the lateral magnification of the second group at the telephoto end; β2w is the lateral magnification of the second group at the wide end; β3t is the lateral magnification of the third group at the telephoto end; and β3w is the lateral magnification of the third group at the wide end).

## Background
This is the U.S. national stage of application No. PCT/JP2012/050663, filed on 16 Jan. 2012. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application Nos. 2011-011794, filed 24 Jan. 2011, and 2011-011807, filed 24 Jan. 2011, the disclosures of both of which are also incorporated herein by reference.
TECHNICAL FIELD
The invention relates to a zoom lens system, an imaging optical device, and a digital apparatus. More specifically, the present invention relates to a high variable power zoom lens system suitable for use in digital apparatuses equipped with an image input function, such as a digital camera that captures an image of a subject by using an image sensing device (for example, a solid-state image sensing device such as a CCD (charge coupled device) type image sensor or a CMOS (complementary metal-oxide semiconductor) type image sensor), an imaging optical device that outputs the image of the subject, which is captured by using the zoom lens system and the image sensing device, in the form of an electric signal, and a digital apparatus equipped with the image input function, such as a digital camera, incorporating the imaging optical device.
BACKGROUND ART
In recent years, along with the widespread use of personal computers, digital cameras capable of easily capturing images have been coming into widespread use. Along with it, there has been demand for more compact digital cameras, and this has naturally led to demand for more compact image sensing optical systems. On the other hand, a year-by-year increasing trend in number of pixels included in image sensing devices has led to demand for image sensing optical systems to have a high optical performance suitable for the increased number of pixels included in image sensing devices and demand for image sensing optical systems to be easy to fabricate to deal with a shorter product life cycle.
Further, various high variable power zoom lens systems having a zoom ratio of over 10× have been proposed as image sensing optical systems for use in video cameras and digital cameras. To meet the demand for more compact and thinner cameras, progress has been being made in size reduction and slimming down of even high variable power zoom lens systems having a zoom ratio of over 10×, by using a technique such as sliding of a lens group, and there is also an expectation for more compact and thinner high variable power zoom lens systems having a zoom ratio of over 20×. To meet these demands, zoom lens systems of various types have been conventionally proposed. For example, Patent Literature 1 listed below proposes a zoom lens system having a zoom ratio of approximately 18× including five lens groups of positive, negative, positive, positive, and positive lens groups, Patent Literature 2 listed below proposes a zoom lens system having a zoom ratio of approximately 20× including four lens groups of positive, negative, positive, and positive lens groups, and Patent Literature 3 listed below proposes a zoom lens system having a zoom ratio of approximately 40× including four lens groups of positive, negative, positive, and positive lens groups.
CITATION LIST
Patent Literature
Patent Literature 1: JP-A-2007-3554
Patent Literature 2: JP-A-2009-282439
Patent Literature 3: JP-A-2008-158062
SUMMARY OF INVENTION
Technical Problem
To achieve size reduction and slimming down of high variable power zoom lens systems, it is necessary to reduce a lens-system moving amount in zooming and/or a lens-system thickness in an optical axis direction. With the zoom lens systems proposed in Patent Literatures 1 and 2, however, each having a large optical total length and a large thickness in the optical axis direction, neither size reduction nor slimming down can be effectively achieved.
For zoom lens systems for digital cameras, angles of view (2ω) thereof have been being made wider to be as wide as about 75° to 80° at a wide angle side. In super high variable power zoom lens systems, however, since demand for higher variable power and demand for a wider angle of view are contradictory in some regards, no sufficiently effective effort has been made to achieve a wider angle of view. For example, the zoom lens systems proposed in Patent Literatures 1 and 2 each have a wide-angle-end angle of view of about 75° to 80°, and a zoom ratio of slightly smaller than 20×, and thus, neither the angle of view nor the variable power is sufficiently increased. The zoom lens system proposed in Patent Literature 3 has a zoom ratio of 40×, but its angle of view at the wide angle end is slightly smaller than 80°, which is not as wide as is desired.
The invention has been made in view of the inconveniences discussed above, and an object of the invention is to provide a high-performance zoom lens system that has high variable power, with a zoom ratio of over 18×, and yet is compact and thin, and an imaging optical device and a digital apparatus that incorporate such a zoom lens system. Another object of the invention is to provide a high-performance zoom lens system that has super high variable power, with a zoom ratio of over 30×, and yet has an angle of view at the wide angle side that is as wide as 88° to 90°, and an imaging optical device and a digital apparatus that incorporate such a zoom lens system.
Solution to Problem
To achieve the above objects, according to a first aspect of the invention, a zoom lens system includes, sequentially from an object side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, and a fourth lens group having a positive optical power. The zoom lens system achieves variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups. The third lens group includes two lens elements at least one of which has an aspherical surface. An object-side lens element of the third lens group is a cemented lens element including, sequentially from the object side, a positive lens element, a negative lens element, and a positive lens element.
According to a second aspect of the invention, in the zoom lens system according to the first aspect of the invention described above, the third lens group satisfies the following conditional formula (A1):

0.5<f3/√(fw×ft)<0.9  (A1)

where
f3 represents a focal length of the third lens group,
fw represents a focal length of a whole system at a wide angle end, and
ft represents a focal length of the whole system at a telephoto end.
According to a third aspect of the invention, in the zoom lens system according to the first or second aspect of the invention described above, the third lens group satisfies the following conditional formula (A2):

0.3<CR32/f3<0.65  (A2)

where
CR32 represents a radius of curvature of an image-side surface of the negative lens element included in the cemented lens element, and
f3 represents the focal length of the third lens group.
According to a fourth aspect of the invention, in the zoom lens system according to any one of the first to third aspects of the invention described above, of the positive lens elements included in the cemented lens element, one that is disposed closest to the object side has an aspherical surface, and a radius of curvature of the aspherical surface is larger than a reference radius of curvature by a larger value farther away from an optical axis.
According to a fifth aspect of the invention, in the zoom lens system according to any one of the first to fourth aspects of the invention described above, the first lens group includes, sequentially from the object side, a cemented lens element including a negative lens element and a positive lens element, and a positive single lens element, and the first lens group satisfies the following conditional formulas (A3) and (A4):

1.86<Nd11<2  (A3)

30<νd11<40  (A4)

where
Nd11 represents a refractive index of the negative lens element included in the first lens group with respect to a d-line, and
νd11 represents an Abbe number of the negative lens element included in the first lens group with respect to the d-line.
According to a sixth aspect of the invention, in the zoom lens system according to any one of the first to fifth aspects of the invention described above, the following conditional formula (A5) is satisfied:

0.3<β4t/β4w<0.7  (A5)

where
β4t represents a lateral magnification of the fourth lens group at the telephoto end, and
β4w represents a lateral magnification of the fourth lens group at the wide angle end.
According to a seventh aspect of the invention, in the zoom lens system according to any one of the first to sixth aspects of the invention described above, the following conditional formula (A6) is satisfied:

−10<{(ywmax−Ymax)/Ymax}×100<−25  (A6)

where
ywmax represents a maximum real image height at the wide angle end, and
Ymax represents a maximum ideal image height.
According to an eighth aspect of the invention, a zoom lens system includes, sequentially from an object side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, and a fourth lens group having a positive optical power. The zoom lens system achieves variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups, and the zoom lens system satisfies the following conditional formulas (B1) to (B3):

7<β2t/β2w<10  (B1)

5<β3t/β3w<12  (B2)

0.7<(β2t/β2w)/(β3t/β3w)<1.65  (B3)

where
β2t represents a lateral magnification of the second lens group at a telephoto end,
β2w represents a lateral magnification of the second lens group at a wide angle end,
β3t represents a lateral magnification of the third lens group at the telephoto end, and
β3w represents a lateral magnification of the third lens group at the wide angle end.
According to a ninth aspect of the invention, in the zoom lens system according to the eighth aspect of the invention described above, the first lens group includes, sequentially from the object side, a cemented lens element including a negative lens element and a positive lens element, and a positive single lens element, and the following conditional formulas (B4) and (B5) are satisfied:

1.86<Nd11<2  (B4)

30<νd11<40  (B5)

where
Nd11 represents a refractive index of the negative lens element included in the first lens group with respect to a d-line, and
νd11 represents an Abbe number of the negative lens element included in the first lens group with respect to the d-line.
According to a tenth aspect of the invention, in the zoom lens system according to the eighth or ninth aspect of the invention described above, the following conditional formula (B6) is satisfied:

0.3<β4t/β4w<0.7  (B6)

where
β4t represents a lateral magnification of the fourth lens group at the telephoto end, and
β4w represents a lateral magnification of the fourth lens group at the wide angle end.
According to an eleventh aspect of the invention, in the zoom lens system according to any one of the eighth to tenth aspects of the invention described above, the following conditional formula (B7) is satisfied:

−10<{(ywmax−Ymax)/Ymax}×100<−25  (B7)

where
ywmax represents a maximum real image height at the wide angle end, and
Ymax represents a maximum ideal image height.
According to a twelfth aspect of the invention, in the zoom lens system according to any one of the eighth to eleventh aspects of the invention described above, in the third lens group, a surface that is located closest to the object side is formed of an aspherical surface.
According to a thirteenth aspect of the invention, in the zoom lens system according to any one of the eighth to twelfth aspects of the invention described above, the second lens group includes, sequentially from the object side, a negative meniscus lens element having a convex surface facing toward the object side, a cemented lens element including a biconcave negative lens element and a biconvex positive lens element, and a negative meniscus lens element having a convex surface facing toward an image side.
According to a fourteenth aspect of the invention, in the zoom lens system according to any one of the eighth to thirteenth aspects of the invention described above, the following conditional formula (B8) is satisfied:

−0.3<m3/TLt<−0.2  (B8)

where
m3 represents an absolute amount of movement of the third lens group in zooming from the wide angle end to the telephoto end (a minus sign indicates movement to the object side), and
TLt represents an optical total length at the telephoto end.
According to a fifteenth aspect of the invention, in the zoom lens system according to any one of the eighth to fourteenth aspects of the invention described above, the following conditional formula (B9) is satisfied:

−0.25<m4/TLt<−0.1  (B9)

where
m4 represents an absolute amount of movement of the fourth lens group in zooming from the wide angle end to the telephoto end (a minus sign indicates movement to the object side), and
TLt represents the optical total length at the telephoto end.
According to a sixteenth aspect of the invention, an imaging optical device includes a zoom lens system of any one of the first to fifteenth aspects of the invention described above, and an image sensing device that converts an optical image formed on a light receiving surface into an electric signal. The zoom lens system is arranged such that an optical image of a subject is formed on the light receiving surface of the image sensing device.
According to a seventeenth aspect of the invention, a digital apparatus includes the imaging optical device of the sixteenth aspect of the invention described above so as to be additionally provided with at least one of a function of shooting a still image of the subject and a function of shooting a moving image of the subject.
According to an eighteenth aspect of the invention, the digital apparatus according to the seventeenth aspect of the invention described above is one of a digital camera, a surveillance camera, and a portable terminal unit equipped with an image input function.
Advantageous Effects of Invention
In the zoom lens system according to the invention, the third lens group includes two lens elements, and at least one of the two lens elements has an aspherical surface; an object-side one of the two lens elements in the third lens group is a cemented lens element including, sequentially from the object side, a positive lens element, a negative lens element, and a positive lens element. With this construction, it is possible to achieve size reduction, slimming down, and higher performance by reducing the lens movement amount in zooming and the thickness in an optical axis direction, while increasing the optical power to be exerted by the third lens group to obtain such a high variable power ratio that the zoom ratio is over 18×. Thus, it is possible to achieve an imaging optical device provided with a compact, high-performance zoom lens system of high variable power. And, by using the imaging optical device according to the invention in a digital apparatus such as a digital camera, it is possible to provide the digital apparatus additionally with a high-performance image input function in a compact manner.
The zoom lens system according to the invention, which is a zoom lens system including four lens groups which are, sequentially from the object side, positive, negative, positive, and positive lens groups, is constructed such that shares of responsibility assigned to the second and third lens groups for achieving variable power satisfy a predetermined condition, and this makes it possible to increase the angle of view at the wide angle side to be as wide as 88° to 90° and achieve high optical performance, while achieving such super high variable power that the zoom ratio is over 30×. Thus, it is possible to achieve an imaging optical device provided with a compact, high-performance zoom lens system having a wide angle of view and capable of achieving super high variable power. And, by using the imaging optical device according to the invention in a digital apparatus such as a digital camera, it is possible to provide the digital apparatus additionally with a high-performance image input function in a compact manner.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a lens construction diagram of a first embodiment (Example 1);
FIG. 2 is a lens construction diagram of a second embodiment (Example 2);
FIG. 3 is a lens construction diagram of a third embodiment (Example 3);
FIG. 4 is a lens construction diagram of a fourth embodiment (Example 4);
FIG. 5 is a lens construction diagram of a fifth embodiment (Example 5);
FIG. 6 is a lens construction diagram of a sixth embodiment (Example 6);
FIG. 7 is a lens construction diagram of a seventh embodiment (Example 7);
FIG. 8 is a lens construction diagram of an eighth embodiment (Example 8);
FIG. 9 is a lens construction diagram of a ninth embodiment (Example 9);
FIG. 10 is a lens construction diagram of a tenth embodiment (Example 10);
FIGS. 11A to 11I are aberration diagrams of Example 1;
FIGS. 12A to 12I are aberration diagrams of Example 2;
FIGS. 13A to 13I are aberration diagrams of Example 3;
FIGS. 14A to 14I are aberration diagrams of Example 4;
FIGS. 15A to 15I are aberration diagrams of Example 5;
FIGS. 16A to 16I are aberration diagrams of Example 6;
FIGS. 17A to 17I are aberration diagrams of Example 7;
FIGS. 18A to 18I are aberration diagrams of Example 8;
FIGS. 19A to 19I are aberration diagrams of Example 9;
FIGS. 20A to 20I are aberration diagrams of Example 10; and
FIG. 21 is a schematic diagram showing an example of an outline of the construction of a digital apparatus incorporating an imaging optical device.



DESCRIPTION OF EMBODIMENTS
Hereinafter, descriptions will be given of zoom lens systems, imaging optical devices, and digital apparatuses according to the invention, by classifying them into two types. A zoom lens system of a first type according to the invention includes, sequentially from the object side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, and a fourth lens group having a positive optical power. The zoom lens system achieves variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups. The third lens group includes two lens elements, at least one of which has an aspherical surface, and an object-side lens element of the third lens group is a cemented lens element including, sequentially from the object side, a positive lens element, a negative lens element, and a positive lens element (optical power is a quantity defined as a reciprocal of a focal length).
A compact but high variable power zoom lens system is achieved typically by enhancing the optical power of each lens group included in the zoom lens system, but here, there is adopted a construction that allows enhancement of the optical power particularly of the third lens group. In a conventional zoom type including four positive, negative, positive, and positive lens groups, a main share of responsibility for achieving variable power is assigned to the second lens group, and in a case of achieving high variable power as well, the optical power of the second lens group is enhanced to achieve compactness and high variable power. In contrast, in the zoom lens system according to the invention, high variable power is achieved by assigning to the third lens group, which conventionally does not bear relatively much responsibility for achieving variable power, a larger share of responsibility for achieving variable power. In this case, it can be expected that the enhanced optical power of the third lens group will lead to excessively strong sensitivity to errors, which will increase a spherical aberration error between lens blocks, making the zoom lens system difficult to produce. To prevent this inconvenience, the lens blocks having strong sensitivity to errors are cemented together so that production difficulty is reduced, and in regard to design, more freedom is given to curvature, to make it possible for the third lens group to perform preferable aberration correction by making use of high-order aberration generated at the cemented surfaces.
With this characteristic construction, it is possible to achieve a high-performance zoom lens system that, despite having high variable power, with a zoom ratio of over 18×, is made compact and thin by reducing the lens movement amount in zooming and the lens thickness in an optical axis direction, and an imaging optical device provided therewith. Furthermore, since the imaging optical device is made light weight and compact, by using the imaging optical device in a digital apparatus such as a digital camera or a portable information terminal unit, it is possible to provide the digital apparatus additionally with a high-performance image input function in a light-weight and compact manner. Thus, the characteristic construction contributes to, for example, reduction in size and cost of, and improvement in performance and functionality of, digital apparatuses. Hereinafter, descriptions will be given of conditions and the like for obtaining these advantages in a well-balanced manner, and for achieving higher optical performance, further compactness, and the like.
In view of achieving a high variable power zoom lens system that is compact and yet holds high optical performance, a zoom ratio of 18× to 38× is preferable. An attempt to obtain a high zoom ratio of approximately 18× to 38× usually makes it difficult to achieve size reduction and improvement in performance of zoom lens systems, but according to the above-described characteristic construction regarding the cemented lens element of the third lens group and the like, it is possible to obtain a high zoom ratio while achieving size reduction and improvement in performance, and so on. This makes it possible to achieve high variable power while achieving both compactness and high performance
It is preferable that the third lens group satisfy the following conditional formula (A1):

0.5<f3/√(fw×ft)<0.9  (A1)

where
f3 represents a focal length of the third lens group,
fw represents a focal length of a whole system at a wide angle end, and
ft represents a focal length of the whole system at a telephoto end.
The conditional formula (A1) defines a preferable focal length of the third lens group, and when the conditional formula (A1) is satisfied, the third lens group has a comparatively strong refractive power. If an upper limit of the conditional formula (A1) is exceeded, the focal length of the third lens group becomes too long, and thus the share of responsibility for achieving variable power assigned to the third lens group decreases, which is not desirable in view of achieving compactness. Besides, in order to effectively achieve size reduction despite the long focal length of the third lens group, it is necessary for the second lens group to bear a larger share of responsibility for achieving variable power. If the refractive power of the second lens group is increased to meet such a requirement, it might invite increase in astigmatism and in field curvature. On the other hand, if a lower limit of the conditional formula (A1) is fallen short of, the focal length of the third lens group becomes too short, and this makes it difficult to correct aberration, particularly spherical aberration, generated in the third lens group within the third lens group.
It is preferable that the third lens group satisfy the following conditional formula (A2):

0.3<CR32/f3<0.65  (A2)

where
CR32 represents a radius of curvature of an image-side surface of the negative lens element included in the cemented lens element, and
f3 represents the focal length of the third lens group.
The conditional formula (A2) relates to the negative lens element included in the cemented lens element in the third lens group, and the conditional formula (A2) defines a preferable radius of curvature of the image-side surface of the negative lens element. The image-side surface of the negative lens element has a curvature such that the surface faces toward the image side as a strongly concave surface, and by generating high-order aberration at the strongly concave surface that satisfies the conditional formula (A2), it is possible to perform preferable aberration correction within the third lens group in a preferable manner. This is particularly effective in correcting coma aberration. The amount of coma aberration tends to be larger where the conditional formula (A2) is not satisfied, and specifically, if a lower limit of the conditional formula (A2) is fallen short of, it becomes difficult to correct coma aberration, while it becomes difficult to correct astigmatism if an upper limit of the conditional formula (A2) is exceeded.
As already mentioned, the third lens group has a cemented lens element including positive, negative, and positive lens elements, and it is preferable that one of the positive lens elements that is disposed closest to the object side have an aspherical surface, and that the radius of curvature of the aspherical surface is larger than a reference radius of curvature by a larger value farther away from the optical axis. The third lens group has a strong positive refractive power, and the major positive refractive power is generated by the above-mentioned positive lens element that is disposed closest to the object side. In this construction, strong positive optical power causes a strong undercorrected spherical aberration to be generated, but such spherical aberration can be corrected by the aspherical surface whose radius of curvature is larger than the reference radius of curvature by a larger value farther away from the optical axis.
It is preferable that the first lens group include, sequentially from the object side, a cemented lens element including a negative lens element and a positive lens element, and a positive single lens element, and that the first lens group satisfy the following conditional formulas (A3) and (A4):

1.86<Nd11<2  (A3)

30<νd11<40  (A4)

where
Nd11 represents a refractive index of the negative lens element included in the first lens group with respect to a d-line, and
νd11 represents an Abbe number of the negative lens element included in the first lens group with respect to the d-line.
In a high variable power zoom lens system, correction of chromatic aberration at the telephoto side is difficult, and it is particularly necessary to reduce chromatic aberration generated in the first lens group. In particular, second spectrum increases, and thus, typically, a lens element having an anomalous dispersion characteristic is often used as a positive lens element of the first lens group to achieve the reduction. Also, the negative lens element needs to have a strong refractive power to achieve a compact zoom lens system, but a strong refractive power leads to a large curvature, allowing strong coma aberration and/or strong astigmatism to be generated. Thus, it is necessary that the negative lens element have a high refractive index so as not to invite increase in the curvature, but unfortunately, glass materials having a refractive index of over 1.85 are usually characterized by having an anomalous dispersion characteristic on the plus side, and thus, even if an anomalous dispersion lens element is used as a positive lens element, it is difficult to correct secondary spectrum.
By selecting a glass material that satisfies the conditional formulas (A3) and (A4), it is possible to select a glass material that has a low anomalous dispersion characteristic and a strong refractive power. If a lower limit of the conditional formula (A3) is fallen short of, the refractive power becomes too weak, and this leads to an undesirably large optical system. An attempt to maintain the optical power at the same level will lead to a large curvature, causing large spherical aberration that is difficult to correct. If an upper limit of the conditional formula (A3) is exceeded, the refractive power of the surface becomes strong, and in particular, sensitivity to manufacturing errors of aspherical waves becomes strong, making it disadvantageously difficult to produce the zoom lens system. If an upper limit of the conditional formula (A4) is exceeded, dispersion values become too large, and it becomes difficult to correct chromatic aberration. If a lower limit of the conditional formula (A4) is fallen short of, it means that a glass material having a high anomalous dispersion characteristic is selected, and thus it is difficult to correct chromatic aberration.
It is preferable that the present zoom lens system adopt one anomalous dispersion lens element as the positive lens element of the first lens group, so as to reduce secondary spectrum. In an area, to which the present optical system belongs, where an optical system at the telephoto end functions as a so-called super-telephoto lens system, correction of secondary spectrum is a problem to be dealt with, and in some cases, a plurality of anomalous dispersion lens elements are used, or, a lens element having a very high anomalous dispersion characteristic, such as a fluorite lens element, is used. The point of this correction is the correction of chromatic aberration on the negative lens element side, and selected as the negative lens element is one that is made of a glass material belonging to an area of small Abbe numbers. With a typically used optical glass material, which has a high positive anomalous dispersion, if it has a small Abbe number, the effect of the anomalous dispersion used in the positive lens element is cancelled, so that the secondary spectrum is corrected only insufficiently. Thus, it can be said to be preferable that the conditional formulas (A3) and (A4) be satisfied.
It is preferable that the following conditional formula (A5) be satisfied:

0.3<β4t/β4w<0.7  (A5)

where
β4t represents a lateral magnification of the fourth lens group at the telephoto end, and
β4w represents a lateral magnification of the fourth lens group at the wide angle end.
The conditional formula (A5) defines a preferable lateral magnification ratio of the fourth lens group between at the telephoto end and at the wide angle end, and the optical total length at the telephoto side is able to be effectively reduced by satisfying the conditional formula (A5). The present optical system, having the small optical total length at the telephoto side despite having a zoom ratio of over 18×, contributes to achieving a compact lens barrel and a compact camera. If simply the optical total length at the telephoto side is reduced, it leads to total increase in the optical power of each of the lens groups, which makes it difficult to correct aberration; in contrast, if the lateral magnification of the fourth lens group at the telephoto end is made comparatively small so as to satisfy the conditional formula (A5), it is possible to reduce the optical total length.
If an upper limit of the conditional formula (A5) is exceeded, a combined focal length of the first to third lens groups becomes short, which makes it difficult to correct aberration, above all, field curvature. If a lower limit of the conditional formula (A5) is fallen short of, the optical total length increases, which is not preferable from the viewpoint of achieving compactness. Furthermore, if the lower limit of the conditional formula (A5) is fallen short of, need arises to increase the refractive power of the second lens group, which may in turn increase astigmatism, and need arises to increase the refractive power of the third lens group, which may in turn increase spherical aberration.
It is preferable that the following conditional formula (A6) be satisfied:

−10<{(ywmax−Ymax)/Ymax}×100<−25  (A6)

where
ywmax represents a maximum real image height at the wide angle end, and
Ymax represents a maximum ideal image height.
The conditional formula (A6) defines a distortion ratio at the wide angle end.
Allowing distortion in the range of the conditional formula (A6) to be generated at the wide angle end is effective particularly to reduce an external diameter of the first lens group. The generated distortion is able to be corrected by electronic means such that the distortion ratio is reduced to a level that does not cause any trouble. If an upper limit of the conditional formula (A6) is exceeded, the distortion ratio becomes so large that it causes an excessively large interpolation error in correcting the distortion by using the electronic means, which unpreferably leads to degradation of performance. If the lower limit of the conditional formula (A6) is fallen short of, the ratio of the generated distortion is low, which leads to a larger external diameter of the first lens group, and as a result, the entire size of a camera incorporating the optical system becomes larger, which is not preferable in terms of compactness.
A construction where a stop is positioned on the object side of the third lens group in the zoom type including the positive, negative, positive, and positive lens groups is strongly asymmetric at the wide angle end, and this leads to generation of a strong negative distortion. The distortion is generated mainly in the second lens group, and it is to be corrected mainly in the first and third lens groups. By generating a correcting effect in a lens element of the third lens group that is located closest to the image, it is possible to correct the distortion in the third lens group, although not very much effectively, because the third lens group is located close to a stop surface. In such a construction, spherical aberration is generated, but by correcting the distortion to be within the range defined by the conditional formula (A6), it becomes possible to preferably correct the spherical aberration within the third lens group.
Next, a description will be given of a zoom lens system of a second type according to the invention. The zoom lens system of the second type according to the invention includes, sequentially from the object side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, and a fourth lens group having a positive optical power. The zoom lens system achieves variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups, and the zoom lens system satisfies the following conditional formulas (B1) to (B3) (optical power is an amount defined by the inverse of a focal length):

7<β2t/β2w<10  (B1)

5<β3t/β3w<12  (B2)

0.7<(β2t/β2w)/(β3t/β3w)<1.65  (B3)

where
β2t represents a lateral magnification of the second lens group at the telephoto end,
β2w represents a lateral magnification of the second lens group at the wide angle end,
β3t represents a lateral magnification of the third lens group at the telephoto end, and
β3w represents a lateral magnification of the third lens group at the wide angle end.
In high variable power zoom lens systems each including four positive, negative, positive, and positive lens groups, it is typical that the second lens group bears a main share of responsibility for achieving variable power while the third lens group is hardly, or only auxiliary, responsible for achieving variable power. Here, by assigning to the third lens group a large share of responsibility for exerting a variable-power function, it is possible to reduce variation in aberration occurring along with achievement of high variable power, and thus to achieve size reduction and improvement in performance.
The conditional formula (B1) defines a lateral magnification ratio of the second lens group between at the telephoto end and at the wide angle end. If an upper limit of the conditional formula (B1) is exceeded, the second lens group is forced to bear too much responsibility for achieving variable power, which makes it difficult to correct coma aberration generated in the second lens group. If a lower limit of the conditional formula (B1) is fallen short of, the third lens group is forced to bear too much responsibility for achieving variable power, which makes it difficult to correct spherical aberration generated in the third lens group.
The conditional formula (B2) defines a lateral magnification ratio of the third lens group between at the telephoto end and at the wide angle end. If an upper limit of the conditional formula (B2) is exceeded, the third lens group is forced to bear too much responsibility for achieving variable power, which makes it difficult to correct spherical aberration generated in the third lens group. If a lower limit of the conditional formula (B2) is fallen short of, the second lens group is forced to bear too much responsibility for achieving variable power, which makes it difficult to correct coma aberration generated in the second lens group.
The conditional formula (B3) defines a ratio between shares of responsibility for achieving variable power assigned to the second lens group and the third lens group. If an upper limit of the conditional formula (B3) is exceeded, the second lens group is forced to bear too much responsibility for achieving variable power, which makes it difficult to correct coma aberration generated in the second lens group. If a lower limit of the conditional formula (B3) is fallen short of, the third lens group is forced to bear too much responsibility for achieving variable power, which makes it difficult to correct spherical aberration generated in the third lens group.
According to the characteristic construction described above, it is possible to achieve a compact, high-performance, and super high variable power zoom lens system that has a zoom ratio of over 30× and yet has a wide-angle-side angle of view that is as wide as 88° to 90°, and an imaging optical device provided with such a zoom lens system. Furthermore, since the imaging optical device is made light weight and compact, by using the imaging optical device in a digital apparatus such as a digital camera or a portable information terminal unit, it is possible to provide the digital apparatus additionally with a high-performance image input function in a light-weight and compact manner. Thus, the characteristic construction contributes to, for example, reduction in size and cost of, and improvement in performance and functionality of, digital apparatuses. Hereinafter, descriptions will be given of conditions and the like for obtaining these advantages in a well-balanced manner, and for achieving higher optical performance, more compactness, and the like.
In view of achieving a compact, high variable power zoom lens system that has a wide angle of view and yet holds high optical performance, a zoom ratio of 30× to 38× is preferable. An attempt to obtain a high zoom ratio of approximately 30× to 38× usually makes it difficult to achieve size reduction, increase in angle of view, and improvement in performance of zoom lens systems, but according to the above-described characteristic construction where the shares of responsibility for achieving variable power assigned to the second and third lens groups satisfy the predetermined condition, it is possible to obtain a high zoom ratio while achieving size reduction, increase in angle of view, and improvement in performance. This makes it possible to achieve a wider angle of view along with higher variable power while achieving both compactness and high performance
It is preferable that the first lens group include, sequentially from the object side, a cemented lens element including a negative lens element and a positive lens element, and a positive single lens element, and that the first lens group satisfy the following conditional formulas (B4) and (B5):

1.86<Nd11<2  (B4)

30<νd11<40  (B5)

where
Nd11 represents a refractive index of the negative lens element included in the first lens group with respect to a d-line, and
νd11 represents an Abbe number of the negative lens element included in the first lens group with respect to the d-line.
In a high variable power zoom lens system, correction of chromatic aberration at the telephoto side is difficult, and it is necessary, in particular, to reduce chromatic aberration generated in the first lens group. Particularly second spectrum increases, and thus, typically, a lens element having an anomalous dispersion characteristic is often used as a positive lens element of the first lens group to achieve the reduction. Also, the negative lens element needs to have a strong refractive power to achieve a compact zoom lens system, but a strong refractive power leads to a large curvature, allowing strong coma aberration and/or strong astigmatism to be generated. Thus, it is necessary that the negative lens element have a high refractive index so as not to invite increase in the curvature, but unfortunately, glass materials having a refractive index of over 1.85 are usually characterized by having an anomalous dispersion characteristic on a plus side, and thus, even if an anomalous dispersion lens element is used as a positive lens element, it is difficult to correct secondary spectrum.
By selecting a glass material that satisfies the conditional formulas (B4) and (B5), it is possible to select a glass material that has a low anomalous dispersion characteristic and a strong refractive power. If a lower limit of the conditional formula (B4) is fallen short of, the refractive power becomes too weak, and this leads to an unpreferably large optical system. An attempt to maintain the optical power at the same level will lead to a large curvature, to cause large spherical aberration, which is difficult to correct. If an upper limit of the conditional formula (B4) is exceeded, surface refractive power becomes strong, and in particular, sensitivity to manufacturing errors of an aspherical wave becomes strong, making it disadvantageously difficult to produce the zoom lens system. If an upper limit of the conditional formula (B5) is exceeded, it leads to a too large dispersion value, and it becomes difficult to correct chromatic aberration. If a lower limit of the conditional formula (B5) is fallen short of, it means that a glass material having a high anomalous dispersion characteristic is selected, and thus it becomes difficult to correct chromatic aberration.
It is preferable that the present zoom lens system adopt one anomalous dispersion lens element as the positive lens element of the first lens group, so as to reduce secondary spectrum. In an area, to which the present optical system belongs, where an optical system at the telephoto end functions as a so-called super-telephoto lens system, correction of secondary spectrum is a problem to be dealt with, and in some cases, a plurality of anomalous dispersion lens elements are used, or, a lens element having a very high anomalous dispersion characteristic, such as a fluorite lens element, is used. The point of this correction is the correction of chromatic aberration on the negative lens element side, and selected as the negative lens element is one that is made of a glass material belonging to an area of small Abbe numbers. With a typically used optical glass material, which has a high positive anomalous dispersion, if it has a small Abbe number, the effect of the anomalous dispersion used in the positive lens element is cancelled, so that the secondary spectrum is corrected only insufficiently. Thus, it can be said to be preferable that the conditional formulas (B4) and (B5) be satisfied.
It is preferable that the following conditional formula (B6) be satisfied:

0.3<β4t/β4w<0.7  (B6)

where
β4t represents a lateral magnification of the fourth lens group at the telephoto end, and
β4w represents a lateral magnification of the fourth lens group at the wide angle end.
The conditional formula (B6) defines a preferable lateral magnification ratio of the fourth lens group between at the telephoto end and at the wide angle end. To reduce the optical total length at the telephoto side, it is effective to satisfy the conditional formula (B6). The present optical system, having the small optical total length at the telephoto side despite having a zoom ratio of over 30×, contributes to achieving a compact lens barrel and a compact camera. If simply the optical total length at the telephoto end is reduced, it leads to total increase in the optical power of each of the lens groups, which makes it difficult to correct aberration; in contrast, if the lateral magnification of the fourth lens group at the telephoto end is made comparatively small so as to satisfy the conditional formula (B6), it is possible to reduce the optical total length.
If an upper limit of the conditional formula (B6) is exceeded, the combined focal length of the first to third lens groups becomes short, which makes it difficult to correct aberration, above all, field curvature. If a lower limit of the conditional formula (B6) is fallen short of, the optical total length is increased, which is not preferable from the viewpoint of achieving compactness. Furthermore, if the lower limit of the conditional formula (B6) is fallen short of, need arises to increase the refractive power of the second lens group, which may in turn increase astigmatism, and need arises to increase the refractive power of the third lens group, which may in turn increase spherical aberration.
It is preferable that the following conditional formula (B7) be satisfied:

−10<{(ywmax−Ymax)/Ymax}×100<−25  (B7)

where

ywmax represents the maximum real image height at the wide angle end, and
Ymax represents the maximum ideal image height.
The conditional formula (B7) defines a distortion ratio at the wide angle end. Allowing distortion in the range of the conditional formula (B7) to be generated at the wide angle end is effective particularly to reduce an external diameter of the first lens group. The generated distortion is able to be corrected by electronic means such that the distortion ratio is reduced to a level that does not cause any trouble. If an upper limit of the conditional formula (B7) is exceeded, the distortion ratio becomes so large that it causes an excessively large interpolation error in correcting the distortion by using the electronic means, which unpreferably leads to degradation of performance. If the lower limit of the conditional formula (B7) is fallen short of, the ratio of the generated distortion is low, which leads to a larger external diameter of the first lens group, and as a result, the entire size of a camera incorporating the optical system becomes larger, which is not preferable in terms of compactness.
A construction where a stop is positioned on the object side of the third lens group in the zoom type including the positive, negative, positive, and positive lens groups is strongly asymmetric at the wide angle end, and this leads to generation of a strong negative distortion. The distortion is generated mainly in the second lens group, and it is to be corrected mainly in the first and third lens groups. By generating a correcting effect in a lens element of the third lens group that is located closest to the image, it is possible to correct the distortion in the third lens group, although not very much effectively, because the third lens group is located close to a stop surface. In such a construction, spherical aberration is generated, but by correcting the distortion to be within the range defined by the conditional formula (B7), it becomes possible to preferably correct the spherical aberration within the third lens group. Note that, although an attempt to achieve a high variable ratio causes distortion aberration to be generated mainly in the second lens group, since a slightly larger share of responsibility for achieving variable power is assigned to the third lens group while a slightly smaller share of responsibility for achieving variable power is assigned to the second lens group according to the conditional formulas (B1) to (B3), as long as within the range of the conditional formula (B7), it is possible to correct, in a well-balanced manner, the distortion aberration generated in the second lens group in the first and third lens groups.
It is desirable that a surface of the third lens group that is located closest to the object side be formed of an aspherical surface. To assign a larger share of responsibility for achieving variable power to the third lens group than in the conventional construction, it is necessary to sufficiently correct spherical aberration in the third lens group. Thus, it is desirable that the lens element of the third lens group that is located closest to the object side have an aspherical surface. The third lens group has a strong positive refractive power, and mainly a lens surface that is disposed closest to the object side is responsible for the positive refractive power. By using an aspherical surface in the lens element located closest to the object side and having the surface with a strong refractive power, it is possible to effectively correct spherical aberration.
It is preferable that the second lens group include, sequentially from the object side, a negative meniscus lens element having a convex surface facing toward the object side, a cemented lens element including a biconcave negative lens element and a biconvex positive lens element, and a negative meniscus lens element having a convex surface facing toward an image side. Generally, a construction where a biconcave lens element and a biconvex lens element are not cemented together but used as two separate single lens elements is more effective in terms of aberration correction than using a cemented lens element made by cementing biconcave and biconvex lens elements together. Unfortunately, however, with an air gap between the biconcave lens element and the biconvex lens element, an error in the interval of the air gap has a great influence on the generation of spherical aberration, which gives rise to difficulty in production. It is possible to achieve a construction with an error of such a level that causes no problem in production, by constructing the second lens group with, as described above, sequentially from the object side, a negative meniscus lens element having a convex surface facing toward the object side, a cemented lens element including a biconcave negative lens element and a biconvex positive lens element, and a negative meniscus lens element having a convex surface facing toward the image side.
It is preferable that the following conditional formula (B8) be satisfied:

−0.3<m3/TLt<−0.2  (B8)

where
m3 represents an absolute amount of movement of the third lens group in zooming from the wide angle end to the telephoto end (a minus sign indicates movement to the object side), and
TLt represents the optical total length at the telephoto end.
If an upper limit of the conditional formula (B8) is exceeded, the amount of movement of the third lens group is reduced, making it difficult for the third lens group to fulfill its share of responsibility for achieving variable power. This results in a larger share of responsibility for achieving variable power to be assigned to the second lens group, which is disadvantageous in terms of aberration correction and makes it difficult to correct astigmatism and field curvature. On the other hand, if the lower limit of the conditional formula (B8) is fallen short of, the amount of movement of the third lens group is increased to increase the optical total length at the telephoto end, which is disadvantageous to compactness. An effort to effectively achieve compactness in spite of the increased amount of movement of the third lens group requires the second lens group to bear an increased share of responsibility for achieving variable power. If the refractive power of the second lens group is increased to meet the requirement, it may in turn increase spherical aberration.
It is preferable that the following conditional formula (B9) be satisfied:

−0.25<m4/TLt<−0.1  (B9)

where
m4 represents an absolute amount of movement of the fourth lens group in zooming from the wide angle end to the telephoto end (a minus sign indicates movement to the object side), and
TLt represents the optical total length at the telephoto end.
If an upper limit of the conditional formula (B9) is exceeded, the amount of movement of the fourth lens group is reduced, and thus difference in lateral magnification between at the wide angle end and at the telephoto end is reduced. As a result, the combined focal length of the first to third lens groups becomes short, which makes it difficult to correct aberration at the telephoto side, and correction of field curvature becomes difficult. On the other hand, if a lower limit of the conditional formula (B9) is fallen short of, the amount of movement of the fourth lens group is increased to increase the optical total length at the telephoto end, which is disadvantageous to compactness.
The above-described zoom lens systems of the first and second types are suitably usable as an imaging lens system for a digital apparatus (such as a digital camera) equipped with an image input function, and by combining the zoom lens systems with an image sensing device or the like, it is possible to construct an imaging optical device that optically takes in an image of a subject and outputs it in the form of an electrical signal. The imaging optical device is an optical device that constitutes a main component of a camera used for shooting a still or moving image of a subject, and the imaging optical device is constructed by being provided with, for example, sequentially from the object (that is, the subject) side, a zoom lens system that forms the optical image of the object, and an image sensing device that converts the optical image formed by the zoom lens system into an electric signal. And, by arranging the zoom lens system having the above-described characteristic construction such that the optical image of the subject is formed on the light receiving surface (that is, the image sensing surface) of the image sensing device, it is possible to realize a low-cost, high-performance, and compact high variable-power imaging optical device and a digital apparatus (for example, a digital camera, a mobile phone) incorporating the imaging optical device.
Examples of the camera include a digital camera, a video camera, a surveillance camera, an on-vehicle camera, a videophone camera, and so on, and also, cameras of a type that is built in, or externally connected to, a personal computer, a digital apparatus (for example, a compact and portable information apparatus terminal such as a mobile phone and a mobile computer), a peripheral apparatus thereof (a scanner, a printer, and the like), any other type of digital apparatus, and the like. As is clear from these examples, it is possible not only to design a camera with the imaging optical device but also to add a camera function to various apparatuses by incorporating the imaging optical device in those apparatuses. For example, it is possible to design a digital apparatus having the image input function such as a camera phone.
FIG. 21 shows, in a schematic sectional view, an example of an outline of the construction of a digital apparatus DU having an image input function. An imaging optical device LU incorporated in the digital apparatus DU shown in FIG. 21 includes, sequentially from the object (that is, the subject) side, a zoom lens system ZL (AX denotes an optical axis, and ST denotes a stop) that forms an optical image (image plane) IM of an object at variable power, a plane parallel plate PT (which corresponds to a cover glass of an image sensing device SR, an optical filter such as an optical low-pass filter or an infrared cutoff filter provided as necessary, or the like), and the image sensing device SR that converts the optical image IM formed on a light receiving surface SS by the zoom lens system ZL into an electric signal. In the case where the digital apparatus DU having the image input function is formed by using the imaging optical device LU, the imaging optical device LU is typically disposed inside a body of the digital apparatus DU, while in the case of realizing the camera function in various apparatuses, any form may be adopted as necessary. For example, a construction is possible in which the imaging optical device LU is formed as a unit so that it is mountable to/demountable from a main body of the digital apparatus DU or pivotable with respect thereto.
As the image sensing device SR, for example, there is adopted a solid-state image sensing device such as a CCD type image sensor or a CMOS type image sensor, which has a plurality of pixels. The zoom lens system ZL is arranged such that the optical image IM of the subject is formed on the light receiving surface SS, which is a photoelectric conversion portion of the image sensing device SR, and thus, the optical image IM formed by the zoom lens system ZL is converted into an electric signal by the image sensing device SR.
In addition to the imaging optical device LU, the digital apparatus DU includes a signal processing portion 1, a control portion 2, a memory 3, an operation portion 4, a display portion 5, and so on. A signal generated at the image sensing device SR is transmitted to the signal processing portion 1, where the signal is subjected to predetermined processing such as digital image processing and image compression processing, as necessary. Then, the signal is recorded as a digital image signal in the memory 3 (a semiconductor memory, an optical disc, or the like), or in some cases, the signal is transmitted to another apparatus via a cable or by being converted into, for example, an infrared signal (as in, for example, a communication function of a mobile phone). The control portion 2 includes a microcomputer, and centrally performs the following controls: control of functions such as a shooting function (for example, a still image shooting function, a moving image shooting function) and an image viewing function, control of a lens moving mechanism for zooming or focusing, and the like. For example, the control portion 2 controls the imaging optical device LU to perform at least one of still image shooting and moving image shooting of the subject. The display portion 5 includes a display such as a liquid crystal monitor, and displays images by using image signals obtained through conversion by the image sensing device SR or by using image information recorded in the memory 3. The operation portion 4 includes an operation member such as an operation button (for example, a release button) and/or an operation dial (for example, a shooting mode dial), and transmits to the control portion 2 information that an operator has inputted by operating the operation member.
The zoom lens system ZL has, as described above, the four-group zoom construction including the four positive, negative, positive, and positive lens groups, where the first to fourth lens groups each move along the optical axis AX to change an inter-group distance between the lens groups to thereby achieve variable power (that is, zooming), and the optical image 1M is formed on the light receiving surface SS of the image sensing device SR. Note that, in the later-described embodiments (FIG. 1 to FIG. 10), as zoom lens groups, the first to fourth lens group Gr1 to Gr4 function as moving lens groups, and in a five-group zoom lens system, a fifth lens group Gr5 functions as a stationary lens group.
Next, dealing with first to tenth embodiments, a further detailed description will be given of the specific optical construction of the zoom lens system ZL. FIGS. 1 to 10 are lens construction diagrams corresponding to zoom lens systems ZL included in the first to tenth embodiments, respectively, each showing a lens arrangement at the wide angle end (W) in optical section. In each of the lens construction diagrams, axial inter-surface distances denoted by di (i=1, 2, 3, . . . ) are, among i-th axial inter-surface distances counted from the object side, axial inter-surface distances that are variable in zooming. In each of the lens construction diagrams, arrows m1, m2, m3, and m4 schematically indicate movement of the first lens group Gr1, the second lens group Gr2, the third lens group Gr3, and the fourth lens group Gr4, respectively, in zooming from the wide angle end (W) to the telephoto end (T). Besides, an arrow m5 illustrated closest to the image plane 1M indicates that the fifth lens group Gr5 and the plane parallel plate PT are stationary in zooming, and an arrow mP illustrated closest to the image plane IM indicates that the plane parallel plate PT is stationary in zooming.
In the first embodiment (FIG. 1), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a positive meniscus lens element convex to the object side, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a biconcave negative lens element, and a cemented lens element including a biconcave negative lens element and a biconvex positive lens element (having an aspherical surface on the image side). A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element L31 (a first lens element) including a positive meniscus lens element (having an aspherical surface on the object side) convex to the object side, a negative meniscus lens element concave to the image side, and a biconvex positive lens element, and a negative meniscus lens element (having an aspherical surface on each side) L32 (a second lens element) concave to the object side. A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a biconvex positive lens element (having an aspherical surface on each side).
In the second embodiment (FIG. 2), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a negative meniscus lens element concave to the image side and a cemented lens element including a biconcave negative lens element and a biconvex positive lens element. A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element L31 (a first lens element) including a positive meniscus lens element (having an aspherical surface on the object side) convex to the object side, a negative meniscus lens element concave to the image side, and a positive meniscus lens element convex to the object side, and a positive meniscus lens element (having an aspherical surface on each side) L32 (a second lens element) convex to the image side. A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a positive meniscus lens element (having an aspherical surface on each side) convex to the object side.
In the third embodiment (FIG. 3), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a negative meniscus lens element concave to the image side, a cemented lens element including a biconcave negative lens element and a biconvex positive lens element, and a negative meniscus lens element (having an aspherical surface on each side) concave to the object side. A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element L31 (a first lens element) including a biconvex positive lens element (having an aspherical surface on the object side), a biconcave negative lens element, and a positive meniscus lens element convex to the object side, and a positive meniscus lens element (having an aspherical surface on each side) L32 (a second lens element) convex to the object side. A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a positive meniscus lens element (having an aspherical surface on each side) convex to the object side.
In the fourth embodiment (FIG. 4), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a biconcave negative lens element, and a cemented lens element including a biconcave negative lens element and a biconvex positive lens element (having an aspherical surface on the image side). A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element L31 (a first lens element) including a biconvex positive lens element (having an aspherical surface on the object side), a biconcave negative lens element, and a positive meniscus lens element convex to the object side, and a biconvex positive lens element (having an aspherical surface on each side) L32 (a second lens element). A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a positive meniscus lens element (having an aspherical surface on each side) convex to the object side.
In the fifth embodiment (FIG. 5), in a four-group zoom construction including positive, negative, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a positive meniscus lens element convex to the object side, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a negative meniscus lens element concave to the image side and a cemented lens element including a biconcave negative lens element and a biconvex positive lens element. A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element L31 (a first lens element) including a positive meniscus lens element (having an aspherical surface on the object side) convex to the object side, a negative meniscus lens element concave to the image side, and a positive meniscus lens element convex to the object side, and a biconvex positive lens element (having an aspherical surface on each side) L32 (a second lens element). A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element.
In the sixth embodiment (FIG. 6), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a biconcave negative lens element, and a cemented lens element including a biconcave negative lens element and a biconvex positive lens element (having an aspherical surface on the image side). A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element including a biconvex positive lens element (having an aspherical surface on the object side), a biconcave negative lens element, and a positive meniscus lens element convex to the object side, and a biconvex positive lens element (having an aspherical surface on each side). A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a biconvex positive lens element (having an aspherical surface on each side).
In the seventh embodiment (FIG. 7), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a negative meniscus lens element concave to the image side, a cemented lens element including a biconcave negative lens element and a biconvex positive lens element, and a negative meniscus lens element (having an aspherical surface on each side) concave to the object side. That is, the second lens group Gr2 includes, sequentially from the object side, a negative meniscus lens element having a convex surface facing toward the object side, a cemented lens element including a biconcave negative lens element and a biconvex positive lens element, and a negative meniscus lens element having a convex surface facing toward the image side. A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element including a biconvex positive lens element (having an aspherical surface on the object side), a biconcave negative lens element, and a positive meniscus lens element convex to the object side, and a positive meniscus lens element (having an aspherical surface on each side) convex to the object side. A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a positive meniscus lens element (having an aspherical surface on each side) convex to the object side.
In the eighth embodiment (FIG. 8), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a negative meniscus lens element concave to the image side, a biconcave negative lens element (having an aspherical surface on each side), and a biconvex positive lens element. A third lens group Gr3 includes, sequentially from the object side, a stop ST, a biconvex positive lens element (having an aspherical surface on each side), a negative meniscus lens element concave to the image side, and a cemented lens element including a negative meniscus lens element concave to the image side and a positive meniscus lens element convex to the object side. A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a positive meniscus lens element (having an aspherical surface on each side) convex to the image side.
In the ninth embodiment (FIG. 9), in a five-group zoom construction including positive, negative, positive, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a biconcave negative lens element, and a cemented lens element including a biconcave negative lens element (having an aspherical surface on the object side) and a biconvex positive lens element. A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element including a biconvex positive lens element (having an aspherical surface on the object side) and a biconcave negative lens element, and a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element (having an aspherical surface on the image side). A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element. A fifth lens group Gr5 includes only a positive meniscus lens element (having an aspherical surface on each side) convex to the image side.
In the tenth embodiment (FIG. 10), in a four-group zoom construction including positive, negative, positive, and positive lens groups, the lens groups are constructed as follows. A first lens group Gr1 includes, sequentially from the object side, a cemented lens element including a negative meniscus lens element concave to the image side and a biconvex positive lens element, and a positive meniscus lens element convex to the object side. A second lens group Gr2 includes, sequentially from the object side, a biconcave negative lens element, and a cemented lens element including a biconcave negative lens element and a biconvex positive lens element (having an aspherical surface on the image side). A third lens group Gr3 includes, sequentially from the object side, a stop ST, a cemented lens element including a biconvex positive lens element (having an aspherical surface on the object side), a biconcave negative lens element, and a positive meniscus lens element convex to the object side, and a positive meniscus lens element (having an aspherical surface on each side) convex to the object side. A fourth lens group Gr4 includes a cemented lens element including a biconvex positive lens element and a biconcave negative lens element.
EXAMPLES
Hereinafter, further specific descriptions will be given of features of the zoom lens systems embodying the invention, such as the construction thereof, with reference to construction data and other data of examples. Examples 1 to 10 (EX1 to EX10) presented below are numerical examples corresponding to the above-described first to tenth embodiments, respectively. Thus, the optical construction diagrams (FIGS. 1 to 10) showing the first to tenth embodiments also show the lens constructions of Examples 1 to 10, respectively.
The construction data of each example includes, as surface data, sequentially from the leftmost column, ri denoting the i-th radius of curvature (in mm), di denoting the i-th axial inter-surface distance (in mm), Ni denoting the i-th refractive index with respect to the d-line (a wavelength of 587.56 nm), vi denoting the i-th Abbe number with respect to the d-line, and the focal length (in mm) of each lens element, where “i-th” indicates an order counted from the object side. A surface whose radius of curvature ri is marked with an asterisk (*) is an aspherical surface, and the surface shape of an aspherical surface is defined by formula (AS) below, employing the local rectangular coordinate system (x, y, z) having an origin at the vertex of the aspherical surface. As aspherical surface data, an aspherical surface coefficient and the like are presented. Note that, in the aspherical surface data of the examples, the coefficient of an unlisted term is zero, and E−n=×10−n applies to all the data.

z=(c·h2)/{1+√(1−ε·c2·h2)}+Σ(Aj·hj)  (AS)

where
h represents a height (h2=x2+y2) in a direction perpendicular to a z-axis (an optical axis AX),
z represents an amount of sag (with respect to a surface vertex) at a position of the height h in a direction of the optical axis AX,
c represents a curvature (the reciprocal of the radius of curvature r) at a surface vertex;
ε represents quadric surface parameter, and
Aj represents an aspherical surface coefficient of the j-th order.
As miscellaneous data, the zoom ratio, the focal length of the entire optical system (f, in mm), the angle of view (2ω, in °), the back focus (BF, in mm), the total lens length (TL, in mm), the F-number (Fno.), and the image height (Y′, in mm) are presented, and the focal length (in mm) of each lens group is presented as zoom lens-group data. Note that the back focus (BF) used here indicates the distance from the image-side surface of a cover glass (corresponding to the plane parallel plate PT) to the image plane. Furthermore, Table 1 and Table 2 show values corresponding to the conditional formulas of the examples.
FIGS. 11A-11I to 20A-20I are aberration diagrams corresponding to Examples 1 to 10 (EX 1 to EX 10), respectively, where (W) denotes the wide-angle end, (M) denotes the middle-focal-length position, and (T) denotes the telephoto end, and FIGS. 11A-11I to 20A-20I show aberrations (sequentially from the leftmost side, spherical aberration and so on, astigmatism, and distortion aberration) at (W), (M), and (T). In FIGS. 11A-11I to 20A-20I, FNO denotes the F number, and Y′ (in mm) denotes the maximum image height (corresponding to the distance from the optical axis AX) on the light receiving surface SS of the image sensing device SR. In the spherical aberration diagrams, a solid line d indicates spherical aberration (in mm) with respect to the d-line, and a broken line SC indicates deviation (in mm) from sine condition to be fulfilled. In the astigmatism diagrams, a broken line DM represents astigmatism (in mm) with respect to the d-line on the meridional surface, and a solid line DS represents astigmatism (in mm) with respect to the d-line on the sagittal surface. Besides, in the distortion diagrams, a solid line represents distortion (in %) with respect to the d-line.
Example 1










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
45.035
d1
1.000
N1
1.91082
ν1
35.25
611.45


r2
22.120
d2
3.707
N2
1.49700
ν2
81.61


r3
6138.359
d3
0.100


r4
23.012
d4
3.164
N3
1.61800
ν3
63.39
40.2










r5
295.850
d5
1.017~11.964~23.790















r6
−43.724
d6
0.600
N4
1.91082
ν4
35.25
−7.88


r7
8.648
d7
3.342


r8
−21.228
d8
0.500
N5
1.88300
ν5
40.80
−47.62


r9
10.866
d9
0.010
N6
1.51400
ν6
42.83


r10
10.866
d10
1.588
N7
2.00272
ν7
19.32










r11*
−110.055
d11
23.216~8.847~1.000















r12 (Stop)
∞
d12
0.300







r13*
7.110
d13
2.294
N8
1.75539
ν8
47.67
11.4


r14
53.277
d14
0.010
N9
1.51400
ν9
42.83


r15
53.277
d15
0.600
N10
1.82425
ν10
33.90


r16
5.676
d16
0.010
N11
1.51400
ν11
42.83


r17
5.676
d17
2.308
N12
1.62616
ν12
55.44


r18
−48.526
d18
0.804


r19*
−16.382
d19
0.703
N13
1.59505
ν13
36.11
−31.33










r20*
−137.366
d20
4.304~8.150~11.237















r21
9.693
d21
2.219
N14
1.57098
ν14
50.80
51.37


r22
−72.911
d22
0.500
N15
1.90366
ν15
31.32










r23
23.133
d23
4.754~15.008~18.716















r24*
3785.441
d24
1.800
N16
1.53048
ν16
55.72
50.21


r25*
−26.822
d25
0.600


r26
∞
d26
0.600
N17
1.51680
ν17
64.20










r27
∞
BF =
2.51~2.49~2.43


Image Plane
∞










Aspherical Surface Data





r11










ε =
1.0000



A4 =
−0.59066086E−04



A6 =
−0.52439324E−06



A8 =
0.56268214E−07



A10 =
−0.17460150E−08







r13










ε =
1.0192



A4 =
−0.16224181E−03



A6 =
−0.37595583E−05



A8 =
0.32264368E−07



A10 =
−0.15562369E−08







r19










ε =
1.0000



A4 =
0.42970217E−02



A6 =
−0.13925291E−03



A8 =
0.28867932E−05



A10 =
−0.45792442E−07







r20










ε =
1.0000



A4 =
0.47558345E−02



A6 =
−0.88669753E−04



A8 =
0.13037719E−05







r24










ε =
1.0000



A4 =
−0.11038475E−02



A6 =
0.99443584E−04



A8 =
−0.59909699E−05



A10 =
0.69558336E−07







r25










ε =
1.0000



A4 =
−0.10987139E−02



A6 =
0.16070476E−03



A8 =
−0.10080126E−04



A10 =
0.16874855E−06











Miscellaneous Data


Zoom Ratio: 17.93















(W)
~
(M)
~
(T)







f =
4.92
~
20.64
~
88.21



2ω =
78.2°
~
21.9°
~
5.2°



BF =
2.51
~
2.49
~
2.43



TL =
62.56
~
73.22
~
83.93



FNO. =
3.04
~
4.96
~
5.70



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
38.25



2nd Group
−6.44



3rd Group
14.91



4th Group
51.37



5th Group
50.21










Example 2










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
74.079
d1
0.800
N1
1.90366
ν1
31.32
−876.7


r2
23.287
d2
3.809
N2
1.49700
ν2
81.61


r3
−124.194
d3
0.100


r4
23.579
d4
2.753
N3
1.77250
ν3
49.62
33.98










r5
219.882
d5
0.600~11.383~22.549















r6
140.300
d6
0.600
N4
1.91082
ν4
35.25
−10.02


r7
8.552
d7
2.556


r8
−9.692
d8
0.500
N5
1.88300
ν5
40.80
−14.74


r9
9.118
d9
0.010
N6
1.51400
ν6
42.83


r10
9.118
d10
1.511
N7
1.94595
ν7
17.98










r11
−63.842
d11
16.607~6.164~0.100















r12 (Stop)
∞
d12
0.400







r13*
6.783
d13
1.767
N8
1.76802
ν8
49.24
14


r14
34.184
d14
0.010
N9
1.51400
ν9
42.83


r15
34.184
d15
0.500
N10
1.80518
ν10
25.46


r16
7.613
d16
0.010
N11
1.51400
ν11
42.83


r17
7.613
d17
1.800
N12
1.65844
ν12
50.85


r18
18.731
d18
1.153


r19*
−23.657
d19
1.013
N13
1.53048
ν13
55.72
92.91










r20*
−16.222
d20
4.441~8.211~10.011















r21
9.854
d21
2.343
N14
1.58913
ν14
61.25
40.9


r22
−34.329
d22
0.400
N15
1.80610
ν15
33.27










r23
24.531
d23
4.801~15.726~20.350















r24*
26.601
d24
1.355
N16
1.53048
ν16
55.72
60.72


r25*
150.050
d25
0.300


r26
∞
d26
0.600
N17
1.51680
ν17
64.20










r27
∞
BF =
2.51~2.53~2.53


Image Plane
∞










Aspherical Surface Data





r13










ε =
1.0192



A4 =
−0.15647940E−03



A6 =
−0.87841026E−05



A8 =
0.57296279E−06



A10 =
−0.23904675E−07







r19










ε =
1.0000



A4 =
0.11598099E−02



A6 =
0.14428944E−03



A8 =
−0.57810222E−05



A10 =
0.10520578E−06







r20










ε =
1.0000



A4 =
0.18845280E−02



A6 =
0.14585656E−03



A8 =
−0.26862244E−05



A10 =
0.86458149E−07







r24










ε =
1.0000



A4 =
−0.19347488E−02



A6 =
0.14096575E−03



A8 =
−0.77666941E−05



A10 =
−0.18451296E−08







r25










ε =
1.0000



A4 =
−0.24212416E−02



A6 =
0.28446863E−03



A8 =
−0.18172092E−04



A10 =
0.29136650E−06











Miscellaneous Data


Zoom Ratio: 18.94















(W)
~
(M)
~
(T)







f =
4.69
~
20.41
~
88.83



2ω =
80.9
~
22.2
~
5.16



BF =
2.51
~
2.53
~
2.53



TL =
53.25
~
68.31
~
79.83



FNO. =
3.10
~
5.00
~
5.70



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
35.06



2nd Group
−5.46



3rd Group
12.98



4th Group
40.9



5th Group
60.72










Example 3










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
81.473
d1
1.200
N1
1.90366
ν1
31.32
480.67


r2
37.397
d2
0.010
N2
1.51400
ν2
42.83


r3
37.397
d3
5.238
N3
1.49700
ν3
81.61


r4
−275.854
d4
0.100


r5
34.764
d5
3.933
N4
1.62229
ν4
53.17
70.01










r6
164.571
d6
0.600~24.900~44.597















r7
51.438
d7
0.600
N5
1.90366
ν5
31.32
−10.58


r8
8.019
d8
4.961


r9
−10.587
d9
0.500
N6
1.83481
ν6
42.72
−33.68


r10
17.404
d10
0.010
N7
1.51400
ν7
42.83


r11
17.404
d11
1.819
N8
1.94595
ν8
17.98


r12
−24.185
d12
0.695


r13*
−22.894
d13
0.800
N9
1.69350
ν9
53.20
−75.01










r14*
−41.473
d14
27.558~8.872~0.669















r15 (Stop)
∞
d15
1.000







r16*
9.321
d16
3.474
N10
1.74330
ν10
49.33
21.75


r17
−15.333
d17
0.010
N11
1.51400
ν11
42.83


r18
−15.333
d18
5.221
N12
1.83400
ν12
37.34


r19
6.180
d19
0.010
N13
1.51400
ν13
42.83


r20
6.180
d20
2.426
N14
1.58913
ν14
61.25


r21
82.678
d21
0.633


r22*
17.586
d22
1.909
N15
1.58313
ν15
59.46
40.16










r23*
67.777
d23
4.306~7.567~15.940















r24
13.648
d24
2.226
N16
1.57098
ν16
50.80
152.2


r25
−66.031
d25
0.010
N17
1.51400
ν17
42.83


r26
−66.031
d26
0.624
N18
1.90366
ν18
31.32










r27
38.024
d27
3.620~19.230~26.452















r28*
22.436
d28
1.812
N19
1.53048
ν19
55.72
78.16


r29*
47.523
d29
1.675


r30
∞
d30
1.100
N20
1.51680
ν20
64.20










r31
∞
BF =
1.96~1.96~2.0


Image Plane
∞










Aspherical Surface Data





r13










ε =
1.0000



A4 =
0.24145862E−03



A6 =
−0.16206578E−04



A8 =
0.29429550E−06



A10 =
−0.38337456E−08







r14










ε =
1.0000



A4 =
0.18468313E−03



A6 =
−0.14191523E−04



A8 =
0.28833960E−06



A10 =
−0.37574697E−08







r16










ε =
1.0192



A4 =
−0.52487646E−04



A6 =
0.56575338E−06



A8 =
−0.89428352E−07



A10 =
0.64262282E−08



A12 =
−0.19917914E−09



A14 =
0.18959592E−11







r22










ε =
1.0000



A4 =
−0.15637754E−03



A6 =
−0.95235497E−05



A8 =
−0.43075007E−06



A10 =
−0.24257873E−08







r23










ε =
1.0000



A4 =
0.58414553E−04



A6 =
−0.70845249E−05



A8 =
−0.51658779E−06



A10 =
0.70563911E−08







r28










ε =
1.0000



A4 =
−0.10576609E−02



A6 =
0.68848314E−04



A8 =
−0.38272657E−05



A10 =
0.56227484E−07







r29










ε =
1.0000



A4 =
−0.14576869E−02



A6 =
0.10080345E−03



A8 =
−0.55396727E−05



A10 =
0.91297524E−07











Miscellaneous Data


Zoom Ratio: 37.85















(W)
~
(M)
~
(T)







f =
4.11
~
24.18
~
155.56



2ω =
88.5°
~
18.8°
~
2.95°



BF =
1.96
~
1.96
~
2.0



TL =
80.04
~
104.52
~
131.65



FNO. =
3.49
~
5.24
~
5.86



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
61.48



2nd Group
−6.4



3rd Group
16.82



4th Group
66.5



5th Group
78.16










Example 4










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
80.025
d1
1.577
N1
1.90366
ν1
31.32
560.18


r2
36.801
d2
4.894
N2
1.49700
ν2
81.61


r3
−341.569
d3
0.100


r4
35.448
d4
4.005
N3
1.62229
ν3
53.17
67.58










r5
215.951
d5
0.869~23.270~43.459















r6
−582.835
d6
0.603
N4
1.91082
ν4
35.25
−9.44


r7
8.727
d7
5.135


r8
−17.747
d8
0.749
N5
1.88300
ν5
40.80
−45.05


r9
14.842
d9
0.010
N6
1.51400
ν6
42.83


r10
14.842
d10
2.672
N7
2.00272
ν7
19.32










r11*
−55.848
d11
38.312~11.399~1.884















r12 (Stop)
∞
d12
1.150







r13*
9.997
d13
3.059
N8
1.74330
ν8
49.33
22.7


r14
−24.000
d14
0.010
N9
1.51400
ν9
42.83


r15
−24.000
d15
5.324
N10
1.83400
ν10
37.34


r16
6.777
d16
0.010
N11
1.51400
ν11
42.83


r17
6.777
d17
2.500
N12
1.61800
ν12
63.39


r18
61.357
d18
0.943


r19*
72.486
d19
1.200
N13
1.53048
ν13
55.72
79.82










r20*
−101.244
d20
6.284~6.662~15.561















r21
13.565
d21
2.455
N14
1.57098
ν14
50.80
56.16


r22
−40.811
d22
0.615
N15
1.90366
ν15
31.32










r23
50.038
d23
4.711~22.059~26.272















r24*
31.947
d24
1.761
N16
1.53048
ν16
55.72
157.63


r25*
50.711
d25
0.618


r26
∞
d26
0.600
N17
1.51680
ν17
64.20










r27
∞
BF =
2.48~2.48~2.41


Image Plane
∞










Aspherical Surface Data





r11










ε =
1.0000



A4 =
−0.29995476E−04



A6 =
0.59300125E−07



A8 =
−0.41239700E−08



A10 =
0.56072596E−10







r13










ε =
1.0192



A4 =
−0.45308335E−04



A6 =
0.16998131E−06



A8 =
−0.10305262E−07



A10 =
0.13671803E−09







r19










ε =
1.0000



A4 =
0.22433487E−05



A6 =
−0.15924835E−04



A8 =
0.48187007E−06



A10 =
−0.11986145E−07







r20










ε =
1.0000



A4 =
0.20224326E−03



A6 =
−0.11886985E−04



A8 =
0.39435590E−06



A10 =
−0.73914496E−08







r24










ε =
1.0000



A4 =
−0.23059971E−02



A6 =
0.15375941E−03



A8 =
−0.89078357E−05



A10 =
0.18303116E−06







r25










ε =
1.0000



A4 =
−0.34012937E−02



A6 =
0.22992180E−03



A8 =
−0.11446638E−04



A10 =
0.21662181E−06











Miscellaneous Data


Zoom Ratio: 34.11















(W)
~
(M)
~
(T)







f =
4.11
~
24.00
~
140.19



2ω =
88.5°
~
18.9°
~
3.27°



BF =
2.48
~
2.48
~
2.41



TL =
92.65
~
105.87
~
129.58



FNO. =
3.13
~
5.02
~
5.90



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
60.83



2nd Group
−7.32



3rd Group
19.73



4th Group
56.16



5th Group
157.63










Example 5










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
52.241
d1
0.800
N1
1.90366
ν1
31.32
−473.92


r2
20.837
d2
3.695
N2
1.49700
ν2
81.61


r3
14579.385
d3
0.100


r4
22.429
d4
2.802
N3
1.77250
ν3
49.62
33.36










r5
163.545
d5
0.600~11.747~22.737















r6
53.461
d6
0.600
N4
1.91082
ν4
35.25
−10.56


r7
8.109
d7
3.623


r8
−8.308
d8
0.500
N5
1.88300
ν5
40.80
−14.38


r9
10.928
d9
0.010
N6
1.51400
ν6
42.83


r10
10.928
d10
1.452
N7
1.94595
ν7
17.98










r11
−33.933
d11
16.559~6.152~0.100















r12 (Stop)
∞
d12
0.400







r13*
6.352
d13
1.969
N8
1.76802
ν8
49.24
13.75


r14
31.977
d14
0.010
N9
1.51400
ν9
42.83


r15
31.977
d15
0.500
N10
1.80518
ν10
25.46


r16
6.893
d16
0.010
N11
1.51400
ν11
42.83


r17
6.893
d17
2.298
N12
1.65844
ν12
50.85


r18
14.350
d18
1.676


r19*
53.489
d19
1.000
N13
1.53048
ν13
55.72
72.01










r20*
−132.762
d20
4.694~8.342~10.120















r21
10.338
d21
2.318
N14
1.58913
ν14
61.25
42.26


r22
−30.041
d22
0.400
N15
1.80610
ν15
33.27










r23
27.344
d23
4.750~15.075~19.581















r24
∞
d24
0.600
N16
1.51680
ν16
64.20











r25
∞
BF =
2.53~2.53~2.52


Image Plane
∞










Aspherical Surface Data





r13










ε =
1.0192



A4 =
−0.12328129E−03



A6 =
−0.61500027E−05



A8 =
0.45743699E−06



A10 =
−0.14914037E−07







r19










ε =
1.0000



A4 =
−0.15593265E−02



A6 =
0.50232743E−04



A8 =
−0.11634268E−04



A10 =
0.51061706E−06







r20










ε =
1.0000



A4 =
−0.34648925E−03



A6 =
0.75190352E−04



A8 =
−0.96402037E−05



A10 =
0.53028998E−06











Miscellaneous Data


Zoom Ratio: 18.94















(W)
~
(M)
~
(T)







f =
5.08
~
22.10
~
96.20



2ω =
76.4°
~
20.5°
~
4.76°



BF =
2.53
~
2.53
~
2.52



TL =
53.9
~
68.61
~
79.82



FNO. =
3.10
~
4.98
~
5.70



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
35.98



2nd Group
−5.41



3rd Group
12.44



4th Group
42.26










Example 6










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
76.426
d1
1.400
N1
1.91082
ν1
35.25
565.6


r2
36.066
d2
5.098
N2
1.49700
ν2
81.61


r3
−401.640
d3
0.100


r4
34.378
d4
4.022
N3
1.61800
ν3
63.39
67.82










r5
182.645
d5
0.874~24.165~43.777















r6
−1503.646
d6
0.600
N4
1.91082
ν4
35.25
−9.44


r7
8.648
d7
5.251


r8
−17.493
d8
0.758
N5
1.88300
ν5
40.80
−44.24


r9
15.220
d9
2.695
N6
2.00272
ν6
19.32










r10*
−54.429
d10
38.344~11.729~1.885















r11 (Stop)
∞
d11
1.150







r12*
9.913
d12
3.106
N7
1.74330
ν7
49.33
22.75


r13
−24.512
d13
4.828
N8
1.83400
ν8
37.34


r14
6.745
d14
2.510
N9
1.61800
ν9
63.39


r15
60.554
d15
0.978


r16*
151.766
d16
1.200
N10
1.53048
ν10
55.72
83.13










r17*
−61.989
d17
6.423~7.890~15.394















r18
13.140
d18
2.442
N11
1.57098
ν11
50.80
54.89


r19
−44.897
d19
0.600
N12
1.90366
ν12
31.32










r20
45.408
d20
4.955~20.962~25.541















r21*
305.301
d21
1.790
N13
1.53048
ν13
55.72
123.98


r22*
−83.660
d22
0.600


r23
∞
d23
0.600
N14
1.51680
ν14
64.20










r24
∞
BF =
2.48~2.52~2.46


Image Plane
∞










Aspherical Surface Data





r10










ε =
1.0000



A4 =
−0.28722625E−04



A6 =
0.70295837E−07



A8 =
−0.68877967E−08



A10 =
0.11192367E−09







r12










ε =
1.0192



A4 =
−0.44021749E−04



A6 =
0.16475507E−06



A8 =
−0.13614245E−07



A10 =
0.25768729E−09







r16










ε =
1.0000



A4 =
−0.34297128E−05



A6 =
−0.67008329E−05



A8 =
0.85895252E−07



A10 =
−0.36761721E−08







r17










ε =
1.0000



A4 =
0.20347612E−03



A6 =
−0.32120885E−05



A8 =
0.35029997E−07







r21










ε =
1.0000



A4 =
−0.30346265E−02



A6 =
0.28884789E−03



A8 =
−0.17816720E−04



A10 =
0.37760197E−06







r22










ε =
1.0000



A4 =
−0.42305201E−02



A6 =
0.39623056E−03



A8 =
−0.21495071E−04



A10 =
0.41555649E−06











Miscellaneous Data


Zoom Ratio: 34.09















(W)
~
(M)
~
(T)







f =
4.12
~
24.04
~
140.45



2ω =
88.3°
~
18.9°
~
3.3°



BF =
2.48
~
2.52
~
2.46



TL =
92.81
~
106.99
~
128.79



FNO. =
3.20
~
5.04
~
5.90



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
61.09



2nd Group
−7.28



3rd Group
19.56



4th Group
54.89



5th Group
123.98










Example 7










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
85.256
d1
1.200
N1
1.90366
ν1
31.32
521.27


r2
37.691
d2
5.306
N2
1.49700
ν2
81.61


r3
−242.539
d3
0.100


r4
35.114
d4
4.012
N3
1.62229
ν3
53.17
68.52










r5
190.221
d5
0.600~24.784~43.639















r6
92.871
d6
0.600
N4
1.90366
ν4
31.32
−10.89


r7
8.873
d7
4.650


r8
−12.152
d8
0.500
N5
1.83481
ν5
42.72
−33.8


r9
14.300
d9
1.903
N6
1.94595
ν6
17.98


r10
−32.698
d10
0.800


r11*
−24.217
d11
0.800
N7
1.58913
ν7
61.25
−66.93










r12*
−63.539
d12
28.378~9.267~0.659















r13 (Stop)
∞
d13
1.000







r14*
9.219
d14
3.483
N8
1.74330
ν8
49.33
19.44


r15
−18.083
d15
3.460
N9
1.83400
ν9
37.34


r16
6.636
d16
2.601
N10
1.61800
ν10
63.39


r17
158.809
d17
0.715


r18*
26.255
d18
1.283
N11
1.53048
ν11
55.72
77.26










r19*
71.828
d19
5.941~9.366~14.168















r20
14.369
d20
2.455
N12
1.57098
ν12
50.80
61.91


r21
−40.101
d21
1.000
N13
1.90366
ν13
31.32










r22
52.671
d22
3.744~18.930~31.379















r23*
36.052
d23
1.800
N14
1.53048
ν14
55.72
72.23


r24*
599.956
d24
0.800


r25
∞
d25
0.600
N15
1.51680
ν15
64.20










r26
∞
BF =
2.52~2.55~2.62


Image Plane
∞










Aspherical Surface Data





r11










ε =
1.0000



A4 =
0.21117130E−03



A6 =
−0.12138508E−04



A8 =
0.10470648E−06



A10 =
0.28570893E−09







r12










ε =
1.0000



A4 =
0.16829279E−03



A6 =
−0.10857180E−04



A8 =
0.14238292E−06



A10 =
−0.63875237E−09







r14










ε =
1.0192



A4 =
−0.51898770E−04



A6 =
0.10802812E−05



A8 =
−0.11611541E−06



A10 =
0.72486478E−08



A12 =
−0.20244033E−09



A14 =
0.18879901E−11







r18










ε =
1.0000



A4 =
−0.16727629E−03



A6 =
−0.15124851E−04



A8 =
−0.39430676E−06



A10 =
−0.83296333E−09







r19










ε =
1.0000



A4 =
0.11343300E−03



A6 =
−0.10863046E−04



A8 =
−0.44368767E−06



A10 =
0.89945171E−08







r23










ε =
1.0000



A4 =
−0.17269178E−02



A6 =
0.13678435E−03



A8 =
−0.80552161E−05



A10 =
0.15082436E−06







r24










ε =
1.0000



A4 =
−0.21618556E−02



A6 =
0.18380507E−03



A8 =
−0.10148114E−04



A10 =
0.18681040E−06











Miscellaneous Data


Zoom Ratio: 37.89















(W)
~
(M)
~
(T)







f =
4.11
~
24.19
~
155.74



2ω =
88.5°
~
18.8°
~
2.9°



BF =
2.52
~
2.55
~
2.62



TL =
80.25
~
103.96
~
131.53



FNO. =
3.09
~
5.11
~
6.66



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
60.85



2nd Group
−6.41



3rd Group
16.91



4th Group
61.91



5th Group
72.23










Example 8










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
84.133
d1
1.400
N1
1.91082
ν1
35.25
662.96


r2
38.068
d2
5.492
N2
1.49700
ν2
81.61


r3
−336.115
d3
0.100


r4
36.950
d4
4.513
N3
1.61800
ν3
63.39
69.13










r5
260.776
d5
0.600~24.917~45.243















r6
150.570
d6
0.700
N4
1.88300
ν4
40.80
−9.56


r7
7.972
d7
4.442


r8*
−16.831
d8
0.700
N5
1.85135
ν5
40.10
−11.57


r9*
24.193
d9
0.080


r10
28.201
d10
2.001
N6
1.94595
ν6
17.98
16.18










r11
−32.321
d11
37.763~12.070~1.837















r12 (Stop)
∞
d12
1.330







r13*
7.942
d13
3.370
N7
1.72903
ν7
54.04
9.9


r14*
−65.147
d14
0.100


r15
31.845
d15
1.002
N8
1.85026
ν8
32.29
−12.27


r16
7.744
d16
0.809


r17
12.361
d17
1.377
N9
2.00069
ν9
25.46
53.34


r18
5.751
d18
1.615
N10
1.64769
ν10
33.84










r19
140.689
d19
5.278~8.518~16.583















r20
15.940
d20
1.997
N11
1.56883
ν11
56.04
63.16


r21
−60.130
d21
0.800
N12
1.91082
ν12
35.25










r22
68.478
d22
4.808~16.773~18.560















r23*
−57.448
d23
1.750
N13
1.53048
ν13
55.72
76.82


r24*
−24.091
d24
0.600


r25
∞
d25
0.600
N14
1.51680
ν14
64.20










r26
∞
BF =
2.51~2.53~2.52


Image Plane
∞










Aspherical Surface Data





r8










ε =
1.0000



A4 =
−0.81577446E−03



A6 =
0.29515896E−04



A8 =
−0.52806794E−06



A10 =
0.32242657E−08







r9










ε =
1.0000



A4 =
−0.81397010E−03



A6 =
0.33215788E−04



A8 =
−0.65385166E−06



A10 =
0.51167455E−08







r13










ε =
1.0192



A4 =
−0.16055191E−03



A6 =
−0.35061340E−05



A8 =
0.52149723E−07



A10 =
−0.34150813E−08







r14










ε =
1.0000



A4 =
0.31171734E−04



A6 =
−0.19424587E−05



A8 =
0.45827221E−07



A10 =
−0.31161108E−08







r23










ε =
1.0000



A4 =
−0.12118886E−04



A6 =
0.74955612E−05



A8 =
−0.31696535E−05



A10 =
0.77455297E−07







r24










ε =
1.0000



A4 =
0.30787651E−03



A6 =
−0.89968884E−05



A8 =
−0.31196660E−05



A10 =
0.84837210E−07











Miscellaneous Data


Zoom Ratio: 34.15















(W)
~
(M)
~
(T)







f =
3.96
~
23.14
~
135.24



2ω =
90.6°
~
19.6°
~
3.4°



BF =
2.51
~
2.53
~
2.52



TL =
85.74
~
99.58
~
119.52



FNO. =
3.11
~
5.01
~
5.90



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
63.03



2nd Group
−7.71



3rd Group
17.77



4th Group
56.41



5th Group
76.82










Example 9










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
70.943
d1
1.400
N1
1.91082
ν1
35.25
540.28


r2
35.473
d2
5.025
N2
1.49700
ν2
81.61


r3
−862.664
d3
0.100


r4
34.115
d4
4.286
N3
1.61800
ν3
63.39
69.81










r5
155.225
d5
0.957~24.468~44.454















r6
−499.848
d6
0.700
N4
1.90366
ν4
31.32
−9.79


r7
9.011
d7
5.209


r8*
−15.202
d8
0.118
N5
1.51790
ν5
52.31
−40.92


r9
−15.437
d9
0.600
N6
1.85135
ν6
40.10


r10
15.988
d10
2.365
N7
1.94595
ν7
17.98










r11
−40.505
d11
38.890~11.816~1.857















r12 (Stop)
∞
d12
1.150







r13*
9.533
d13
2.815
N8
1.72903
ν8
54.04
37.88


r14
−22.443
d14
3.910
N9
1.83481
ν9
42.72


r15
13.103
d15
0.903


r16
15.256
d16
2.500
N10
1.90366
ν10
31.32
30.89


r17
7.375
d17
1.828
N11
1.62263
ν11
58.16










r18*
−67.295
d18
6.830~8.362~16.157















r19
12.510
d19
2.474
N12
1.57098
ν12
50.80
50.41


r20
−64.719
d20
0.700
N13
1.90366
ν13
31.32










r21
39.234
d21
5.095~20.828~25.304















r22*
−52.951
d22
1.800
N14
1.53048
ν14
55.72
94.98


r23*
−26.122
d23
0.600


r24
∞
d24
0.600
N15
1.51680
ν15
64.20










r25
∞
BF =
2.50~2.56~2.59


Image Plane
∞










Aspherical Surface Data





r8










ε =
1.0000



A4 =
0.84203098E−04



A6 =
−0.37506313E−06



A8 =
0.31714128E−07



A10 =
−0.36749906E−09







r13










ε =
1.0192



A4 =
−0.48766973E−04



A6 =
−0.13321288E−06



A8 =
0.30172647E−08



A10 =
−0.19794136E−09







r18










ε =
1.0000



A4 =
0.17150084E−03



A6 =
0.19458234E−05



A8 =
0.85501879E−07







r22










ε =
1.0000



A4 =
−0.15044471E−02



A6 =
0.55604525E−04



A8 =
−0.23243027E−05



A10 =
−0.65929710E−09







r23










ε =
1.0000



A4 =
−0.21486983E−02



A6 =
0.12910881E−03



A8 =
−0.57900978E−05



A10 =
0.77972516E−07











Miscellaneous Data


Zoom Ratio: 34.13















(W)
~
(M)
~
(T)







f =
4.15
~
24.23
~
141.65



2ω =
87.9°
~
18.8°
~
3.2°



BF =
2.50
~
2.56
~
2.59



TL =
93.36
~
107.12
~
129.44



FNO. =
3.24
~
5.08
~
5.90



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
62.51



2nd Group
−7.37



3rd Group
20.13



4th Group
50.41



5th Group
94.98










Example 10










Unit: mm







Surface Data











Radius of
Axial
Refractive
Abbe
Focal


Curvature
Distance
Index
Number
Length


















Object Plane
∞
d0
∞







r1
73.999
d1
1.413
N1
1.90366
ν1
31.32
799.11


r2
35.944
d2
4.685
N2
1.49700
ν2
81.61


r3
−1956.105
d3
0.100


r4
36.812
d4
3.972
N3
1.62229
ν3
53.17
67.94










r5
272.976
d5
1.027~23.596~45.275















r6
−851.086
d6
0.600
N4
1.91082
ν4
35.25
−8.54


r7
7.856
d7
6.249


r8
−30.245
d8
0.600
N5
1.88300
ν5
40.80
−89.04


r9
15.542
d9
2.266
N6
2.00272
ν6
19.32










r10*
−101.708
d10
39.736~11.108~1.918















r11 (Stop)
∞
d11
1.150







r12*
10.265
d12
3.280
N7
1.74330
ν7
49.33
21.92


r13
−32.346
d13
4.797
N8
1.83400
ν8
37.34


r14
6.533
d14
2.510
N9
1.61800
ν9
63.39


r15
201.541
d15
0.769


r16*
39.369
d16
1.411
N10
1.53048
ν10
55.72
97.88










r17*
160.826
d17
6.292~6.678~15.559















r18
17.301
d18
2.488
N11
1.57098
ν11
50.80



r19
−27.438
d19
1.000
N12
1.90366
ν12
31.32
97.88










r20
124.407
d20
6.295~23.628~27.861















r21
∞
d21
0.600
N13
1.51680
ν13
64.20
67.98










r22
∞
BF =
2.51~2.51~2.49


Image Plane
∞










Aspherical Surface Data





r10










ε =
1.0000



A4 =
−0.50672659E−04



A6 =
−0.80963140E−08



A8 =
−0.64752836E−08



A10 =
−0.81677878E−11







r12










ε =
1.0192



A4 =
−0.41532358E−04



A6 =
0.21860484E−06



A8 =
−0.14205445E−07



A10 =
0.22199007E−09







r16










ε =
1.0000



A4 =
0.28338729E−04



A6 =
−0.13228681E−04



A8 =
0.59833721E−06



A10 =
−0.20040570E−07







r17










ε =
1.0000



A4 =
0.18633951E−03



A6 =
−0.10061279E−04



A8 =
0.47437869E−06



A10 =
−0.15522887E−07











Miscellaneous Data


Zoom Ratio: 34.13















(W)
~
(M)
~
(T)







f =
4.11
~
24.01
~
140.28



2ω =
88.5
~
18.9°
~
3.3°



BF =
2.51
~
2.51
~
2.49



TL =
93.74
~
105.41
~
130.99



FNO. =
3.01
~
4.89
~
5.90



Y′ =
4.0
~
4.0
~
4.0











Zoom Lens Group Data










Group
Focal Length







1st Group
63.31



2nd Group
−7.43



3rd Group
19.38



4th Group
67.98
























TABLE 1







Conditional
Conditional
Conditional
Conditional
Conditional
Conditional



Formula(A1)
Formula(A2)
Formula(A3)
Formula(A4)
Formula(A5)
Formula(A6)



f3/√(fw × ft)
CR32/f3
Nd11
νd11
β4t/β4w
dist*






















EX1
0.71
0.38
1.91082
35.25
0.62
−19.6


EX2
0.64
0.59
1.90366
31.32
0.44
−19.1


EX3
0.67
0.37
1.90366
31.32
0.56
−18.7


EX4
0.82
0.34
1.90366
31.32
0.49
−19.8


EX5
0.56
0.55
1.90366
31.32
0.52
−19.0





*dist = {(ywmax − Ymax)/Ymax} × 100


















TABLE 2








Condi-
Condi-
Condi-
Condi-
Condi-



tional
tional
tional
tional
tional



Formula
Formula
Formula
Formula
Formula



(B1)
(B2)
(B3)
(B4)
(B5)



β2t/ β2w
β3t/ β3w
(B1)/(B2)
Nd11
νd11





EX6
8.81
7.81
1.13
1.91082
35.25


EX7
8.37
10.69
0.78
1.90366
31.32


EX8
8.91
5.61
1.59
1.91082
35.25


EX9
8.84
8.86
1.00
1.91082
35.25


EX10
7.99
7.09
1.13
1.90366
31.32

















Condi-
Condi-
Condi-
Condi-




tional
tional
tional
tional




Formula
Formula
Formula
Formula




(B6)
(B7)
(B8)
(B9)




β4t/ β4w
dist*
m3/TLt
m4/TLt







EX6
0.50
−19.8
−0.23
−0.16



EX7
0.42
−19.8
−0.27
−0.21



EX8
0.68
−20.1
−0.21
−0.12



EX9
0.44
−19.8
−0.23
−0.16



EX10
0.60
−19.8
−0.24
−0.16







*dist = {(ywmax − Ymax/Ymax} × 100






LIST OF REFERENCE SYMBOLS


    
    
        DU digital apparatus
        LU imaging optical device
        ZL zoom lens system
        Gr1 first lens group
        Gr2 second lens group
        Gr3 third lens group
        Gr4 fourth lens group
        Gr5 fifth lens group
        L31 first lens element (cemented lens element)
        L32 second lens element
        ST stop (aperture stop)
        SR image sensing device
        SS light receiving surface (imaging surface)
        IM image plane (optical image)
        AX optical axis
        1 signal processing portion
        2 control portion
        3 memory
        4 operation portion
        5 display portion

## Claims

1. A zoom lens system comprising, sequentially from an object side:
a first lens group having a positive optical power;
a second lens group having a negative optical power;
a third lens group having a positive optical power; and
a fourth lens group having a positive optical power,
the zoom lens system achieving variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups,
wherein
the third lens group includes two lens elements at least one of which has an aspherical surface,
an object-side lens element of the third lens group is a cemented lens element including, sequentially from the object side, a positive lens element, a negative lens element, and a positive lens element, and
the third lens group satisfies the following conditional formula (A2):


0.3<CR32/f3<0.65  (A2)


where
CR32 represents a radius of curvature of an image-side surface of the negative lens element included in the cemented lens element, and
f3 represents a focal length of the third lens group.

2. A zoom lens system comprising, sequentially from an object side:
a first lens group having a positive optical power;
a second lens group having a negative optical power;
a third lens group having a positive optical power; and
a fourth lens group having a positive optical power,
the zoom lens system achieving variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups,
wherein
the third lens group includes two lens elements at least one of which has an aspherical surface,
an object-side lens element of the third lens group is a cemented lens element including, sequentially from the object side, a positive lens element, a negative lens element, and a positive lens element,
the first lens group includes, sequentially from the object side, a cemented lens element including a negative lens element and a positive lens element, and a positive single lens element, and
the first lens group satisfies the following conditional formulas (A3) and (A4):


1.86<Nd11<2  (A3)



30<νd11<40  (A4)


where
Nd11 represents a refractive index of the negative lens element included in the first lens group with respect to a d-line, and
νd11 represents an Abbe number of the negative lens element included in the first lens group with respect to the d-line.

3. A zoom lens system comprising, sequentially from an object side:
a first lens group having a positive optical power;
a second lens group having a negative optical power;
a third lens group having a positive optical power; and
a fourth lens group having a positive optical power,
the zoom lens system achieving variable power by moving the first to fourth lens groups to change an inter-group distance between the lens groups,
wherein
the third lens group includes two lens elements at least one of which has an aspherical surface,
an object-side lens element of the third lens group is a cemented lens element including, sequentially from the object side, a positive lens element, a negative lens element, and a positive lens element, and
the following conditional formula (A5) is satisfied:


0.3<β4t/β4w<0.7  (A5)


where
β4t represents a lateral magnification of the fourth lens group at a telephoto end, and
β4w represents a lateral magnification of the fourth lens group at a wide angle end.

4. The zoom lens system according to claim 1,
wherein
the third lens group satisfies the following conditional formula (A1):


0.5<f3/√(fw×ft)<0.9  (A1)


where
f3 represents the focal length of the third lens group,
fw represents a focal length of a whole system at a wide angle end, and
ft represents a focal length of the whole system at a telephoto end.

5. The zoom lens system according to claim 1,
wherein,
of the positive lens elements included in the cemented lens element, one that is disposed closest to the object side has an aspherical surface, and
a radius of curvature of the aspherical surface is larger than a reference radius of curvature by a larger value farther away from an optical axis.

6. The zoom lens system according to claim 1, wherein the following conditional formula (A6) is satisfied:


−10<{(ywmax−Ymax)/Ymax}×100<−25  (A6)

where
ywmax represents a maximum real image height at a wide angle end, and
Ymax represents a maximum ideal image height.

7. The zoom lens system according to claim 1, wherein the following conditional formulas (B1) to (B3) are satisfied:


7<β2t/β2w<10  (B1)



5<β3t/β3w<12  (B2)



0.7<(β2t/β2w)/(β3t/(β3w)<1.65  (B3)

where
β2t represents a lateral magnification of the second lens group at a telephoto end,
β2w represents a lateral magnification of the second lens group at a wide angle end,
β3t represents a lateral magnification of the third lens group at the telephoto end, and
β3w represents a lateral magnification of the third lens group at the wide angle end.

8. The zoom lens system according to claim 2,
wherein
the third lens group satisfies the following conditional formula (A1):


0.5<f3/√(fw×ft)<0.9  (A1)


where
f3 represents a focal length of the third lens group,
fw represents a focal length of a whole system at a wide angle end, and
ft represents a focal length of the whole system at a telephoto end.

9. The zoom lens system according to claim 2,
wherein,
of the positive lens elements included in the cemented lens element, one that is disposed closest to the object side has an aspherical surface, and
a radius of curvature of the aspherical surface is larger than a reference radius of curvature by a larger value farther away from an optical axis.

10. The zoom lens system according to claim 2, wherein the following conditional formula (A6) is satisfied:


−10<{(ywmax−Ymax)/Ymax}×100<−25  (A6)

where
ywmax represents a maximum real image height at a wide angle end, and
Ymax represents a maximum ideal image height.

11. The zoom lens system according to claim 2, wherein the following conditional formulas (B1) to (B3) are satisfied:


7<β2t/β2w<10  (B1)



5<β3t/β3w<12  (B2)



0.7<(β2t/β2w)/(β3t/β3w)<1.65  (B3)

where
β2t represents a lateral magnification of the second lens group at a telephoto end,
β2w represents a lateral magnification of the second lens group at a wide angle end,
β3t represents a lateral magnification of the third lens group at the telephoto end, and
β3w represents a lateral magnification of the third lens group at the wide angle end.

12. The zoom lens system according to claim 3, wherein
the third lens group satisfies the following conditional formula (A1):


0.5<f3/√(fw×ft)<0.9  (A1)


where
f3 represents a focal length of the third lens group,
fw represents a focal length of a whole system at the wide angle end, and
ft represents a focal length of the whole system at the telephoto end.

13. The zoom lens system according to claim 3,
wherein,
of the positive lens elements included in the cemented lens element, one that is disposed closest to the object side has an aspherical surface, and
a radius of curvature of the aspherical surface is larger than a reference radius of curvature by a larger value farther away from an optical axis.

14. The zoom lens system according to claim 3, wherein the following conditional formula (A6) is satisfied:


−10<{(ywmax−Ymax)/Ymax}×100<−25  (A6)

where
ywmax represents a maximum real image height at the wide angle end, and
Ymax represents a maximum ideal image height.

15. The zoom lens system according to claim 3, wherein the following conditional formulas (B1) to (B3) are satisfied:


7<β2t/β2w<10  (B1)



5<β3t/β3w<12  (B2)



0.7<(β2t/β2w)/(β3t/β3w)<1.65  (B3)

where
β2t represents a lateral magnification of the second lens group at the telephoto end,
β2w represents a lateral magnification of the second lens group at the wide angle end,
β3t represents a lateral magnification of the third lens group at the telephoto end, and
β3w represents a lateral magnification of the third lens group at the wide angle end.

16. An imaging optical device comprising:
a zoom lens system according to claim 1; and
an image sensing device that converts an optical image formed on a light receiving surface into an electric signal,
wherein
the zoom lens system is arranged such that an optical image of a subject is formed on the light receiving surface of the image sensing device.

17. A digital apparatus comprising the imaging optical device according to claim 16 so as to be additionally provided with at least one of a function of shooting a still image of the subject and a function of shooting a moving image of the subject.

18. The digital apparatus according to claim 17,
wherein
the digital apparatus is one of a digital camera, a surveillance camera, and a portable terminal unit equipped with an image input function.

19. An imaging optical device comprising:
a zoom lens system according to claim 2; and
an image sensing device that converts an optical image formed on a light receiving surface into an electric signal,
wherein
the zoom lens system is arranged such that an optical image of a subject is formed on the light receiving surface of the image sensing device.

20. An imaging optical device comprising:
a zoom lens system according to claim 3; and
an image sensing device that converts an optical image formed on a light receiving surface into an electric signal,
wherein
the zoom lens system is arranged such that an optical image of a subject is formed on the light receiving surface of the image sensing device.