JP5373514B2 - Zoom lens and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens and an imaging device achieving miniaturization as a whole by lessening the number of lenses. <P>SOLUTION: The zoom lens includes a negative first lens group G1, a positive second lens group G2, a negative third lens group G3, and a positive fourth lens group G4. The first lens group G1 is constituted of a negative lens L11, a reflection member (rectangular prism LP), and a positive lens L12. The second lens group G2 is constituted of two positive lenses. The third lens group G3 is constituted of two or less lenses including a negative lens directing a concave face to an image face side. When an abbe's number for a d line of the negative lens L11 in the first lens group G1 is &nu;d1n, an abbe's number for a d line of the positive lens L12 is &nu;d1p, a refractive index for a d line of the negative lens L11 is Nd1n, an entire system focal distance in a wide angle end is fw, and a focal distance of the second lens group G2 is f2, the following conditional inequalities are satisfied. The inequality (1): &nu;d1n&gt;40, the inequality (2): 15&lt;&nu;d1p&lt;30, the inequality (3): Nd1n&gt;1.55, and the inequality (4): 0.9&lt;f2/fw&lt;2.5. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a zoom lens and an imaging apparatus that are suitably used for a video camera, a digital still camera, a personal digital assistant (PDA), and the like.

  In recent years, in an imaging apparatus such as a digital still camera, as the imaging element such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) has been miniaturized, the entire apparatus is required to be downsized. On the other hand, as a small zoom lens system that is most suitable for digital still cameras and portable terminal devices, a so-called bendable zoom lens is conventionally provided with a reflecting member such as a right-angle prism in the lens system and the optical path is bent at a right angle in the middle. Is known (see Patent Documents 1 to 5). A so-called negative lead type in which the first lens group has a negative refractive power is known as a bending zoom lens that is advantageous for downsizing and widening the angle. For example, in Patent Documents 1 to 3, negative, positive, negative, and positive lens groups are arranged in order from the object side, and the bending type is configured to perform zooming by moving the second lens group and the third lens group. A zoom lens is disclosed.

JP 2006-330349 A JP 2006-284790 A JP 2007-86307 A JP 2003-302575 A JP 2006-119324 A

  Although the bendable zoom lenses described in Patent Documents 1 to 3 are reduced in size, it is necessary to further reduce the size particularly when they are mounted on a camera for a portable terminal device. As a configuration common to Patent Documents 1 to 3, two lenses are provided on the image plane side with respect to the reflecting member of the first lens group. If even one of these lenses can be reduced, the lens is small. And cost reduction can be realized. Since the lenses arranged in the first lens group have a large outer diameter, the cost is greatly affected. Further, by reducing the number of lenses in the first lens group, it is possible to increase the amount of movement of the second lens group when considering the same total lens length. Thereby, the power which each lens bears can be made small, and the sensitivity of the performance deterioration with respect to a manufacturing error or an assembly error can be lowered. Furthermore, image plane fluctuations accompanying zooming can be suppressed.

  Another configuration common to Patent Documents 1 to 3 is that the second lens group is composed of two positive lenses and one negative lens. Therefore, it is conceivable to reduce the number of lenses for the second lens group. However, it is not easy to reduce the number of positive lenses. This is because the power distributed to the two positive lenses needs to be supplemented by one positive lens. If the power of a single lens becomes too strong, aberration correction becomes difficult, and the sensitivity of performance deterioration to manufacturing errors and assembly errors increases, which is not preferable. In order to prevent this, it is necessary to weaken the power of the second lens group, which is disadvantageous for downsizing. Therefore, it is conceivable to reduce the negative lens and to configure with two positive lenses. By devising the power and materials of the two positive lenses, chromatic aberration can be corrected well. By eliminating the negative lens from the second lens group, the power of the entire second lens group can be increased with the same power as the positive lens in the case of the three-lens configuration, so that the amount of movement of the second lens group can be reduced and the size can be reduced. It becomes advantageous for the conversion.

  Patent Document 4 discloses an example in which the number of lenses arranged on the image plane side of the reflecting member in the first lens group is one, but the zoom ratio is as small as about 2 times. In addition, since the first lens group is made of a material having a low refractive index and low dispersion, when the magnification is increased, the negative lens disposed closest to the object side of the first lens group becomes large. The thickness of the bent lens unit is undesirably increased. Further, as described in Patent Document 5, many examples have been proposed in which the prism itself as the reflecting member has power. In this case, there are many examples in which the lens is not arranged on the image plane side of the prism in the first lens group. However, when such a prism is processed, it is not preferable because it takes much time and cost.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a zoom lens and an image pickup apparatus that have a small number of lenses and are reduced in size as a whole.

The first zoom lens according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. The fourth lens group has a positive refractive power, and zooming is performed by changing the interval on the optical axis of each lens group. The first lens group includes, in order from the object side, a negative lens, a reflecting member that reflects incident light and bends the optical path, and a positive lens. The second lens group is composed of two positive lenses. The third lens group includes two or less lenses including a negative lens having a concave surface facing the image surface side. The Abbe number for the d-line of the negative lens in the first lens group is νd1n, the Abbe number for the d-line of the positive lens in the first lens group is νd1p, and the refractive index for the d-line of the negative lens in the first lens group. Is Nd1n, the focal length of the entire system at the wide angle end is fw, the focal length of the second lens group is f2 , and the refractive index for the d-line of the material constituting the reflecting member in the first lens group is Nd1p , The conditional expression is satisfied.
νd1n> 40 (1)
15 <νd1p <30 (2)
Nd1n> 1.55 (3)
0.9 <f2 / fw <2.5 (4)
Nd1p> 1.78 (8)
The second zoom lens according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens having a negative refractive power. The lens unit is composed of a group and a fourth lens group having a positive refractive power, and zooming is performed by changing the interval on the optical axis of each lens group. The first lens group includes, in order from the object side, a negative lens, a reflecting member that reflects incident light and bends the optical path, and a positive lens. The second lens group is composed of two positive lenses. The third lens group includes two or less lenses including a negative lens having a concave surface facing the image surface side. The fourth lens group is fixed during zooming. The Abbe number for the d-line of the negative lens in the first lens group is νd1n, the Abbe number for the d-line of the positive lens in the first lens group is νd1p, and the refractive index for the d-line of the negative lens in the first lens group. Is Nd1n, the focal length of the entire system at the wide-angle end is fw, and the focal length of the second lens group is f2, the following conditional expression is satisfied.
νd1n> 40 (1)
15 <νd1p <30 (2)
Nd1n> 1.55 (3)
0.9 <f2 / fw <2.5 (4)

In the zoom lens according to the present invention, since the optical path is bent by the reflecting member disposed in the first lens group, the thickness direction of the optical system is maintained while maintaining good optical performance. Can be reduced, and it is easy to reduce the thickness when incorporated in an imaging apparatus. Further, in order from the object side, four lens groups having refractive powers of negative, positive, negative, and positive are arranged, and zooming is performed by changing the interval on the optical axis of each lens group. By using a group-type zoom lens, the overall length can be easily shortened. Further, by optimizing the configuration of each lens group while suppressing the number of lenses by configuring each of the first lens group and the second lens group with two lenses, the number of lenses is reduced, and the optical system The overall size can be easily reduced.
Further, by appropriately adopting and satisfying the following preferable configuration, it becomes easy to further reduce the size while maintaining good optical performance as the entire lens system.

In the zoom lens according to the present invention, it is preferable that the following conditional expression is satisfied when the Abbe number with respect to the d-line of at least one positive lens in the second lens group is νd2p.
νd2p> 60 (5)

The second lens group may be composed of one plastic lens and one glass lens. In this case, it is preferable that the following conditional expression is satisfied when the focal length of the plastic lens in the second lens group is f2p.
2.5 <f2p / f2 <6.0 (6)

Further, when the focal length of the first lens group is f1, and the focal length of the positive lens in the first lens group is f1p, it is preferable that the following conditional expression is satisfied.
| F1p / f1 |> 4.0 (7)

  The first lens group preferably has at least one aspheric lens. Further, it is preferable that the reflecting member is a right-angle prism, and the incident surface and the output surface of the right-angle prism do not have refractive power.

  In addition, a stop may be disposed between the second lens group and the third lens group. In this case, the aperture may be moved integrally with the third lens group at the time of zooming.

Also, it may be adapted to perform focusing by moving the third lens group or the fourth lens group on the optical axis.

An image pickup apparatus according to the present invention includes the zoom lens according to the present invention and an image pickup element that outputs an image pickup signal corresponding to an optical image formed by the zoom lens.
In the image pickup apparatus according to the present invention, the high-performance zoom lens of the present invention that has been reduced in size is used as the image pickup lens, whereby the entire apparatus can be reduced in size.

  According to the zoom lens of the present invention, the basic configuration is a flexural four-group zoom configuration that is advantageous for miniaturization, and each of the first lens group and the second lens group is composed of two lenses. Since the configuration of each lens group is optimized while suppressing the number of lenses, the number of lenses is smaller than in the prior art, and the overall size can be reduced.

  Further, according to the imaging apparatus of the present invention, since the high-performance zoom lens of the present invention, which has been reduced in size, is used as an imaging lens, the overall size of the apparatus can be reduced while maintaining good imaging performance. Can be achieved.

FIG. 1 is a lens cross-sectional view illustrating a first configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 1; FIG. 2 is a lens cross-sectional view illustrating a second configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 2; FIG. 9 is a lens cross-sectional view illustrating a third configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 3; 4 is a lens cross-sectional view illustrating a fourth configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 4; FIG. 5 is a lens cross-sectional view illustrating a fifth configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 5. FIG. FIG. 2 is a lens cross-sectional view illustrating the zoom lens illustrated in FIG. 1 in a state where an optical path is bent. FIG. 4 is an aberration diagram showing various aberrations at the wide-angle end of the zoom lens according to Example 1; (A) shows spherical aberration, (B) shows astigmatism, (C) shows distortion, and (D) shows lateral chromatic aberration. FIG. 4 is an aberration diagram showing various aberrations at the telephoto end of the zoom lens according to Example 1, where (A) shows spherical aberration, (B) shows astigmatism, (C) shows distortion, and (D) shows lateral chromatic aberration. FIG. 6 is an aberration diagram showing various aberrations at the wide-angle end of the zoom lens according to Example 2, where (A) shows spherical aberration, (B) shows astigmatism, (C) shows distortion, and (D) shows lateral chromatic aberration. FIG. 6 is an aberration diagram showing various aberrations at the telephoto end of the zoom lens according to Example 2, where (A) shows spherical aberration, (B) shows astigmatism, (C) shows distortion, and (D) shows lateral chromatic aberration. FIG. 6 is an aberration diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 3, wherein (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 6 is an aberration diagram showing various aberrations at the telephoto end of the zoom lens according to Example 3, where (A) shows spherical aberration, (B) shows astigmatism, (C) shows distortion, and (D) shows lateral chromatic aberration. FIG. 6A is an aberration diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 4; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 6 is an aberration diagram illustrating various aberrations at the telephoto end of the zoom lens according to Example 4, where (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 9A is an aberration diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 5; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 6A is an aberration diagram illustrating various aberrations at a telephoto end of the zoom lens according to Example 5; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. 1 is a front external view illustrating a configuration example of a digital camera as an imaging apparatus according to an embodiment of the present invention. It is a back side appearance figure showing an example of 1 composition of a digital camera as an imaging device concerning one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A and 1B show a first configuration example of a zoom lens according to an embodiment of the present invention. This configuration example corresponds to the lens configuration of the first numerical example described later. 1A shows the arrangement of the optical system at the infinity in-focus state and at the wide-angle end (shortest focal length state), and FIG. 1B shows the infinity in-focus state and the telephoto end (longest focal length state). This corresponds to the arrangement of the optical system. Similarly, cross-sectional configurations of second to fifth configuration examples corresponding to lens configurations of second to fifth numerical examples described later are shown in FIGS. 2 (A), 2 (B) to 5 (A), respectively. Shown in (B). In FIGS. 1A and 1B to FIGS. 5A and 5B, the symbol Ri increases sequentially toward the image side (imaging side), with the most object side component surface being the first. In this way, the radius of curvature of the i-th surface that is labeled is shown. The symbol Di indicates the surface interval on the optical axis Z1 between the i-th surface and the i + 1-th surface. In addition, about the code | symbol Di, the code | symbol is attached | subjected only to the surface interval (For example, D6, D10, D13 about a 1st structural example) of the part which changes with magnification.

  This zoom lens includes a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 in order from the object side along the optical axis Z1. The optical aperture stop St is disposed between the second lens group G2 and the third lens group G3.

  This zoom lens can be mounted not only on photographing devices such as a video camera and a digital still camera but also on an information portable terminal such as a PDA. On the image side of the zoom lens, a member corresponding to the configuration of the photographing unit of the mounted camera is arranged. For example, an imaging element 100 such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) is disposed on the image plane (imaging plane) of the zoom lens. The image sensor 100 outputs an image signal corresponding to the optical image formed by the zoom lens. At least the zoom lens and the image sensor 100 constitute the image pickup apparatus in the present embodiment. Various optical members GC may be arranged between the final lens group (fourth lens group G4) and the image sensor 100 according to the configuration on the camera side where the lens is mounted. For example, a flat optical member such as a cover glass for protecting the imaging surface or an infrared cut filter may be disposed.

  This zoom lens performs zooming by changing the interval on the optical axis of each lens group. For example, the second lens group G2 and the third lens group G3 move on the optical axis Z1 during zooming. Further, the third lens group G3 or the fourth lens group G4 may be moved at the time of focusing. The first lens group G1 is preferably always fixed during zooming and focusing. The fourth lens group G4 is preferably fixed at the time of zooming. The aperture stop St moves with the third lens group G3, for example. In FIGS. 1A and 1B to FIGS. 5A and 5B, the trajectory of each moving group when zooming from the wide-angle end to the telephoto end is indicated by solid-line arrows.

  The first lens group G1 has a negative refractive power as a whole. The first lens group G1 includes, in order from the object side, a negative lens L11, a right-angle prism LP as a reflecting member that reflects incident light and bends the optical path, and a positive lens L12. The first lens group G1 preferably has at least one aspheric lens.

  Here, the zoom lens according to the present embodiment is a bending optical system. Actually, as shown in FIG. 6, in the first lens group G1, for example, the optical path is approximately 90 ° on the internal reflection surface of the right-angle prism LP. It is bent. FIG. 6 corresponds to the first configuration example shown in FIG. 1A, but the same applies to other configuration examples. In FIGS. 1A and 1B to FIGS. 5A and 5B, the optical axis Z1 is a straight line, the internal reflection surface of the right-angle prism LP is omitted, and the same is developed in the same direction. It is shown as a typical optical system. Instead of the right-angle prism LP, another reflecting member such as a reflecting mirror may be used. However, it is preferable to use the right-angle prism LP as the reflecting member because the apparent optical path length can be shortened compared to the case where the reflecting mirror is used. Therefore, the first lens group G1 can be reduced in size, and the whole can be reduced in size. . Further, the entrance surface and the exit surface of the right-angle prism LP are preferably flat surfaces (curvature radius ∞) with respect to the optical axis Z1, and preferably have no refractive power. Thereby, cost reduction can be achieved.

  The second lens group G2 has a positive refractive power as a whole. The second lens group G2 is composed of two positive lenses. Of the two positive lenses in the second lens group G2, it is preferable that one is a plastic lens and the other is a glass lens. For example, the first positive lens L21 made of a plastic lens and the second positive lens L22 made of glass are preferable. The second lens group G2 preferably has at least one aspheric lens.

  The third lens group G3 has a negative refractive power as a whole. The third lens group G3 is composed of two or less lenses (only the first lens L31, or the first lens L31 and the second lens L32), and includes a negative lens having a concave surface facing the image plane side. . In the first to second configuration examples shown in FIGS. 1A and 1B to FIGS. 2A and 2B, the third lens group G3 includes only the first lens L31. In this example, the first lens L31 is a negative lens having a concave surface on the image plane side. In the third to fifth configuration examples shown in FIGS. 3A and 3B to FIGS. 5A and 5B, the third lens group G3 includes the first lens L31 and the second lens L32. In this example, the second lens L32 is a negative lens having a concave surface directed to the image plane side.

  The fourth lens group G4 has a positive refractive power as a whole. The fourth lens group G4 includes two or less lenses (only the first lens L41, or the first lens L41 and the second lens L42).

In this zoom lens, the Abbe number with respect to the d line of the negative lens L11 in the first lens group G1 is νd1n, the Abbe number with respect to the d line of the positive lens L12 is νd1p, the refractive index with respect to the d line of the negative lens L11 is Nd1n, and the wide angle end. When the focal length of the entire system is fw and the focal length of the second lens group G2 is f2, the following conditional expression is satisfied.
νd1n> 40 (1)
15 <νd1p <30 (2)
Nd1n> 1.55 (3)
0.9 <f2 / fw <2.5 (4)

Further, when the Abbe number with respect to the d-line of at least one positive lens in the second lens group G2 is νd2p, it is preferable that the following conditional expression is satisfied.
νd2p> 60 (5)

Further, when the focal length of the plastic lens (first positive lens L21) in the second lens group G2 is f2p, it is preferable that the following conditional expression is satisfied.
2.5 <f2p / f2 <6.0 (6)

Further, when the focal length of the first lens group G1 is f1, and the focal length of the positive lens L12 in the first lens group G1 is f1p, it is preferable that the following conditional expression is satisfied.
| F1p / f1 |> 4.0 (7)

Further, it is preferable that the following conditional expression is satisfied when the refractive index with respect to the d-line of the material constituting the reflecting member (right angle prism LP) in the first lens group G1 is Nd1p.
Nd1p> 1.78 (8)

  17 and 18 show a digital still camera as an example of an image pickup apparatus on which the zoom lens is mounted. In particular, FIG. 17 shows the external appearance of the digital still camera 10 viewed from the front side, and FIG. 18 shows the external appearance of the digital still camera 10 viewed from the back side. The digital still camera 10 includes a strobe light emitting unit 21 that emits strobe light at an upper central portion on the front side. In addition, on the front side thereof, a photographing opening 22 through which light from a photographing target enters is provided in a side portion of the strobe light emitting unit 21. The digital still camera 10 also includes a release button 23 and a power button 24 on the upper surface side. The digital still camera 10 also includes a display unit 25 and operation units 26 and 27 on the back side. The display unit 25 is for displaying a captured image. In this digital still camera 10, by pressing the release button 23, a still image for one frame is shot, and image data obtained by this shooting is a memory card (not shown) attached to the digital still camera 10. Recorded).

  The digital still camera 10 includes an imaging lens 1 inside a casing. As the imaging lens 1, the zoom lens according to the present embodiment is used. The imaging lens 1 is arranged so that the lens L11 closest to the object side is positioned in the photographing aperture 22 provided on the front side. The imaging lens 1 is incorporated in the vertical direction as a whole inside the digital still camera 10 so that the optical axis Z1 after bending by the right-angle prism LP coincides with the vertical direction of the camera body. The optical axis Z1 after bending may be incorporated in the horizontal direction as a whole inside the digital still camera 10 so that the optical axis Z1 is in the horizontal direction of the camera body.

Next, operations and effects of the zoom lens configured as described above will be described.
In this zoom lens, since the optical path is bent by a reflecting member disposed in the first lens group G1, the optical system is maintained in the thickness direction of the optical system while maintaining good optical performance. The length is suppressed, and it is easy to reduce the thickness when incorporated in an imaging apparatus. Further, in order from the object side, four lens groups having refractive powers of negative, positive, negative, and positive are arranged, and zooming is performed by changing the interval on the optical axis of each lens group. By using a group-type zoom lens, the overall length can be easily shortened. The first lens group G1 and the second lens group G2 are each composed of two lenses, and the configuration of each lens group is optimized while suppressing the number of lenses, thereby reducing the number of lenses. It is easy to reduce the size of the entire optical system.

  This type of zoom lens has an FNo. The fluctuation of is large. Therefore, FNo. In order to brighten the FNo. Needs to be brightened (open diameter is increased). However, FNo. If the lens is made brighter than necessary, aberration correction becomes difficult and the lens becomes large. Therefore, by controlling the opening diameter to be different for each zoom magnification (opening restriction), such as making the opening diameter at the wide-angle end smaller than the opening diameter at the telephoto end, the variation in brightness can be increased. Such control may be performed as necessary.

  Hereinafter, the operation and effect relating to the conditional expression described above will be described in more detail.

Conditional expression (1) defines the Abbe number of the negative lens L11 in the first lens group G1. Conditional expression (2) defines the Abbe number of the positive lens L12 in the first lens group G1. Conditional expressions (1) and (2) are conditions for satisfactorily correcting chromatic aberration over the entire zoom range. If the lower limit of conditional expression (1) is exceeded, or if the lower limit or lower limit of conditional expression (2) is exceeded, it will be difficult to satisfactorily correct chromatic aberration over the entire zoom range. Further, it is difficult to balance axial chromatic aberration and lateral chromatic aberration, which is not preferable.
In order to obtain higher optical performance, the numerical ranges of conditional expressions (1) and (2) are
νd1n> 45 (1 ′)
16 <νd1p <29 (2 ′)
It is desirable that

Conditional expression (3) defines the refractive index of the negative lens L11 in the first lens group G1. If the lower limit of conditional expression (3) is not reached, the curvature of the lens becomes large, and the thickness after bending becomes large, which is not preferable.
In order to obtain higher optical performance, the numerical range of conditional expression (3) is
Nd1n> 1.56 (3 ')
It is desirable that

Conditional expression (4) is obtained by normalizing the focal length f2 of the second lens group G2 with the focal length fw of the entire system at the wide angle end. If the lower limit of conditional expression (4) is not reached, the curvature of the lens in the second lens group G2 becomes large, making it difficult to correct aberrations and increasing aberration fluctuations accompanying zooming, which is not preferable. In addition, it is preferable to use a low dispersion material for the positive lens of the second lens group G2, but a material with low dispersion also has a low refractive index, so it is necessary if it falls below the lower limit of conditional expression (4). This is not preferable because the center thickness for securing a large edge (edge) is increased. Furthermore, the sensitivity of performance degradation due to manufacturing errors and assembly errors increases, which is not preferable. Conversely, if the upper limit of conditional expression (4) is exceeded, the amount of movement of the second lens group G2 will increase and the lens will become larger.
In order to obtain higher optical performance, the numerical range of conditional expression (4) is
1.0 <f2 / fw <2.4 (4 ')
It is desirable that

Conditional expression (5) defines the average Abbe number of the positive lenses constituting the second lens group G2, and contributes to the correction of chromatic aberration of magnification over the entire zoom range. If the lower limit of conditional expression (5) is not reached, chromatic aberration increases, and fluctuations in chromatic aberration associated with zooming increase.
In order to obtain higher optical performance, the numerical range of conditional expression (5) is
νd2p> 65 (5 ′)
It is desirable that

Conditional expression (6) is obtained by normalizing the focal length f2p of the plastic lens (first positive lens L21) arranged in the second lens group G2 with the focal length f2 of the second lens group G2. If the lower limit of conditional expression (6) is not reached, characteristic changes such as image plane position fluctuations increase with temperature change, which is not preferable. On the contrary, if the value exceeds the upper limit, the amount of movement of the second lens group G2 becomes large and the lens system becomes large, which is not preferable.
In order to obtain higher optical performance, the numerical range of conditional expression (6) is
2.7 <f2p / f2 <5.9 (6 ′)
It is desirable that

Conditional expression (7) is obtained by normalizing the focal length f1p of the positive lens L12 arranged in the first lens group G1 with the focal length f1 of the first lens group G1. If the lower limit of conditional expression (7) is not reached, the powers of the positive lens L12 and the negative lens L11 arranged in the first lens group G1 are both strong, and the thickness and length of the bent lens system are preferably increased. Absent. If the lens power is weak enough to satisfy the range of conditional expression (7), the lens may be made of plastic, and at that time, cost reduction can be realized.
In order to obtain higher optical performance, the numerical range of conditional expression (7) is
| F1p / f1 |> 4.5 (7 ')
It is desirable that

Conditional expression (8) defines the refractive index of the reflecting member (right-angle prism LP) disposed in the first lens group G1. In a lens type in which the power of the first lens group G1 is negative, such as this zoom lens, the first negative lens L11 arranged closest to the object side needs to be made of a material having a small dispersion. In general, a material with low dispersion has a low refractive index, and if the first lens group G1 is made of such a material, the curvature of the lens becomes large. In that case, there arises a problem that the thickness of the bent lens unit becomes large. Therefore, it is preferable to take measures such as reducing the effective diameter of the first negative lens L11 or reducing the reflective member by using a high refractive index material as the material constituting the reflective member.
In order to obtain higher optical performance, the numerical range of conditional expression (8) is
Nd1p> 1.80 (8 ')
It is desirable that

  As described above, according to the zoom lens according to the present embodiment, the basic configuration is a flexural four-group zoom configuration that is advantageous for downsizing, and the first lens group G1 and the second lens group G2 are each two. Since the configuration of each lens unit is optimized while suppressing the number of lenses by configuring the lens with a single lens, the number of lenses is smaller than in the prior art, and the overall size can be reduced. In addition, according to the imaging apparatus equipped with the zoom lens according to the present embodiment, it is possible to reduce the size of the entire apparatus while maintaining good imaging performance.

  Next, specific numerical examples of the zoom lens according to the present embodiment will be described. Hereinafter, a plurality of numerical examples will be described in part.

[Numerical Example 1]
[Table 1] to [Table 3] show specific lens data corresponding to the configuration of the zoom lens shown in FIGS. In particular, [Table 1] shows the basic lens data, and [Table 2] and [Table 3] show other data. In the field of the surface number Si in the lens data shown in [Table 1], for the zoom lens according to Example 1, the surface of the component closest to the object side is the first, and is increased sequentially toward the image side. The number of the i-th surface to which the reference numeral is attached is shown. In the column of the radius of curvature Ri, the value (mm) of the radius of curvature of the i-th surface from the object side is shown in correspondence with the reference symbol Ri in FIG. Similarly, the column of the surface interval Di indicates the interval (mm) on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the object side. In the column Ndj, the refractive index value for the d-line (587.6 nm) of the j-th optical element from the object side is shown. The column of νdj shows the Abbe number value for the d-line of the j-th optical element from the object side.

  In the zoom lens according to Example 1, since the second lens group G2 and the third lens group G3 move on the optical axis with zooming, the front-to-rear surface distances D6, D10, and D13 of these moving groups. The value of is variable. [Table 2] shows values at the wide-angle end and the telephoto end as data at the time of zooming of these variable surface intervals D6, D10, and D13. [Table 2] also shows values of paraxial focal length f (mm), field angle (2ω), and F number (FNo.) Of the entire system at the wide-angle end and the telephoto end as various data.

  In the lens data of [Table 1], the symbol “*” attached to the left side of the surface number indicates that the lens surface has an aspherical shape. The zoom lens according to Example 1 includes an image-side surface S6 of the positive lens L12 in the first lens group G1, both surfaces S7 and S8 of the first positive lens L21 in the second lens group G2, and a fourth lens. Both surfaces S14 and S15 of the first lens L41 in the group G4 are aspherical. The basic lens data in [Table 1] shows numerical values of the radius of curvature near the optical axis as the radius of curvature of these aspheric surfaces.

Table 3 shows aspherical data in the zoom lens according to Example 1. In the numerical values shown as aspherical data, the symbol “E” indicates that the subsequent numerical value is a “power exponent” with a base of 10, and the numerical value represented by an exponential function with the base of 10 is Indicates that the value before “E” is multiplied. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”.

As the aspheric surface data of the zoom lens according to Example 1, the values of the coefficients RA _i and KA in the aspheric surface equation represented by the following equation (A) are described. More specifically, Z is the length (mm) of a perpendicular line drawn from a point on the aspheric surface at a height h from the optical axis to the tangential plane (plane perpendicular to the optical axis) of the apex of the aspheric surface. Show.
Z = C · h ² / {1+ (1−KA · C ² · h ² ) ^1/2 } + ΣRA _i · h ⁱ (A)
(I = n, n: an integer of 3 or more)
However,
Z: Depth of aspheric surface (mm)
h: Distance from the optical axis to the lens surface (height) (mm)
KA: aspheric constant C: paraxial curvature = 1 / R
(R: paraxial radius of curvature)
RA _i : i-th aspheric coefficient

[Numerical Examples 2 to 5]
Similar to the zoom lens according to Example 1 above, specific lens data corresponding to the configuration of the zoom lens shown in FIGS. Table 6] shows. Similarly, specific lens data corresponding to the configuration of the zoom lens shown in FIGS. 3A and 3B to FIGS. 5A and 5B is set as Examples 3 to 5 [Table 7]. ] To [Table 15].

  [Table 16] shows a summary of the values for the conditional expressions described above for each example. As can be seen from Table 16, the conditions of conditional expressions (1) to (8) are satisfied for each example.

[Aberration diagram]
7A to 7D respectively show spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide angle end in the zoom lens according to Example 1. FIG. 8A to 8D show similar aberrations at the telephoto end. Each aberration diagram shows an aberration with the d-line (587.6 nm) as a reference wavelength. The spherical aberration diagram and the lateral chromatic aberration diagram also show aberrations at a wavelength of 460 nm and a wavelength of 615 nm. In the astigmatism diagram, the solid line indicates the sagittal direction and the broken line indicates the tangential direction. FNO. Indicates an F value, and ω indicates a half angle of view.

  Similarly, various aberrations regarding the zoom lens according to Example 2 are shown in FIGS. 9A to 9D (wide-angle end) and FIGS. 10A to 10D (telephoto end). Similarly, various aberrations of the zoom lenses according to Examples 3 to 7 are shown in FIGS. 11 to 16 (A) to (D).

  As can be seen from the above numerical data and aberration diagrams, in each example, various aberrations are corrected well in each zooming range, and while the zooming ratio is high, the total lens length is short and downsizing is achieved. Zoom lens has been realized.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible. For example, the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the above numerical examples, and may take other values.

  GC ... optical member, G1 ... first lens group, G2 ... second lens group, G3 ... third lens group, G4 ... fourth lens group, LP ... right angle prism (reflective member), St ... aperture stop, Ri ... object Radius of curvature of the i-th lens surface from the side, Di... The surface interval between the i-th and i + 1-th lens surfaces from the object side, Z1... The optical axis, 100.

Claims (11)

In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power It is made up of a group, and is made to perform zooming by changing the interval on the optical axis of each lens group,
The first lens group includes, in order from the object side, a negative lens, a reflecting member that reflects incident light and bends the optical path, and a positive lens.
The second lens group is composed of two positive lenses,
The third lens group is composed of two or less lenses including a negative lens having a concave surface on the image plane side,
The Abbe number for the d-line of the negative lens in the first lens group is νd1n, the Abbe number for the d-line of the positive lens in the first lens group is νd1p, and the refraction of the negative lens in the first lens group with respect to the d-line. When the refractive index is Nd1n, the focal length of the entire system at the wide angle end is fw, the focal length of the second lens group is f2 , and the refractive index of the material constituting the reflecting member in the first lens group with respect to the d-line is Nd1p. a zoom lens which satisfies the following condition.
νd1n> 40 (1)
15 <νd1p <30 (2)
Nd1n> 1.55 (3)
0.9 <f2 / fw <2.5 (4)
Nd1p> 1.78 (8) In order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens having a positive refractive power It is made up of a group, and is made to perform zooming by changing the interval on the optical axis of each lens group,
The first lens group includes, in order from the object side, a negative lens, a reflecting member that reflects incident light and bends the optical path, and a positive lens.
The second lens group is composed of two positive lenses,
The third lens group is composed of two or less lenses including a negative lens having a concave surface on the image plane side,
The fourth lens group is fixed at the time of zooming,
The Abbe number for the d-line of the negative lens in the first lens group is νd1n, the Abbe number for the d-line of the positive lens in the first lens group is νd1p, and the refraction of the negative lens in the first lens group with respect to the d-line. A zoom lens characterized by satisfying the following conditional expression, where Nd1n is the rate, fw is the focal length of the entire system at the wide-angle end, and f2 is the focal length of the second lens group.
νd1n> 40 (1)
15 <νd1p <30 (2)
Nd1n> 1.55 (3)
0.9 <f2 / fw <2.5 (4) Wherein when an Abbe number was νd2p the d-line of the at least one positive lens in the second lens group, the zoom lens according to claim 1 or 2, characterized by satisfying the following conditional expression.
νd2p> 60 (5) The zoom lens according to any one of claims 1 to 3, wherein the second lens group includes one plastic lens and one glass lens. The zoom lens according to claim 4 , wherein the following conditional expression is satisfied when a focal length of the plastic lens in the second lens group is f2p.
2.5 <f2p / f2 <6.0 (6) The focal length of the first lens group f1, when the f1p the focal length of the positive lens in said first lens group, any one of claims 1 to 5, characterized by satisfying the following condition The zoom lens according to item.
| F1p / f1 |> 4.0 (7) The zoom lens according to any one of claims 1 to 6, wherein the first lens group includes at least one aspheric lens. The zoom lens according to any one of claims 1 to 7, wherein the reflecting member is a right-angle prism, and an incident surface and an output surface of the right-angle prism do not have refractive power. The zoom lens according to any one of claims 1 to 8, wherein a diaphragm is disposed between the second lens group and the third lens group. 10. The zoom lens according to claim 9, wherein the aperture is configured to move integrally with the third lens group at the time of zooming. The zoom lens according to any one of claims 1 to 10 ,
An imaging device comprising: an imaging element that outputs an imaging signal corresponding to an optical image formed by the zoom lens.

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