JP2011059496A - Zoom lens and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens and an imaging device with small characteristic change accompanying temperature change of plastic lenses while securing superior optical performance at low cost. <P>SOLUTION: The zoom lens includes a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power. The first lens group G1 includes a first lens (negative lens) L11 constituted of glass, a reflection member (rectangular prism LP) folding an optical path, and two or less lenses including the plastic lenses with smaller absolute values of refractive power than that of the negative lens L11. The second lens group G2 includes a positive lens constituted of glass and three or less lenses including the plastic lenses. When a composite focal distance of the plastic lenses included in an entire system is fpr, and an entire system focal distance in a wide angle end is fw, the following conditional inequality (1) is satisfied. The inequality (1):-0.3&lt;(1/fpr)&times;fw&lt;0.6. <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. It has been known. 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 and 2, 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 2007-86307 A

  Although the bendable zoom lenses described in Patent Documents 1 and 2 are reduced in size, it is indispensable to adopt an aspherical lens because of the reduction in size. Here, when the aspherical lens is formed of a glass mold lens, it becomes very expensive. However, it is difficult to simply substitute the glass mold lens with a plastic lens. The reason is that if a plastic lens with poor material selectivity is used, it becomes difficult to correct chromatic aberration, but first, the plastic lens has a large change in refractive power with a change in temperature compared to a glass lens. This is because a change in characteristics such as a change in image plane position becomes large. Therefore, it is necessary to have a power arrangement and a lens configuration that can employ a plastic lens.

  For example, regarding the first lens group, it may be possible to configure the lens with a single negative lens as the simplest configuration, but it is preferable to provide an aspherical shape when ensuring optical performance. However, since the negative lens has a strong negative power, it is difficult to form it with plastic. In that case, it is considered optimal to use a glass mold lens. Therefore, it is conceivable to provide one plastic aspherical lens in addition to the negative lens made of glass as the lens of the first lens group. Also for the moving groups such as the second lens group and the third lens group, the lens group needs to have a strong power for miniaturization, and the power of each lens tends to be strong. In this case, instead of using a plastic lens as a lens that requires power, the power distribution is devised to reduce the change in characteristics due to temperature changes by configuring a relatively weak lens with a plastic lens. Can do.

  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 imaging apparatus in which a characteristic change accompanying a temperature change of a plastic lens is small while ensuring good optical performance at a low cost. It is in.

The 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, a third lens group having a negative refractive power, and a positive lens It is composed of a fourth lens group having 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 made of glass, a reflecting member that reflects incident light and bends the optical path, and a plastic lens that has an absolute value of refractive power smaller than that of the negative lens. The second lens group is composed of three or less lenses including a positive lens made of glass and a plastic lens. When the combined focal length of the plastic lens included in the entire system is fpr and the focal length of the entire system at the wide angle end is fw, the following conditional expression is satisfied.
−0.3 <(1 / fpr) · fw <0.6 (1)
However,
1 / fpr = Σ (1 / fpri)
(I = integer greater than or equal to 2, fpri: focal length of i-th plastic lens)
And

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. By providing a plurality of plastic lenses, cost reduction can be realized. Furthermore, on the premise of using multiple plastic lenses, we have optimized the power distribution of the plastic lens and optimized the configuration of each lens group, ensuring good optical performance and characteristics associated with temperature changes. Change is suppressed.
Furthermore, by properly adopting and satisfying the following preferable configuration, it becomes easier to suppress the characteristic change accompanying the temperature change to be smaller 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 focal length of the first lens unit is f1.
1.4 <| f1 / fw | <2.5 (2)

Further, when the focal length of the second lens unit is f2, it is preferable that the following conditional expression is satisfied.
0.9 <f2 / fw <1.9 (3)

Further, when the focal length of the first lens group is f1 and the focal length of the plastic lens in the first lens group is f1p, it is preferable that the following conditional expression is satisfied.
| F1p / f1 |> 3.0 (4)

Further, when the focal length of the second lens group is f2 and the focal length of the plastic lens in the second lens group is f2p, it is preferable that the following conditional expression is satisfied.
| F2p / f2 |> 2.0 (5)

Further, when the refractive index with respect to the d-line of the material constituting the reflecting member in the first lens group is Nd1p, it is preferable that the following conditional expression is satisfied.
Nd1p> 1.78 (6)

  The first lens group may be composed of, in order from the object side, a negative lens, a reflecting member, and a plastic lens having a smaller refractive power than the negative lens. In addition, the first lens group includes, in order from the object side, a first negative lens made of glass, a reflecting member, a second negative lens made of glass, and a refractive power than the first negative lens. It may be configured of a plastic lens having a positive refractive power with a small absolute value. Further, the first lens group may be composed of a negative lens, a reflecting member, and two plastic lenses having a refractive power smaller than that of the negative lens in order from the object side.

  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.

  The fourth lens group may be fixed during zooming. Further, focusing may be performed 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 cost reduction and the high performance of the entire apparatus can be achieved by using the zoom lens of the present invention with the low cost and high performance as the image pickup lens.

  According to the zoom lens of the present invention, the basic configuration is a flexure type four-group zoom configuration that is advantageous for miniaturization, and furthermore, the optimization of the power distribution of the plastic lens and each Since the configuration of the lens group is optimized, it is possible to reduce the characteristic change accompanying the temperature change of the plastic lens while securing good optical performance at a low cost.

  In addition, according to the imaging apparatus of the present invention, the high-performance zoom lens with the low cost and high performance of the present invention is used as the imaging lens, so that while maintaining good imaging performance, Cost reduction and high performance of the entire apparatus 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. 6 is a lens cross-sectional view illustrating a sixth configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 6; FIG. 7 is a lens cross-sectional view illustrating a seventh configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 7. FIG. 8 is an eighth example configuration of the zoom lens according to an embodiment of the present invention, and is a lens cross-sectional view corresponding to Example 8. FIG. 9 is a lens cross-sectional view illustrating a ninth configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 9. 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. 10 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. FIG. 9A is an aberration diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 6; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 7A is an aberration diagram illustrating various types of aberration at the telephoto end of the zoom lens according to Example 6; (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 7; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 9A is an aberration diagram illustrating various types of aberration at the telephoto end of the zoom lens according to Example 7; (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 8; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 9A is an aberration diagram illustrating various types of aberration at the telephoto end of the zoom lens according to Example 8; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 10A is an aberration diagram illustrating various aberrations at the wide-angle end of the zoom lens according to Example 9; (A) illustrates spherical aberration, (B) illustrates astigmatism, (C) illustrates distortion, and (D) illustrates lateral chromatic aberration. FIG. 10A is an aberration diagram illustrating aberrations at the telephoto end of the zoom lens according to Example 9; (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 ninth configuration examples corresponding to lens configurations of second to ninth numerical examples described later are shown in FIGS. 2 (A), (B) to FIG. 9 (A), Shown in (B). In FIGS. 1 (A), (B) to 9 (A), (B), 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, D15 about the 1st structural example) of the part which changes with zooming.

  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. 9A and 9B, 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 first lens (negative lens) L11 made of glass, and a right-angle prism LP as a reflecting member that reflects incident light and bends an optical path. . The first lens group G1 also has two or less lenses (only the second lens L12, or the second lens L12 and the third lens L13) on the image side of the right-angle prism LP. The two or less lenses disposed on the image side with respect to the right-angle prism LP include a positive or negative plastic lens having an absolute value of refractive power smaller than that of the first lens L11. In the first to sixth configuration examples shown in FIGS. 1A and 1B to FIGS. 6A and 6B, the first lens group G1 has one piece closer to the image side than the right-angle prism LP. The example which has arrange | positioned only a lens (2nd lens L12) is shown. The second lens L12 is configured by a plastic lens having a smaller absolute value of refractive power than the first lens L11.

In the seventh to ninth configuration examples shown in FIGS. 7A and 7B to FIGS. 9A and 9B, the first lens group G1 includes two lenses closer to the image side than the right-angle prism LP. An example in which lenses (second lens L12 and third lens L13) are arranged is shown. In particular, in the seventh to eighth configuration examples, the first lens L11 arranged on the front side of the right-angle prism LP is used as the first negative lens, and the second lens L12 arranged on the image side of the right-angle prism LP is used. The second negative lens is made of glass. Further, the third lens L13 disposed further on the image side is composed of a plastic lens having a positive refractive power having a smaller absolute value of refractive power than the first lens L11.
In the ninth configuration example, the two lenses L12 and L13 on the image side of the right-angle prism LP are both plastic lenses. More specifically, the second lens L12 is a plastic lens having a negative refractive power whose absolute value is smaller than that of the first lens L11, and the third lens L13 is more than the first lens L11. The plastic lens has a positive refractive power with a small absolute value of refractive power.

  Here, the zoom lens according to the present embodiment is a bending optical system. Actually, as shown in FIG. 10, 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. 10 corresponds to the first configuration example shown in FIG. 1A, but the same applies to the other configuration examples. 1 (A), (B) to FIGS. 9 (A), (B), the optical axis Z1 is linear, 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 includes three or less lenses including a positive lens made of glass and a positive or negative plastic lens. In FIGS. 1A and 1B to FIGS. 9A and 9B, an example in which the second lens group G2 includes two lenses, a first lens L21 and a second lens L22, In addition, an example in which the first to third lenses L21 to L23 are configured by three lenses is shown.

  The third lens group G3 has a negative refractive power as a whole. The third lens group G3 includes, for example, two lenses, a first lens L31 and a second lens L32. In this case, it is preferable that the two lenses constituting the third lens group G3 are two negative lenses, or one positive lens and one negative lens. It is preferable to dispose a negative lens having a concave surface on the image surface side on the most image side in the third lens group G3.

  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) including at least one positive lens (first lens L41). Has been.

This zoom lens is configured to satisfy the following conditional expression, where fpr is the combined focal length of the plastic lenses included in the entire system, and fw is the focal length of the entire system at the wide angle end.
−0.3 <(1 / fpr) · fw <0.6 (1)
However,
1 / fpr = Σ (1 / fpri)
(I = integer greater than or equal to 2, fpri: focal length of i-th plastic lens)
And

Further, when the focal length of the first lens group G1 is f1, it is preferable that the following conditional expression is satisfied.
1.4 <| f1 / fw | <2.5 (2)

Further, when the focal length of the second lens group G2 is f2, it is preferable that the following conditional expression is satisfied.
0.9 <f2 / fw <1.9 (3)

Further, when the focal length of the first lens group G1 is f1, and the focal length of the plastic lens in the first lens group G1 is f1p, it is preferable that the following conditional expression is satisfied.
| F1p / f1 |> 3.0 (4)
When there are a plurality of plastic lenses in the first lens group G1, f1p is the focal length of each of the plurality of plastic lenses. It is preferable that conditional expression (4) is satisfied for each of the plurality of plastic lenses.

Further, when the focal length of the second lens group G2 is f2, and the focal length of the plastic lens in the second lens group G2 is f2p, it is preferable that the following conditional expression is satisfied.
| F2p / f2 |> 2.0 (5)
When there are a plurality of plastic lenses in the second lens group G2, f2p is the focal length of each of the plurality of plastic lenses. It is preferable that conditional expression (5) is satisfied for each of the plurality of plastic lenses.

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 (6)

  FIG. 29 and FIG. 30 show a digital still camera as an example of an imaging apparatus on which this zoom lens is mounted. In particular, FIG. 29 shows an appearance of the digital still camera 10 as viewed from the front side, and FIG. 30 shows an appearance of the digital still camera 10 as 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. By providing a plurality of plastic lenses, cost reduction can be realized. Furthermore, on the premise of using multiple plastic lenses, we have optimized the power distribution of the plastic lens and optimized the configuration of each lens group, ensuring good optical performance and characteristics associated with temperature changes. Change is suppressed.

  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) is obtained by normalizing the combined focal length fpr of the plastic lens included in the entire system by the focal length fw of the entire system at the wide-angle end, and suppresses the fluctuation of the image plane position due to the temperature change. This is the condition. For example, if the entire system includes a positive plastic lens and a negative plastic lens, in order to minimize the fluctuation of the image plane position due to temperature changes, the combination of the positive plastic lens and the negative plastic lens It is preferable that the powers cancel each other, and the difference is preferably small. If the upper limit of conditional expression (1) is exceeded, the fluctuation of the image plane position becomes large, which is not preferable. The lens barrel of the imaging device to which the lens is applied is often made of plastic. If possible, if the power of the plastic lens synthesis is set to be weak positive, the lens barrel can be expanded and contracted as the temperature changes. The movement of the image position accompanying the change in the refractive power of the plastic lens is preferable because the change in the apparent image position can be suppressed. When power distribution as described above is difficult and the total power of the plastic lens is negative, the absolute value is preferably as small as possible, and preferably exceeds the lower limit of conditional expression (1).
In order to obtain higher optical performance, the numerical range of conditional expression (1) is
−0.2 <(1 / fpr) · fw <0.55 (1 ′)
It is desirable that More preferably,
0 <(1 / fpr) · fw <0.5 (1 ″)
It is good to be.

Conditional expression (2) is obtained by normalizing the focal length f1 of the first lens group G1 with the focal length fw of the entire system at the wide-angle end. If the lower limit of conditional expression (2) is not reached, it is difficult to increase the zoom ratio. On the other hand, if the upper limit of conditional expression (2) is exceeded, the back focus becomes longer than necessary, and the lens system becomes large. That is, it is a condition for achieving both a zoom ratio of about 2.8 times and a reduction in size.
In order to obtain higher optical performance, the numerical range of conditional expression (2) is
1.5 <| f1 / fw | <2.4 (2 ′)
It is desirable that

Conditional expression (3) 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 (3) is not reached, it is advantageous for downsizing, but the power of the second lens group G2 becomes too strong, making it difficult to correct aberrations and increasing aberration fluctuations accompanying zooming. This is not preferable. In addition, the power of the plastic lens is increased, and the image plane position fluctuation accompanying the temperature change is increased, which is not preferable. Further, the positive lens constituting the second lens group G2 has a large curvature, which is not preferable because the lens becomes thick in order to secure a necessary edge. Conversely, if the upper limit is exceeded, the amount of movement of the second lens group G2 becomes large, which is not preferable.
In order to obtain higher optical performance, the numerical range of conditional expression (3) is
1.0 <f2 / fw <1.8 (3 ′)
It is desirable that

Conditional expression (4) defines the relationship between the focal length f1p of the plastic lens in the first lens group G1 and the focal length f1 of the first lens group G1. If the lower limit of conditional expression (4) is not reached, the fluctuation of the image plane position accompanying the temperature change becomes large, which is not preferable.
In order to obtain higher optical performance, the numerical range of conditional expression (4) is
| F1p / f1 |> 3.5 (4 ')
It is desirable that

Conditional expression (5) defines the relationship between the focal length f2p of the plastic lens in the second lens group G2 and the focal length f2 of the second lens group G2. If the lower limit of conditional expression (5) is not reached, the fluctuation of the image plane position accompanying the temperature change becomes large, which is not preferable.
In order to obtain higher optical performance, the numerical range of conditional expression (5) is
| F2p / f2 |> 2.5 (5 ')
It is desirable that

Conditional expression (6) 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 (6) is
Nd1p> 1.80 (6 ')
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 furthermore, optimization of power distribution of the plastic lens and each lens group Thus, it is possible to reduce the characteristic change accompanying the temperature change of the plastic lens while ensuring good optical performance at low cost. In addition, according to the imaging apparatus equipped with the zoom lens according to the present embodiment, it is possible to reduce the cost and improve the performance 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 with a reference numeral 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, the second lens group G2 and the third lens group G3 move on the optical axis with zooming. 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 D15. [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 is a plastic lens. In the zoom lens according to Example 1, the second lens L12 in the first lens group G1 and the first lens L21 in the second lens group G2 are plastic lenses.

  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. In the zoom lens according to Example 1, both surfaces S5 and S6 of the second lens L12 in the first lens group G1 and both surfaces S7 and S8 of the first lens L21 in the second lens group G2 are all aspherical surfaces. It has a shape. 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 9]
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. 9A and 9B is set as Examples 3 to 9 [Table 7]. ] To [Table 27].

  [Table 28] shows a summary of the values for the conditional expressions described above for each example. As can be seen from [Table 28], the conditions of the conditional expressions (1) to (6) are satisfied for each example.

[Aberration diagram]
FIGS. 11A to 11D show spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration at the wide angle end in the zoom lens according to Example 1, respectively. 12A to 12D 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. 13A to 13D (wide-angle end) and FIGS. 14A to 14D (telephoto end). Similarly, various aberrations of the zoom lenses according to Examples 3 to 9 are shown in FIGS. 15 to 28 (A) to (D).

  As can be seen from the above numerical data and aberration diagrams, for each example, the power distribution of the plastic lens and the configuration of each lens group are optimized on the assumption that a plurality of plastic lenses are used. As a result, various aberrations are satisfactorily corrected in each zoom range, and a zoom lens with a short zoom lens length and a small size can be realized while having a high zoom ratio.

  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 (13)

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 made of glass, a reflecting member that reflects incident light and bends an optical path, and a plastic lens that has a smaller absolute value of refractive power than the negative lens. It consists of two or less lenses,
The second lens group includes three or less lenses including a positive lens made of glass and a plastic lens,
A zoom lens, wherein the following conditional expression is satisfied, where fpr is a synthetic focal length of a plastic lens included in the entire system, and fw is a focal length of the entire system at the wide-angle end.
−0.3 <(1 / fpr) · fw <0.6 (1)
However,
1 / fpr = Σ (1 / fpri)
(I = integer greater than or equal to 2, fpri: focal length of i-th plastic lens)
And The zoom lens according to claim 1, wherein the following conditional expression is satisfied when a focal length of the first lens group is f1.
1.4 <| f1 / fw | <2.5 (2) 3. The zoom lens according to claim 1, wherein the following conditional expression is satisfied when a focal length of the second lens group is f <b> 2.
0.9 <f2 / fw <1.9 (3) The following conditional expression is satisfied, where f1 is a focal length of the first lens group, and f1p is a focal length of the plastic lens in the first lens group. The zoom lens according to item.
| F1p / f1 |> 3.0 (4) The following conditional expression is satisfied, where f2 is a focal length of the second lens group and f2p is a focal length of the plastic lens in the second lens group. The zoom lens according to item.
| F2p / f2 |> 2.0 (5) The following conditional expression is satisfied, where Nd1p is a refractive index with respect to the d-line of the material constituting the reflecting member in the first lens group. Zoom lens.
Nd1p> 1.78 (6) The first lens group includes, in order from the object side, the negative lens, the reflecting member, and a plastic lens having an absolute value of refractive power smaller than that of the negative lens. The zoom lens according to any one of the above. The first lens group, in order from the object side, is refracted more than the first negative lens made of glass, the reflection member, the second negative lens made of glass, and the first negative lens. The zoom lens according to claim 1, comprising a plastic lens having a positive refractive power and a small absolute value of force. The first lens group includes, in order from the object side, the negative lens, the reflecting member, and two plastic lenses having an absolute value of refractive power smaller than that of the negative lens. 7. The zoom lens according to any one of items 6 to 6. The zoom lens according to any one of claims 1 to 9, wherein a diaphragm is disposed between the second lens group and the third lens group. 11. The zoom lens according to claim 10, wherein at the time of zooming, the diaphragm moves integrally with the third lens group. The zoom lens according to any one of claims 1 to 11, wherein the fourth lens group is fixed at the time of zooming. The zoom lens according to any one of claims 1 to 12,
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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