JP5354326B2 - Zoom lens and optical apparatus having the same - Google Patents

Description

The present invention relates to a zoom lens and an optical apparatus having the same .

  In recent years, digital cameras have come to use zoom lenses that include a wide angle of view that enables shooting over a wider range. In addition, solid-state image sensors such as CCDs and CMOSs to be mounted are more highly integrated and high-pixel ones are provided. Therefore, high imaging performance has been demanded for zoom lenses for digital cameras.

In order to meet such demands, various zoom lenses have been proposed. For example, in order from the object side along the optical axis, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a negative refractive power A zoom lens composed of a fourth lens group has been proposed. (For example, see Patent Document 1).
Japanese Laid-Open Patent Publication No. 2003-043358

  However, the conventional zoom lens has a narrow angle of view at the wide-angle end state and a small zoom ratio. Further, the thickness of each lens group in the optical axis direction is large, and it cannot be said that the size in the retracted state at the time of storage is sufficiently compact.

The present invention has been made in view of such problems, and is a small zoom lens that achieves high performance while having a wide angle of view at a wide-angle end state and a wide-angle high-magnification zoom, and an optical apparatus having the same The purpose is to provide.

In order to achieve such an object, the zoom lens of the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a positive refraction arranged in order from the object side. The third lens group having power and the fourth lens group having negative refractive power are substantially composed of four lens groups, and the first lens group is composed of two or less lenses and is in a wide-angle end state. At the time of zooming to the telephoto end state, the distance between the first to fourth lens groups is changed, the fourth lens group is fixed with respect to the image plane, and the third lens group is a positive lens 1. When the focal length of the third lens group is f3, the focal length of the fourth lens group is f4, and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, .99 ≦ f3 / fw <5.0 and 3.0 <(− 4) to satisfy the / fw <10.0 of conditions.
The zoom lens according to the present invention includes a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, which are arranged in order from the object side. And a fourth lens group having a negative refractive power, and substantially consisting of four lens groups, the first lens group is composed of two or less lenses, and zooming from the wide-angle end state to the telephoto end state in the interval of the first to the fourth lens group with changing respectively, the fourth lens group is fixed relative to the image surface, the third lens group moves toward the image side, the third lens group Is composed of one positive lens, the focal length of the third lens group is f3, the focal length of the fourth lens group is f4, and the combined focal length of the entire zoom lens system in the wide-angle end state is fw. Then, the following formula 2.99 ≦ f3 / fw <5.0 and 3. <(- f4) is satisfied / fw <10.0 of conditions.

  The first lens group is preferably composed of two lenses, a negative lens and a positive lens.

  Further, when the focal length of the second lens group is f2 and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, the following formula 1.8 <f2 / fw <3.5 is satisfied. It is preferable.

  Further, it is preferable that the fourth lens group is composed of one negative lens.

  Further, it is preferable that the third lens group is moved to perform focusing from an infinitely focused state to an object at a finite distance.

  Further, when the focal length of the first lens unit is f1 and the focal length of the second lens unit is f2, the following condition 0.8 <(− f1) / f2 <1.3 is satisfied. Is preferred.

  The first lens group preferably has an aspherical surface.

  The second lens group preferably has an aspherical surface.

  The third lens group preferably has an aspherical surface.

  Further, the present invention is an optical apparatus having any one of the above zoom lenses.

According to the present invention, it is possible to provide a zoom lens that achieves high performance while having a wide angle of view at a wide-angle end state and a wide-angle high-magnification zoom, and an optical apparatus having the zoom lens .

  Hereinafter, preferred embodiments will be described with reference to the drawings. As shown in FIG. 1, the zoom lens according to the present embodiment includes a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, arranged in order from the object side, and a positive lens. A third lens group G3 having a refractive power of 4 and a fourth lens group G4 having a negative refractive power, and the first lens group G1 includes a negative lens and a positive lens (lens L11 and L12 in FIG. 1). When changing the magnification from the wide-angle end state to the telephoto end state, the distance between the first lens group G1 to the fourth lens group G4 is changed, and the fourth lens group G4 is fixed to the image plane I. To do.

  In the zoom lens in which the first lens group G1 has negative refractive power, the front lens diameter can be reduced with respect to the maximum angle of view, which is suitable for a wide-angle zoom lens including a wide angle of view. However, in order to satisfactorily correct the lateral chromatic aberration and distortion in a wide angle of view, the first lens group G1 needs to have three or more lenses, and the first lens group G1 is thick, so that it is stored. The so-called retracted state at the time becomes thick, and the camera becomes large. Therefore, in the zoom lens according to the present embodiment, the fourth lens group G4 having a negative refractive power is disposed on the image side from the third lens group G3, and the first lens group G1 includes two lenses, a negative lens and a positive lens. With this configuration, it is possible to correct lateral chromatic aberration and distortion occurring in the first lens group G1 with the fourth lens group G4. Further, the first lens group G1 can be thinned.

  Based on the above configuration, when the focal length of the third lens group G3 is f3, the focal length of the fourth lens group G4 is f4, and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, It is preferable to satisfy the conditions of the following formulas (1) and (2).

2.3 <f3 / fw <5.0 (1)
3.0 <(− f4) / fw <10.0 (2)

  Conditional expression (1) defines the focal length f3 of the third lens group G3. By satisfying this conditional expression (1), astigmatism in the wide-angle end state and spherical aberration in the telephoto end state can be corrected appropriately, and good optical performance can be obtained. If the lower limit of conditional expression (1) is not reached, the refractive power of the third lens group G3 increases, the spherical aberration in the telephoto end state worsens, and the lens group on the object side is larger than the third lens group G3. It will become. On the other hand, if the upper limit value of conditional expression (1) is exceeded, the refractive power of the third lens group G3 becomes small, astigmatism in the wide-angle end state deteriorates, and an appropriate exit pupil position cannot be maintained.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (1) to 2.8. In order to further secure the effect of the present embodiment, it is preferable to set the lower limit value of conditional expression (1) to 2.5. In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (1) to 4.5. In order to further secure the effect of the present embodiment, it is preferable to set the upper limit value of conditional expression (1) to 4.0.

  Conditional expression (2) defines the focal length f4 of the fourth lens group G4. By satisfying this conditional expression (2), it is possible to appropriately correct lateral chromatic aberration and distortion in the wide-angle end state, and good optical performance can be obtained. If the lower limit of conditional expression (2) is not reached, the refractive power of the fourth lens group G4 increases, the spherical aberration and axial chromatic aberration in the telephoto end state worsen, and the fourth lens group G4 increases in size. End up. On the other hand, if the upper limit value of conditional expression (2) is exceeded, the refractive power of the fourth lens group G4 becomes small, and the lateral chromatic aberration and distortion in the wide-angle end state deteriorate.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 3.5. In order to further secure the effect of the present embodiment, it is preferable to set the upper limit value of conditional expression (2) to 7.5.

  In this embodiment, when the focal length of the second lens group G2 is f2, and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, the condition of the following expression (3) may be satisfied. preferable.

  1.8 <f2 / fw <3.5 (3)

  Conditional expression (3) defines the focal length f2 of the second lens group G2. By satisfying this conditional expression (3), spherical aberration and aberration fluctuations due to zooming are suppressed, and good optical performance and downsizing of the lens system are achieved. If the lower limit of conditional expression (3) is not reached, the refractive power of the second lens group G2 increases, and the astigmatism variation due to spherical aberration and zooming at the telephoto end state worsens. On the other hand, if the upper limit value of conditional expression (3) is exceeded, the refractive power of the second lens group G2 decreases, the amount of movement of the second lens group G2 required for zooming increases, and the total lens length and lens barrel structure are large. It will become.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 2.0. In order to further secure the effect of the present embodiment, it is preferable to set the upper limit value of conditional expression (3) to 3.0.

  In the present embodiment, it is preferable that the third lens group G3 is composed of one positive lens. With this configuration, the lens barrel structure is simplified and the size can be reduced.

  In the present embodiment, it is preferable that the fourth lens group G4 is composed of one negative lens. With this configuration, the thickness in the so-called retracted state at the time of storage can be reduced.

  In the present embodiment, it is preferable that the third lens group G3 moves toward the image side upon zooming from the wide-angle end state to the telephoto end state. With this configuration, when the distance between the third lens group G3 and the fourth lens group G4 is narrowed in the telephoto end state, deterioration of lateral chromatic aberration and spherical aberration can be prevented.

  In the present embodiment, it is preferable to move the third lens group G3 to perform focusing from an infinitely focused state to a finite distance object. With this configuration, the amount of movement at the time of focusing can be reduced, and aberration fluctuations at the time of focusing can also be reduced.

  In the present embodiment, it is preferable that the condition of the following expression (4) is satisfied when the focal length of the first lens group G1 is f1 and the focal length of the second lens group G2 is f2.

  0.8 <(− f1) / f2 <1.3 (4)

  Conditional expression (4) defines the relationship between the focal length f1 of the first lens group G1 and the focal length f2 of the second lens group G2. By satisfying this conditional expression (4), it is possible to reduce the size of the lens system while maintaining good optical performance. If the lower limit of conditional expression (4) is not reached, the amount of movement required for zooming becomes large and the total lens length becomes large. In addition, variations in spherical aberration and coma due to zooming increase. On the other hand, if the upper limit value of conditional expression (4) is exceeded, the total lens length in the telephoto end state increases and astigmatism deteriorates.

  In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.9. In order to further secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (4) to 1.2.

  In the present embodiment, it is preferable that the first lens group G1 has an aspherical surface. With this configuration, it is possible to satisfactorily correct distortion aberration in the wide-angle end state.

  In the present embodiment, it is preferable that the second lens group G2 has an aspherical surface. With this configuration, spherical aberration in the telephoto end state can be corrected well.

  In the present embodiment, it is preferable that the third lens group G3 has an aspherical surface. With this configuration, it is possible to satisfactorily correct astigmatism in the wide-angle end state.

  7 and 8 show a configuration of a digital still camera 1 (optical apparatus) provided with the zoom lens having the above configuration as a photographic lens ZL. In this digital still camera 1, when a power button (not shown) is pressed, a shutter (not shown) is opened, and light from a subject (not shown) is collected by the photographing lens ZL, and an image sensor C disposed on the image plane I is arranged. (E.g., film, CCD, CMOS, etc.). The subject image formed on the image sensor C is displayed on the liquid crystal monitor 2 disposed behind the camera 1. The photographer determines the composition of the subject image while looking at the liquid crystal monitor 2 and then depresses the release button 3. Then, the subject image is taken by the image sensor C and recorded and stored in a memory (not shown).

  The camera 1 includes an auxiliary light emitting unit 4 that emits auxiliary light when the subject is dark, and a wide (W) -telephone when zooming the photographing lens ZL from the wide-angle end state (W) to the telephoto end state (T). A (T) button 5 and function buttons 6 used for setting various conditions of the digital still camera 1 are arranged.

  Hereinafter, each example according to the present embodiment will be described with reference to the drawings. Tables 1 to 3 are shown below, but these are tables of specifications in the first to third examples. In [Overall specifications], f represents the focal length of the zoom lens, FNO represents the F number, and ω represents a half angle of view (maximum incident angle. Unit is degree [°]). In [Lens data], the surface number is the order of the lens surfaces from the object side along the direction in which the light beam travels, r is the radius of curvature of each lens surface, and d is the next optical surface from each optical surface (or The distance between the surfaces, which is the distance on the optical axis to the image plane), nd is the refractive index for the d-line (wavelength 587.6 nm), and νd is the Abbe number for the d-line. When the lens surface is aspherical, an asterisk is attached to the surface number, and the paraxial radius of curvature is indicated in the column of the radius of curvature r. The curvature radius “0.0000” indicates a plane or an opening. Further, the description of the refractive index “1.00000” of air is omitted. In [variable interval data], f indicates the focal length of the zoom lens, Di (where i is an integer), the variable surface interval of the i-th surface, Bf indicates the back focus, and TL indicates the total lens length. In [Each Group Focal Length Data], the initial surface and focal length of each group are shown. In [Conditional Expression Corresponding Value], values corresponding to the conditional expressions (1) to (4) are shown.

In [Aspherical data], the shape of the aspherical surface shown in [Lens data] is shown by the following equation (a). That is, y is the height in the direction perpendicular to the optical axis, and S (y) is the distance (sag amount) along the optical axis from the tangent plane at the apex of the aspheric surface to the position on the aspheric surface at height y. When the radius of curvature (paraxial radius of curvature) of the reference spherical surface is r, the conic coefficient is K, and the n-th aspherical coefficient is An, the following equation (a) is given. In each example, the secondary aspheric coefficient A2 is 0, and the description thereof is omitted. Further, En represents × 10 ^n. For example, 1.234E-05 = 1.234 × 10 ⁻⁵ .

S (y) = (y ² / r) / {1+ (1−K · y ² / r ² ) ^1/2 }
^{+ A4 × y 4 + A6 ×} y 6 + A8 × y 8 + A10 × y 10 ... (a)

  In the table, “mm” is generally used as the unit of focal length f, radius of curvature r, surface interval d, and other lengths. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used.

  The description of the above table is the same in other examples, and the description thereof is omitted.

(First embodiment)
A first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. FIG. 1 shows a lens configuration diagram and zoom locus of the first embodiment. As shown in FIG. 1, the zoom lens according to the first example includes a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power arranged in order from the object side along the optical axis. G3, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L11 having a concave surface facing the image side and a positive meniscus lens L12 having a convex surface facing the object side. The image side surface of the negative lens L11 is an aspherical surface.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface facing the object side, a positive lens L22 having a biconvex surface, and a negative lens L23 having a biconcave surface having a concave surface facing the image side. It has a cemented lens and a biconvex positive lens L24. Note that both surfaces of the positive meniscus lens L21 are aspheric.

  The third lens group G3 has a biconvex positive lens L31. The object side surface of the positive lens L31 is an aspherical surface.

  The fourth lens group G4 includes a negative meniscus lens L41 having a concave surface directed toward the object side.

  Further, in the present embodiment, an aperture stop S is disposed on the object side of the second lens group G2, and a filter FL for cutting wavelengths in the infrared region is disposed on the object side of the image plane I.

  In the zoom lens according to the present embodiment having such a configuration, the air gap between the first lens group G1 and the second lens group G2 is reduced during zooming from the wide-angle end state to the telephoto end state, and the second lens The first lens group G1 has a convex locus on the image side so that the air gap between the group G2 and the third lens group G3 increases and the air gap between the third lens group G3 and the fourth lens group G4 decreases. The second lens group moves toward the object side, and the third lens group G3 moves toward the image side. At this time, the fourth lens group G4 is fixed with respect to the image plane I.

  Table 1 below shows values of various specifications of the zoom lens according to the first example. The surface numbers 1 to 18 in Table 1 correspond to the surfaces 1 to 18 shown in FIG.

(Table 1)
[Overall specifications]
Wide-angle end state Intermediate focal length state Telephoto end state f 6.18 to 12.00 to 20.80
FNO 2.76 to 3.79 to 5.88
ω 39.9 〜 22.6 〜 11.5
[Lens data]
Surface number r d nd νd
1 44.9756 1.5000 1.801387 45.45
* 2 6.9025 3.7000
3 11.3383 1.8000 1.922860 18.90
4 16.1942 (D4)
5 0.0000 0.4500 (Aperture stop)
* 6 8.0361 1.8000 1.589129 61.25
* 7 20.1690 0.4000
8 7.8861 1.7000 1.729157 54.68
9 -19.2601 0.7000 1.720467 34.71
10 5.8826 1.0000
11 133.7982 1.5000 1.497820 82.52
12 -12.3827 (D12)
* 13 22.2872 2.4000 1.497820 82.52
14 -16.2104 (D14)
15 -14.2000 0.9000 1.754999 52.32
16 -52.5096 0.5000
17 0.0000 1.5000 1.516330 64.14
18 0.0000 (Bf)
[Aspherical data]
Second surface κ = 0.3743, C4 = 2.60060E-05, C6 = 3.889930E-07, C8 = 0.00000E + 00, C10 = 0.00000E + 00
6th surface κ = 1.1348, C4 = 1.56200E-04, C6 = -7.37090E-07, C8 = 0.00000E + 00, C10 = 0.00000E + 00
7th surface κ = 10.0000, C4 = 4.03610E-04, C6 = 0.00000E + 00, C8 = 0.00000E + 00, C10 = 0.00000E + 00
13th surface κ = -21.5269, C4 = 1.33980E-04, C6 = -1.54180E-06, C8 = 0.00000E + 00, C10 = 0.00000E + 00
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state
f 6.16 12.00 20.80
D4 19.7089 7.5752 2.0009
D12 5.4762 13.5448 23.9941
D14 3.3578 2.5443 1.5082
Bf 0.9705 0.9705 0.9705
TL 49.3635 44.4848 48.3238
[Each group focal length data]
Group number Group first surface Group focal length G1 1 -15.8431
G2 6 14.3072
G3 13 19.2502
G4 15 -26.0426
[Conditional expression values]
Conditional expression (1) f3 / fw = 3.11
Conditional expression (2) (−f4) /fw=4.21
Conditional expression (3) f2 / fw = 2.31
Conditional expression (4) (−f1) /f2=1.11

  From the table of specifications shown in Table 1, it can be seen that the zoom lens according to Example 1 satisfies all the conditional expressions (1) to (4).

  2A and 2B are graphs showing various aberrations of the zoom lens according to Example 1. FIG. 2A shows graphs showing various aberrations in the wide-angle end state (f = 6.18), and FIG. Various aberration diagrams, (c) are various aberration diagrams in the telephoto end state (f = 20.8). In each aberration diagram, FNO represents an F number, and Y represents an image height (unit: mm). The spherical aberration diagram shows the F-number value corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum image height, and the coma diagram shows the value of each image height. Further, d indicates various aberrations with respect to the d-line (wavelength 587.6 nm), g indicates various aberrations with respect to the g-line (wavelength 435.8 nm), and those not described indicate various aberrations with respect to the d-line. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. The explanation of the above aberration diagrams is the same in the other examples, and the explanation is omitted.

  As is apparent from the respective aberration diagrams, in the first example, it is understood that various aberrations are well corrected and excellent imaging performance is obtained in each focal length state from the wide-angle end state to the telephoto end state.

(Second embodiment)
The second embodiment will be described with reference to FIGS. 3 and 4 and Table 2. FIG. FIG. 3 shows a lens configuration diagram and zoom locus of the second embodiment. As shown in FIG. 3, the zoom lens according to the second example includes a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power arranged in order from the object side along the optical axis. G3, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L11 having a concave surface facing the image side and a positive meniscus lens L12 having a convex surface facing the object side. The image side surface of the negative lens L11 is an aspherical surface.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface facing the object side, a positive lens L22 having a biconvex surface, and a negative lens L23 having a biconcave surface having a concave surface facing the image side. It has a cemented lens and a positive meniscus lens L24 with a convex surface facing the image side. Note that both surfaces of the positive meniscus lens L21 are aspheric.

  The third lens group G3 has a biconvex positive lens L31. The object side surface of the positive lens L31 is an aspherical surface.

  The fourth lens group G4 includes a negative meniscus lens L41 having a concave surface directed toward the object side.

  Further, in the present embodiment, an aperture stop S is disposed on the object side of the second lens group G2, and a filter FL for cutting wavelengths in the infrared region is disposed on the object side of the image plane I.

  In the zoom lens according to the present embodiment having such a configuration, the air gap between the first lens group G1 and the second lens group G2 is reduced during zooming from the wide-angle end state to the telephoto end state, and the second lens The first lens group G1 has a convex locus on the image side so that the air gap between the group G2 and the third lens group G3 increases and the air gap between the third lens group G3 and the fourth lens group G4 decreases. The second lens group moves toward the object side, and the third lens group G3 moves toward the image side. At this time, the fourth lens group G4 is fixed with respect to the image plane I.

  Table 2 below shows values of various specifications of the zoom lens according to the second example. In addition, the surface numbers 1-18 in Table 2 respond | correspond to the surfaces 1-18 shown in FIG.

(Table 2)
[Overall specifications]
Wide-angle end state Intermediate focal length state Telephoto end state f 6.26 to 12.00 to 23.80
FNO 2.85-3.93-6.09
ω 39.8 〜 22.3 〜 11.5
[Lens data]
Surface number r d nd νd
1 90.0000 1.5000 1.801387 45.45
* 2 6.8960 3.2000
3 12.1002 2.0000 1.808095 22.76
4 24.8949 (D4)
5 0.0000 0.4500 (Aperture stop)
* 6 6.8658 1.8000 1.589129 61.25
* 7 99.8907 0.2500
8 11.2762 1.7000 1.729157 54.68
9 -26.6839 0.7000 1.720467 34.71
10 5.4874 0.8000
11 -64.4493 1.7000 1.497820 82.52
12 -12.0132 (D12)
* 13 30.5625 2.4000 1.497820 82.52
14 -15.5133 (D14)
15 -14.5000 0.9000 1.762001 40.10
16 -31.6441 0.5000
17 0.0000 1.5000 1.516330 64.14
18 0.0000 (Bf)
[Aspherical data]
Second surface κ = 0.5249, C4 = -8.94010E-05, C6 = 4.03040E-07, C8 = -2.62060E-08, C10 = 8.58000E-12
6th surface κ = 0.794, C4 = -4.67970E-05, C6 = 0.000000 + 00, C8 = 0.00000E + 00, C10 = 0.00000E + 00
7th surface κ = 20.0000, C4 = 2.37650E-04, C6 = 0.00000E + 00, C8 = 0.00000E + 00, C10 = 0.00000E + 00
13th surface κ = 1.000, C4 = -4.13120E-05, C6 = 0.000000 + 00, C8 = 0.00000E + 00, C10 = 0.00000E + 00
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state
f 6.26 12.00 23.80
D4 20.9958 8.7977 1.9551
D12 4.5103 12.9614 27.4715
D14 4.2960 3.4351 2.1307
Bf 0.8826 0.8826 0.8826
TL 50.0849 45.4770 51.8401
[Each group focal length data]
Group number Group first surface Group focal length G1 1 -16.3105
G2 6 14.9043
G3 13 21.0344
G4 15 -35.9388
[Conditional expression values]
Conditional expression (1) f3 / fw = 3.35
Conditional expression (2) (−f4) /fw=5.74
Conditional expression (3) f2 / fw = 2.38
Conditional expression (4) (-f1) /f2=1.09

  From the table of specifications shown in Table 2, it can be seen that the zoom lens according to Example 2 satisfies all the conditional expressions (1) to (4).

  4A and 4B are graphs showing various aberrations of the zoom lens according to Example 2. FIG. 4A is a diagram showing various aberrations in the wide-angle end state (f = 6.26), and FIG. Aberration diagrams (c) are aberration diagrams in the telephoto end state (f = 23.8). As is apparent from the respective aberration diagrams, in the second embodiment, it is understood that various aberrations are favorably corrected and excellent imaging performance is obtained in each focal length state from the wide-angle end state to the telephoto end state.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 5 and 6 and Table 3. FIG. FIG. 5 shows a lens configuration diagram and zoom locus of the third embodiment. As shown in FIG. 5, the zoom lens according to the third example includes a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power arranged in order from the object side along the optical axis. G3, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L11 having a concave surface facing the image side and a positive meniscus lens L12 having a convex surface facing the object side. The image side surface of the negative lens L11 is an aspherical surface.

  The second lens group G2 includes, in order from the object side, a positive meniscus lens L21 having a convex surface facing the object side, a positive lens L22 having a biconvex surface, and a negative lens L23 having a biconcave surface having a concave surface facing the image side. It has a cemented lens and a positive meniscus lens L24 with a convex surface facing the image side. Note that both surfaces of the positive meniscus lens L21 are aspheric.

  The third lens group G3 has a biconvex positive lens L31. The object side surface of the positive lens L31 is an aspherical surface.

  The fourth lens group G4 includes a negative meniscus lens L41 having a concave surface directed toward the object side.

  Further, in the present embodiment, an aperture stop S is disposed on the object side of the second lens group G2, and a filter FL for cutting wavelengths in the infrared region is disposed on the object side of the image plane I.

  In the zoom lens according to the present embodiment having such a configuration, the air gap between the first lens group G1 and the second lens group G2 is reduced during zooming from the wide-angle end state to the telephoto end state, and the second lens The first lens group G1 has a convex locus on the image side so that the air gap between the group G2 and the third lens group G3 increases and the air gap between the third lens group G3 and the fourth lens group G4 decreases. The second lens group moves toward the object side, and the third lens group G3 moves toward the image side. At this time, the fourth lens group G4 is fixed with respect to the image plane I.

  Table 3 below shows values of various specifications of the zoom lens according to the third example. In addition, the surface numbers 1-18 in Table 3 respond | correspond to the surfaces 1-18 shown in FIG.

(Table 3)
[Overall specifications]
Wide-angle end state Intermediate focal length state Telephoto end state f 6.18 to 12.00 to 23.00
FNO 2.92 to 4.00 to 6.02
ω 39.8 〜 22.0 〜 11.6
[Lens data]
Surface number r d nd νd
1 56.0124 1.5000 1.801387 45.45
* 2 6.4909 2.8000
3 10.5547 2.5000 1.808095 22.76
4 19.7442 (D4)
5 0.0000 0.1500 (Aperture stop)
* 6 8.6185 1.8000 1.589129 61.25
* 7 112.8141 0.4000
8 10.5967 1.7000 1.729157 54.68
9 -16.5521 0.7000 1.720467 34.71
10 6.7330 1.0000
11 -20.5606 1.5000 1.497820 82.52
12 -8.4651 (D12)
* 13 25.3947 2.4000 1.497820 82.52
14 -14.0125 (D14)
15 -14.2000 0.9000 1.772499 49.60
16 -52.5096 0.5000
17 0.0000 1.5000 1.516330 64.14
18 0.0000 (Bf)
[Aspherical data]
Second surface κ = 0.5520, C4 = -4.90720E-05, C6 = -9.31820E-07, C8 = -1.49130E-08, C10 = -5.60420E-10
6th surface κ = 1.0851, C4 = 1.30650E-04, C6 = -3.313420-06, C8 = 1.40210E-07, C10 = -2.41600E-09
7th surface κ = 10.0000, C4 = 5.14360E-04, C6 = 0.00000E + 00, C8 = 0.00000E + 00, C10 = 0.00000E + 00
13th surface κ = 1.2777, C4 = -1.06780E-04, C6 = 0.000000 + 00, C8 = 0.00000E + 00, C10 = 0.00000E + 00
[Variable interval data]
Wide-angle end state Intermediate focal length state Telephoto end state
f 6.18 12.00 23.00
D4 20.0065 7.8773 1.6040
D12 5.4771 13.5495 26.2636
D14 3.3577 2.5362 1.1699
Bf 1.0338 1.0338 1.0338
TL 49.2253 44.3469 49.4213
[Each group focal length data]
Group number Group first surface Group focal length G1 1 -16.0675
G2 6 14.3308
G3 13 18.5136
G4 15 -25.4560
[Conditional expression values]
Conditional expression (1) f3 / fw = 2.99
Conditional expression (2) (−f4) /fw=4.12
Conditional expression (3) f2 / fw = 2.32
Conditional expression (4) (−f1) /f2=1.12

  From the table of specifications shown in Table 3, it can be seen that the zoom lens according to Example 3 satisfies all the conditional expressions (1) to (4).

  6A and 6B are graphs showing various aberrations of the zoom lens according to Example 3. FIG. 6A shows graphs showing various aberrations in the wide-angle end state (f = 6.18), and FIG. Various aberration diagrams, (c) are various aberration diagrams in the telephoto end state (f = 23.0). As is apparent from the respective aberration diagrams, in the third example, it is understood that various aberrations are well corrected and excellent imaging performance is obtained in each focal length state from the wide-angle end state to the telephoto end state.

  In the above-described embodiment, the following description can be appropriately adopted as long as the optical performance is not impaired.

  In the above embodiment, a zoom lens having a four-group configuration is shown, but the present invention can also be applied to other group configurations such as a fifth group and a sixth group. Further, a configuration in which a lens or a lens group is added to the most object side, or a configuration in which a lens or a lens group is added to the most image side may be used. The lens group refers to a portion having at least one lens separated by an air interval that changes during zooming.

  In addition, a single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to be a focusing lens group that performs focusing from an object at infinity to a near object. The focusing lens group can be applied to autofocus, and is also suitable for driving a motor for autofocus (such as an ultrasonic motor). In particular, the third lens group G3 is preferably a focusing lens group.

  In addition, the lens group or the partial lens group is vibrated so as to have a component in a direction perpendicular to the optical axis, or the imaging surface is vibrated in a direction perpendicular to the optical axis to correct image blur caused by camera shake. A vibration lens group may be used. The movement may be rotational movement (swing) with a certain point on the optical axis as the rotation center. In particular, it is preferable that at least a part of the second lens group G2 is an anti-vibration lens group.

  Further, the lens surface may be formed as a spherical surface, a flat surface, or an aspherical surface. It is preferable that the lens surface is a spherical surface or a flat surface because lens processing and assembly adjustment are facilitated, and deterioration of optical performance due to errors in processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. On the other hand, when the lens surface is an aspheric surface, the aspheric surface is an aspheric surface by grinding, a glass mold aspheric surface made of glass with an aspheric shape, or a composite type non-spherical surface made of resin on the glass surface. Any aspherical surface may be used. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  The aperture stop S is preferably disposed in or near the second lens group G2, but the role of the aperture stop may be substituted by a lens frame without providing a member as an aperture stop.

  Further, each lens surface may be provided with an antireflection film having a high transmittance in a wide wavelength range in order to reduce flare and ghost and achieve high optical performance with high contrast.

  In the zoom lens according to the present embodiment, the zoom ratio is about 2.5 to 5.0, more preferably about 3.0 to 4.5.

  In the zoom lens according to the present embodiment, it is preferable that the first lens group G1 has one positive lens component and one negative lens component. In the first lens group G1, in order from the object side, it is preferable to dispose the lens components in a negative and positive order with an air gap interposed therebetween.

  In the zoom lens according to the present embodiment, it is preferable that the second lens group G2 includes at least two positive lenses and one negative lens.

  In the zoom lens according to the present embodiment, it is preferable that the third lens group G3 has one positive lens component.

  In the zoom lens according to the present embodiment, it is preferable that the fourth lens group G4 has one negative lens component.

  In addition, in order to make this invention intelligible, although demonstrated with the component requirement of embodiment, it cannot be overemphasized that this invention is not limited to this.

It is a figure which shows the structure and zoom locus | trajectory of the zoom lens which concern on 1st Example. FIG. 4A is a diagram illustrating various aberrations of the zoom lens according to Example 1, where FIG. 9A illustrates various aberrations in the wide-angle end state, FIG. 9B illustrates various aberrations in the intermediate focal length state, and FIG. FIG. It is a figure which shows the structure and zoom locus | trajectory of the zoom lens which concerns on 2nd Example. FIG. 6 is a diagram illustrating various aberrations of the zoom lens according to Example 2, wherein (a) illustrates various aberrations in the wide-angle end state, (b) illustrates various aberrations in the intermediate focal length state, and (c) illustrates various aberrations in the telephoto end state. FIG. It is a figure which shows the structure and zoom locus | trajectory of the zoom lens which concern on 3rd Example. FIG. 7A is a diagram illustrating various aberrations of the zoom lens according to Example 3. FIG. 9A is a diagram illustrating aberrations at the wide-angle end state, FIG. 9B is a diagram illustrating aberrations at the intermediate focal length state, and FIG. FIG. The digital still camera which has the zoom lens which concerns on this embodiment is shown, (a) is a front view, (b) is a rear view. It is sectional drawing along the AA 'line of Fig.7 (a).

Explanation of symbols

G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group S Aperture I Image surface 1 Digital still camera (optical equipment)

Claims (11)

A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a first lens group having a negative refractive power, arranged in order from the object side. It consists of 4 lens groups by 4 lens groups,
The first lens group is composed of two or less lenses,
At the time of zooming from the wide-angle end state to the telephoto end state, the distance between the first to fourth lens groups is changed, and the fourth lens group is fixed with respect to the image plane.
The third lens group includes one positive lens,
When the focal length of the third lens group is f3, the focal length of the fourth lens group is f4, and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, the following formula 2.99 ≦ f3 / fw <5.0
3.0 <(− f4) / fw <10.0
A zoom lens that satisfies the following conditions. A first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a first lens group having a negative refractive power, arranged in order from the object side. It consists of 4 lens groups by 4 lens groups,
The first lens group is composed of two or less lenses,
During zooming from the wide-angle end state to the telephoto end state, the distance between the first to fourth lens groups is changed, the fourth lens group is fixed with respect to the image plane, and the third lens group is Move to the image side,
The third lens group includes one positive lens,
When the focal length of the third lens group is f3, the focal length of the fourth lens group is f4, and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, the following formula 2.99 ≦ f3 / fw <5.0
3.0 <(− f4) / fw <10.0
A zoom lens that satisfies the following conditions. Wherein the first lens group, a zoom lens according to claim 1 or 2, characterized in that it is composed of two negative lenses and a positive lens. When the focal length of the second lens group is f2 and the combined focal length of the entire zoom lens system in the wide-angle end state is fw, the following formula 1.8 <f2 / fw <3.5
The zoom lens according to any one of claims 1 to 3, characterized by satisfying the condition. The fourth lens group, the zoom lens according to any one of claims 1 to 4, characterized in that it is composed of one negative lens. The zoom lens according to any one of claims 1 to 5 , wherein the third lens group is moved to perform focusing from an infinitely focused state to an object at a finite distance. When the focal length of the first lens group is f1, and the focal length of the second lens group is f2, the following formula 0.8 <(− f1) / f2 <1.3
The zoom lens according to any one of claims 1 to 6, characterized by satisfying the condition. Wherein the first lens group, a zoom lens according to any one of claims 1 to 7, characterized in that it has an aspherical surface. The second lens group, the zoom lens according to any one of claims 1-8, characterized in that it has an aspherical surface. The third lens group, a zoom lens according to any one of claims 1 to 9, characterized in that it has an aspherical surface. An optical apparatus characterized by having a zoom lens according to any one of claims 1-10.

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