JP4507543B2 - Zoom lens - Google Patents

Description

  The present invention relates to a zoom lens, and more particularly to an internal focusing type high-magnification zoom lens used for a single-lens reflex camera or the like.

  Conventionally, since a so-called negative lead type zoom lens preceded by a lens group having a negative refractive power is relatively easy to widen, various proposals have been made.

  On the other hand, focusing of the zoom lens is generally performed by extending the lens group closest to the object side. This focusing method is still widely used because the amount of extension is almost the same in all zoom regions for a subject at the same distance, and the configuration of the lens barrel is relatively simple.

However, the zoom lens having such a configuration has a drawback that the focusing lens group becomes large and heavy when a high zoom ratio and a large aperture are achieved. Thus, in recent years, with the spread of autofocus cameras, various proposals have been made to reduce the weight of the focusing lens group (see, for example, Patent Document 1).
JP-A-5-173070

  However, the zoom lens disclosed in Patent Document 1 has a problem that the large aperture, the high zoom ratio, and the total lens length are not shortened.

  Therefore, the present invention has been made in view of the above problems, and has a large aperture and a high zoom ratio, is focused by a lens group other than the lens group closest to the object side, and is lightweight but zoomed. An object of the present invention is to provide a zoom lens with a small focal point shift and a simple lens barrel configuration.

In order to solve the above problems, the present invention
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 consists of a group,
During zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, and the distance between the second lens group and the third lens group. In a zoom lens in which the distance between the third lens group and the fourth lens group decreases,
The second lens group includes, in order from the object side, a front group having a positive refractive power and a rear group having a positive refractive power,
When focusing from infinity to short distance, focusing is performed by moving the front group along the optical axis,
The first lens group to the rear group form a substantially afocal system at least at a part of the focal length in the focal length region from the wide-angle end state to the telephoto end state,
The most object side lens in the front group is a single lens or a cemented lens,
When the lens closest to the object side in the front group is the single lens, it is an aspherical surface whose positive refractive power decreases as at least one lens surface of the single lens moves away from the optical axis,
When the most object side lens in the front group is the cemented lens, the refractive index of the object side lens of the cemented lens is smaller than the refractive index of the image side lens, the cemented surface is concave on the object side,
Provided is a zoom lens that satisfies the following conditional expression .
1 . 8 <| β2a | min
1.69 ≦ (−f1) / fw <2.3
1.03 ≦ f2 / (fw × ft) ^1/2 ≦ 1.28
However,
| β2a | min: the minimum absolute value of the magnification used in the front group at infinity
f1: Focal length of the first lens group
fw: focal length of the entire zoom lens system in the wide-angle end state
ft: focal length of the entire zoom lens system in the telephoto end state

  According to the present invention, focusing is performed by a lens unit other than the lens unit closest to the object side while having a large aperture and a high zoom ratio, and the focal point movement due to zooming is small while being lightweight, and the configuration of the lens barrel is simple. Zoom lens can be provided.

  The zoom lens of 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 And a fourth lens group having refractive power. Then, during zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, the distance between the second lens group and the third lens group increases, The distance between the third lens group and the fourth lens group decreases.

In the zoom lens according to the present invention, the second lens group includes, in order from the object side, a front group having a positive refractive power and a rear group having a positive refractive power, and focuses on focusing from infinity to a short distance. In this case, focusing is performed by moving the front group along the optical axis, and at least part of the focal length in the focal length region from the wide-angle end state to the telephoto end state moves from the first lens group to the rear group. When forming a substantially afocal system, the most object side lens in the front group is a single lens or a cemented lens, and when the most object side lens in the front group is a single lens, at least one lens surface of the single lens Is an aspheric surface whose positive refractive power decreases as it moves away from the optical axis, and when the most object side lens in the front group is a cemented lens, the refractive index of the object side lens of the cemented lens is the refractive index of the image side lens. Than refractive index Fence bonding surface is concave toward the object side, the following conditional expression (1) is satisfied.
(1) 1.8 <| β2a | min
However,
| β2a | min: the minimum absolute value of the magnification used in the front group at infinity

  In the zoom lens of the present invention, in order to shorten the total lens length while ensuring a high zoom ratio and a short shortest shooting distance, the amount of movement and focusing of the second lens group (front group + rear group) which is a zooming group It is necessary to appropriately secure the amount of movement of the front group that is the lens group.

  When the zoom lens of the present invention is zoomed from the wide-angle end state to the telephoto end state in the focusing method, the first lens group and the front group change from the converged state to the divergent state through the afocal state. Further, the passing state of each light beam with respect to the lens on the most object side in the front group and the rear group differs depending on the amount of movement of the front group that moves during focusing and the thickness of the entire second lens group.

  Light rays that pass through the peripheral part of the lens closest to the object side in the front group of the second lens group are, in order from the optical axis, the land ray in the wide-angle end state, the off-axis principal ray in the wide-angle end state, and the off-axis in the telephoto end state. The main ray, the land ray in the telephoto end state. For this reason, the lens closest to the object side in the front group deteriorates the curvature of field and slightly deteriorates the spherical aberration in the wide-angle end state. Further, in the telephoto end state, the field curvature is deteriorated, and the spherical aberration is particularly deteriorated. Here, the above-mentioned land ray refers to a ray farthest from the optical axis among rays reaching an image height of zero.

  In the zoom lens of the present invention, the front group in the second lens group moves to the image side along the optical axis as the object is focused on a short-distance object.

  For this reason, when the lens closest to the object side in the front group is a single lens, at least one lens surface of the single lens is configured as an aspheric surface that has a positive refractive power that decreases as the distance from the optical axis increases. It is possible to satisfactorily correct the negative meridional curvature of field in each focal length state generated by the two lens groups and the negative spherical aberration in the wide-angle end state, and it is possible to suppress short-distance fluctuations due to focusing. .

  Further, when the most object side lens in the front group is a cemented lens, the refractive index of the object side lens is smaller than the refractive index of the image side lens, and the cemented surface is constituted by a concave cemented lens on the object side. As described above, it is possible to achieve the same effect as when the aspherical surface is introduced into the most object side lens in the front group in the second lens group.

  It should be noted that introducing an aspherical surface to the lens closest to the object side in the front group is more advantageous in securing the amount of movement of the front group than in the case where the lens closest to the object side in the front group is formed of the above-described cemented lens. It is.

  On the other hand, in the zoom lens of the present invention, it is effective to increase the refractive power of the front group which is a focusing lens group in order to enable close-up photography while achieving both high zoom ratio and miniaturization. However, this leads to significant performance degradation.

  In the zoom lens of the present invention, it is desirable that the amount of extension of the front group which is a focusing lens group is constant over the entire zoom range (all focal length states from the wide-angle end state to the telephoto end state). For this reason, it is necessary to ensure that the minimum magnification (| β2a | min) in the infinite state of the focusing lens group is larger than a predetermined value.

Here, the movement amount (feeding amount ΔX) of the focusing lens group for focusing is expressed by the following equation.
(R−TL−f1) ΔX = (D0−f1) ΔX
= (F1 ² (ΔX + β2a × f2a) / [ΔX {ΔX
+ (Β2a ² −1) × (f2a / β2a)])
However,
R: Shooting distance TL: Length of the entire zoom lens (length from the object side principal point of the first lens group to the image plane)
f1: Focal length D0 of the first lens group: Distance ΔX from the object side principal point of the first lens group to the object ΔX: Advancing amount of the focusing lens group for focusing (the movement from the object side to the image side is positive) The amount of movement of the focusing lens group to focus on the object at the shooting distance R)
β2a: lateral magnification of the focusing lens group when the shooting distance is infinity f2a: focal length of the focusing lens group

The above equation can be approximated as:
(D0-f1) ΔX ≒ f1 2 × β2a 2 / (β2a 2 -1)

  From this equation, if β2a is sufficiently large, the extension amount ΔX of the focusing lens group can be regarded as constant regardless of the focal length state.

  The conditional expression (1) is a conditional expression for appropriately defining the absolute value of the absolute value of the use magnification of the front group (focusing lens group) in the infinity state. If | β2a | min becomes too small below the lower limit value of conditional expression (1), the amount of extension of the focusing lens group in each focal length state is not preferable.

According to a preferred aspect of the present invention, it is desirable that the zoom lens of the present invention satisfies the following conditional expression (2).
(2) 1.0 <f2a / f2b <1.6
However,
f2a: Focal length of the front group in the second lens group f2b: Focal length of the rear group in the second lens group

  The conditional expression (2) is a conditional expression for appropriately setting the ratio of the focal length of the front group and the focal length of the rear group in the second lens group.

  If the upper limit of conditional expression (2) is exceeded and the focal length of the front group becomes too large, the focal length of the rear group in the telephoto end state becomes too small even if the focal length of the entire second lens group is the same. For this reason, the amount of extension of the front group for focusing differs depending on the focal length state. In addition, the amount of extension for focusing is increased, and the entire length of the zoom lens is enlarged.

  On the other hand, if the focal length of the front group becomes too small below the lower limit of conditional expression (2), the focal length of the rear group in the wide-angle end state becomes small even if the focal length of the entire second lens group is the same. Pass. For this reason, the amount of extension of the front group for focusing differs depending on the focal length state. Further, it is not preferable because spherical aberration occurs particularly in the telephoto end state.

  According to a preferred aspect of the present invention, in the zoom lens according to the present invention, it is desirable that at least one lens surface of the rear group is an aspheric surface whose positive refractive power increases as the distance from the optical axis increases.

  Light rays that pass through the peripheral part of the lens closest to the object side in the rear group of the second lens group are, in order from the optical axis, off-axis principal rays in the wide-angle end state, land rays in the wide-angle end state, and off-axis in the telephoto end state. The main ray, the land ray in the telephoto end state. For this reason, the lens on the most object side in the rear group hardly affects field curvature, spherical aberration, and the like in the wide-angle end state, but particularly deteriorates spherical aberration in the telephoto end state.

  As described above, the most object-side lens in the front group of the second lens group particularly deteriorates spherical aberration in the telephoto end state. For this reason, if a large zoom ratio is ensured, aberrations will be excessively corrected to the plus side. Therefore, if an aspherical surface whose positive refractive power increases as it moves away from the optical axis is arranged in the rear group that deteriorates only spherical aberration in the telephoto end state, only spherical aberration can be corrected well in the telephoto end state. It becomes possible.

According to a preferred aspect of the present invention, it is desirable that the zoom lens of the present invention satisfies the following conditional expressions (3) and (4).
(3) 1.5 <(− f1) / fw <2.3
(4) 0.75 <f2 / (fw × ft) ^1/2 <1.6
However,
f1: Focal length of the first lens unit fw: Focal length of the entire zoom lens system in the wide-angle end state ft: Focal length of the entire zoom lens system in the telephoto end state

  The conditional expression (3) is a conditional expression for appropriately setting the focal length of the first lens group.

  If the upper limit of conditional expression (3) is exceeded, the focal length of the first lens group becomes too large, and it becomes difficult to reduce the front lens diameter (the diameter of the lens arranged on the object side). End up.

  On the other hand, if the lower limit of conditional expression (3) is not reached, the focal length of the first lens group becomes too small, and it becomes difficult to correct distortion, coma, and field curvature in the wide-angle end state. For this reason, in the telephoto end state, it is difficult to make the refractive power arrangement of the zoom lens of the present invention a so-called telephoto type, and it becomes difficult to secure the F number in the telephoto end state.

  The conditional expression (4) is a conditional expression for appropriately setting the focal length of the second lens group.

  Exceeding the upper limit of conditional expression (4) is not preferable because the focal length of the second lens group becomes too large and the amount of movement of the second lens group due to zooming becomes too large. In addition, the diameter of the diaphragm in the telephoto end state becomes too large, and the diameter of the lens barrel increases.

  On the other hand, if the lower limit value of conditional expression (4) is not reached, the focal length of the second lens group becomes too small, and it becomes difficult to correct coma aberration and particularly spherical aberration in the telephoto end state.

According to a preferred aspect of the present invention, it is desirable that the zoom lens of the present invention satisfies the following conditional expressions (6) and (7).
(5) 0.6 <(− f3) / f2 <1.2
(6) 0.8 <f4 / (fw × ft) ^1/2 <2.0
However,
f2: focal length of the second lens group f3: focal length of the third lens group f4: focal length of the fourth lens group

  Conditional expression (5) sets an appropriate ratio between the focal length of the second lens group and the focal length of the third lens group, and ensures the back focus and enhances the performance of the zoom lens according to the present invention. Is a conditional expression for achieving both.

  If the upper limit of conditional expression (5) is exceeded, the focal length of the third lens group becomes too large compared to the second lens group, making it difficult to ensure back focus in the wide-angle end state.

  On the other hand, if the lower limit value of conditional expression (5) is not reached, the focal length of the third lens group becomes too small compared to the second lens group, and spherical aberration, coma aberration, and astigmatism generated in the third lens group. Aberrations increase, making it difficult to correct these in a balanced manner.

  The conditional expression (6) is a conditional expression for appropriately setting the focal length of the fourth lens group.

  If the upper limit of conditional expression (6) is exceeded, the focal length of the fourth lens group becomes too large, making it difficult to ensure back focus in the wide-angle end state, and a sufficient zoom ratio is achieved. It will also be difficult to secure.

  On the other hand, if the lower limit value of conditional expression (6) is not reached, the focal length of the fourth lens group becomes too small, and variations in various aberrations due to zooming increase, making it difficult to correct aberrations over the entire zoom range. turn into.

  According to a preferred aspect of the present invention, the zoom lens of the present invention has an aperture stop on the image side of the second lens group and in or near the third lens group. desirable.

  Hereinafter, zoom lenses according to embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a diagram showing a lens configuration of a zoom lens according to Example 1 of the present invention. FIG. 1 also shows a movement locus from the wide-angle end state W to the telephoto end state T.

  As shown in FIG. 1, the zoom lens according to the present example includes, in order from the object side, a first lens group G1 having a negative refractive power, a second lens group G2 having a positive refractive power, and a negative refraction. It comprises a third lens group G3 having power and a fourth lens group G4 having positive refractive power. In the zoom lens according to the present embodiment, the distance between the first lens group G1 and the second lens group G2 decreases during zooming from the wide-angle end state to the telephoto end state, and the second lens group G2 The distance between the third lens group G3 increases and the distance between the third lens group G3 and the fourth lens group G4 decreases.

  In addition, an aperture stop S is disposed on the image side of the second lens group G2 and in the vicinity of the third lens group G3. The aperture stop S and the third lens group G3 emit light when zooming. It is configured to move along the axis.

  The configuration described above is a configuration common to all the embodiments after this embodiment. For this reason, the description is abbreviate | omitted in each following Example.

  In the zoom lens according to the present embodiment, the second lens group G2 includes a front group 2a and a rear group 2b in order from the object side. The front group 2a includes, in order from the object side, a cemented lens of a biconvex positive lens and a negative meniscus lens having a concave surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a convex surface facing the object side. And a cemented lens with a positive meniscus lens. The rear group 2b is composed of a biconvex positive lens.

  In the zoom lens according to the present embodiment having the above configuration, focusing from infinity to a short distance is performed by moving the front group 2a in the second lens group G2 to the image side along the optical axis. .

  Table 1 below lists values of specifications of the zoom lens according to the first example of the present invention.

  In (Overall specifications), f represents a focal length, FNO represents an F number, and 2A represents an angle of view.

  In (lens data), the surface represents the order of the lens surfaces from the object side, r represents the radius of curvature of the lens surfaces, and d represents the distance between the lens surfaces. N represents the refractive index for the d-line (λ = 587.6 nm), and ν represents the Abbe number for the d-line (λ = 587.6 nm).

Here, an aspheric surface in the zoom lens according to the present embodiment is represented by the following aspheric expression. Here, y is the height from the optical axis, x is the sag amount, c is the curvature of the reference spherical surface (paraxial curvature), κ is the conic constant, and C ₄ , C ₆ , C ₈ , C ₁₀ and C ₁₂ are 4 each. , 6, 8, 10, 12th order aspheric coefficients.
x = cy ² / {1+ (1-κc ² y ² ) ^1/2 }
+ C ₄ y ⁴ + C ₆ y ⁶ + C ₈ y ⁸ + C ₁₀ y ¹⁰ + C ₁₂ y ¹²

The aspherical surface expressed as described above is marked with * in the surface number in (lens data) and the paraxial radius of curvature is listed in the field of curvature radius r, and in κ and each aspherical surface in (aspherical data). Coefficients are posted. In (aspherical surface data), “En” indicates “× 10 ⁻ⁿ ”. For example, “1.234E-05” indicates “1.234 × 10 ⁻⁵ ”.

  Further, in (magnification of each lens block), β represents an imaging magnification between the object and the image. In addition, 1-POS indicates infinite focus in the wide-angle end state, 2-POS indicates infinite focus in the intermediate focal length state, and 3-POS indicates infinite focus in the telephoto end state. POS is in the wide-angle end state when focusing at β = -0.02500, 5-POS is in the intermediate focal length state when focusing at β = -0.02500, and 6-POS is in the telephoto end state and focusing at β = -0.02500 7-POS is when focusing at close range in the wide-angle end state, 8-POS is when focusing at close range in the intermediate focal length state, and 9-POS is when focusing at close range in the telephoto end state. Show. B (m−n) denotes a lens block including all lenses positioned between the lens surface with surface number m and the lens surface with surface number n.

  Here, “mm” is generally used as a unit for the focal length, the radius of curvature, and the other lengths listed in all the specification values of the following embodiments. However, since the optical system can obtain the same optical performance even when proportionally enlarged or reduced, the unit is not limited to “mm”.

  In addition, the same code | symbol as a present Example is used also in the specification value of all the following Examples.

[Table 1]
(Overall specifications)
Wide-angle end state Intermediate focal length state Telephoto end state f = 17.55 to 29.61 to 53.4
2A = 83.36 to 53.34 to 31.1
FNO = 2.89

(Lens data)
Surface r d N v
1) 41.7490 2.0000 1.799520 42.24
2) 22.5226 14.4873
3) 74.2071 2.0000 1.796681 45.37
* 4) 38.7933 8.0658
5) -92.4063 1.3000 1.569070 71.31
6) 58.4359 0.0000
7) 58.4359 3.7360 1.846660 23.78
8) 289.3259 D8 (variable)

9) 180.6275 4.2583 1.696800 55.52
10) -50.6496 1.0000 1.846660 23.78
11) -80.4575 0.1000
12) 41.9083 1.0000 1.846660 23.78
13) 25.4611 6.0000 1.487490 70.24
14) 157.3587 1.0024

* 15) 43.2622 5.7575 1.713000 53.85
16) -259.6633 D16 (variable)

17> Aperture stop S 1.2000
18) 128.9726 4.3615 1.846660 23.78
19) -24.3308 1.0000 1.804000 46.58
20) 49.4407 2.5995
21) -31.3713 1.0000 1.804000 46.58
22) 115.9859 D22 (variable)

23) 368.8076 5.0000 1.497820 82.52
24) -28.1873 0.1000
25) 159.2657 2.7000 1.618000 63.38
26) -123.3241 0.1000
27) 65.0663 5.7301 1.497820 82.52
28) -28.1289 1.0000 1.846660 23.78
29) -106.6177

(Aspheric data)
Face κ C4 C6 C8 C10
4 0.0000 -3.19380E-06 -4.94320E-09 7.51060E-13 -1.32410E-14
C12
-0.44693E-17
Face κ C4 C6 C8 C10
15 1.0000 1.00000E-08 3.75250E-10 1.08920E-12 0.00000E + 00

(Variable interval data)
Wide-angle end state Intermediate focal length state Telephoto end state
D8 39.33590 16.23690 1.75000
D16 1.35000 10.85920 22.23130
D22 17.07340 12.51060 5.52610

(Magnification of each lens block)
1-POS 2-POS 3-POS 4-POS 5-POS 6-POS
β -0.02500 -0.02500 -0.02500
B (1-8) 0.00000 0.00000 0.00000 0.04277 0.02511 0.01387
B (9-14) -3.80389 12.59026 3.40003 -3.78623 12.59237 3.40648
B (15-16) 0.14366 -0.07072 -0.43257 0.14360 -0.07077 -0.43262
B (17-22) -2.78220 -2.33000 -1.35946 -2.78119 -2.32934 -1.35927
B (23-29) -0.38982 -0.48203 -0.90196 -0.38994 -0.48215 -0.90208

7-POS 8-POS 9-POS
β -0.066 -0.107 -0.197
B (1-8) 0.11503 0.10862 0.10999
B (9-14) -3.76723 12.47409 3.43905
B (15-16) 0.14323 -0.07178 -0.43562
B (17-22) -2.77512 -2.31783 -1.34763
B (23-29) -0.39065 -0.48422 -0.90944

  FIGS. 2A, 2B, and 2C are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state of the zoom lens according to Example 1 of the present invention. Indicates.

  In each aberration diagram, FNO indicates an F number, and A indicates a half angle of view. In the astigmatism diagram and the distortion diagram, the maximum value of the half field angle A is shown. D and g indicate aberration curves of the d-line (λ = 587.6 nm) and the g-line (λ = 435.8 nm), respectively.

  In the spherical aberration diagram, FNO indicates the value of the F number corresponding to the maximum aperture.

  In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane.

  The coma aberration diagram represents the coma aberration at each half angle of view.

  In addition, in the various aberration diagrams of each example described below, the same reference numerals as those in this example are used.

  From the various aberration diagrams, it can be seen that the zoom lens according to the present embodiment corrects various aberrations well and has excellent imaging performance in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state. .

(Second embodiment)
FIG. 3 is a diagram showing a lens configuration of a zoom lens according to Example 2 of the present invention, and FIG. 3 also shows a movement locus from the wide-angle end state W to the telephoto end state T.

  In the zoom lens according to the present embodiment, the second lens group G2 includes a front group 2a and a rear group 2b in order from the object side. The front group 2a includes, in order from the object side, a cemented lens of a biconvex positive lens and a negative meniscus lens having a concave surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a convex surface facing the object side. And a cemented lens with a positive meniscus lens. The rear group 2b is composed of a biconvex positive lens.

  In the zoom lens according to the present embodiment having the above-described configuration, focusing from infinity to a short distance is performed by moving the front group 2a in the second lens group G2 to the image side along the optical axis.

  Table 2 below provides values of specifications of the zoom lens according to the second example of the present invention.

[Table 2]
(Overall specifications)
Wide-angle end state Intermediate focal length state Telephoto end state f = 17.55 to 30.79 to 53.4
2A = 83.34 to 51.24 to 30.98
FNO = 2.89

(Lens data)
Surface r d N v
1) 40.9179 2.0000 1.806100 40.94
2) 21.9529 14.9387
3) 85.5860 2.0000 1.796681 45.37
* 4) 41.8649 6.6331
5) -88.8627 1.3000 1.569070 71.31
6) 79.4414 0.0000
7) 79.4414 3.4131 1.846660 23.78
8) 4482.0238 D8 (variable)

9) 265.6240 4.1124 1.696800 55.52
10) -53.0226 1.0000 1.805180 25.43
11) -85.4782 0.1000
12) 48.4579 1.0000 1.846660 23.78
13) 28.3332 6.0000 1.487490 70.24
14) 609.7882 1.0047

15) 44.0030 5.8155 1.696800 55.52
16) -207.9680 D16 (variable)

17> Aperture stop S 1.2000
18) 132.9964 4.2981 1.846660 23.78
19) -24.6683 1.0000 1.804000 46.58
20) 52.5868 2.6051
21) -31.0252 1.0000 1.804000 46.58
22) 108.4429 D22 (variable)

23) 1202.2229 5.0000 1.497820 82.52
24) -26.9875 0.1000
25) 152.4677 2.7000 1.618000 63.38
26) -129.6517 0.1000
27) 54.2036 6.0000 1.497820 82.52
28) -30.0273 1.0000 1.846660 23.78
29) -162.9006

(Aspheric data)
Face κ C4 C6 C8 C10
4 0.0000 -4.05780E-06 -3.17270E-09 -1.99470E-11 5.77110E-14
C12
-0.94474E-16

(Variable interval data)
Wide-angle end state Intermediate focal length state Telephoto end state
D8 40.95880 15.53650 1.75000
D16 1.35000 12.25530 23.90170
D22 17.41550 13.09280 6.05810

(Magnification of each lens block)
1-POS 2-POS 3-POS 4-POS 5-POS 6-POS
β -0.02500 -0.02500 -0.02500
B (1-8) 0.00000 0.00000 0.00000 0.04449 0.02510 0.01443
B (9-14) -3.82942 10.11327 3.40001 -3.81121 10.11878 3.40667
B (15-16) 0.13758 -0.08740 -0.41103 0.13752 -0.08746 -0.41108
B (17-22) -2.61985 -2.38465 -1.57100 -2.61895 -2.38397 -1.57075
B (23-29) -0.41289 -0.47443 -0.78981 -0.41301 -0.47455 -0.78993

7-POS 8-POS 9-POS
β -0.066 -0.111 -0.195
B (1-8) 0.12027 0.11285 0.11327
B (9-14) -3.79169 10.05288 3.44006
B (15-16) 0.13714 -0.08853 -0.41394
B (17-22) -2.61348 -2.37106 -1.55587
B (23-29) -0.41373 -0.47678 -0.79712

  FIGS. 4A, 4B, and 4C are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state of the zoom lens according to Example 2 of the present invention. Indicates.

  From the various aberration diagrams, it can be seen that the zoom lens according to the present embodiment corrects various aberrations well and has excellent imaging performance in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state. .

(Third embodiment)
FIG. 5 is a diagram showing a lens configuration of a zoom lens according to a third example of the present invention. FIG. 5 also shows a movement locus from the wide-angle end state W to the telephoto end state T.

  In the zoom lens according to the present embodiment, the second lens group G2 includes a front group 2a and a rear group 2b in order from the object side. The front group 2a includes, in order from the object side, a biconvex positive lens, and a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens. The rear group 2b is composed of a biconvex positive lens.

  In the zoom lens according to the present embodiment having the above-described configuration, focusing from infinity to a short distance is performed by moving the front group 2a in the second lens group G2 to the image side along the optical axis.

  Table 3 below lists values of specifications of the zoom lens according to the third example of the present invention.

[Table 3]
(Overall specifications)
Wide-angle end state Intermediate focal length state Telephoto end state f = 17.55 to 33.80 to 53.4
2A = 83.36 to 46.86 to 30.78
FNO = 2.89

(Lens data)
Surface r d N v
1) 88.4857 2.0000 1.569070 71.31
2) 23.1237 12.5909
3) 1676.3197 2.0000 1.796681 45.37
* 4) 37.3077 5.6615
5) 79.7028 3.3257 1.805180 25.43
6) 1620.6953 D6 (variable)

* 7) 134.8418 5.0000 1.677900 55.34
8) -102.4648 0.1000
9) 125.7885 1.0000 1.805180 25.43
10) 33.4567 7.0000 1.618000 63.38
11) -2913.5812 5.5422

* 12) 53.4429 6.0000 1.589130 61.18
13) -123.9664 D13 (variable)

14> Aperture stop S 1.2000
15) 152.1655 4.0000 1.846660 23.78
16) -31.2559 1.0000 1.804000 46.58
17) 104.9708 1.8127
18) -39.8203 1.0000 1.804000 46.58
19) 91.7813 D19 (variable)

20) -530.1722 4.9750 1.618000 63.38
21) -31.9506 1.7123
22) 193.3336 3.0000 1.518601 69.98
23) -83.1397 0.1000 1.000000
24) 58.3456 5.0292 1.518601 69.98
25) -31.3537 1.0000 1.846660 23.78
26) -447.5858

(Aspheric data)
Face κ C4 C6 C8 C10
4 0.0000 -5.36480E-06 -1.71290E-09 4.22100E-12 -2.13050E-14
C12
0.16581E-16
Face κ C4 C6 C8 C10
7 1.0000 -2.14990E-06 2.70180E-09 -1.00150E-12 0.00000E + 00
Face κ C4 C6 C8 C10
12 1.0000 1.65360E-06 -2.67510E-09 2.47720E-12 -3.01900E-15

(Variable interval data)
Wide-angle end state Intermediate focal length state Telephoto end state
D6 44.20260 13.46390 1.75000
D13 1.35000 19.48370 33.77710
D19 18.02270 11.52620 2.63440

(Magnification of each lens block)
1-POS 2-POS 3-POS 4-POS 5-POS 6-POS
β -0.02500 -0.02500 -0.02500
B (1-6) 0.00000 0.00000 0.00000 0.04882 0.02507 0.01584
B (7-11) -4.30819 6.45890 3.30819 -4.28973 6.46779 3.31537
B (12-13) 0.13576 -0.16783 -0.48561 0.13568 -0.16790 -0.48567
B (14-19) -3.17928 -2.82367 -1.87713 -3.17785 -2.82263 -1.87673
B (20-26) -0.27919 -0.32670 -0.52381 -0.27930 -0.32680 -0.52392

7-POS 8-POS 9-POS
β -0.067 -0.123 -0.196
B (1-6) 0.13309 0.12456 0.12490
B (7-11) -4.27360 6.46338 3.35220
B (12-13) 0.13521 -0.16954 -0.48946
B (14-19) -3.16900 -2.79827 -1.85197
B (20-26) -0.27996 -0.32931 -0.53049

  FIGS. 6A, 6B, and 6C are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state of the zoom lens according to Example 3 of the present invention. Indicates.

  From the various aberration diagrams, it can be seen that the zoom lens according to the present embodiment corrects various aberrations well and has excellent imaging performance in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state. .

(Fourth embodiment)
FIG. 7 is a diagram showing the lens configuration of a zoom lens according to Example 4 of the present invention. (A), (b), and (c) are the wide-angle end state W, the intermediate focal length state M, and the telephoto, respectively. The end state T is shown.

  In the zoom lens according to the present embodiment, the second lens group G2 includes a front group 2a and a rear group 2b in order from the object side. The front group 2a includes, in order from the object side, a biconvex positive lens, and a cemented lens of a negative meniscus lens having a convex surface facing the object side and a biconvex positive lens. The rear group 2b is composed of a biconvex positive lens.

  In the zoom lens according to the present embodiment having the above-described configuration, focusing from infinity to a short distance is performed by moving the front group 2a in the second lens group G2 to the image side along the optical axis.

  Table 4 below provides values of specifications of the zoom lens according to Example 4 of the present invention.

[Table 4]
(Overall specifications)
Wide-angle end state Intermediate focal length state Telephoto end state f = 17.50 to 31.433 to 53.4
2A = 83.44 to 49.96 to 30.78
FNO = 2.88

(Lens data)
Surface r d N v
1) 61.1778 2.5000 1.796681 45.37
* 2) 23.8595 22.2571
3) -53.4452 1.3000 1.497820 82.52
4) 74.5711 0.0000
5) 74.5711 2.8345 1.805180 25.43
6) 251.1650 D6 (variable)

* 7) 144.7881 3.2432 1.669100 55.39
8) -101.9877 0.1000
9) 115.7173 1.0000 1.846660 23.78
10) 33.8371 5.6799 1.618000 63.38
11) -316.7089 1.0036

* 12) 54.0448 4.9363 1.744429 49.52
13) -201.4533 D13 (variable)

14> Aperture stop S 1.2000
15) 195.2821 3.6562 1.846660 23.78
16) -28.8371 1.0000 1.804000 46.58
17) 92.5612 1.9195
18) -39.0662 1.0000 1.804000 46.58
19) 115.0637 D19 (variable)

20) -89.5048 3.2808 1.497820 82.52
21) -27.7764 0.1000
22) 335.0242 2.6731 1.618000 63.38
23) -64.1525 0.1077
24) 49.9637 6.1661 1.497820 82.52
25) -32.4974 1.0000 1.846660 23.78
26) -283.4287

(Aspheric data)
Face κ C4 C6 C8 C10
2 0.0000 4.59450E-06 6.67330E-10 7.66470E-12 -9.79900E-15
C12
0.59536E-17
Face κ C4 C6 C8 C10
7 1.0000 -1.84030E-06 -3.89750E-12 2.85600E-12 0.00000E + 00
Face κ C4 C6 C8 C10
12 1.0000 1.39700E-06 -3.54520E-11 -6.71070E-13 -4.17940E-16

(Variable interval data)
Wide-angle end state Intermediate focal length state Telephoto end state
D6 42.84360 14.89650 1.75000
D13 1.35000 13.32930 27.30380
D19 19.73850 14.04300 5.54860

(Magnification of each lens block)
1-POS 2-POS 3-POS 4-POS 5-POS 6-POS
β -0.02500 -0.02500 -0.02500
B (1-6) 0.00000 0.00000 0.00000 0.04513 0.02496 0.01468
B (7-11) -4.15384 7.21257 3.15345 -4.13339 7.22343 3.16041
B (12-13) 0.13506 -0.14079 -0.52025 0.13506 -0.14079 -0.52025
B (14-19) -4.57979 -2.96156 -1.73145 -4.57979 -2.96157 -1.73145
B (20-26) -0.21668 -0.33252 -0.59806 -0.21668 -0.33252 -0.59806

7-POS 8-POS 9-POS
β -0.065 -0.112 -0.194
B (1-6) 0.11855 0.11125 0.11209
B (7-11) -4.10010 7.26096 3.20652
B (12-13) 0.13506 -0.14079 -0.52025
B (14-19) -4.57979 -2.96156 -1.73145
B (20-26) -0.21668 -0.33252 -0.59806

  FIGS. 8A, 8B, and 8C are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state of the zoom lens according to Example 4 of the present invention. Indicates.

  From the various aberration diagrams, it can be seen that the zoom lens according to the present embodiment corrects various aberrations well and has excellent imaging performance in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state. .

  Here, the values corresponding to the conditional expressions of the zoom lens according to each embodiment of the present invention are listed in Table 5 below.

[Table 5]
(Values for conditional expressions)
First Example Second Example Third Example Fourth Example Conditional Expression (1) 3.40 3.40 3.31 3.15
Conditional expression (2) 1.29 1.34 1.24 1.28
Conditional expression (3) 1.69 1.75 1.93 1.80
Conditional expression (4) 1.03 1.04 1.28 1.10
Conditional expression (5) 0.78 0.77 0.88 0.97
Conditional expression (6) 1.05 1.06 1.92 1.20

  As described above, according to each embodiment of the present invention, the angle of view in the wide-angle end state is 75 degrees or more, the zoom ratio is 3 times or more, the aperture is large, and the lens group other than the lens group closest to the object side is used. It is possible to realize a zoom lens that performs focusing and is lightweight but has a small focal point movement due to zooming and has a simple lens barrel configuration.

It is a figure which shows the lens structure of the zoom lens which concerns on 1st Example of this invention. (A), (b), and (c) show various aberration diagrams at the time of focusing at infinity in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 1 of the present invention. FIG. It is a figure which shows the lens structure of the zoom lens which concerns on 2nd Example of this invention. (A), (b), and (c) show various aberration diagrams at the time of focusing at infinity in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 2 of the present invention. FIG. It is a figure which shows the lens structure of the zoom lens which concerns on 3rd Example of this invention. (A), (b), and (c) are graphs showing various aberrations during focusing at infinity in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 3 of the present invention. FIG. It is a figure which shows the lens structure of the zoom lens which concerns on 4th Example of this invention. (A), (b), and (c) are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, intermediate focal length state, and telephoto end state of the zoom lens according to Example 4 of the present invention. FIG.

Explanation of symbols

G1 First lens group G2 Second lens group 2a Front group in second lens group 2b Rear group in second lens group G3 Third lens group G4 Fourth lens group I Image plane W Wide-angle end state M Intermediate focal length state T Telephoto End state

Claims (5)

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 consists of a group,
During zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group and the second lens group decreases, and the distance between the second lens group and the third lens group increases. In the zoom lens in which the distance between the third lens group and the fourth lens group is reduced,
The second lens group includes, in order from the object side, a front group having a positive refractive power and a rear group having a positive refractive power,
When focusing from infinity to short distance, focusing is performed by moving the front group along the optical axis,
The first lens group to the rear group form a substantially afocal system at least at a part of the focal length in the focal length region from the wide-angle end state to the telephoto end state,
The most object side lens in the front group is a single lens or a cemented lens,
When the lens closest to the object side in the front group is the single lens, it is an aspherical surface whose positive refractive power decreases as at least one lens surface of the single lens moves away from the optical axis,
When the most object side lens in the front group is the cemented lens, the refractive index of the object side lens of the cemented lens is smaller than the refractive index of the image side lens, the cemented surface is concave on the object side,
A zoom lens satisfying the following conditional expression:
1.8 <| β2a | min
1.69 ≦ (−f1) / fw <2.3
1.03 ≦ f2 / (fw × ft) ^1/2 ≦ 1.28
However,
| β2a | min: the minimum absolute value of the magnification used in the front group at infinity
f1: Focal length of the first lens group
fw: focal length of the entire zoom lens system in the wide-angle end state
ft: focal length of the entire zoom lens system at the telephoto end The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
1.0 <f2a / f2b <1.6
However,
f2a: focal length of the front group in the second lens group f2b: focal length of the rear group in the second lens group   3. The zoom lens according to claim 1, wherein at least one lens surface of the rear group is an aspherical surface whose positive refractive power increases as the distance from the optical axis increases. The zoom lens according to any one of claims 1 to 3 , wherein the following conditional expression is satisfied.
0.6 <(− f3) / f2 <1.2
0.8 <f4 / (fw × ft) ^1/2 <2.0
However,
f2: focal length of the second lens group f3: focal length of the third lens group f4: focal length of the fourth lens group Having an aperture stop,
The aperture stop is a image side of the second lens group, and the claim 1, characterized in that it is arranged in or on the third lens vicinity group the third lens group according to claim 4 The zoom lens according to any one of the above.

Images