JP2008151949A - Wide angle lens, imaging apparatus, and focusing method of the wide angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide angle lens which has a large back focus and a large photographic angle of view, can make the entire lens system compact, while making a front lens diameter smaller, can be quickly focused, is small in aberration fluctuations in focusing, can excellently correct various aberrations over the whole screen and has high optical performance, and the like. <P>SOLUTION: The wide angle lens has a first lens group G1 which is positive as a whole; an aperture diaphragm S and a second lens group G2 which is positive as a whole, in order from an object side. The first lens group G1 has a front group Gf comprising first, second and third negative meniscus lenses L11, L12 and L13 having convex surfaces on the object side and a positive lens L14, in order from the object side. The front group Gf has at least one aspheric surface and the first lens group G1 is fixed and the second lens group G2 is moved along an optical axis, when a focusing from an infinite object to a short-distance object is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wide-angle lens, an imaging device, and a focusing method for a wide-angle lens.

Conventionally, a so-called retrofocus (reverse telephoto) wide-angle lens preceded by a negative lens group is known as a wide-angle lens having a large back focus compared to the focal length (see, for example, Patent Document 1). .
JP 49-121527 A

  In general, the lens arrangement of a retro-focus type wide-angle lens is asymmetric as a whole by arranging a negative lens group and a positive lens group in order from the object side. There was a problem that was difficult. In addition to this problem, there is a problem that aberration variation due to focusing increases and it is very difficult to realize high optical performance over the entire object distance range.

  In recent years, there has been a demand for downsizing the entire lens system of a taking lens used in a photographic camera, a video camera, or the like as the camera body is downsized. However, if an attempt is made to reduce the size of the entire lens system while reducing the front lens diameter while maintaining a large shooting angle of view with a retrofocus type lens, a large amount of aberrations will occur. In order to realize high optical performance, the number of lenses has to be increased, and the entire lens system is increased in size.

  Therefore, the present invention has been made in view of the above problems, and has a large back focus, a large shooting angle of view, and the entire lens system is reduced in size while reducing the front lens diameter. To provide a wide-angle lens, an image pickup apparatus, and a wide-angle lens focusing method that have high optical performance that enables quick focusing and small aberration fluctuations during focusing and that can satisfactorily correct various aberrations over the entire screen. With the goal.

In order to solve the above problems, the present invention
In order from the object side, the first lens group having a positive refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole,
The first lens group includes, in order from the object side, a first negative meniscus lens having a convex surface facing the object side, a second negative meniscus lens having a convex surface facing the object side, and a third negative meniscus lens having a convex surface facing the object side. And a front group consisting of a positive lens,
In the front group, at least one aspheric surface is provided,
A wide-angle lens is provided in which the front group is fixed and the rear group moves along the optical axis when focusing from an object at infinity to an object at a short distance.

  In addition, an imaging apparatus comprising the wide-angle lens of the present invention is provided.

The present invention also provides
In the focusing method of a wide-angle lens having, in order from the object side, a first lens group having a positive refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole,
The first lens group includes, in order from the object side, a front group including a first negative meniscus lens, a second negative meniscus lens, a third negative meniscus lens, and a positive lens having a convex surface directed toward the object side.
In the front group, at least one aspheric surface is provided,
A focusing method for a wide-angle lens is provided, wherein the first lens group is fixed and the second lens group moves along an optical axis when focusing from an object at infinity to an object at a short distance.

  According to the present invention, the entire lens system can be miniaturized while having a large back focus and a large shooting angle of view, while reducing the diameter of the front lens lens, enabling quick focusing and focusing. It is possible to provide a wide-angle lens, an imaging device, and a focusing method for a wide-angle lens that have high optical performance capable of satisfactorily correcting various aberrations over the entire screen.

Hereinafter, the wide-angle lens, the imaging device, and the focusing method of the present application will be described.
The wide-angle lens includes, in order from the object side, a first lens group having a positive refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole, and the first lens group. In order from the object side, a first negative meniscus lens having a convex surface facing the object side, a second negative meniscus lens having a convex surface facing the object side, a third negative meniscus lens having a convex surface facing the object side, and a positive lens The front lens group includes at least one aspherical surface, and the first lens group is fixed and the second lens group is fixed when focusing from an object at infinity to a near object. The lens group is configured to move along the optical axis.

  In general, a retrofocus type wide-angle lens needs to secure back focus, and the rear lens diameter is limited, so that the off-axis light beam (chief ray) incident at a large incident angle can be emitted at a small emission angle. The light is ejected to form an image at a predetermined image height. In general, a wide-angle lens having a symmetrical lens arrangement does not need to ensure back focus, and therefore can be configured to allow off-axis light beams to be incident at a large incident angle and to be emitted at a larger emission angle. For this reason, it is necessary to reduce the angle of the off-axis light beam with respect to the optical axis mainly in the lens group on the object side (first lens group).

  In general, the larger the incident angle with respect to a certain lens surface, the more aberrations occur. Therefore, it is preferable to dispose a lens surface having an extremely large incident angle in the lens group on the object side of the retrofocus type wide-angle lens. In other words, it is desirable not to give the lens a large refractive power.

  Therefore, this wide-angle lens has at least three negative lenses and a positive lens in the first lens group in order to gradually refract the off-axis light beam and gradually reduce the emission angle. By making these three negative lenses an aplanatic surface, that is, a negative meniscus lens toward the aperture stop, it is possible to prevent the incident angle and the emission angle from becoming extremely large on each lens surface. As a result, the wide-angle lens can easily perform aberration correction over a wide range of field angles.

  However, with only the negative meniscus lens described above in the first lens group, it is not possible to correct distortion that is a problem in the retrofocus type wide-angle lens. Therefore, in order to solve this, it is effective to make at least one lens surface of the negative meniscus lens an aspherical surface having a shape in which the convergence increases toward the periphery of the lens, and similarly, distortion aberration is reduced. This is advantageous because the aspherical surface can eliminate the increase in front lens diameter caused by arranging a positive lens for correction.

Here, in a retrofocus type wide-angle lens, when a so-called overall extension method is adopted in which the entire lens is extended at the time of focusing from an object at infinity to an object at a short distance, the curvature of field significantly changes to the plus side. For this reason, this wide-angle lens adopts a floating system that changes the distance of a part of the lens system to reduce the variation in curvature of field when focusing from an object at infinity to a close object. The first lens group is fixed at the time of focusing, and focusing is performed only with the second lens group having a small aperture. As a result, the variation in field curvature is reduced, and the focusing weight (the weight of the lens that is driven during focusing) is reduced, so that more rapid focusing can be performed.
In addition, it is desirable that this wide-angle lens satisfies the following conditional expression (1).
(1) D2 / f <1.00
However,
f: focal length of the entire wide-angle lens system D2: distance on the optical axis between the lens surface closest to the object side of the second lens group and the lens surface closest to the image side of the second lens group Conditional expression (1) Is a setting of an optimum range for securing a moving space for focusing and focusing on an object at a shorter distance with good optical performance. By satisfying conditional expression (1), the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side of the second lens group is reduced, that is, the so-called total thickness of the entire second lens group is reduced. Thus, miniaturization can be achieved. For this reason, a sufficient moving space for focusing can be secured, focusing can be performed up to a closer object, and the fitting length of the focusing lens group can be secured, so various aberrations such as coma during focusing can be prevented. It is preferable because good optical performance with little fluctuation can be obtained. Further, since the load for driving the focusing lens can be reduced by downsizing, it is preferable because rapid focusing can be performed.
If the upper limit value of conditional expression (1) is exceeded, the focusing lens group becomes large, it is not possible to secure a sufficient moving space for focusing, and it becomes impossible to focus to a closer object, Variations in various aberrations such as coma during focusing increase, which makes it impossible to obtain good optical performance. Further, the increase in the size increases the load for driving the focusing lens, which makes it impossible to perform rapid focusing.
In addition, if the upper limit of conditional expression (1) is set to 0.90, the effect of this invention can be exhibited more.
In the wide-angle lens, it is preferable that the second lens group is composed of five or less lenses.
This is preferable because the second lens group can be made small in size and the fitting length can be secured, so that favorable optical performance can be obtained with little fluctuation in various aberrations such as coma during focusing. Further, since the load for driving the focusing lens can be reduced by downsizing, it is preferable because rapid focusing can be performed.
If the number of lenses in the second lens group exceeds 5, it is not preferable because the focusing lens group becomes large and fluctuations in various aberrations such as coma during focusing become large and it becomes impossible to obtain good optical performance. Further, the increase in the size increases the load for driving the focusing lens, which makes it impossible to perform rapid focusing.

Further, it is desirable that the wide-angle lens satisfies the following conditional expressions (2) and (3).
(2) 2.50 <f1 / f <30.00
(3) 0.30 <D12 / f <1.50
However,
f: Focal length of the entire wide-angle lens system f1: Focal length of the first lens group D12: Light from the most image side lens surface of the first lens group and the most object side lens surface of the second lens group Axis distance

Conditional expression (2) is a conditional expression for prescribing the focal length of the first lens group in this wide-angle lens and correcting various aberrations satisfactorily while increasing the back focus. Note that the values of the symbols f and f1 in the conditional expression (2) and the symbols D12, f2, f1a, and f1b in the conditional expressions described later are values at the time of focusing on an object at infinity.
If the upper limit of conditional expression (2) is exceeded and the focal length of the first lens unit becomes too large, the light beam convergence action is reduced, which is advantageous for securing the back focus. However, a large amount of distortion is generated, and it becomes difficult to correct this by the second lens group.
In addition, if the upper limit of conditional expression (2) is set to 25.00, the effect of this invention can be exhibited more.

On the other hand, if the focal length of the first lens group becomes too small below the lower limit value of conditional expression (2), the converging effect of the light beam will increase, making it difficult to ensure sufficient back focus. In order to compensate for this, the focal length of the second lens group must be increased, and the amount of focusing movement of the second lens group increases accordingly, resulting in large fluctuations in various aberrations.
In addition, if the lower limit of conditional expression (2) is set to 3.00, the effect of the present invention can be exhibited more.

Conditional expression (3) defines the distance between the first lens group and the second lens group at the time of focusing on an object at infinity in the wide-angle lens, and the first lens group is fixed and good focusing is performed by the second lens group. Is a conditional expression for performing
If the interval becomes too large exceeding the upper limit value of conditional expression (3), it is possible to secure a sufficient space for moving the second lens group when focusing from an object at infinity to a near object. However, it is difficult to secure the back focus, and the total thickness of the second lens group must be reduced, so that various aberrations, particularly coma aberration, cannot be corrected sufficiently.
In addition, if the upper limit of conditional expression (3) is set to 1.00, the effect of this invention can be exhibited more.

On the other hand, if the distance becomes too small below the lower limit value of the conditional expression (3), it is not possible to secure a sufficient space for moving the second lens group when focusing from an object at infinity to a near object. End up. For this reason, it is necessary to increase the refractive power of the second lens group, and this mainly deteriorates the spherical aberration.
In addition, if the lower limit of conditional expression (3) is set to 0.50, the effect of the present invention can be exhibited more. If the lower limit value of conditional expression (3) is set to 0.60, the effects of the present invention can be exhibited to the maximum.

In addition, it is preferable that the wide-angle lens satisfies the following conditional expression (4).
(4) 0.70 <f1 / f2 <13.00
However,
f1: focal length of the first lens group f2: focal length of the second lens group

Conditional expression (4) defines the ratio of the focal lengths of the first lens group and the second lens group in the wide-angle lens, reduces aberration fluctuations during focusing, and ensures sufficient back focus. It is a conditional expression for realizing both of the above.
If the upper limit of conditional expression (4) is exceeded and the refractive power of the second lens unit becomes too large, the spherical aberration will deteriorate.
In addition, if the upper limit of conditional expression (4) is set to 10.00, the effect of this invention can be exhibited more.

On the other hand, if the refractive power of the second lens group becomes too small below the lower limit value of conditional expression (4), the amount of movement of the second lens group during focusing increases, and the enlargement of the first lens group is avoided. Therefore, it is necessary to reduce the number of lenses constituting the first lens group, and the field angle aberration (distortion aberration and astigmatism) is mainly deteriorated.
In addition, if the lower limit of conditional expression (4) is set to 1.00, the effect of the present invention can be exhibited more.

In the wide-angle lens, it is preferable that the second lens group includes a plurality of positive lenses and a plurality of negative lenses, and satisfies the following conditional expression (5).
(5) 36.00 <Δν2
However,
Δν2: difference between the average dispersion value of the positive lens and the average dispersion value of the negative lens in the second lens group

Conditional expression (5) is a conditional expression that defines the dispersion value of each lens constituting the second lens group in the wide-angle lens.
If the lower limit of conditional expression (5) is not reached, correction of chromatic aberration by the second lens group will be insufficient, and in particular, lateral chromatic aberration will deteriorate.
In addition, if the lower limit of conditional expression (5) is set to 37.50, the effect of the present invention can be exhibited more.

In the wide-angle lens, it is preferable that the first lens group has a rear group on the image side of the front group and satisfies the following conditional expression (6).
(6) 0.25 <(− f1a) / f1b <2.00
However,
f1a: focal length of the front group f1b: focal length of the rear group

Conditional expression (6) is a conditional expression that defines the negative refractive power of the front group and the degree of retrofocus in the first lens group in the wide-angle lens.
If the upper limit of conditional expression (6) is exceeded and the focal length of the rear group becomes relatively small, spherical aberration and coma will deteriorate.
In addition, if the upper limit of conditional expression (6) is set to 1.30, the effect of this invention can be exhibited more.

If the focal length of the front group becomes too small relatively below the lower limit value of conditional expression (6), off-axis aberrations such as distortion and astigmatism will deteriorate.
In addition, if the lower limit of conditional expression (6) is set to 0.35, the effect of the present invention can be exhibited more.

  Further, in the present wide-angle lens, the second lens group has essentially positive refracting power, and passes through the second lens group (the light beam farthest from the optical axis among the light beams reaching the image height 0). Is called a land ray) from the optical axis higher than the first lens group. For this reason, correction of spherical aberration is insufficient, and correction of annular spherical aberration tends to be insufficient. Therefore, in the present wide-angle lens, by providing a cemented surface in the second lens group, spherical aberration is corrected, and at the same time, coma aberration, axial chromatic aberration, and lateral chromatic aberration are corrected well.

The imaging device of the present application includes the wide-angle lens having the above-described configuration.
As a result, the lens system has a large back focus, a large shooting angle of view, and a small F-number, and the entire lens system is miniaturized while reducing the front lens diameter, enabling rapid focusing, and It is possible to realize an image pickup apparatus that has high optical performance with small aberration fluctuations during focusing and that can satisfactorily correct various aberrations over the entire screen.

The wide-angle lens focusing method of the present application includes, in order from the object side, a wide-angle lens including a first lens group having a positive refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole. In the lens focusing method, the first lens group includes a first negative meniscus lens, a second negative meniscus lens, a third negative meniscus lens, and a positive lens having a convex surface directed toward the object side in order from the object side. And the front lens group includes at least one aspherical surface, and the first lens group is fixed at the time of focusing from an object at infinity to a near object, and the second lens group Is characterized by moving along the optical axis.
As a result, the lens system has a large back focus, a large shooting angle of view, and a small F-number, and the entire lens system is miniaturized while reducing the front lens diameter, enabling rapid focusing, and It is possible to realize a focusing method for a wide-angle lens that has a small aberration variation during focusing and has high optical performance that can satisfactorily correct various aberrations over the entire screen.

Hereinafter, wide angle lenses according to numerical examples of the present application will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a wide-angle lens according to a first example of the present application.
The wide-angle lens according to the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power as a whole, an aperture stop S, and a second lens group G2 having a positive refractive power as a whole. Has been.

The first lens group G1 includes a front group Gf and a rear group Gr in order from the object side.
The front group Gf includes, in order from the object side, a first negative meniscus lens L11 having a convex surface facing the object side and an aspheric lens surface on the image side, a second negative meniscus lens L12 having a convex surface facing the object side, It consists of a third negative meniscus lens L13 having a convex surface on the side and a biconvex positive lens L14.
The rear group Gr includes, in order from the object side, a cemented lens of a biconcave negative lens L15, a biconvex positive lens L16, and a negative meniscus lens L17 having a convex surface facing the image side, and a convex surface facing the object side. The negative meniscus lens L18 and a cemented lens of a biconvex positive lens L19 having an aspheric lens surface on the image side.

In order from the object side, the second lens group G2 includes a biconvex positive lens L21, a cemented lens of a biconcave negative lens L22 and a biconvex positive lens L23, and a convex surface facing the image side. And a positive meniscus lens L24 having an aspheric surface.
Under such a lens configuration, the position of the first lens group G1 is fixed and the second lens group G2 is positioned on the optical axis when the infinite-range object is focused on from a near-distance object. Move along. At this time, the aperture stop S moves integrally with the second lens group G2. In the wide-angle lens according to the present embodiment, the focusing lens is driven manually or by various motors such as a DC motor, an ultrasonic motor, and a stepping motor.

Table 1 below lists values of specifications of the wide-angle lens according to the first example of the present application.
In [Overall specifications], f represents a focal length, FNO represents an F number, and 2ω represents an angle of view (unit: “°”).
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. Further, nd represents the refractive index with respect to the d line (λ = 587.6 nm), and νd represents the Abbe number with respect to the d line (λ = 587.6 nm). Furthermore, an aspherical surface in the lens data is marked with an asterisk (*) and the paraxial radius of curvature is indicated in the column of curvature radius r, and κ and each aspherical coefficient are described in the column of [Aspherical data]. To do. Further, the radius of curvature r = 0.000 indicates a plane, and the refractive index nd = 1.00000 of air is omitted from the description.

In [Aspherical data], “En” indicates “× 10 ⁻ⁿ ”. The rotationally symmetric aspherical surface shown in the specification table has a distance (sag amount) along the optical axis direction from the tangential plane of the apex of each aspherical surface at a height y in the vertical direction from the optical axis, X (y), Where r is the radius of curvature, κ is the conic coefficient, and Cn is the nth-order aspherical coefficient, the following aspherical expression is used. Note that the description of the aspherical coefficient that is 0 (zero) is omitted.
X (y) = (y ² / r) / [1+ (1−κ · y ² / r ² ) ^1/2 ]
+ C4 ・ y ⁴ + C6 ・ y ⁶ + C8 ・ y ⁸ + C10 ・ y ¹⁰ + C12 ・ y ¹²

In [Lens data] and [Variable interval data], [beta] indicates a photographing magnification and BF indicates a back focus.
Here, the unit of the focal length f, the radius of curvature r, and other lengths listed in all the following specification values is generally “mm”. However, the optical system is not limited to this because an equivalent optical performance can be obtained even when proportional expansion or proportional reduction is performed.
In addition, also in the specification values of all the following examples, the same symbols as in this example are used.

(Table 1)
[Overall specifications]
f = 24.6247
FNO = 3.6
2ω = 101

[Lens data]
Surface r d nd νd
1 44.5890 2.5451 1.804000 46.58
* 2 18.1996 7.1548
3 34.2392 1.9000 1.785900 44.20
4 20.1842 5.3994
5 40.2830 1.4000 1.846660 23.78
6 27.4397 8.2301
7 73.5927 5.2273 1.647690 33.79
8 -61.8011 1.1114
9 -40.7165 1.5264 1.497000 81.6
10 32.3777 0.7682
11 44.8121 7.7994 1.548140 45.79
12 -26.0180 2.9973 1.806100 40.94
13 -168.3155 0.1000
14 49.8685 1.6168 1.804000 46.58
15 27.1315 6.3541 1.548 140 45.79
16 -31.5874 D16
17 0.0000 7.0438 Aperture stop S
18 33.0817 10.0751 1.497000 81.6
19 -35.4241 0.2254
20 -55.1034 1.2000 1.834000 37.17
21 26.0656 5.4164 1.497000 81.6
22 -69.1727 0.6000
23 -110.7003 3.1719 1.516330 64.14
* 24 -45.9845 BF

[Aspherical data]
<Second lens surface>
κ = -1.00000
C4 = + 9.44230E-06
C6 = + 1.74360E-09
C8 = + 4.05660E-1
C10 = -9.91430E-14
C12 = + 0.11557E-15

<24th lens surface>
κ = 0.00000
C4 = + 1.01520E-05
C6 = + 1.68300E-08
C8 = -1.82820E-11
C10 = + 9.95310E-14

[Variable interval data]
f or β 24.6247 -1 / 30x -1 / 10x
D16 14.119 13.296 11.654
BF 56.000 56.823 58.465

[Conditional expression values]
(1) D2 / f = 0.840
(2) f1 / f = 23.59
(3) D12 / f = 0.86
(4) f1 / f2 = 8.47
(5) Δν2 = 38.62
(6) (−f1a) /f1b=0.41

FIGS. 2A, 2B, and 2C are graphs when the wide-angle lens according to Example 1 of the present application is in focus at infinity, and when the imaging magnification β = −1 / 30, −1/10, respectively. An aberration diagram is shown.
In each aberration diagram, FNO represents an F number, NA represents a numerical aperture, and Y represents an image height. In the astigmatism diagram and the distortion diagram, the maximum value of the image height Y 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 astigmatism diagram, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. The coma aberration diagram shows coma aberration at each image height.
In addition, in the various aberration diagrams of each example shown below, the same reference numerals as those in this example are used.
From the various aberration diagrams, it can be seen that the wide-angle lens according to the present example corrects various aberrations well over the entire object distance range and has excellent imaging performance.

(Second embodiment)
FIG. 3 is a diagram showing a configuration of a wide-angle lens according to the second example of the present application.
The wide-angle lens according to the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power as a whole, an aperture stop S, and a second lens group G2 having a positive refractive power as a whole. Has been.

The first lens group G1 includes a front group Gf and a rear group Gr in order from the object side.
The front group Gf includes, in order from the object side, a first negative meniscus lens L11 having a convex surface facing the object side, a second negative meniscus lens L12 having a convex surface facing the object side, and a third negative meniscus having a convex surface facing the object side. It consists of a meniscus lens L13 and a biconvex positive lens L14. Each of the first negative meniscus lens L11 and the third negative meniscus lens L13 is a composite aspherical lens in which an aspherical surface is formed by providing a resin layer on the glass lens surface on the image side.
The rear group Gr includes, in order from the object side, a cemented lens of a biconcave negative lens L15, a biconvex positive lens L16, and a negative meniscus lens L17 having a convex surface facing the image side, and a convex surface facing the object side. And a cemented lens of a negative meniscus lens L18 and a biconvex positive lens L19.

In order from the object side, the second lens group G2 includes a biconvex positive lens L21, a cemented lens of a biconcave negative lens L22 and a biconvex positive lens L23, and a convex surface facing the image side. And a positive meniscus lens L24 having an aspheric surface.
Under such a lens configuration, the position of the first lens group G1 is fixed and the second lens group G2 is positioned on the optical axis when the infinite-range object is focused on from a near-distance object. Move along. At this time, the aperture stop S moves integrally with the second lens group G2. In the wide-angle lens according to the present embodiment, the focusing lens is driven manually or by various motors such as a DC motor, an ultrasonic motor, and a stepping motor.
Table 2 below lists values of specifications of the wide-angle lens according to the second example of the present application.

(Table 2)
[Overall specifications]
f = 24.64209
FNO = 3.6
2ω = 101

[Lens data]
Surface r d nd νd
1 51.3085 2.3000 1.804000 46.58
2 23.3997 0.2000 1.553890 38.09
* 3 17.9290 5.7000
4 35.3343 1.9000 1.801000 34.96
5 19.4911 6.0000
6 45.0079 1.4000 1.583130 59.38
7 28.3075 0.1000 1.553890 38.09
* 8 26.4860 7.3000
9 50.5648 7.5000 1.581440 40.75
10 -36.7513 0.9000
11 -35.7288 1.5500 1.497000 81.61
12 30.3482 0.7500
13 41.6778 9.0000 1.548140 45.79
14 -25.7030 1.2000 1.806100 40.94
15 -564.5828 0.2000
16 49.3653 1.5000 1.804000 46.58
17 26.3180 10.0000 1.548140 45.79
18 -31.7447 D18
19 0.0000 6.5426 Aperture stop S
20 34.7596 9.3000 1.497000 81.61
21 -34.7596 0.2500
22 -54.5882 1.2000 1.834000 37.17
23 26.7220 5.4000 1.497000 81.61
24 -70.0880 0.8000
25 -84.7454 3.3000 1.516330 64.14
* 26 -40.1302 BF

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = -4.13510E-07
C6 = -6.54140E-09
C8 = + 4.34370E-11
C10 = -1.52710E-13
C12 = + 0.22759E-15

<Eighth lens surface>
κ = -1.00000
C4 = + 1.11340E-05
C6 = -1.45900E-08
C8 = + 1.29450E-11
C10 = + 2.41080E-14
C12 = -0.97211E-15

<26th lens surface>
κ = 0.00000
C4 = + 9.31650E-06
C6 = + 1.97700E-08
C8 = -4.09340E-11
C10 = + 1.60590E-13

[Variable interval data]
f or β 24.64209 -1 / 30x -1 / 10x
D18 11.681 10.857 9.213
BF 56.500 57.324 58.968

[Conditional expression values]
(1) D2 / f = 0.822
(2) f1 / f = 16.40
(3) D12 / f = 0.74
(4) f1 / f2 = 5.82
(5) Δν2 = 38.62
(6) (−f1a) /f1b=0.59

FIGS. 4A, 4B, and 4C are graphs when the wide-angle lens according to the second embodiment of the present application is in focus at infinity, and when the imaging magnification β = −1 / 30, −1/10, respectively. An aberration diagram is shown.
From the various aberration diagrams, it can be seen that the wide-angle lens according to the present example corrects various aberrations well over the entire object distance range and has excellent imaging performance.

(Third embodiment)
FIG. 5 is a diagram showing a configuration of a wide-angle lens according to the third example of the present application.
The wide-angle lens according to the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power as a whole, an aperture stop S, and a second lens group G2 having a positive refractive power as a whole. Has been.

The first lens group G1 includes a front group Gf and a rear group Gr in order from the object side.
The front group Gf includes, in order from the object side, a first negative meniscus lens L11 having a convex surface facing the object side, a second negative meniscus lens L12 having a convex surface facing the object side, and a third negative meniscus having a convex surface facing the object side. It consists of a meniscus lens L13 and a biconvex positive lens L14. Each of the first negative meniscus lens L11 and the third negative meniscus lens L13 is a composite aspherical lens in which an aspherical surface is formed by providing a resin layer on the glass lens surface on the image side.
The rear group Gr includes, in order from the object side, a three-piece cemented lens including a biconcave negative lens L15, a biconvex positive lens L16, and a negative meniscus lens L17 having a convex surface facing the image side, and a convex surface on the object side. It consists of a negative meniscus lens L18 facing and a cemented lens of a biconvex positive lens L19.

In order from the object side, the second lens group G2 includes a biconvex positive lens L21, a cemented lens of a biconcave negative lens L22 and a biconvex positive lens L23, and a convex surface facing the image side. And a positive meniscus lens L24 having an aspheric surface.
Under such a lens configuration, the position of the first lens group G1 is fixed and the second lens group G2 is positioned on the optical axis when the infinite-range object is focused on from a near-distance object. Move along. At this time, the aperture stop S moves integrally with the second lens group G2. In the wide-angle lens according to the present embodiment, the focusing lens is driven manually or by various motors such as a DC motor, an ultrasonic motor, and a stepping motor.
Table 3 below lists values of specifications of the wide-angle lens according to the third example of the present application.

(Table 3)
[Overall specifications]
f = 24.69043
FNO = 3.6
2ω = 101

[Lens data]
Surface r d nd νd
1 43.0018 2.3000 1.806100 40.94
2 21.8991 0.2000 1.553890 38.09
* 3 17.4502 7.6472
4 38.0255 1.9000 1.806100 40.94
5 18.8395 5.2852
6 32.7413 1.4000 1.583130 59.38
7 22.9016 0.1500 1.553890 38.09
* 8 20.3389 5.7062
9 103.7214 5.8047 1.581440 40.75
10 -36.4908 1.2003
11 -40.5352 1.8000 1.497000 81.61
12 33.1255 0.0000
13 33.1255 7.5345 1.548140 45.79
14 -22.0402 2.1984 1.804000 46.58
15 -122.0119 0.1000
16 67.8702 3.0000 1.806100 40.94
17 27.7482 10.0000 1.548140 45.79
18 -27.7482 D18
19 0.0000 6.9075 Aperture stop S
20 35.5867 8.0994 1.497000 81.61
21 -35.5867 0.2000
22 -63.4325 1.2000 1.834000 37.17
23 24.3718 5.1949 1.497000 81.61
24 -77.3922 1.2573
25 -56.3711 3.1682 1.516330 64.14
* 26 -33.7079 BF

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = + 4.92000E-06
C6 = -1.20370E-09
C8 = + 5.07120E-11
C10 = -1.47630E-13
C12 = + 0.22115E-15

<Eighth lens surface>
κ = -1.00000
C4 = + 1.60170E-05
C6 = -2.17020E-08
C8 = + 1.88280E-11
C10 = -1.80070E-13
C12 = -0.87696E-15

<26th lens surface>
κ = 0.00000
C4 = + 8.82640E-06
C6 = + 2.33260E-08
C8 = -5.99580E-11
C10 = + 1.81080E-13

[Variable interval data]
f or β 24.69043 -1 / 30x -1 / 10x
D18 11.746 10.910 9.246
BF 56.500 57.336 59.000

[Conditional expression values]
(1) D2 / f = 0.774
(2) f1 / f = 7.76
(3) D12 / f = 0.76
(4) f1 / f2 = 2.59
(5) Δν2 = 38.62
(6) (−f1a) /f1b=0.47

FIGS. 6A, 6B, and 6C are graphs when the wide-angle lens according to the third example of the present application is in focus at infinity, and when the imaging magnification β = −1 / 30, −1/10, respectively. An aberration diagram is shown.
From the various aberration diagrams, it can be seen that the wide-angle lens according to the present example corrects various aberrations well over the entire object distance range and has excellent imaging performance.

(Fourth embodiment)
FIG. 7 is a diagram showing a configuration of a wide-angle lens according to the fourth example of the present application.
The wide-angle lens according to the present embodiment includes, in order from the object side, a first lens group G1 having a positive refractive power as a whole, an aperture stop S, and a second lens group G2 having a positive refractive power as a whole. Has been.

The first lens group G1 includes a front group Gf and a rear group Gr in order from the object side.
The front group Gf includes, in order from the object side, a first negative meniscus lens L11 having a convex surface facing the object side, a second negative meniscus lens L12 having a convex surface facing the object side, and a third negative meniscus having a convex surface facing the object side. It consists of a meniscus lens L13 and a biconvex positive lens L14. Each of the first negative meniscus lens L11 and the third negative meniscus lens L13 is a composite aspherical lens in which an aspherical surface is formed by providing a resin layer on the glass lens surface on the image side.
The rear group Gr includes, in order from the object side, a biconcave negative lens L15, a cemented lens of a biconvex positive lens L16 and a biconcave negative lens L17, a biconvex positive lens L18, and the image side. And a cemented lens with a negative meniscus lens L19 having a convex surface facing the surface.

The second lens group G2 includes, in order from the object side, a cemented lens of a biconvex positive lens L21 and a negative meniscus lens L22 having a convex surface facing the image side, a biconcave negative lens L23, and a biconvex positive lens. It consists of a cemented lens with the lens L24, and a positive meniscus lens L25 having a convex surface facing the image side and an aspheric lens surface on the image side.
Under such a lens configuration, the position of the first lens group G1 is fixed and the second lens group G2 is positioned on the optical axis when the infinite-range object is focused on from a near-distance object. Move along. At this time, the aperture stop S moves integrally with the second lens group G2. In the wide-angle lens according to the present embodiment, the focusing lens is driven manually or by various motors such as a DC motor, an ultrasonic motor, and a stepping motor.
Table 4 below lists values of specifications of the wide-angle lens according to the fourth example of the present application.

(Table 4)
[Overall specifications]
f = 24.60120
FNO = 3.6
2ω = 101

[Lens data]
Surface r d nd νd
1 58.8763 2.3000 1.804000 46.58
2 22.4479 0.2000 1.553890 38.09
* 3 17.0971 5.6174
4 30.8722 1.9000 1.834000 37.17
5 19.1278 5.7404
6 36.3932 1.4151 1.516330 64.14
7 23.2496 0.1500 1.553890 38.09
* 8 23.2379 4.4929
9 38.2990 8.4533 1.581440 40.75
10 -40.2014 0.5346
11 -123.6574 2.0000 1.497820 82.52
12 20.7771 1.6043
13 33.8209 7.5020 1.581440 40.75
14 -20.9268 1.4887 1.806100 40.94
15 66.9557 3.4604
16 63.9128 6.3060 1.581440 40.75
17 -16.0627 2.1385 1.805180 25.43
18 -22.1168 D18
19 0.0000 3.0000 Aperture stop S
20 44.6388 4.5296 1.487490 70.24
21 -31.0458 3.0803 1.846660 23.78
22 -36.3078 0.4427
23 -62.3780 1.2000 1.834000 37.17
24 29.6093 4.8724 1.497820 82.52
25 -84.9981 0.9000
26 -64.0280 3.5268 1.516330 64.15
* 27 -31.6410 BF

[Aspherical data]
<Third lens surface>
κ = -1.00000
C4 = -3.29690E-06
C6 = + 8.79930E-09
C8 = -1.38400E-11
C10 = + 7.04010E-14
C12 = -0.66095E-17

<Eighth lens surface>
κ = -1.00000
C4 = + 2.00230E-05
C6 = -1.43890E-08
C8 = + 7.24700E-11
C10 = -7.17480E-13
C12 = + 0.42285E-15

<27th lens surface>
κ = 0.00000
C4 = + 8.21060E-06
C6 = + 9.57030E-09
C8 = -1.04180E-12
C10 = + 6.59260E-14

[Variable interval data]
f or β 24.60120 -1 / 30x -1 / 10x
D18 12.000 11.120 9.376
BF 56.500 57.379 59.123

[Conditional expression values]
(1) D2 / f = 0.754
(2) f1 / f = 3.76
(3) D12 / f = 0.66
(4) f1 / f2 = 1.13
(5) Δν2 = 41.83
(6) (−f1a) /f1b=1.20

FIGS. 8A, 8B, and 8C are graphs when the wide-angle lens according to the fourth example of the present application is in focus at infinity, and when the shooting magnification β = −1 / 30, −1/10, respectively. An aberration diagram is shown.
From the various aberration diagrams, it can be seen that the wide-angle lens according to the present example corrects various aberrations well over the entire object distance range and has excellent imaging performance.

  According to each of the above embodiments, the lens system has a large back focus, a shooting angle of view of about 100 degrees, and an F number of about 3.5, and the entire lens system can be reduced in size while reducing the diameter of the front lens. Therefore, it is possible to realize a wide-angle lens having high optical performance capable of rapid focusing, having small aberration fluctuations during focusing, and capable of satisfactorily correcting various aberrations over the entire screen.

In the wide-angle lens of the present application, in order to correct image blur caused by camera shake, a part of the lens group or one lens group may be moved as a vibration-proof lens group in a direction perpendicular to the optical axis. Good. In the wide-angle lens of the present application, it is particularly preferable that the rear group Gr of the first lens group G1 is an anti-vibration lens group.
The lens surface of the lens constituting the wide-angle lens of the present application may be an aspherical surface. This aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface obtained by molding glass into an aspherical shape, or a composite aspherical surface in which a resin provided on the glass surface is formed into an aspherical shape.

Further, an antireflection film having a high transmittance in a wide wavelength range may be applied to the lens surface of the lens constituting the wide-angle lens of the present application. Thereby, flare and ghost can be reduced, and high optical performance can be achieved with high contrast.
In addition, each said Example has shown one specific example of this invention, and this invention is not limited to these.

Next, a camera equipped with the wide-angle lens of the present application will be described with reference to FIG.
FIG. 9 is a diagram illustrating a configuration of a camera including the wide-angle lens of the present application.
The camera 1 is a digital single-lens reflex camera provided with the wide-angle lens according to the first embodiment as a photographing lens 2 as shown in FIG.

  In the camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 and imaged on the focusing screen 4 through the quick return mirror 3. The light imaged on the focusing screen 4 is reflected in the pentaprism 5 a plurality of times and guided to the eyepiece lens 6. Thus, the photographer can observe the subject image as an erect image through the eyepiece 6.

  When the release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted out of the optical path, and light from the subject (not shown) reaches the image sensor 7. Thereby, the light from the subject is picked up by the image pickup device 7 and recorded as a subject image in a memory (not shown). In this way, the photographer can shoot the subject with the camera 1.

Here, the wide-angle lens according to the first embodiment mounted on the camera 1 as the photographing lens 2 has a large back focus and a focusing method as described in the first embodiment, due to its characteristic lens configuration and focusing method. It has a large shooting angle of view and a small F-number, and the entire lens system is downsized while reducing the diameter of the front lens, enabling rapid focusing and small fluctuations in aberrations during focusing. Thus, high optical performance capable of satisfactorily correcting various aberrations over the entire screen is realized. Thereby, this camera 1 can have the same effect.
Note that the present application is not limited to the above, and the same effect as that of the camera 1 can be obtained even if a camera in which the wide-angle lens according to the second embodiment, the third embodiment, or the fourth embodiment is mounted as the photographing lens 2 is configured. Of course you can play.

  As described above, the lens system has a large back focus, a large shooting angle of view, and a small F number, and the entire lens system is miniaturized while reducing the diameter of the front lens, enabling rapid focusing, and A wide-angle lens, an image pickup apparatus, and a wide-angle lens focusing method that have high optical performance with small aberration fluctuations during focusing and that can satisfactorily correct various aberrations over the entire screen can be realized.

It is a figure which shows the structure of the wide angle lens which concerns on 1st Example of this application. (A), (b), and (c) are graphs showing various aberrations when the wide-angle lens according to Example 1 of the present application is in focus at infinity and the shooting magnification β = −1 / 30, −1/10. Indicates. It is a figure which shows the structure of the wide angle lens which concerns on 2nd Example of this application. (A), (b), and (c) are graphs showing various aberrations when the wide-angle lens according to the second embodiment of the present application is in focus at infinity and the shooting magnification β = −1 / 30, −1/10. Indicates. It is a figure which shows the structure of the wide angle lens which concerns on 3rd Example of this application. (A), (b), and (c) are graphs showing various aberrations when the wide-angle lens according to Example 3 of the present application is in focus at infinity and the photographing magnification β = −1 / 30, −1/10. Indicates. It is a figure which shows the structure of the wide angle lens which concerns on 4th Example of this application. (A), (b), and (c) are graphs showing various aberrations when the wide-angle lens according to the fourth example of the present application is in focus at infinity and when the imaging magnification β = −1 / 30, −1/10. Indicates. It is a figure which shows the structure of the camera provided with the wide angle lens of this application.

Explanation of symbols

G1 First lens group G2 Second lens group Gf Front group Gr Rear group S Aperture stop

Claims (9)

In order from the object side, the first lens group having a positive refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole,
The first lens group includes, in order from the object side, a first negative meniscus lens having a convex surface facing the object side, a second negative meniscus lens having a convex surface facing the object side, and a third negative meniscus lens having a convex surface facing the object side. And a front group consisting of a positive lens,
In the front group, at least one aspheric surface is provided,
A wide-angle lens, wherein the first lens group is fixed and the second lens group moves along an optical axis when focusing from an object at infinity to an object at a short distance. The wide-angle lens according to claim 1, wherein the following conditional expression is satisfied.
D2 / f <1.00
However,
f: focal length of the entire wide-angle lens system D2: distance on the optical axis between the most object side lens surface of the second lens group and the most image side lens surface of the second lens group   The wide-angle lens according to claim 1, wherein the second lens group includes five or less lenses. The wide-angle lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
2.50 <f1 / f <30.00
0.30 <D12 / f <1.50
However,
f: Focal length of the entire wide-angle lens system f1: Focal length of the first lens group D12: Light from the most image side lens surface of the first lens group and the most object side lens surface of the second lens group Axis distance The wide-angle lens according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
0.70 <f1 / f2 <13.00
However,
f1: focal length of the first lens group f2: focal length of the second lens group The second lens group includes a plurality of positive lenses and a plurality of negative lenses,
The wide-angle lens according to claim 1, wherein the following conditional expression is satisfied.
36.00 <Δν2
However,
Δν2: difference between the average dispersion value of the positive lens and the average dispersion value of the negative lens in the second lens group The first lens group has a rear group on the image side of the front group,
The wide angle lens according to any one of claims 1 to 6, wherein the following conditional expression is satisfied.
0.25 <(− f1a) / f1b <2.00
However,
f1a: focal length of the front group f1b: focal length of the rear group   An imaging apparatus comprising the wide-angle lens according to any one of claims 1 to 7. In the focusing method of a wide-angle lens having, in order from the object side, a first lens group having a positive refractive power as a whole, an aperture stop, and a second lens group having a positive refractive power as a whole,
The first lens group includes, in order from the object side, a front group including a first negative meniscus lens, a second negative meniscus lens, a third negative meniscus lens, and a positive lens having a convex surface directed toward the object side.
In the front group, at least one aspheric surface is provided,
A focusing method for a wide-angle lens, wherein the first lens group is fixed and the second lens group moves along an optical axis when focusing from an object at infinity to an object at a short distance.

Images