JP5320995B2 - Wide-angle lens, optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide-angle lens having higher optical performance, an optical apparatus using thereof, and a method for focusing the wide-angle lens. <P>SOLUTION: The wide-angle lens includes, in order from an object, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. Upon focusing to an object, the first lens group G1 is fixed, and the second lens group G2 and the third lens group G3 are moved to the object side. The second lens group G2 includes a negative refractive power lens component L21 to the most object side, and the most object side lens surface of the lens component L21 is a concave surface facing the object. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a wide-angle lens suitable for a single-lens reflex camera, a digital camera, and the like, an optical device having the same, and a focusing method for the wide-angle lens.

Conventionally, a retrofocus lens preceded by a lens group having a negative refractive power is known as a wide-angle lens that can secure a back focus enough to be used in a single-lens reflex camera, a digital camera, or the like even with a short focal length. This lens type has been proposed with a large aperture of about F1.4 (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-30743

  Conventional wide-angle lenses have not been sufficient to correct various aberrations.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-performance wide-angle lens, an optical device having the same, and a focusing method for the wide-angle lens.

In order to solve the above-described problem, the present invention substantially includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. Each having three lens groups, and having an aperture stop between the second lens group and the third lens group, and fixing the first lens group, the second lens group and the third lens group, The second lens group has a lens component having a negative refractive power closest to the object side, and the lens surface closest to the object side of the lens component has a concave surface on the object side. Provided is a wide-angle lens characterized by having an oriented shape. The lens component refers to a single lens or a cemented lens.

  The present invention also provides an optical device comprising the wide-angle lens.

  According to the present invention, it is possible to provide a high-performance wide-angle lens, an optical device having the same, and a focusing method for the wide-angle lens.

  Hereinafter, a wide-angle lens according to an embodiment of the present invention will be described.

  The wide-angle lens according to the present embodiment includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The group is fixed, the second lens group and the third lens group are moved to the object side to perform focusing on the object, and the second lens group has a lens component having a negative refractive power closest to the object side. In this configuration, the lens surface closest to the object side of the component has a concave surface facing the object side.

  In a retrofocus lens, the negative lens group on the object side and the positive lens group on the image side are asymmetrical refractive power arrangements, so it is impossible to cancel out aberrations between the groups, resulting in negative distortion and coma. Correction is particularly difficult. Therefore, it is necessary to correct aberrations as much as possible in the group alone. For this purpose, it is effective to reduce the refractive power of the first lens unit having a negative refractive power, but if used in a single-lens reflex camera, the back focus is insufficient.

  This embodiment is characterized in that the most object side of the second lens group is a lens component having a negative refractive power. This takes the configuration of a retrofocus lens because the negative lens component comes first in the synthesis of the second lens group and the third lens group. This can increase the back focus. Further, off-axis chief rays around the screen are incident on the second lens group with a large angle. Therefore, by disposing a lens component having negative refractive power on the most object side of the second lens group, a light beam parallel to the optical axis is guided to the lens closer to the image plane than the negative lens component. This is advantageous for correcting external coma aberration.

  Further, the present embodiment is also characterized in that the lens surface closest to the object side of the lens component of the second lens group has a shape with a concave surface facing the object side. In the second lens group, since the incident height of the axial light beam is higher than that in the first lens group, the involvement in spherical aberration becomes strong. Therefore, for the axial light beam that is divergent light in the first lens unit having a negative refractive power, if the declination at the lens surface is large, a large spherical aberration occurs, which is not preferable. In that respect, the most object-side lens surface of the lens component of the second lens group has a concave surface facing the object side, so that the declination can be kept small. This prevents overcorrection of spherical aberration that is a problem. As a result, the number of lenses in the second lens group and the third lens group can be reduced, and the overall length can be shortened. In addition, for the peripheral luminous flux, coma aberration, particularly sagittal coma aberration, is effective because the lens surface closest to the object side of the lens component of the second lens group has a concave surface facing the object side. Can be corrected. As a result, good aberration correction can be realized without increasing the filter diameter.

  The wide-angle lens according to the present embodiment preferably has an aperture stop between the second lens group and the third lens group.

  With this configuration, spherical aberration and coma can be favorably corrected.

Moreover, it is desirable that the wide-angle lens according to the present embodiment satisfies the following conditional expression (1).
(1) 1.00 <f2 / f3 <2.00
Here, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.

  Conditional expression (1) defines an appropriate range of the refractive power ratio of the second lens group and the third lens group of the positive lens group.

  If the upper limit of conditional expression (1) is exceeded, the positive refracting power is biased toward the third lens group, and accordingly, the refracting power of the third lens group becomes stronger, making it difficult to correct negative spherical aberration and coma aberration, and suddenly. Since it deteriorates, it is not preferable. If the lower limit of conditional expression (1) is not reached, it is difficult to ensure the back focus, which is not preferable. In addition, spherical aberration is worsened.

  In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (1) to 1.90. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (1) to 1.30.

  In the wide-angle lens according to the present embodiment, it is desirable that the most image side surface of the lens component of the second lens group is concave on the image side.

  With this configuration, spherical aberration and coma can be favorably corrected with the most image-side surface of the lens component of the second lens group and the lens component immediately thereafter.

  In the wide-angle lens according to the present embodiment, the first lens group preferably includes three negative lenses in order from the object side.

  With this configuration, it is possible to reduce negative distortion, coma, and positive curvature of field that occur in the first lens group.

In addition, it is desirable that the wide-angle lens according to the present embodiment satisfies the following conditional expression (2).
(2) 0.30 <f / f3 <1.00
However, f is the focal length of the entire system, and f3 is the focal length of the third lens group.

  Conditional expression (2) defines an appropriate range of the refractive power ratio between the entire system and the third lens group.

  If the upper limit value of conditional expression (2) is exceeded, the refractive power of the third lens group becomes too strong, and it becomes difficult to correct negative spherical aberration and coma aberration. If the lower limit value of conditional expression (2) is not reached, the refractive power of the third lens group becomes too weak. As a result, the refractive power of the second lens group becomes too strong, and the same aberration deterioration as when the upper limit value is exceeded. In other words, it is difficult to ensure the back focus, and as a result, the negative refractive power of the first lens unit is increased, which causes undesirable positive curvature of field and negative distortion.

  In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (2) to 0.90. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (2) to 0.40.

The wide-angle lens according to the present embodiment preferably includes at least one positive lens that satisfies both the following conditional expressions (3) and (4) in the first lens group.
(3) n1p> 1.800
(4) ν1p> 28.00
Where n1p is the average refractive index of the d-line (wavelength λ = 587.6 nm) of the positive lens included in the first lens group, and ν1p is the average Abbe number of the d-line of the positive lens included in the first lens group. Value.

  Conditional expressions (3) and (4) define the characteristics of the positive lens glass material in the first lens group.

  Negative distortion, positive curvature of field, and coma generated in the negative lens group of the retrofocus lens can be reduced by introducing a positive lens having a high refractive index in the negative lens group. However, in general, a glass material with a high refractive index has a large dispersion, that is, a small Abbe number, so that the amount of chromatic aberration of magnification differs between the negative lens and the positive lens depending on the height of the image height. If the chromatic aberration of magnification is high and the image height is high, positive chromatic aberration of magnification tends to occur rapidly.

  If the lower limit of conditional expression (3) is not reached, it is generally easy to select a glass material having a large Abbe number, so that it is easy to correct lateral chromatic aberration, but distortion aberration caused by a negative lens, curvature of field, The coma aberration cannot be corrected.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (3) to 1.840. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (3) to 1.900.

  If the lower limit of conditional expression (4) is not reached, it is generally easy to select a glass material having a high refractive index, so that correction of distortion, curvature of field and coma becomes easy. Since the value increases rapidly, the lateral chromatic aberration cannot be corrected sufficiently, which is not preferable.

  In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (4) to 30.00. In order to further secure the effect of the embodiment, it is more preferable to set the lower limit of conditional expression (4) to 31.00.

In the wide-angle lens according to the present embodiment, it is desirable that the second lens group and the third lens group satisfy the following conditional expression (5) during the focusing.
(5) 1.00 ≦ Δ3 / Δ2 <1.50
However, Δ3 is the amount of movement of the third lens group, and Δ2 is the amount of movement of the second lens group.

  Conditional expression (5) defines the reduction degree of the interval by defining the moving speed ratio between the second lens group and the third lens group.

  When the first lens unit is fixed and the second lens unit and the third lens unit having positive refractive power are moved toward the object side to perform focusing on a short distance object, the increased aberration mainly includes spherical aberration and coma. Aberration and astigmatism. These can be satisfactorily corrected by reducing the distance between the second lens group, the aperture stop, and the third lens group with focusing.

  If the lower limit of conditional expression (5) is not reached, the distance between the second and third lens groups will increase due to focusing, which will mainly increase spherical aberration, coma and astigmatism. On the other hand, if the upper limit value of conditional expression (5) is exceeded, the movement of the third lens group becomes too large, and mainly spherical aberration, coma aberration, and astigmatism are overcorrected, and the aberration is worsened.

  In order to secure the effect of the embodiment, it is preferable to set the upper limit of conditional expression (5) to 1.30. In order to secure the effect of the embodiment, it is preferable to set the lower limit of conditional expression (5) to 1.05.

  In the wide-angle lens according to the present embodiment, it is desirable that the second lens group and the third lens group move to the object side with the same movement amount during the focusing.

  With this configuration, the second lens group and the third lens group can be integrated, and the configuration can be simplified. It is possible to reduce aberration fluctuations during focusing caused by manufacturing errors.

(Example)
Hereinafter, each example according to the present embodiment will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration of a wide-angle lens according to the first example.

  The wide-angle lens according to the first example includes, in order from the object side along the optical axis, a first lens group G1 having negative refractive power and a second lens having positive refractive power having a lens component having negative refractive power closest to the object side. It includes a group G2, an aperture stop S, and a third lens group G3 having a positive refractive power.

  During focusing from an object at infinity to a close object, the first lens group G1 is fixed, and both the second lens group G2 and the third lens group G3 move in the object direction. At that time, the second lens group G2 and the third lens group G3 are moved at different speeds.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a convex surface facing the object side, a negative meniscus lens L13 having a convex surface facing the object side, and a biconvex shape. The lens surface on the image plane I side of the negative meniscus lens L12 is an aspherical surface.

  The second lens group G2 includes a biconcave negative lens L21, and a cemented lens of a biconvex positive lens L22 and a negative meniscus lens L23 having a convex surface facing the image plane I side.

  The third lens group G3 includes a cemented lens of a biconcave negative lens L31 and a biconvex positive lens L32, a biconvex positive lens L33, and a positive meniscus lens L34 having a convex surface facing the image plane I. The lens surface on the image plane I side of the positive lens L32 is an aspherical surface.

  The positive lens L14 of the first lens group G1 is a positive lens having a refractive index of 1.800 or more and an Abbe number of 30.00 or more.

  Table 1 below lists specifications of the wide-angle lens according to the first example.

  In (surface data) in the table, the object surface is the object surface, the surface number is the surface number from the object side, r is the radius of curvature, d is the surface spacing, and nd is the refraction at the d-line (wavelength λ = 587.6 nm). The ratio, νd is the Abbe number in the d-line (wavelength λ = 587.6 nm), (variable) is the variable surface interval in focusing, (diaphragm) is the aperture stop S, and the image plane is the image plane I. Note that the refractive index of air nd = 1.000 000 is omitted. Further, “∞” in the curvature radius r and the surface interval d column indicates a plane.

In (Aspheric data), the aspheric surface is expressed by the following equation.
X (y) = (y ² / r) / [1+ [1-κ (y ² / r ² )] ^1/2 ]
+ A4 × y ⁴ + A6 × y ⁶ + A8 × y ⁸ + A10 × y ¹⁰ + A12 × y ¹²

Here, the height in the direction perpendicular to the optical axis is y, the amount of displacement in the optical axis direction at height y is X (y), the radius of curvature of the reference sphere (paraxial radius of curvature) is r, the cone coefficient is κ, Let the n-th order aspheric coefficient be An. “En” represents “× 10 ⁻ⁿ ”, for example “1.234E-05” represents “1.234 × 10 ⁻⁵ ”. Each aspherical surface is indicated with “*” on the right side of the surface number in (surface data).

  In (various data), f is the focal length of the d-line, FNO is the F number, 2ω is the angle of view (unit: “°”), Y is the image height, TL is the total lens length, and Bf is the back when focused at infinity. Each represents a focus.

  In (variable interval data), β represents a magnification, and di represents a variable surface interval value for surface number i.

  (Conditional expression corresponding value) indicates the corresponding value of each conditional expression.

  In all the following specification values, “mm” is generally used as the focal length f, radius of curvature r, surface interval d and other lengths, etc. unless otherwise specified, but the optical system is proportional. Even if it is enlarged or proportionally reduced, the same optical performance can be obtained. Further, the unit is not limited to “mm”, and other appropriate units may be used. Further, the explanation of these symbols is the same in the other embodiments, and the explanation is omitted.

(Table 1)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 67.18 2.60 1.804000 46.57
2 27.00 6.23
3 45.00 2.30 1.772499 49.60
4 * 28.80 6.75
5 97.97 1.60 1.496999 81.54
6 47.69 7.40
7 62.34 6.10 1.903660 31.31
8 -167.37 (variable)

9 -101.31 1.20 1.804000 46.57
10 83.83 0.56
11 37.28 7.84 1.816000 46.62
12 -44.22 1.20 1.784723 25.68
13 -97.41 (variable)

14 (Aperture) ∞ 7.30
15 -20.21 1.20 1.805181 25.46
16 58.98 8.00 1.816000 46.62
17 * -52.18 1.91
18 676.80 6.57 1.729157 54.68
19 -32.13 0.20
20 -56.11 4.21 1.729157 54.68
21 -32.58 (Bf)
Image plane ∞

(Aspheric data)
4th surface κ = 0.00000E + 00
A4 = 1.49400E-06
A6 = -4.07170E-09
A8 = 1.23490E-11
A10 = -2.37110E-14
A12 = 1.08520E-17
17th surface κ = 1.01920E + 00
A4 = 1.57740E-05
A6 = 1.57400E-08
A8 = -3.06580E-11
A10 = 0.00000E + 00
A12 = 0.00000E + 00

(Various data)
f = 24.70
FNO = 1.44
2ω = 82.34
Y = 21.60
TL = 129.69
Bf = 38.10

(Variable interval data)
Infinitely focused state Medium distance focused state Close range focused state β 0.00 -0.033 -0.33
d8 9.00 8.26 2.30
d13 9.40 9.29 8.40

(Values for conditional expressions)
(1) f2 / f3 = 1.73
(2) f / f3 = 0.57
(3) n1p = 1.904
(4) ν1p = 31.31
(5) Δ3 / Δ2 = 1.15

  2A and 2B are graphs showing various aberrations of the wide-angle lens according to the first example. FIG. 2A is a diagram when focusing on infinity (β = 0.00), and FIG. 2B is a graph when focusing on an intermediate distance (β = −0.033). (C) shows various aberration diagrams when focusing on a close range (β = −0.33).

  In each aberration diagram, FNO represents an F number, Y represents an image height, and NA represents a numerical aperture. The spherical aberration diagram shows the F-number or numerical aperture value corresponding to the maximum aperture, the astigmatism diagram and the distortion diagram show the maximum image height, and the coma diagram shows the value of each image height. . D represents the d-line (λ = 587.6 nm), and G represents the g-line (λ = 435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane.

  In the following examples, the same symbols are used, and the following description is omitted.

  It can be seen from the respective aberration diagrams that the wide-angle lens according to the first example has excellent imaging performance with various aberrations corrected well.

(Second embodiment)
FIG. 3 is a diagram illustrating a configuration of a wide-angle lens according to the second example.

  The wide-angle lens according to the second example includes, in order from the object side along the optical axis, a first lens group G1 having negative refractive power and a second lens having positive refractive power having a lens component having negative refractive power closest to the object side. It includes a group G2, an aperture stop S, and a third lens group G3 having a positive refractive power.

  During focusing from an object at infinity to a close object, the first lens group G1 is fixed, and both the second lens group G2 and the third lens group G3 move in the object direction. At that time, the second lens group G2 and the third lens group G3 are moved at the same speed.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a convex surface facing the object side, a negative meniscus lens L13 having a convex surface facing the object side, and a biconvex shape. The lens surface on the image plane I side of the negative meniscus lens L12 is an aspherical surface.

  The second lens group G2 includes a biconcave negative lens L21, and a cemented lens of a biconvex positive lens L22 and a negative meniscus lens L23 having a convex surface facing the image plane I side.

  The third lens group G3 includes a cemented lens of a biconcave negative lens L31 and a biconvex positive lens L32, a positive meniscus lens L33 having a convex surface facing the image plane I, and a convex surface facing the image plane I. The positive meniscus lens L34 faces the lens surface, and the lens surface on the image plane I side of the positive lens L32 is an aspherical surface.

  The positive lens L14 of the first lens group G1 is a positive lens having a refractive index of 1.800 or more and an Abbe number of 30.00 or more.

  Table 2 below lists specifications of the wide-angle lens according to the second example.

(Table 2)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 72.00 2.60 1.804000 46.57
2 27.50 6.20
3 45.00 2.10 1.772499 49.60
4 34.10 0.20 1.553890 38.09
5 * 28.60 7.50
6 64.43 1.60 1.496999 81.54
7 35.37 7.49
8 56.25 6.50 1.903660 31.31
9 -233.35 (variable)

10 -106.99 1.30 1.804000 46.57
11 86.24 0.20
12 35.91 7.54 1.816000 46.62
13 -56.08 1.30 1.860740 23.06
14 -98.62 9.33
15 (Aperture) ∞ 7.00
16 -20.59 1.30 1.846660 23.78
17 48.93 6.00 1.796680 45.34
18 * -51.58 2.37
19 -941.51 5.07 1.804000 46.57
20 -37.73 0.20
21 -70.87 4.92 1.804000 46.57
22 -30.78 (Bf)
Image plane ∞

(Aspheric data)
5th surface κ = 0.00000E + 00
A4 = -4.57380E-07
A6 = -8.82940E-09
A8 = 2.29950E-11
A10 = -4.35790E-14
A12 = 2.46620E-17
18th surface κ = 1.01920E + 00
A4 = 1.71730E-05
A6 = 1.89790E-08
A8 = -3.90560E-11
A10 = 0.00000E + 00
A12 = 0.00000E + 00

(Various data)
f = 24.70
FNO = 1.44
2ω = 82.34
Y = 21.60
TL = 127.49
Bf = 38.10

(Variable interval data)
Infinitely focused state Medium distance focused state Close range focused state β 0.00 -0.033 -0.25
d9 8.67 7.84 2.35

(Values for conditional expressions)
(1) f2 / f3 = 1.63
(2) f / f3 = 0.56
(3) n1p = 1.904
(4) ν1p = 31.31
(5) Δ3 / Δ2 = 1.00

  FIG. 4 shows various aberration diagrams of the wide-angle lens according to the second example, where (a) is in focus at infinity (β = 0.00), (b) is in focus at intermediate distance (β = −0.033), (C) shows various aberration diagrams when focusing on a close range (β = −0.25).

  From the respective aberration diagrams, it can be seen that the wide-angle lens according to the second example has excellent imaging performance with various aberrations corrected well.

(Third embodiment)
FIG. 5 is a diagram illustrating a configuration of a wide-angle lens according to the third example.

  The wide-angle lens according to the third example includes, in order from the object side along the optical axis, a first lens group G1 having negative refractive power and a second lens having positive refractive power having a lens component having negative refractive power closest to the object side. It includes a group G2, an aperture stop S, and a third lens group G3 having a positive refractive power.

  During focusing from an object at infinity to a close object, the first lens group G1 is fixed, and both the second lens group G2 and the third lens group G3 move in the object direction. At that time, the second lens group G2 and the third lens group G3 are moved at different speeds.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface facing the object side, a negative meniscus lens L12 having a convex surface facing the object side, a negative meniscus lens L13 having a convex surface facing the object side, and a biconvex shape. The lens surface on the image plane I side of the negative meniscus lens L12 is an aspherical surface.

  The second lens group G2 includes a biconcave negative lens L21, and a cemented lens of a biconvex positive lens L22 and a negative meniscus lens L23 having a convex surface facing the image plane I side.

  The third lens group G3 includes a cemented lens of a biconcave negative lens L31 and a biconvex positive lens L32, a positive meniscus lens L33 having a convex surface facing the image plane I, and a convex surface facing the image plane I. The positive meniscus lens L34 faces the lens surface, and the lens surface on the image plane I side of the positive lens L32 is an aspherical surface.

  The positive lens L14 of the first lens group G1 is a positive lens having a refractive index of 1.800 or more and an Abbe number of 30.00 or more.

  Table 3 below lists specifications of the wide-angle lens according to the third example.

(Table 3)

(Surface data)
Surface number rd nd νd
Object ∞ ∞
1 70.00 2.60 1.804000 46.57
2 27.46 6.04
3 45.00 2.10 1.772499 49.60
4 33.68 0.20 1.553890 38.09
5 * 28.60 6.50
6 71.73 1.60 1.496999 81.54
7 36.88 8.58
8 59.20 6.50 1.903660 31.31
9 -201.97 (variable)

10 -112.04 1.30 1.804000 46.57
11 85.44 0.20
12 35.99 7.58 1.816000 46.62
13 -54.18 1.30 1.860740 23.06
14 -100.10 (variable)

15 (Aperture) ∞ 7.00
16 -20.45 1.30 1.846660 23.78
17 59.55 6.00 1.796680 45.34
18 * -53.33 2.11
19 -1673.35 5.20 1.772499 49.60
20 -36.24 0.20
21 -71.75 4.87 1.804000 46.57
22 -30.85 (Bf)
Image plane ∞

(Aspheric data)
5th surface κ = 0.00000E + 00
A4 = -2.64810E-08
A6 = -8.96440E-09
A8 = 2.41970E-11
A10 = -4.46660E-14
A12 = 2.44010E-17
18th surface κ = 1.01920E + 00
A4 = 1.72770E-05
A6 = 1.78190E-08
A8 = -4.07240E-11
A10 = 0.00000E + 00
A12 = 0.00000E + 00

(Various data)
f = 24.70
FNO = 1.44
2ω = 82.34
Y = 21.60
TL = 127.44
Bf = 38.10

(Variable interval data)
Infinitely focused state Intermediate distance focused state Close range focused state β 0.00 -0.033 -0.30
d9 8.70 7.93 1.97
d14 9.48 9.40 8.47

(Values for conditional expressions)
(1) f2 / f3 = 1.62
(2) f / f3 = 0.55
(3) n1p = 1.904
(4) ν1p = 31.31
(5) Δ3 / Δ2 = 1.15

  FIG. 6 shows various aberration diagrams of the wide-angle lens according to Example 3, wherein (a) is in focus at infinity (β = 0.00), (b) is in focus at intermediate distance (β = −0.033), (C) shows various aberration diagrams when focusing on a close range (β = 0.30).

  From the respective aberration diagrams, it can be seen that the wide-angle lens according to the third example has excellent imaging performance with various aberrations corrected well.

  As described above, according to this embodiment, the maximum field angle is a wide field angle of 80 ° or more, and the aperture F value is a large aperture of about 1.4. A wide-angle lens suitable for the above can be provided.

  Next, a camera equipped with the wide-angle lens according to the present embodiment will be described. Although the case where the wide-angle lens according to the first example is mounted will be described, the same applies to other examples.

  FIG. 7 is a diagram illustrating a configuration of a camera including the wide-angle lens according to the first example.

  In FIG. 7, the camera 1 is a digital single-lens reflex camera provided with the wide-angle lens according to the first embodiment as the photographing lens 2. In the camera 1, light from an object (subject) (not shown) is collected by the taking lens 2 and is focused on the focusing screen 4 via 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. As a result, light from the subject is picked up by the image sensor 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.

  By mounting the wide-angle lens according to the first embodiment as the photographing lens 2 on the camera 1, a camera having high performance can be realized.

  The contents described below can be appropriately adopted as long as the optical performance is not impaired.

  In the embodiment, the three-group configuration is shown, but the present invention can also be applied to other group configurations such as the fourth group and the fifth group.

  Alternatively, a single lens group, a plurality of lens groups, or a partial lens group may be moved in the optical axis direction to be a focusing lens group that performs focusing from an object at infinity to a near object.

  The focusing lens group can also be applied to autofocus, and is also suitable for driving a motor for autofocus (such as an ultrasonic motor). In particular, it is preferable that the second and third lens groups be the focusing lens group.

  Alternatively, the lens group or the partial lens group may be vibrated in a direction perpendicular to the optical axis so as to correct an image blur caused by camera shake. In particular, it is preferable that at least a part of the second or third lens group is an anti-vibration lens group.

  The lens surface may be an aspherical surface. The aspherical surface may be any of an aspherical surface by grinding, a glass mold aspherical surface in which a glass is formed into an aspherical shape, or a composite aspherical surface in which a resin is formed in an aspherical shape on the glass surface.

  The aperture stop is preferably arranged in the vicinity of the third lens group, but it can also be arranged in the vicinity of the second lens group, and the role of the lens frame is substituted instead of providing a member as an aperture stop. You may do it.

  If each lens surface is provided with an antireflection film having a high transmittance in a wide wavelength range, flare and ghost can be reduced and high contrast and high optical performance can be achieved.

  In addition, in order to explain the present invention in an easy-to-understand manner, the configuration requirements of the embodiment have been described, but it goes without saying that the present invention is not limited to this.

1 shows a configuration of a wide-angle lens according to a first example. The aberration diagrams of the wide-angle lens according to Example 1 are shown. (A) is in focus at infinity (β = 0.00), (b) is in focus at an intermediate distance (β = −0.033), and (c) is in focus. Aberration diagrams at close focus (β = -0.33) are shown. The structure of the wide-angle lens which concerns on 2nd Example is shown. The aberration diagrams of the wide-angle lens according to the second example are shown, (a) is in focus at infinity (β = 0.00), (b) is in focus at intermediate distance (β = −0.033), and (c) is in focus. Aberration diagrams at close focus (β = -0.25) are shown. The structure of the wide angle lens which concerns on 3rd Example is shown. The aberration diagrams of the wide-angle lens according to Example 3 are shown, (a) is in focus at infinity (β = 0.00), (b) is in focus at intermediate distance (β = −0.033), and (c) is in focus. Aberration diagrams at close focus (β = 0.30) are shown respectively. 1 shows a configuration of a camera including a wide-angle lens according to a first example.

Explanation of symbols

G1 First lens group G2 Second lens group G3 Third lens group L11 Negative meniscus lens L12 Negative meniscus lens L13 Negative meniscus lens L14 Positive lens L21 Negative lens S Aperture stop I Image plane 1 Camera

Claims (9)

In order from the object side, the first lens group having negative refractive power, the second lens group having positive refractive power, and the third lens group having positive refractive power substantially consist of three lens groups ,
An aperture stop is provided between the second lens group and the third lens group;
The first lens group is fixed and the second lens group and the third lens group are moved to the object side to perform focusing on the object,
The second lens group has a lens component with negative refractive power closest to the object side, and the lens surface closest to the object side of the lens component has a shape with a concave surface facing the object side. .
The lens component refers to a single lens or a cemented lens. The wide-angle lens according to claim 1 , wherein the following condition is satisfied.
1.00 <f2 / f3 <2.00
However,
f2: focal length of the second lens group f3: focal length of the third lens group The surface of the most image side of the lens component in the second lens group, a wide-angle lens according to claim 1 or 2, characterized in that a concave surface facing the image side. The wide-angle lens according to any one of claims 1 to 3 , wherein the first lens group includes three negative lenses in order from the object side. Wide-angle lens according to claim 1, any one of 4, characterized in that the following condition is satisfied.
0.30 <f / f3 <1.00
However,
f: focal length of the entire system f3: focal length of the third lens group Wide-angle lens according to any one of claims 1 to 5, characterized in that it comprises at least one positive lens that satisfies both the following conditions in the first lens group.
n1p> 1.800
ν1p> 28.00
However,
n1p: average value of refractive index of d-line of positive lens included in the first lens group ν1p: average value of Abbe number of d-line of positive lens included in the first lens group In the focusing, a wide-angle lens according to any one of claims 1 to 6, and the second lens group and the third lens group satisfies the following condition.
1.00 ≦ Δ3 / Δ2 <1.50
However,
Δ3: movement amount of the third lens group Δ2: movement amount of the second lens group In the focusing, a wide-angle lens according to any one of claims 1 to 7, and the second lens group and the third lens group is thus being moved toward the object side in the same amount of movement. Optical apparatus characterized by having a wide-angle lens according to any one of claims 1 to 8.

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