JP2010176018A - Wide-angle lens, imaging apparatus, and method for manufacturing the wide-angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide-angle lens which secures back focus and has high imaging performance, an imaging apparatus including the same, and a method for manufacturing the wide-angle lens. <P>SOLUTION: The wide-angle lens includes, in order from an object side, a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power. The first lens group G1 includes at least one negative meniscus lens component L12 turning its convex surface to the object side. The second lens group G2 includes, in order from the object side, two positive lens components L21 and L22, a negative lens component L23, and two positive lens components L24 and L25, and the negative lens component includes a negative lens. The wide-angle lens satisfies a predetermined condition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wide-angle lens, an imaging device, and a method for manufacturing a wide-angle lens that are optimal for a photographing optical system.

  Conventionally, a thin wide-angle lens used in a camera has been proposed (for example, Patent Document 1).

Japanese Patent Laid-Open No. 3-288109

  However, the conventional thin wide-angle lens has a problem that it is difficult to maintain high imaging performance if further back focus is to be secured.

In order to solve the above problems, the present invention includes, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and the first lens group includes: Consists of at least one negative meniscus lens component having a convex surface facing the object side, and the second lens group has two positive lens components, a negative lens component, and two positive lens components in order from the object side. The negative lens component includes a negative lens, and satisfies the following conditions.
| RNR |-| RNF |> 0 (Unit: mm)
1.30 <BF / f0 <2.50

  Where RNF is the radius of curvature of the object side lens surface of the negative lens component of the negative lens component of the second lens group, and RNR is the radius of curvature of the image side lens surface of the negative lens component of the negative lens component of the second lens group, BF is the distance from the apex of the lens surface closest to the image side of the wide-angle lens to the paraxial image plane, and f0 is the focal length of the wide-angle lens when focusing on infinity.

  In addition, the present invention provides an imaging apparatus including the wide-angle lens.

The present invention is also a method for manufacturing a wide-angle lens having, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, the first lens group. A negative meniscus lens component having a convex surface facing the object side, and two positive lens components, a negative lens component, and two positive lens components in the second lens group in order from the object side. A method of manufacturing a wide-angle lens is provided, wherein a negative lens is disposed in the negative lens component so that the wide-angle lens satisfies the following conditions.
| RNR |-| RNF |> 0 (Unit: mm)
1.30 <BF / f0 <2.50

  Where RNF is the radius of curvature of the object side lens surface of the negative lens component of the negative lens component of the second lens group, and RNR is the radius of curvature of the image side lens surface of the negative lens component of the negative lens component of the second lens group, BF is the distance from the apex of the lens surface closest to the image side of the wide-angle lens to the paraxial image plane, and f0 is the focal length of the wide-angle lens when focusing on infinity.

  According to the present invention, it is possible to provide a wide-angle lens that secures back focus and has high imaging performance, an imaging apparatus having the same, and a method for manufacturing a wide-angle lens.

It is sectional drawing which shows the lens structure in the infinite point focusing state of the wide angle lens which concerns on 1st Example. FIG. 7 is a diagram illustrating various aberrations of the wide-angle lens according to Example 1 in an infinitely focused state. It is sectional drawing which shows the lens structure in the infinite point focusing state of the wide angle lens which concerns on 2nd Example. FIG. 12 is a diagram illustrating various aberrations of the wide-angle lens according to Example 2 in a focused state at infinity. It is sectional drawing which shows the lens structure in the infinite point focusing state of the wide angle lens which concerns on 3rd Example. FIG. 12 is a diagram illustrating various aberrations of the wide-angle lens according to Example 3 in the infinitely focused state. It is a figure which shows the structure of the imaging device (camera) provided with the wide angle lens which concerns on 1st Example. It is a figure which shows the manufacturing process of the wide angle lens which concerns on embodiment.

  Hereinafter, a wide-angle lens according to an embodiment of the present invention will be described. The following embodiments are only for facilitating understanding of the invention, and exclude additions and substitutions that can be performed by those skilled in the art without departing from the technical idea of the present invention. Is not intended.

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 and a second lens group having a positive refractive power, and the first lens group includes an object side. The second lens group includes, in order from the object side, two positive lens components, a negative lens component, and two positive lens components. The negative lens component has a negative lens and satisfies the following conditional expressions (1) and (2).
(1) | RNR |-| RNF |> 0 (Unit: mm)
(2) 1.30 <BF / f0 <2.50

  Where RNF is the radius of curvature of the object side lens surface of the negative lens component of the negative lens component of the second lens group, and RNR is the radius of curvature of the image side lens surface of the negative lens component of the negative lens component of the second lens group, BF is the distance from the apex of the lens surface closest to the image side of the wide-angle lens to the paraxial image surface (so-called back focus), and f0 is the focal length of the wide-angle lens when focusing on infinity.

  With this configuration, the wide-angle lens can achieve a wide-angle lens having high imaging performance while ensuring a desired back focus.

  In this wide-angle lens, the first lens group has at least one negative meniscus lens component having a convex surface facing the object side, thereby correcting off-axis aberrations, particularly field curvature, astigmatism, and coma. It can be done well.

  In the wide-angle lens, the second lens group includes two positive lens components, a negative lens component, and two positive lens components in order from the object side, and the negative lens component includes a negative lens. Even when the second lens unit is thin, it is possible to achieve a good spherical aberration and optimize the Petzval sum.

  The negative lens of the second lens group may be a lens component that exists in the cemented lens or a lens component that exists independently in the air. Moreover, a lens component shows the lens which consists of a single lens or a cemented lens.

  With the above configuration, the wide-angle lens can achieve a so-called thin wide-angle lens while maintaining a brightness and enabling an extremely thin angle at the same time as increasing the angle of view. As the total lens thickness of the wide-angle lens is reduced, the on-axis and off-axis aberration correction is simultaneously performed on the same lens surface, and the number of constituent lenses is also limited due to the reduction in thickness. I can not take a proper configuration. Accordingly, it is particularly difficult to correct off-axis aberrations, and the optical system tends to have large coma. This wide-angle lens is characterized in that good aberration characteristics are achieved by the optimum lens configuration and refractive power arrangement of each lens group.

  Conditional expression (1) is a conditional expression regarding the lens surface shape of the negative lens of the second lens group. By satisfying conditional expression (1), this wide-angle lens can obtain an optimal back focus while maintaining good spherical aberration and coma. If the conditional expression (1) is not satisfied, the back focus is shortened and cannot be used as an interchangeable lens for a single-lens reflex camera. If the back focus is forcibly ensured, the upper coma aberration will worsen in terms of aberration correction.

  Conditional expression (2) is a condition in which the back focus of the wide-angle lens is defined by the focal length of the wide-angle lens. This is an important measure when a wide-angle lens is used in a single-lens reflex camera. By satisfying conditional expression (2), it is possible to secure a back focus and achieve a wide-angle lens having high imaging performance.

  If the upper limit value of conditional expression (2) is exceeded, it means that the back focus is longer than the focal length of the wide-angle lens. In this case, the refractive power of the first lens unit is remarkably increased with the retrofocus configuration, and as a result, field curvature, astigmatism, and coma are deteriorated.

  Various aberrations can be corrected satisfactorily by setting the upper limit of conditional expression (2) to 2.30. Further, various aberrations can be corrected more favorably by setting the upper limit of conditional expression (2) to 2.00. Further, by setting the upper limit of conditional expression (2) to 1.80, various aberrations can be corrected more satisfactorily, and the effects of the present invention can be maximized.

  When the lower limit of conditional expression (2) is not reached, sufficient back focus cannot be obtained. In that case, it becomes difficult to use the wide-angle lens for a single-lens reflex camera. In addition, since the exit pupil approaches the image plane, the wide-angle lens is disadvantageous for use in a digital camera. Therefore, if the lower limit value of conditional expression (2) is not reached, it is necessary to move the exit pupil away from the image plane, and if it is attempted to move away from the image plane, correction of off-axis aberrations, particularly coma aberration, cannot be performed satisfactorily.

  Various aberrations can be corrected well by setting the lower limit of conditional expression (2) to 1.40. Further, various aberrations can be corrected more favorably by setting the lower limit value of conditional expression (2) to 1.45. Further, by setting the lower limit value of conditional expression (2) to 1.50, various aberrations can be corrected even better. Further, by setting the lower limit of conditional expression (2) to 1.52, various aberrations can be sufficiently corrected, and the effects of the present invention can be exhibited to the maximum.

In addition, it is desirable that this wide-angle lens satisfies the following conditional expression (3).
(3) 0.90 <Σd / Ymax <2.00

  Where Σd is the distance on the optical axis from the lens surface closest to the object side of the wide-angle lens to the lens surface closest to the image (hereinafter referred to as total lens thickness), and Ymax is the image height when the wide-angle lens has the maximum angle of view. (Hereinafter referred to as the maximum image height).

  Conditional expression (3) defines the optimum range of the ratio between the total lens thickness and the maximum image height of the wide-angle lens. When the value of (Σd / Ymax) indicates a small value, it can be said that the lens is a thin wide-angle lens compared to the format size. However, since there is a limit in securing a desired back focus and aberration correction, it is necessary to define conditional expression (3). By satisfying conditional expression (3), it is possible to achieve a wide-angle lens having a high angle of view and high imaging performance.

  When the upper limit value of conditional expression (3) is exceeded, the maximum image height becomes small in a wide-angle lens having a certain total lens thickness. In that case, the peripheral luminous flux is scattered and the image circle becomes smaller. In addition, when the maximum image height is constant, the entire lens thickness is increased, and the original wide-angle lens cannot be achieved. Also, increasing the thickness of the entire lens leads to an increase in the filter size. In order to reduce the diameter in this state, a refractive power arrangement and a lens arrangement that reduce the incident height of off-axis rays are required, and as a result, field curvature, distortion, and the like deteriorate.

  Note that downsizing can be achieved by setting the upper limit of conditional expression (3) to 1.85. Moreover, size reduction can be achieved by setting the upper limit of conditional expression (3) to 1.80. Further, the size can be further reduced by setting the upper limit value of the conditional expression (3) to 1.70. Further, by making the upper limit value of conditional expression (3) 1.50, further miniaturization can be achieved, and the effect of the present invention can be ensured. In addition, when the upper limit value of conditional expression (3) is set to 1.38, it is possible to sufficiently reduce the size, and to maximize the effects of the present invention.

  When the lower limit value of conditional expression (3) is not reached, the maximum image height is increased in a wide-angle lens having a certain total lens thickness. In that case, the peripheral imaging performance deteriorates, and in particular, field curvature, astigmatism, and coma become worse. Further, when the maximum image height is constant, the total lens thickness is remarkably reduced. In this case, curvature of field, astigmatism, and coma are particularly deteriorated.

  Various aberrations can be corrected well by setting the lower limit of conditional expression (3) to 0.95. Further, various aberrations can be corrected more favorably by setting the lower limit value of conditional expression (3) to 0.98. Further, by setting the lower limit value of conditional expression (3) to 1.00, various aberrations can be corrected more satisfactorily, and the effects of the present invention can be maximized.

In addition, it is preferable that the wide-angle lens satisfies the following conditional expression (4).
(4) 0.10 <(− f1) / f0 <2.00

  Here, f1 represents the focal length of the first lens group, and f0 represents the focal length of the wide-angle lens when focusing on infinity.

  Conditional expression (4) is a conditional expression in which the focal length of the first lens group is defined by the focal length of the wide-angle lens. The magnitude of the refractive power of the first lens group is necessary to satisfactorily correct the size of the wide-angle lens and off-axis aberrations. By satisfying conditional expression (4), a wide-angle lens having high imaging performance can be achieved.

  If the upper limit value of conditional expression (4) is exceeded, it means that the absolute value of the focal length of the first lens group becomes large, that is, the negative refractive power becomes weak. When the negative refractive power is weakened, the diameter of the first lens group is increased, the diameter of the wide-angle lens is increased, and the back focus is shortened, so that the conditional expressions (1) and (2) are not satisfied. Further, in terms of aberration correction, the refractive power balance between the first lens group having a negative refractive power and the second lens group having a positive refractive power is lost, so that the distortion aberration cannot be corrected satisfactorily.

  The effect of the present invention can be ensured by setting the upper limit value of conditional expression (4) to 1.60. Moreover, the effect of this invention can be made more reliable by making the upper limit of conditional expression (4) 1.40. Moreover, the effect of this invention can be made more reliable by making the upper limit of conditional expression (4) 1.10. Moreover, the effect of this invention can be made more reliable by making the upper limit of conditional expression (4) into 1.00. Moreover, the effect of this invention can be exhibited to the maximum by making the upper limit of conditional expression (4) 0.93.

  When the lower limit value of conditional expression (4) is not reached, it means that the absolute value of the focal length of the first lens group becomes small, that is, the negative refractive power of the first lens group becomes extremely strong. In this case, the back focus is remarkably long and it is difficult to reduce the size of the wide-angle lens, and as a result, conditional expressions (1) and (2) are not satisfied. In terms of aberration correction, a significantly negative refractive power increases off-axis aberrations, and in particular, field curvature, astigmatism, and coma become worse.

  Various aberrations can be corrected well by setting the lower limit of conditional expression (4) to 0.20. Further, various aberrations can be corrected more favorably by setting the lower limit of conditional expression (4) to 0.40. Further, by setting the lower limit of conditional expression (4) to 0.50, various aberrations can be corrected more satisfactorily, and the effects of the present invention can be maximized.

In addition, it is desirable that this wide-angle lens satisfies the following conditional expression (5).
(5) 0.40 <f2 / f0 <1.50

  Here, f2 indicates the focal length of the second lens group, and f0 indicates the focal length of the wide-angle lens when focusing on infinity.

  Conditional expression (5) is a conditional expression that defines an optimum value of the focal length of the second lens group. Optimizing the refractive power of the second lens group having a positive refractive power is necessary to satisfactorily correct spherical aberration and coma. By satisfying conditional expression (5), a wide-angle lens having high imaging performance can be achieved.

  If the upper limit value of conditional expression (5) is exceeded, it means that the focal length of the second lens group becomes long and the refractive power becomes weak, and the spherical aberration becomes excessively corrected. In this case, coma aberration is deteriorated. Further, in this case, the second lens unit is increased in size, and thus the wide-angle lens is increased.

  Various aberrations can be favorably corrected by setting the upper limit value of conditional expression (5) to 1.30. Further, by setting the upper limit value of conditional expression (5) to 1.10, various aberrations can be corrected more favorably. Further, various aberrations can be corrected more favorably by setting the upper limit of conditional expression (5) to 1.00. Further, by setting the upper limit of conditional expression (5) to 0.90, various aberrations can be corrected more satisfactorily, and the effects of the present invention can be maximized.

  If the lower limit value of conditional expression (5) is not reached, it means that the focal length of the second lens group becomes short, that is, the positive refractive power becomes strong, and the spherical aberration becomes insufficiently corrected. In this case, the back focus is shortened as a result.

  Various aberrations can be corrected well by setting the lower limit of conditional expression (5) to 0.45. Further, various aberrations can be corrected more favorably by setting the lower limit value of conditional expression (5) to 0.55. Further, by setting the lower limit of conditional expression (5) to 0.60, various aberrations can be corrected more satisfactorily, and the effects of the present invention can be maximized.

  In this wide-angle lens, it is desirable that the aperture stop be disposed closer to the object side than the most image side lens of the second lens group. The aperture stop determines the F number of the wide-angle lens. This wide-angle lens can satisfactorily correct field curvature, distortion, and lateral chromatic aberration by disposing the aperture stop closer to the object side than the most image side lens of the second lens group.

  In the wide-angle lens, it is desirable that the first lens group has at least one aspheric surface. With such a configuration, a wide-angle lens can be configured with a small number of lenses, so that downsizing can be achieved. Also, with this configuration, it is possible to satisfactorily correct off-axis aberrations, particularly field curvature, coma aberration, and distortion aberration.

  Hereinafter, each numerical example of the wide-angle lens according to the present embodiment will be described with reference to the accompanying drawings.

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

  The wide-angle lens according to the first example includes, in order from the object side, a first lens group G1 having negative refractive power and a second lens group G2 having positive refractive power.

  The first lens group G1, in order from the object side, includes a negative meniscus lens L11 having a convex surface facing the object side and an aspheric surface on the image side lens surface, and a negative meniscus lens L12 having a convex surface facing the object side. Yes.

  The second lens group G2, in order from the object side, includes a biconvex positive lens L21, an aperture stop S that determines an F-number, a biconvex positive lens L22, a biconcave negative lens L23, and an image. It is composed of a positive meniscus lens L24 having a convex surface on the side and a positive meniscus lens L25 having a convex surface on the image side.

  Table 1 below shows specification values of the wide-angle lens according to the first example.

  In (surface data) in the table, the surface number is the number of the lens surface counted from the object side, r is the radius of curvature of the lens surface, d is the surface spacing of the lens surface, and nd is the d-line (wavelength λ = 587.6 nm). And νd represents the Abbe number for the d-line (wavelength λ = 587.6 nm). The object plane indicates the object plane, (aperture) indicates the aperture stop S, and the image plane indicates the image plane I. Note that “∞” in the radius of curvature r column indicates a plane. If the lens surface is aspherical, the surface number is marked with * and the paraxial radius of curvature is shown in the radius of curvature column.

(Aspherical data) shows the aspherical coefficient when the shape of the aspherical surface shown in (Surface data) 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 + A14 × y ¹⁴ + A16 × y ¹⁶

Here, the height in the direction perpendicular to the optical axis is y, the displacement (sag amount) in the optical axis direction at the height y is X (y), the radius of curvature of the reference sphere (paraxial radius of curvature) is r, and the cone The coefficient is κ, and the nth-order aspheric coefficient is An. “En” represents “× 10 ⁻ⁿ ”, for example “1.234E-05” represents “1.234 × 10 ⁻⁵ ”.

  In (various data), f is the focal length, FNO is the F number, ω is the half angle of view (unit: °), Y is the image height, TL is the total length of the lens system, and Σd is the lens surface on the most object side of the wide-angle lens. The distance on the optical axis from the lens surface to the lens surface closest to the image, BF, represents the back focus.

  (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, and the present invention is not limited to these. Further, the unit is not limited to “mm”, and other appropriate units may be used. Further, these symbols are the same in the other embodiments described below, and the description thereof is omitted.

(Table 1) (First Example)
(Surface data)
Surface number rd nd νd
Object ∞ ∞
1) 13.0000 1.0000 1.603000 65.47
2) * 6.5788 4.0000 1.000000
3) 16.3065 1.0000 1.497820 82.56
4) 9.3200 3.0000 1.000000
5) 35.6227 3.0000 1.672700 32.11
6) -45.2913 1.0000 1.000000
7> (Aperture) ∞ 1.0000 1.000000
8) 58.1986 5.0000 1.497820 82.56
9) -11.9480 1.6000 1.000000
10) -25.4154 1.5000 1.850260 32.35
11) 28.5178 1.2000 1.000000
12) -34.8646 2.5000 1.497820 82.56
13) -12.2372 0.1000 1.000000
14) -148.0797 2.5000 1.603000 65.47
15) -22.6787 38.0226 1.000000
Image plane ∞

(Aspheric data)
Second side κ = 0.7798
A4 = -1.89600E-05
A6 = 6.76130E-06
A8 = -5.07050E-07
A10 = 2.17350E-08
A12 = -0.45673E-09
A14 = 0.37979E-11
A16 = 0.10000E-17

(Various data)
f = 24.401
FNO = 3.62
ω = 42.31 °
Y = 21.6
TL = 66.423
Σd = 28.400
BF = 38.023

(Lens group data)
Group Start surface Focal length
G1 1 -14.488
G2 5 17.812

(Values for conditional expressions)
(1): | RNR | − | RNF | = 4.10
(2): BF / f0 = 1.56
(3): Σd / Ymax = 1.31
(4): (−f1) /f0=0.594
(5): f2 / f0 = 0.730

  FIG. 2 shows various aberrations when the wide-angle lens according to Example 1 is focused at infinity.

  In each aberration diagram, FNO is an F number, Y is an image height, ω is a half angle of view (unit: degree), d is a d-line (wavelength λ = 587.6 nm), and g is a g-line (wavelength λ = 435. 8 nm). In astigmatism, the solid line indicates the sagittal image plane, and the dotted line indicates the meridional image plane. The solid line in coma indicates meridional coma. In the aberration diagrams of other examples shown below, the same reference numerals as those in this example are used and the description thereof is omitted.

  From the various aberration diagrams, it can be seen that the wide-angle lens according to Example 1 has excellent imaging performance with various aberrations corrected satisfactorily.

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

  The wide-angle lens according to Example 2 includes, in order from the object side, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes, in order from the object side, a negative meniscus lens L11 having a convex surface facing the object side, and a negative meniscus lens L12 having a convex surface facing the object side and an aspheric surface on the image side lens surface. Yes.

  The second lens group G2, in order from the object side, includes a biconvex positive lens L21, a biconvex positive lens L22, an aperture stop S that determines an F-number, a biconcave negative lens L23, and an image. It is composed of a positive meniscus lens L24 having a convex surface on the side and a positive meniscus lens L25 having a convex surface on the image side.

Table 2 below shows specification values of the wide-angle lens according to the second example.
(Table 2) 2nd Example (surface data)
Surface number rd nd νd
Object ∞ ∞
1) 16.0478 1.0000 1.755000 52.29
2) 7.9274 3.0000 1.000000
3) 10.0991 1.0000 1.589130 61.18
4) * 6.8029 4.0000 1.000000
5) 32.0272 3.0000 1.717360 29.52
6) -43.9577 1.0000 1.000000
7) 32.6637 5.0000 1.487490 70.45
8) -11.6735 0.5000 1.000000
9> (Aperture) ∞ 1.5000 1.000000
10) -17.5914 1.5000 1.903660 31.27
11) 26.5782 1.0000 1.000000
12) -56.3638 2.5000 1.593190 67.87
13) -12.4855 0.1000 1.000000
14) -31.8451 2.0000 1.603000 65.47
15) -14.5224 37.9778 1.000000
Image plane ∞

(Aspheric data)
4th surface κ = 0.8089
A4 = -3.23490E-05
A6 = 7.06440E-08
A8 = -1.25010E-07
A10 = 3.45160E-09
A12 = -0.60254E-10
A14 = 0.00
A16 = 0.00

(Various data)
f = 24.401
FNO = 3.62
ω = 42.31 °
Y = 21.6
TL = 65.078
Σd = 27.100
BF = 37.978

(Lens group data)
Group Start surface Focal length
G1 1 -13.163
G2 5 16.844

(Values for conditional expressions)
(1): | RNR |-| RNF | = 8.99
(2): BF / f0 = 1.56
(3): Σd / Ymax = 1.25
(4): (−f1) /f0=0.539
(5): f2 / f0 = 0.690

  FIG. 4 shows various aberrations when the wide-angle lens according to Example 2 is in focus at infinity. From the various aberration diagrams, it can be seen that the wide-angle lens according to the second example has excellent imaging performance with various aberrations corrected satisfactorily.

(Third embodiment)
FIG. 5 is a cross-sectional view showing a lens 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, a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power.

  The first lens group G1 includes a negative meniscus lens L11 having a convex surface on the object side and an aspheric surface on the image side lens surface.

  The second lens group G2, in order from the object side, includes a biconvex positive lens L21, a biconvex positive lens L22, an aperture stop S that determines an F-number, a biconcave negative lens L23, and an image. It is composed of a positive meniscus lens L24 having a convex surface on the side and a positive meniscus lens L25 having a convex surface on the image side.

Table 3 below shows specifications of the wide-angle lens according to the third example.
(Table 3) Third Example (surface data)
Surface number rd nd νd
Object ∞ ∞
1) 16.0478 1.0000 1.755000 52.29
2) * 6.7924 5.0000 1.000000
3) 23.7034 5.0000 1.755200 27.51
4) -103.0800 1.0000 1.000000
5) 491.5870 3.0000 1.603000 65.47
6) -31.7952 0.5000 1.000000
7> (Aperture) ∞ 1.5000 1.000000
8) -27.9362 1.5000 1.805180 25.43
9) 32.4779 1.1599 1.000000
10) -47.5563 2.0000 1.593190 67.87
11) -13.1659 0.1000 1.000000
12) -33.7926 2.5000 1.603000 65.47
13) -12.9041 37.8784 1.000000
Image plane ∞

(Aspheric data)
Second side κ = 0.9337
A4 = -5.24830E-05
A6 = -4.30110E-06
A8 = 2.22250E-07
A10 = -8.38110E-09
A12 = 0.69851E-10
A14 = 0.00
A16 = 0.00

(Various data)
f = 24.401
FNO = 3.60
ω = 42.47 °
Y = 21.6
TL = 62.138
Σd = 24.260
BF = 37.878

(Lens group data)
Group Start surface Focal length
G1 1 -16.359
G2 3 18.317

(Values for conditional expressions)
(1): | RNR |-| RNF | = 4.54
(2): BF / f0 = 1.55
(3): Σd / Ymax = 1.12
(4): (−f1) /f0=0.670
(5): f2 / f0 = 0.751

  FIG. 6 shows various aberrations of the wide-angle lens according to Example 3 when focusing on infinity. From the various aberration diagrams, it can be seen that the wide-angle lens according to the fifth example has excellent imaging performance with various aberrations corrected satisfactorily.

  According to each of the above-described embodiments, the inclusive angle exceeds 2ω = 84 °, and has an aperture of about F2.8 to F3.6, and is small, thin, high performance, spherical aberration, field curvature, astigmatism. A wide-angle lens in which coma aberration is corrected well can be realized.

  In addition, the following content can be appropriately employed as long as the optical performance of the wide-angle lens of the present application is not impaired.

  The numerical example of the wide-angle lens of the present application is shown as having a two-group configuration, but the present application is not limited to this, and a wide-angle lens of another group configuration (for example, three groups) can also be configured. Specifically, a configuration in which a lens or a lens group is added to the most object side or the most image side of the wide-angle lens of the present application may be used. The lens group refers to a portion having at least one lens separated by an air interval.

  The wide-angle lens of the present application uses a part of a lens group, an entire lens group, or a plurality of lens groups as a focusing lens group in order to perform focusing from an object at infinity to a short-distance object. It is good also as a structure moved to. In particular, it is preferable that the whole or at least a part of the second lens group or at least two parts in the whole be the focusing lens group. Such a focusing lens group can also be applied to autofocus, and is also suitable for driving by an autofocus motor, such as an ultrasonic motor.

  In the wide-angle lens of the present application, either the entire lens group or a part thereof is moved so as to include a component perpendicular to the optical axis as an anti-vibration lens group, or rotationally moved in an in-plane direction including the optical axis ( The image blur caused by the camera shake can be corrected by swinging). In particular, in the wide-angle lens of the present application, it is preferable that at least a part of the second lens group is an anti-vibration lens group.

  The lens surface of the lens constituting the wide-angle lens of the present application may be a spherical surface, a flat surface, or an aspheric surface. When the lens surface is a spherical surface or a flat surface, it is preferable because lens processing and assembly adjustment are easy, and deterioration of optical performance due to errors in lens processing and assembly adjustment can be prevented. Further, even when the image plane is deviated, it is preferable because there is little deterioration in drawing performance. When the lens surface is aspherical, any of aspherical surface by grinding, glass mold aspherical surface in which glass is molded into an aspherical shape, or composite aspherical surface in which resin provided on the glass surface is formed in an aspherical shape Good. The lens surface may be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

  In the wide-angle lens of the present application, it is preferable that the aperture stop is disposed in or near the second lens group, but the role may be substituted by a lens frame without providing a member as the aperture stop.

  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 with high contrast can be achieved.

  In the wide-angle lens of the present application, it is preferable that the first lens group has one negative lens component. In the wide-angle lens of the present application, it is preferable that the first lens group has two negative lens components.

  In the wide-angle lens of the present application, it is preferable that the second lens group has four positive lens components and one negative lens component. In the second lens group, it is preferable to arrange the lens components in the order of positive, negative, positive and positive in order from the object side with an air gap interposed therebetween.

  Next, an image pickup apparatus including the wide-angle lens of the present application will be described with reference to the drawings. FIG. 7 is a diagram illustrating a configuration of an imaging apparatus (camera) including the wide-angle lens according to the first example.

  This 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.

  Further, when a release button (not shown) is pressed by the photographer, the quick return mirror 3 is retracted to the outside of the optical path, and the light from the subject (not shown) collected by the photographing lens 2 forms a subject image on the image sensor 7. Form. 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.

  Here, as described in the first embodiment, the wide-angle lens according to the first embodiment mounted on the camera 1 as the photographing lens 2 has a curvature of field and astigmatism due to its characteristic lens configuration. Realizes a wide-angle lens with little coma. As a result, the camera 1 can realize a thin imaging device capable of wide-angle imaging with less curvature of field, astigmatism, and coma.

  In the above embodiment, the camera 1 is configured by mounting the wide-angle lens according to the first embodiment as the photographing lens 2, but the wide-angle lens according to the embodiment other than the first embodiment is mounted. Needless to say, the same effects as those of the camera 1 can be obtained.

  Hereinafter, the outline of the manufacturing method of the wide-angle lens of this application is demonstrated based on FIG. FIG. 8 is a diagram showing a manufacturing method of the wide-angle lens of the present application.

  The wide-angle lens manufacturing method of the present application is a method for manufacturing a wide-angle lens having, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power. Each step S1 to S3 shown is included.

Step S1:
In step S1, an optical member including at least one negative meniscus lens is disposed in the first lens group.

Step S2:
In step S2, in order from the object side, two positive lens components, a negative lens component including a negative lens, and an optical member including two positive lens components are arranged in the second lens group.

Step S3:
In step S3, the optical member including the first lens group and the second lens group is disposed from the object side in the cylindrical barrel so that the wide-angle lens satisfies the following conditional expressions (1) and (2). .
(1) | RNR |-| RNF |> 0 (Unit: mm)
(2) 1.30 <BF / f0 <2.50

  Where RNF is the radius of curvature of the object side lens surface of the negative lens of the second lens group, RNR is the radius of curvature of the negative lens component image side of the negative lens component of the second lens group, and BF is the most wide-angle lens. The distance from the apex of the lens surface on the image side to the paraxial image plane (so-called back focus), f0 is the focal length of the wide-angle lens when focusing on infinity.

  According to such a wide-angle lens manufacturing method of the present application, a wide-angle lens having a wide field angle and good optical performance can be manufactured.

  In addition, each said Example has shown one specific example of this invention, and this invention is not limited to these.

G1: First lens group G2: Second lens group S: Aperture stop I: Image plane 1: Camera 2: Shooting lens 3: Quick return mirror 4: Focus plate 5: Penta prism 6: Eyepiece lens 7: Image sensor

Claims (8)

In order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power,
The first lens group includes at least one negative meniscus lens component having a convex surface facing the object side,
The second lens group includes, in order from the object side, two positive lens components, a negative lens component, and two positive lens components,
The negative lens component comprises a negative lens;
A wide-angle lens that satisfies the following conditions.
| RNR |-| RNF |> 0 (Unit: mm)
1.30 <BF / f0 <2.50
However,
RNF: radius of curvature of the object side lens surface of the negative lens component of the negative lens component of the second lens group RNR: radius of curvature of the image side lens surface of the negative lens component of the negative lens component of the second lens group BF: the wide angle The distance from the apex of the lens surface closest to the image side to the paraxial image surface of the lens f0: the focal length of the wide-angle lens when focusing on infinity The wide-angle lens according to claim 1, wherein the following condition is satisfied.
0.90 <Σd / Ymax <2.00
However,
Σd: 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 wide-angle lens Ymax: image height when the wide-angle lens has the maximum field angle The wide angle lens according to claim 1, wherein the following condition is satisfied.
0.10 <(− f1) / f0 <2.00
However,
f1: Focal length of the first lens group f0: Focal length of the wide-angle lens when focusing on infinity The wide angle lens according to any one of claims 1 to 3, wherein the following condition is satisfied.
0.40 <f2 / f0 <1.50
However,
f2: Focal length of the second lens group f0: Focal length of the wide-angle lens when focusing on infinity   5. The wide-angle lens according to claim 1, further comprising an aperture stop closer to the object side than a lens closest to the image side of the second lens group.   The wide-angle lens according to any one of claims 1 to 5, wherein the first lens group includes at least one aspherical surface.   An imaging apparatus comprising the wide-angle lens according to any one of claims 1 to 6. A method of manufacturing a wide-angle lens having, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power,
A negative meniscus lens component having a convex surface facing the object side is disposed in the first lens group;
In the second lens group, in order from the object side, two positive lens components, a negative lens component, and two positive lens components are arranged, and a negative lens is arranged in the negative lens component,
A method of manufacturing a wide-angle lens, wherein the wide-angle lens satisfies the following conditions.
| RNR |-| RNF |> 0 (Unit: mm)
1.30 <BF / f0 <2.50
However,
RNF: radius of curvature of the object side lens surface of the negative lens component of the negative lens component of the second lens group RNR: radius of curvature of the image side lens surface of the negative lens component of the negative lens component of the second lens group BF: the wide angle The distance from the apex of the lens surface closest to the image side to the paraxial image surface of the lens f0: the focal length of the wide-angle lens when focusing on infinity

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