JP2013238684A - Fisheye lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fisheye lens with sufficient back focus and high optical performance.SOLUTION: A fisheye lens comprises, in order from an object side, a front group Gof positive refractive power, an optical diaphragm S, and a rear group Gof positive refractive power. The rear group Gis arranged with a space left from the front group G. In particular, the front group Gis composed by arranging, in order from the object side, a first lens Lof negative refractive power, a second lens Lof positive refractive power, a third lens Lof negative refractive power, and a fourth lens Lof positive refractive power. By satisfying predetermined conditions, a small fisheye lens with sufficient back-focus and high optical performance can be realized.

Description

  The present invention relates to a fisheye lens, and more particularly to a small fisheye lens suitable for a digital camera, particularly a digital single lens reflex camera.

  The fish-eye lens is used only for a specific purpose such as science because an image is formed by a special projection method. However, in recent years, it has been increasingly used for other purposes aiming at the effect of the negative distortion caused by the special projection method. Therefore, in recent years, a fish-eye lens having excellent optical performance that can be used for a digital device equipped with an image sensor with an increased number of pixels that has been widely used has also been proposed (see, for example, Patent Document 1 below).

  Although it is a fish-eye lens that has come to be used in various applications, it is also used in single-lens reflex cameras as one of its applications. In recent years, as for single-lens reflex cameras, instead of single-lens reflex cameras of 35 mm film size, digital single-lens reflex cameras equipped with a small image sensor of APS-C format or less have become mainstream.

  By the way, if a fish-eye lens suitable for a single-lens reflex camera having a 35 mm film size is attached to a digital single-lens reflex camera having a small screen size, the diagonal angle of view becomes remarkably narrow, and it becomes difficult to obtain effects specific to fish-eye lenses. In this case, it is possible to secure a diagonal angle of view according to the image sensor by proportionally reducing the fisheye lens. However, the back focus becomes too short to attach to a digital single-lens reflex camera, which may interfere with the quick return mirror.

  The fish-eye lens disclosed in Patent Document 1 has an excellent aberration correction capability while being small. However, this fish-eye lens is not suitable for a digital single-lens reflex camera because sufficient back focus cannot be secured. Therefore, a fish-eye lens that can be used for a digital single-lens reflex camera has been proposed (see, for example, Patent Documents 2 and 3 below).

Japanese Patent No. 4633379 JP 2009-58817 A Japanese Patent No. 4432330

  The fisheye lens disclosed in Patent Document 2 has an excellent aberration correction capability in addition to sufficient back focus. However, shortening of the total length of the optical system is insufficient. In other words, this fisheye lens maintains aberration between the negative lens power and back focus by keeping a large distance between the two or three negative lenses arranged on the object side and the rear group. However, as a result, the total length is longer. Therefore, it is not suitable for a recent digital single-lens reflex camera in which further downsizing is desired.

  The fisheye lens disclosed in Patent Document 3 is small in size and has a sufficient back focus. However, correction for astigmatism and coma is particularly insufficient. In this fisheye lens, in order to secure the back focus, the negative power of the front group arranged closer to the object side than the aperture is increased, so the positive power of the rear group must be increased, and as a result Aberration correction is insufficient.

  An object of the present invention is to provide a small fish-eye lens having sufficient back focus and high optical performance in order to solve the above-described problems caused by the prior art.

In order to solve the above-described problems and achieve the object, a fisheye lens according to the present invention includes, in order from the object side, a front group having a plurality of negative lens components and a negative or positive refractive power as a whole, and an optical aperture And a rear group which is arranged with an axial interval with respect to the front group and has a positive refractive power as a whole, and satisfies the following conditions.
(1) 9.0 ≦ | f1 | / Gn1B
(2) 0.33 ≦ (Gn1B + Gn2B) /Σd≦0.70
Where f1 is the focal length of the front group, Gn1B is the air distance from the lens closest to the object side as the negative lens component to the next lens component in the front group, and Gn2B is the negative lens component in the front group , Σd represents the distance from the lens surface closest to the object side to the lens surface closest to the image side in the fisheye lens.

  According to the present invention, it is possible to provide a smaller fisheye lens having a sufficient back focus and higher optical performance. According to the present invention, it is possible to provide a fisheye lens that is preferable for a digital camera, particularly a digital single-lens reflex camera, which is recently required to be smaller and have high optical performance.

The fisheye lens according to the present invention is characterized in that, in the above-described invention, the following conditional expressions are further satisfied.
(3) 600 ≦ BF / (f / | f1 |)
Where BF is the back focus of the fisheye lens, f is the focal length of the entire fisheye lens system, and f1 is the focal length of the front group.

  According to the present invention, it is possible to provide a small fisheye lens having a sufficient back focus and high optical performance.

  According to the present invention, there is an effect that it is possible to provide a small fisheye lens having a sufficient back focus and high optical performance. The fisheye lens of the present invention is suitable for a small digital camera, particularly a digital single lens reflex camera.

1 is a cross-sectional view along the optical axis showing the configuration of a fisheye lens according to Example 1. FIG. FIG. 6 is a diagram illustrating various aberrations of the fisheye lens according to Example 1 with respect to the d line. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a fisheye lens according to Example 2. FIG. 10 is a diagram illustrating various aberrations of the fisheye lens according to Example 2 with respect to the d line. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a fisheye lens according to Example 3; FIG. 9 is a diagram illustrating various aberrations of the fisheye lens according to Example 3 with respect to the d line. FIG. 6 is a cross-sectional view along the optical axis showing the configuration of a fisheye lens according to Example 4; FIG. 10 is a diagram illustrating various aberrations of the fisheye lens according to Example 4 with respect to the d line. FIG. 10 is a cross-sectional view along the optical axis showing the configuration of a fisheye lens according to Example 5; FIG. 10 is a diagram illustrating various aberrations of the fisheye lens according to Example 5 with respect to the d line.

  Hereinafter, a preferred embodiment of a fisheye lens according to the present invention will be described in detail.

  The fish-eye lens according to the present invention includes, in order from the object side, a front group having a plurality of negative lens components and having negative or positive refractive power as a whole, an optical aperture, and an axial interval with respect to the front group. And a rear group having a positive refractive power as a whole.

  An object of the present invention is to provide a small-sized fisheye lens suitable for a small-sized digital camera, particularly a digital single-lens reflex camera, in which an image pickup device with a remarkable increase in pixels is mounted in recent years. In order to achieve this object, the fisheye lens is required to have sufficient back focus and high optical performance. Therefore, in the present invention, various conditions as shown below are set in order to meet such a requirement.

First, in the fisheye lens according to the present invention, the focal length of the front group of the fisheye lens is f1, and the air distance from the lens disposed closest to the object side as the negative lens component to the next lens component is Gn1B in the front group. , Gn2B is the air distance from the lens disposed second from the object side as the negative lens component to the next lens component, and Σd is the distance from the most object side lens surface to the most image side lens surface in the fisheye lens. It is preferable that the following conditional expression is satisfied.
(1) 9.0 ≦ | f1 | / Gn1B
(2) 0.33 ≦ (Gn1B + Gn2B) /Σd≦0.70

  Conditional expression (1) is an expression that defines the ratio between the focal length of the front group and the air distance in the front group from the lens disposed closest to the object side as the negative lens component to the next lens component. Conditional expression (2) is obtained from the air distance from the lens arranged closest to the object side as the negative lens component to the next lens component and the lens arranged second from the object side as the negative lens component in the front group. This is an expression that defines the ratio of the sum of the air gap to the next lens component and the total length of the optical system.

  From the viewpoint of aberration correction, it is desirable to ensure a certain amount of air space after the negative lens component in the front group. On the other hand, from the viewpoint of shortening the total length of the optical system, it is better that the air interval after the negative lens component in the front group is shorter. Therefore, in the present invention, the conditional expressions (1) and (2) are set in consideration of the balance between the two. Satisfying both the conditional expressions (1) and (2) makes it possible to correct aberrations and shorten the total length of the optical system. If either one of the conditional expressions (1) and (2) is out of the range, the air space after the negative lens component in the front group becomes insufficient, and the power of the negative lens cannot be fully utilized. Correction for point aberration and coma becomes insufficient.

If the conditional expressions (1) and (2) satisfy the following range, better aberration correction and shortening of the total length of the optical system can be expected.
(1a) 11.0 ≦ | f1 | / Gn1B
(2a) 0.35 ≦ (Gn1B + Gn2B) /Σd≦0.60
By satisfying the ranges defined by the conditional expressions (1a) and (2a), it is possible to realize a smaller fisheye lens having a higher aberration correction capability while ensuring a sufficient back focus.

Furthermore, it is preferable that the conditional expressions (1a) and (2a) satisfy the following ranges.
(1b) 40.0 ≦ | f1 | / Gn1B
(2b) 0.36 ≦ (Gn1B + Gn2B) /Σd≦0.50
By satisfying the ranges defined by the conditional expressions (1b) and (2b), it is possible to achieve both aberration correction and shortening of the total length of the optical system in a balanced manner while ensuring a sufficient back focus.

In the fisheye lens according to the present invention, it is preferable that the following conditional expression is satisfied, where BF is the back focus of the fisheye lens, f is the focal length of the entire fisheye lens system, and f1 is the focal length of the front group of the fisheye lens.
(3) 600 ≦ BF / (f / | f1 |)

  Conditional expression (3) is an expression that defines the relationship among the focal length of the entire optical system, the focal length of the front group, and the back focus. If the lower limit of conditional expression (3) is not reached, the following inconvenience occurs. First, the back focus cannot be secured sufficiently. In this case, there is a possibility of interfering with the quick return mirror, and it cannot be used for a digital single lens reflex camera. In addition, when negative refractive power is applied to the front group, the negative refractive power becomes too strong, and in order to maintain the balance of the optical system, it is necessary to increase the positive refractive power of the rear group. As a result, correction for various aberrations, particularly astigmatism and coma, becomes insufficient. In addition, the overall length of the optical system is extended, making it difficult to reduce the size of the fisheye lens. On the other hand, when positive refractive power is given to the front group, the positive refractive power becomes too strong. If this happens, it will no longer be possible to establish a fisheye lens.

In addition, if the said conditional expression (3) satisfies the range shown next, a more preferable effect can be anticipated.
(3a) 700 ≦ BF / (f / | f1 |)
By satisfying the range defined by the conditional expression (3a), it is possible to realize a smaller fisheye lens having a higher aberration correction capability while ensuring a sufficient back focus.

Furthermore, it is preferable that the conditional expression (3a) satisfies the following range.
(3b) 1000 ≦ BF / (f / | f1 |)
By satisfying the range defined by the conditional expression (3b), it is possible to realize a small fish-eye lens that is optimal for a digital single-lens reflex camera and has an extremely high aberration correction capability while ensuring a sufficient back focus. it can.

  As described above, the fisheye lens according to the present invention is a small fisheye lens having sufficient back focus and high optical performance by satisfying the conditional expression. This fisheye lens is suitable for a small digital camera, particularly a digital single lens reflex camera. Further, this fisheye lens can be mounted not only on a digital camera but also on a conventional single-lens reflex camera of 35 mm film size.

  In the present invention, if the conditional expressions (1) and (2) are satisfied or the conditional expression (3) is satisfied, the above object can be sufficiently achieved. However, by satisfying all of the conditional expressions (1) to (3), it is possible to realize a small fisheye lens having higher ideal optical performance for a digital single lens reflex camera.

  Embodiments of a fisheye lens according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by the following examples.

FIG. 1 is a cross-sectional view along the optical axis showing the configuration of the fisheye lens according to the first embodiment. The fisheye lens includes, in order from the object side, a front group G ₁₁ having a positive refractive power, and includes an optical stop S, a group G ₁₂ after having a positive refractive power. Rear group G ₁₂ is spaced relative to the front group G _11.

The front group G ₁₁ includes, in order from the object side, a first lens L ₁₁₁ having a negative refractive power, a second lens L ₁₁₂ having a positive refractive power, a third lens L ₁₁₃ having a negative refractive power, a fourth lens L ₁₁₄ having a positive refractive power, is configured are arranged.

The rear group G ₁₂ includes, in order from the object side, a first lens L ₁₂₁ having a negative refractive power, a second lens L ₁₂₂ having a positive refractive power, a third lens L ₁₂₃ having a positive refractive power, A fourth lens L ₁₂₄ having a negative refractive power and a fifth lens L ₁₂₅ having a positive refractive power are arranged. The first lens L ₁₂₁ and the second lens L ₁₂₂ are cemented. The third lens L ₁₂₃ and the fourth lens L ₁₂₄ are also cemented.

  Various numerical data relating to the fisheye lens according to Example 1 will be described below.

f (focal length of whole fisheye lens) = 10.21
Fno. (F number) = 2.88
2ω (angle of view) = 181.00

(Lens data)
r ₁ = 56.405
d ₁ = 2.000 nd ₁ = 1.773 νd ₁ = 49.62
r ₂ = 14.086
d ₂ = 12.528
r ₃ = 130.190
d ₃ = 2.807 nd ₂ = 1.847 νd ₂ = 23.78
r ₄ = −101.634
d ₄ = 1.200
r ₅ = -49.961
d ₅ = 1.500 nd ₃ = 1.773 νd ₃ = 49.62
r ₆ = 14.033
d ₆ = 10.827
r ₇ = 23.432
d ₇ = 3.291 nd ₄ = 1.673 νd ₄ = 32.17
r ₈ = -46.771
d ₈ = 8.000
r ₉ = ∞ (aperture)
d ₉ = 2.000
r ₁₀ = −81.119
d ₁₀ = 1.000 nd ₅ = 1.835 νd ₅ = 42.72
r ₁₁ = 13.620
d ₁₁ = 3.666 nd ₆ = 1.569 νd ₆ = 56.04
r ₁₂ = -26.901
d ₁₂ = 0.200
r ₁₃ = 76.761
d ₁₃ = 4.781 nd ₇ = 1.517 νd ₇ = 64.20
r ₁₄ = -9.796
d ₁₄ = 1.000 nd ₈ = 1.904 νd ₈ = 31.32
r ₁₅ = -26.947
d ₁₅ = 0.200
r ₁₆ = 4557.962
d ₁₆ = 5.000 nd ₉ = 1.517 νd ₉ = 64.20
r ₁₇ = -15.544
d ₁₇ = 35.000
r ₁₈ = ∞ (imaging plane)

(Numerical values related to conditional expression (1))
Gn1B (air distance from the first lens L ₁₁₁ to the second lens L ₁₁₂ ) = 12.53
| F1 | /Gn1B=107.18

(Numerical value related to conditional expression (2))
Gn2B (the air gap from the second lens L ₁₁₂ to the third lens L ₁₁₃ ) = 10.83
Σd (total length of optical system) = 60.00
(Gn1B + Gn2B) /Σd=0.39

(Numerical values related to conditional expression (3))
BF (back focus) = 35.00
f1 (the focal length of the front group G ₁₁₎ = 1342.77
BF / (f / | f1 |) = 4601.00

  FIG. 2 is a diagram illustrating various aberrations of the fish-eye lens according to Example 1 with respect to the d-line (λ = 587.56 nm). In the astigmatism diagrams, S and M represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively. Further, in the distortion diagram, the shift amount by the equal solid angle projection method (Y = 2 × f × sin (θ / 2)) is displayed (Y: image height, f: focal length of the entire optical system, θ: half angle of view).

FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the fisheye lens according to the second embodiment. This fisheye lens includes, in order from the object side (not shown), a front group G ₂₁ having a negative refractive power, an optical aperture S, and a rear group G ₂₂ having a positive refractive power. The rear group G ₂₂ is arranged with a space from the front group G ₂₁ .

The front group G ₂₁ includes, in order from the object side, a first lens L ₂₁₁ having a negative refractive power, a second lens L ₂₁₂ having a negative refractive power, a third lens L ₂₁₃ having a positive refractive power, Are arranged and configured.

The rear group G ₂₂ includes, in order from the object side, a first lens L ₂₂₁ having a negative refractive power, a second lens L ₂₂₂ having a positive refractive power, a third lens L ₂₂₃ having a positive refractive power, A fourth lens L ₂₂₄ having a negative refractive power and a fifth lens L ₂₂₅ having a positive refractive power are arranged. The first lens L ₂₂₁ and the second lens L ₂₂₂ are cemented. The third lens L ₂₂₃ and the fourth lens L ₂₂₄ are also cemented.

  Various numerical data related to the fisheye lens according to Example 2 are shown below.

f (focal length of the whole fisheye lens) = 10.13
Fno. (F number) = 2.88
2ω (angle of view) = 181.00

(Lens data)
r ₁ = 52.649
d ₁ = 2.000 nd ₁ = 1.835 νd ₁ = 42.72
r ₂ = 13.727
d ₂ = 18.639
r ₃ = 864.452
d ₃ = 1.500 nd ₂ = 1.835 νd ₂ = 42.72
r ₄ = 16.178
d ₄ = 9.561
r ₅ = 24.957
d ₅ = 2.967 nd ₃ = 1.847 νd ₃ = 23.78
r ₆ = -89.732
d ₆ = 8.000
r ₇ = ∞ (aperture)
d ₇ = 2.000
r ₈ = -385.019
d ₈ = 1.000 nd ₄ = 1.835 νd ₄ = 42.72
r ₉ = 14.251
d ₉ = 3.498 nd ₅ = 1.569 νd ₅ = 56.04
r ₁₀ = -37.816
d ₁₀ = 0.200
r ₁₁ = -712.655
d ₁₁ = 4.435 nd ₆ = 1.517 νd ₆ = 64.20
r ₁₂ = -10.052
d ₁₂ = 1.000 nd ₇ = 1.847 νd ₇ = 23.78
r ₁₃ = -25.161
d ₁₃ = 0.200
r ₁₄ = 94.658
d ₁₄ = 5.000 nd ₈ = 1.517 νd ₈ = 64.20
r ₁₅ = -19.165
d ₁₅ = 35.000
r ₁₆ = ∞ (imaging plane)

(Numerical values related to conditional expression (1))
Gn1B (air distance from the first lens L ₂₁₁ to the second lens L ₂₁₂ ) = 18.64
| F1 | /Gn1B=618.81

(Numerical value related to conditional expression (2))
Gn2B (the air distance from the second lens L ₂₁₂ to the third lens L ₂₁₃ ) = 9.56
Σd (total length of optical system) = 60.00
(Gn1B + Gn2B) /Σd=0.47

(Numerical values related to conditional expression (3))
BF (back focus) = 35.00
f1 (the focal length of the front group G ₂₁₎ = - 11533.60
BF / (f / | f1 |) = 39848.14

  FIG. 4 is a diagram illustrating various aberrations of the fish-eye lens according to Example 2 with respect to the d-line (λ = 587.56 nm). In the astigmatism diagrams, S and M represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively. Further, in the distortion diagram, the shift amount by the equal solid angle projection method (Y = 2 × f × sin (θ / 2)) is displayed (Y: image height, f: focal length of the entire optical system, θ: half angle of view).

FIG. 5 is a cross-sectional view along the optical axis showing the configuration of the fisheye lens according to the third embodiment. This fish-eye lens includes, in order from the object side (not shown), a front group G ₃₁ having a negative refractive power, an optical aperture S, and a rear group G ₃₂ having a positive refractive power. The rear group G ₃₂ is spaced relative to the front group G _31.

The front group G ₃₁ includes, in order from the object side, a first lens L ₃₁₁ having a negative refractive power, a second lens L ₃₁₂ having a negative refractive power, a third lens L ₃₁₃ having a positive refractive power, Are arranged and configured.

The rear group G ₃₂ includes, in order from the object side, a first lens L ₃₂₁ having a negative refractive power, a second lens L ₃₂₂ having a positive refractive power, a third lens L ₃₂₃ having a positive refractive power, A fourth lens L ₃₂₄ having a negative refractive power and a fifth lens L ₃₂₅ having a positive refractive power are arranged. The first lens L ₃₂₁ and the second lens L ₃₂₂ are cemented. The third lens L ₃₂₃ and the fourth lens L ₃₂₄ are also cemented.

  Various numerical data related to the fisheye lens according to Example 3 are shown below.

f (focal length of the whole fisheye lens system) = 9.71
Fno. (F number) = 2.89
2ω (angle of view) = 181.00

(Lens data)
r ₁ = 41.319
d ₁ = 2.000 nd ₁ = 1.835 νd ₁ = 42.72
r ₂ = 11.869
d ₂ = 14.730
r ₃ = -169.463
d ₃ = 1.500 nd ₂ = 1.835 νd ₂ = 42.72
r ₄ = 16.222
d ₄ = 9.981
r ₅ = 28.509
d ₅ = 3.850 nd ₃ = 1.847 νd ₃ = 23.78
r ₆ = -61.058
d ₆ = 8.000
r ₇ = ∞ (aperture)
d ₇ = 2.000
r ₈ = 158.181
d ₈ = 1.000 nd ₄ = 1.835 νd ₄ = 42.72
r ₉ = 10.937
d ₉ = 4.601 nd ₅ = 1.569 νd ₅ = 56.04
r ₁₀ = -18.731
d ₁₀ = 0.200
r ₁₁ = 106.697
d ₁₁ = 5.095 nd ₆ = 1.517 νd ₆ = 64.20
r ₁₂ = -9.051
d ₁₂ = 1.000 nd ₇ = 1.904 νd ₇ = 31.32
r ₁₃ = -59.451
d ₁₃ = 0.200
r ₁₄ = -124.297
d ₁₄ = 5.844 nd ₈ = 1.517 νd ₈ = 64.20
r ₁₅ = -12.181
d ₁₅ = 35.000
r ₁₆ = ∞ (imaging plane)

(Numerical values related to conditional expression (1))
Gn1B (the air gap from the first lens L ₃₁₁ to the second lens L ₃₁₂ ) = 14.73
| F1 | /Gn1B=12.36

(Numerical value related to conditional expression (2))
Gn2B (the air distance from the second lens L ₃₁₂ to the third lens L ₃₁₃ ) = 9.98
Σd (total length of optical system) = 60.00
(Gn1B + Gn2B) /Σd=0.41

(Numerical values related to conditional expression (3))
BF (back focus) = 35.00
f1 (the focal length of the front group G ₃₁₎ = - 182.13
BF / (f / | f1 |) = 656.65

  FIG. 6 is a diagram illustrating various aberrations of the fish-eye lens according to Example 3 with respect to the d-line (λ = 587.56 nm). In the astigmatism diagrams, S and M represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively. Further, in the distortion diagram, the shift amount by the equal solid angle projection method (Y = 2 × f × sin (θ / 2)) is displayed (Y: image height, f: focal length of the entire optical system, θ: half angle of view).

FIG. 7 is a cross-sectional view along the optical axis showing the configuration of the fisheye lens according to the fourth example. The fisheye lens includes, in order from the object side (not shown), a front group G ₄₁ having a negative refractive power, an optical aperture S, and a rear group G ₄₂ having a positive refractive power. The rear group G ₄₂ is spaced relative to the front group G _41.

The front group _G41 includes, in order from the object side, a first lens _L411 having a negative refractive power, a second lens _L412 having a negative refractive power, a third lens _L413 having a positive refractive power, Are arranged and configured.

The rear group G ₄₂ includes, in order from the object side, a first lens L ₄₂₁ having a negative refractive power, a second lens L ₄₂₂ having a positive refractive power, a third lens L ₄₂₃ having a positive refractive power, A fourth lens L ₄₂₄ having a negative refractive power and a fifth lens L ₄₂₅ having a positive refractive power are arranged. The first lens L ₄₂₁ and the second lens L ₄₂₂ are cemented. The third lens L ₄₂₃ and the fourth lens L ₄₂₄ are also cemented.

  Various numerical data related to the fisheye lens according to Example 4 are shown below.

f (focal length of the whole fisheye lens) = 10.31
Fno. (F number) = 2.88
2ω (angle of view) = 181.00

(Lens data)
r ₁ = 61.013
d ₁ = 2.000 nd ₁ = 1.773 νd ₁ = 49.62
r ₂ = 13.628
d ₂ = 16.466
r ₃ = 190.095
d ₃ = 1.500 nd ₂ = 1.773 νd ₂ = 49.62
r ₄ = 17.569
d ₄ = 12.394
r ₅ = 27.079
d ₅ = 2.743 nd ₃ = 1.847 νd ₃ = 23.78
r ₆ = -187.828
d ₆ = 8.000
r ₇ = ∞ (aperture)
d ₇ = 2.000
r ₈ = -114.164
d ₈ = 1.000 nd ₄ = 1.835 νd ₄ = 42.72
r ₉ = 15.547
d ₉ = 3.440 nd ₅ = 1.569 νd ₅ = 56.04
r ₁₀ = -32.849
d ₁₀ = 0.200
r ₁₁ = 6833.044
d ₁₁ = 4.058 nd ₆ = 1.517 νd ₆ = 64.20
r ₁₂ = -11.254
d ₁₂ = 1.000 nd ₇ = 1.847 νd ₇ = 23.78
r ₁₃ = -26.607
d ₁₃ = 0.200
r ₁₄ = 72.111
d ₁₄ = 5.000 nd ₈ = 1.517 νd ₈ = 64.20
r ₁₅ = -21.587
d ₁₅ = 35.000
r ₁₆ = ∞ (imaging plane)

(Numerical values related to conditional expression (1))
Gn1B (air distance from the first lens L ₄₁₁ to the second lens L ₄₁₂ ) = 16.47
| F1 | /Gn1B=102.66

(Numerical value related to conditional expression (2))
Gn2B (the air gap from the second lens L ₄₁₂ to the third lens L ₄₁₃ ) = 12.39
Σd (total length of optical system) = 60.00
(Gn1B + Gn2B) /Σd=0.48

(Numerical values related to conditional expression (3))
BF (back focus) = 35.00
f1 (the focal length of the front group G ₄₁₎ = - 1690.40
BF / (f / | f1 |) = 5740.12

  FIG. 8 is a diagram illustrating various aberrations of the fish-eye lens according to Example 4 with respect to the d-line (λ = 587.56 nm). In the astigmatism diagrams, S and M represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively. Further, in the distortion diagram, the shift amount by the equal solid angle projection method (Y = 2 × f × sin (θ / 2)) is displayed (Y: image height, f: focal length of the entire optical system, θ: half angle of view).

FIG. 9 is a cross-sectional view along the optical axis showing the configuration of the fisheye lens according to the fifth example. This fisheye lens includes, in order from the object side (not shown), a front group G ₅₁ having a negative refractive power, an optical aperture S, and a rear group G ₅₂ having a positive refractive power. The rear group G ₅₂ is arranged with a space from the front group G ₅₁ .

The front group G ₅₁ includes, in order from the object side, a first lens L ₅₁₁ having a negative refractive power, a second lens L ₅₁₂ having a negative refractive power, a third lens L ₅₁₃ having a positive refractive power, A fourth lens L ₅₁₄ having a positive refractive power and a fifth lens L ₅₁₅ having a negative refractive power are arranged. The second lens L ₅₁₂ and the third lens L ₅₁₃ are cemented. Aspheric surfaces are formed on both surfaces of the fourth lens L ₅₁₄ and both surfaces of the fifth lens L ₅₁₅ , respectively.

The rear group G ₅₂ includes, in order from the object side, a first lens L ₅₂₁ having a negative refractive power, a second lens L ₅₂₂ having a positive refractive power, a third lens L ₅₂₃ having a negative refractive power, A fourth lens L ₅₂₄ having a positive refractive power, a fifth lens L ₅₂₅ having a negative refractive power, and a sixth lens L ₅₂₆ having a positive refractive power are arranged. The first lens L ₅₂₁ and the second lens L ₅₂₂ are cemented. The third lens L ₅₂₃ , the fourth lens L _524, and the fifth lens L ₅₂₅ are also cemented.

  Various numerical data relating to the fisheye lens according to Example 5 will be described below.

f (focal length of the whole fisheye lens system) = 10.00
Fno. (F number) = 1.84
2ω (angle of view) = 181.00

(Lens data)
r ₁ = 55.944
d ₁ = 2.000 nd ₁ = 1.835 νd ₁ = 42.72
r ₂ = 18,000
d ₂ = 18,000
r ₃ = -129.530
d ₃ = 1.800 nd ₂ = 1.835 νd ₂ = 42.72
r ₄ = 12.000
d ₄ = 3.853 nd ₃ = 1.593 νd ₃ = 35.45
r ₅ = 18.690
d ₅ = 7.402
r ₆ = 52.952 (aspherical surface)
d ₆ = 3.577 nd ₄ = 1.821 νd ₄ = 24.06
r ₇ = -26.214 (aspherical surface)
d ₇ = 5.885
r ₈ = 70.904 (aspherical surface)
d ₈ = 1.800 nd ₅ = 0.182 νd ₅ = 24.06
r ₉ = 55.352 (aspherical surface)
d ₉ = 2.500
r ₁₀ = ∞ (aperture)
d ₁₀ = 2.000
r ₁₁ = -33.525
d ₁₁ = 1.000 nd ₆ = 1.835 νd ₆ = 42.72
r ₁₂ = 22.892
d ₁₂ = 4.540 nd ₇ = 1.517 νd ₇ = 64.20
r ₁₃ = -29.656
d ₁₃ = 0.200
r ₁₄ = 51.093
d ₁₄ = 1.000 nd ₈ = 1.847 νd ₈ = 23.78
r ₁₅ = 23.535
d ₁₅ = 7.457 nd ₉ = 1.517 νd ₉ = 64.20
r ₁₆ = -13.647
d ₁₆ = 1.800 nd ₁₀ = 1.847 νd ₁₀ = 23.78
r ₁₇ = -22.100
d ₁₇ = 0.100
r ₁₈ = 67.935
d ₁₈ = 5.086 nd ₁₁ = 1.639 νd ₁₁ = 55.45
r ₁₉ = -35.590
d ₁₉ = 35.000
r ₂₀ = ∞ (imaging plane)

Cone coefficient (k) and aspheric coefficient (A, B, C, D)
(Sixth surface)
k = 0,
A = 7.7924 × 10 ⁻⁶ , B = 2.3492 × 10 ⁻⁷ ,
C = -1.0597 × 10 ^-9 , D = -9.1928 × 10 ^-13
(Seventh side)
k = 0,
A = 5.7805 × 10 ^-5 , B = -9.1061 × 10 ^-8 ,
C = -4.6051 × 10 ⁻¹⁰ , D = 1.7741 × 10 ⁻¹³
(8th page)
k = 0,
A = 2.9260 × 10 ⁻⁴ , B = −2.2708 × 10 ⁻⁶ ,
C = 1.4574 × 10 ⁻⁸ , D = −8.1449 × 10 ⁻¹¹
(9th page)
k = 0,
A = 2.5034 × 10 ⁻⁴ , B = −1.7984 × 10 ⁻⁶ ,
C = 1.0737 × 10 ⁻⁸ , D = −8.0718 × 10 ⁻¹¹

(Numerical values related to conditional expression (1))
Gn1B (the air gap from the first lens L ₅₁₁ to the second lens L ₅₁₂ ) = 18.00
| F1 | /Gn1B=11.12

(Numerical value related to conditional expression (2))
Gn2B (the air distance from the third lens L ₅₁₃ to the fourth lens L ₅₁₄ ) = 7.40
Σd (total length of optical system) = 70.00
(Gn1B + Gn2B) /Σd=0.36

(Numerical values related to conditional expression (3))
BF (back focus) = 35.00
f1 (the focal length of the front group G ₅₁₎ = - 200.10
BF / (f / | f1 |) = 700.35

  FIG. 10 is a diagram illustrating various aberrations of the fish-eye lens according to Example 5 with respect to the d-line (λ = 587.56 nm). In the astigmatism diagrams, S and M represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively. Further, in the distortion diagram, the shift amount by the equal solid angle projection method (Y = 2 × f × sin (θ / 2)) is displayed (Y: image height, f: focal length of the entire optical system, θ: half angle of view).

In the numerical data in the above embodiments, r ₁ , r ₂ ,... Are the radius of curvature of each lens and diaphragm surface, d ₁ , d ₂ ,. ... Nd ₁ , nd ₂ ,... Is the refractive index of each lens with respect to the d-line (λ = 587.56 nm), and νd ₁ , νd ₂ ,. Abbe number with respect to (λ = 587.56 nm). The unit of length is all “mm”, and the unit of angle is “°”.

  In addition, each of the above aspheric shapes has a depth of the aspheric surface Z, a curvature c (1 / r), a height from the optical axis h, a cone coefficient k, 4th order, 6th order, 8th order, 10th order. When the following aspheric coefficients are A, B, C, and D, respectively, and the traveling direction of light is positive, the following aspheric coefficients are expressed by the following equations.

  As described above, the fish-eye lens of each of the above embodiments is a small fish-eye lens having a sufficient back focus and high optical performance by satisfying each conditional expression. This fisheye lens is suitable for a small digital camera, particularly a digital single lens reflex camera. Further, this fisheye lens can be mounted not only on a digital camera but also on a conventional single-lens reflex camera of 35 mm film size. In addition, by arranging a lens or a cemented lens in which an aspheric surface is appropriately formed, the aberration correction capability can be improved with a small number of lenses.

  As described above, the fisheye lens according to the present invention is useful for a digital camera that is small and requires high optical performance, and is particularly suitable for a digital single-lens reflex camera.

_{G 11, G 21, G 31} , G 41, G 51 front group _{G 12, G 22, G 32} , G 42, G 52 RLG _{L 111, L 121, L 211} , L 221, L 311, L 321, L ₄₁₁ , L ₄₂₁ , L ₅₁₁ , L ₅₂₁ First lens L ₁₁₂ , L ₁₂₂ , L ₂₁₂ , L ₂₂₂ , L ₃₁₂ , L ₃₂₂ , L ₄₁₂ , L ₄₂₂ , L ₅₁₂ , L ₅₂₂ Second lens L ₁₁₃ , L ₁₂₃ , L ₂₁₃ , L ₂₂₃ , L ₃₁₃ , L ₃₂₃ , L ₄₁₃ , L ₄₂₃ , L ₅₁₃ , L ₅₂₃ Third lens L ₁₁₄ , L ₁₂₄ , L ₂₂₄ , L ₃₂₄ , L ₄₂₄ , L ₅₁₄ , L ₅₂₄ fourth Lenses L ₁₂₅ , L ₂₂₅ , L ₃₂₅ , L ₄₂₅ , L ₅₁₅ , L ₅₂₅ Fifth lens L ₅₂₆ Sixth lens S Optical aperture

Claims (2)

In order from the object side, a front group having a plurality of negative lens components and having negative or positive refractive power as a whole, an optical aperture, and an axial interval with respect to the front group are arranged and are positive as a whole. A rear group having refractive power,
A fish-eye lens satisfying the following conditional expression:
(1) 9.0 ≦ | f1 | / Gn1B
(2) 0.33 ≦ (Gn1B + Gn2B) /Σd≦0.70
Where f1 is the focal length of the front group, Gn1B is the air distance from the lens closest to the object side as the negative lens component to the next lens component in the front group, and Gn2B is the negative lens component in the front group , Σd represents the distance from the lens surface closest to the object side to the lens surface closest to the image side in the fisheye lens. The fisheye lens according to claim 1, wherein the following conditional expression is satisfied.
(3) 600 ≦ BF / (f / | f1 |)
Where BF is the back focus of the fisheye lens, f is the focal length of the entire fisheye lens system, and f1 is the focal length of the front group.

Images