JP2599311B2 - Super wide angle lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-wide-angle lens having a large distortion, and more particularly to an ultra-wide-angle lens which is most suitable for a monitor camera, an on-vehicle television camera and the like.

[0002]

2. Description of the Related Art In general, it is desired that a lens used for a surveillance or on-vehicle television camera is lightweight, compact and has a large angle of view.
In order to cover a wide field of view, an object having an angle of view of 130 ° or more has been desired.

[0003]

However, conventional ultra-wide-angle lenses generally have 8 to 10 or more lenses, such as those disclosed in JP-A-1-113714 and JP-A-1-156711. There are many structures.

[0004] Therefore, the conventional ultra-wide-angle lens has a problem that the cost is high and the total number of lenses is long because of the large number of lenses, which is not suitable for downsizing the camera. In many cases, the angle of view is 130 ° or less, which makes it impossible to meet recent demands.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a wide angle of view of 130 ° and an FN with a small number of lens elements such as seven in six groups.
o. It is an object of the present invention to obtain an ultra-wide-angle lens having a sufficient brightness of 2.1, a short overall lens length, and excellent correction of various aberrations.

In summary, the super-wide-angle lens according to the present invention comprises, in order from the object side, a first group of a negative meniscus single lens, a second group of a negative meniscus single lens, and a concave meniscus single lens. Third of negative lens consisting of lens
Group, a fourth group of a positive lens composed of a biconvex single lens, a fifth group of a positive lens composed of a biconvex single lens, and a positive lens having at least one aspheric surface formed by laminating a concave meniscus lens and a biconvex lens. The sixth group is composed of seven elements in six groups, and satisfies the conditions defined in Expressions 1 to 3.

[Equation 1] f <| f _1,2 | <2f

[ _Equation 2] ν _6N <ν _6P , N _6N > N _6P

| R ₁ | <| R ₂ | where f: combined focal length of the entire system f _1,2 : combined focal length of the first and second groups ν _6N : Abbe number of the concave meniscus lens of the sixth group ν _6P : Abbe number of the biconvex lens of the sixth group N _6N : refractive index of the concave meniscus lens of the sixth group N _6P : refractive index of the biconvex lens of the sixth group R ₁ : curvature of the object side surface of the fifth group Radius R ₂ : radius of curvature of the image-side surface of the fifth lens unit

[0007]

According to the present invention, by using at least one aspherical lens of six groups, distortion and coma at an ultra-wide angle are corrected, and the number of lens elements is reduced.
The overall length of the lens has been reduced.

The condition of Equation 1 is a condition for forming the front group divergence system, and is a condition relating to astigmatism, coma aberration, and miniaturization of the entire system. When | f ₁ | is shorter than f, the coma generated in the divergent system becomes extremely large, and it becomes difficult to correct the aberration even if a lens is used for the aspherical surface. Also, | f ₁ |
When f exceeds f, the back focus becomes short, and it becomes difficult to correct astigmatism.

The condition of Equation 2 is a condition relating to correction of chromatic aberration. If this condition is not satisfied, chromatic aberration will increase, making correction difficult.

The condition of Equation 3 is a condition for correcting astigmatism and coma in the rear group convergence system. If this condition is not satisfied, astigmatism and coma will increase significantly, making it difficult to correct aberrations even with an aspheric lens.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. As shown in the optical axis cross-sectional views of FIG. 1 (first embodiment) and FIG. 6 (second embodiment), the super-wide-angle lens of the present invention is a negative lens composed of a concave meniscus single lens 1 in order from the object side. The first group, the second group of the negative lens composed of the concave meniscus single lens 2, and the third group of the negative lens composed of the concave meniscus single lens 3
Group, a fourth group of positive lenses composed of a biconvex single lens 4, a fifth group of positive lenses composed of a biconvex single lens 5, at least one lens composed of a cemented concave meniscus lens 6 and a biconvex lens 7.
The sixth lens unit includes a sixth lens unit including a sixth lens unit having a surface aspherical surface, and satisfies the above-described conditions defined in Expressions 1 to 3.

[0012] Further, in the first and second embodiments described above, the surface r ₁₃ of the image plane side of the biconvex lens 7 forms an aspherical surface,
The aspheric shape is defined by the following equation (4).

[0013]

Equation 4] ^{Cy 2 Z = ────────────── + Dy 4} + Ey 5 + Fy 8 + Gy 10 1+ (1-εC 2 y 2) 1/2 Here, in Equation 4, Z: The distance from the tangent plane of the aspherical vertex of the point on the aspheric surface whose height from the optical axis is y. y: height from the optical axis. C: curvature of the aspherical vertex (= 1 / r). ε: conical constant. D, E, F, G: aspherical surface coefficients. Shall be expressed.

Next, specific numerical values of the first embodiment are shown in Table 1.
Table 2 shows specific numerical values of the second embodiment. In the table, r _{1 to} r ₁₃ indicate the radius of curvature of each lens surface in order from the object side, d ₁ to d ₁₂ indicate the wall pressure of each lens or the air gap between each lens surface in order from the object side, and n _{1 to} n ₇ indicate the refractive index of each lens sequentially from the object side, and ν _{1 to} ν ₇ indicate the Abbe number of each lens sequentially from the object side.

FIG. 2 shows the spherical aberration of the first embodiment, FIG. 3 shows the astigmatism of the first embodiment, and FIG. 4 shows the distortion of the first embodiment.
5 is chromatic aberration of the first embodiment, FIG. 7 is spherical aberration of the second embodiment, FIG. 8 is astigmatism of the second embodiment, FIG. 9 is distortion of the second embodiment, and FIG. The chromatic aberrations of the examples are respectively shown.
In these characteristic curves, d is the d line, F is the F line,
C indicates the C line, and SC indicates the sign condition. 3 and 8, S is the sagittal direction,
M indicates the meridional direction.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

As described above, according to the present invention, as can be seen from the above-described embodiment and the aberration curve, a wide lens having an angle of view of 130 ° or more can be obtained even though the number of lens elements is as small as 6 elements and 7 elements. It covers a wide range, has an F-number of 2.1, has a sufficient brightness, has a short overall lens length, and can provide an ultra-wide-angle lens with excellent correction of various aberrations. Characteristics suitable as a lens for a television camera can be obtained.

[Brief description of the drawings]

FIG. 1 is an optical axis cross-sectional view of an ultra-wide-angle lens according to a first example of the present invention.

FIG. 2 is a diagram showing the spherical aberration of the first embodiment.

FIG. 3 is a diagram showing astigmatism of the first embodiment.

FIG. 4 is a diagram showing the distortion of the first embodiment.

FIG. 5 is a diagram illustrating chromatic aberration according to the first embodiment.

FIG. 6 is an optical-axis sectional view of an ultra-wide-angle lens according to a second embodiment of the present invention.

FIG. 7 is a diagram showing the spherical aberration of the second embodiment.

FIG. 8 is a diagram showing astigmatism of the second embodiment.

FIG. 9 is a diagram illustrating distortion of the second embodiment.

FIG. 10 is a diagram showing chromatic aberration according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens 7 7th lens

Claims (1)

(57) [Claims] 1. A first group of negative lenses composed of a concave meniscus single lens, a second group of negative lenses composed of a concave meniscus single lens, a third group of negative lenses composed of a concave meniscus single lens, in order from the object side. A fourth group of positive lenses formed of a biconvex single lens, a fifth group of positive lenses formed of a biconvex single lens, and a sixth group of positive lenses formed by bonding a concave meniscus lens and a biconvex lens and having at least one aspheric surface. An ultra-wide-angle lens comprising seven elements in six groups and satisfying the following conditions (1), (2) and (3). (1) f <| f _1,2 | <2f (2) ν _6N <ν _6P , N _6N > N _6P (3) | R ₁ | <| R ₂ | where f: composite focal length f of the whole system _1,2 : Composite focal length of the first and second groups ν _6N : Abbe number of the concave meniscus lens of the sixth group ν _6P : Abbe number of the biconvex lens of the sixth group N _6N : Refraction of the concave meniscus lens of the sixth group Rate N _6P : Refractive index of the biconvex lens of the sixth group R ₁ : Radius of curvature of the object-side surface of the fifth group R ₂ : Curvature radius of the image-side surface of the fifth group