JP2000321490A - Photographic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photographic lens which has a >=60 deg. photographic view angle without degrading the optical performance. SOLUTION: This photographic lens 10 has six-group constitution of a 1st lens group 11 to a 6th lens group 16 having negative, positive, positive, negative, positive, and negative power values in this order from the object side, and a stop 17 is provided between the 3rd lens group 13 and 4th lens group 14. The 1st lens group 11 is composed of a biconcave lens and the 6th lens group 16 has an aspherical concave surface on the object side. The 3rd lens group 13 consists of a cemented lens of an object side biconvex lens and an image- plane side meniscus negative lens and the 4th lens group 14 is formed of a cemented lens of an object side biconcave lens and an image-plane side biconvex lens. The photographic lens 10 has a >=60 deg. photographic field angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The above is related to the large-diameter photographic lens.

[0002]

2. Description of the Related Art As a large-diameter photographic lens, a Gauss-type lens is generally known. In a Gauss type photographic lens, the focal length becomes longer as the aperture ratio becomes larger. In a standard lens of F2 to F1.4, the focal length becomes 5 mm.
Generally, it is configured to be about 0 mm. For this reason,
Recently, a large-diameter photographic lens having a focal length of about 35 mm in which the entire length of the lens is shortened has been desired.

[0003]

However, in the case of a conventional Gaussian type photographic lens, when the focal length is set to about 35 mm, it is limited to about F2.0 and a brighter photographic lens is to be formed. In addition, coma aberration and field curvature are deteriorated, and these cannot be suppressed.

The present invention has been made in consideration of the above circumstances, and has a photographic angle of view of 60 without deteriorating optical performance.
The objective is to provide a photographic lens of at least °.

[0005]

In order to achieve the above object, a photographic lens according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a positive lens unit. The third lens group includes a third lens group having a refractive power, a fourth lens group having a negative refractive power, a fifth lens group having a positive refractive power, and a sixth lens group having a negative refractive power. An aperture is provided between the fourth lens group, the first lens group is composed of a biconcave lens, and the lens surface on the object side of the sixth lens group is an aspheric concave surface.

Further, the third lens group is arranged in order from the object side.
It is composed of a cemented lens of a biconvex lens and a meniscus negative lens. Further, the fourth lens group includes, in order from the object side, a cemented lens of a biconcave lens and a biconvex lens.

[0007]

The first lens group is a biconcave lens, and the object side lens surface of the negative lens constituting the sixth lens group is formed to be aspherical, so that spherical aberration can be achieved without increasing the lens diameter. Can be kept in a good state, and deterioration of the field curvature can be suppressed.

The third lens group is constituted by a cemented lens of a biconvex lens and a negative meniscus lens.
By forming the fourth lens group by a cemented lens of a biconcave lens and a biconvex lens, it is possible to suppress the occurrence of chromatic aberration and astigmatism. Therefore, by setting the lens configuration as described above, it is possible to maintain a good balance of various aberrations.

[0009]

FIG. 1 shows a lens configuration of a photographic lens according to the present invention. The photographic lens 10 is 60 °
A large-aperture photographic lens having the above-mentioned angle of view, comprising, in order from the object side, a first lens group 11 having a negative refractive power, a second lens group 12 having a positive refractive power, and a third lens having a positive refractive power. Group 1
3, the fourth lens group 14 having a negative refractive power, and the fifth lens group 14 having a positive refractive power
The sixth lens group 15 includes a lens group 15 and a sixth lens group 16 having a negative refractive power. Third lens group 13 and fourth lens group 14
An aperture 17 is provided between the two. First lens group 11
Consists of a biconcave lens. The sixth lens group 16 has an aspherical concave surface on the object side lens surface 16a, and includes a negative meniscus lens.

The third lens group 13 includes a biconvex lens 13a.
And a cemented lens of the negative meniscus lens 13b. The fourth lens group 14 includes a biconcave lens 14.
a and a biconvex lens 14b.

The photographic lens 10 has a focal length f of 33.
mm ≦ f ≦ 38 mm, and the aperture ratio is 1:
1.6 or more.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment The specifications of the photographic lens of the first embodiment shown in FIG. 1 are as follows. f = 36.05 mm F _NO = 1.64 In the above data, f is the focal length of the photographic lens, F _NO
Indicates an F number.

Table 1 below shows the lens data of the photographic lens of the first embodiment. The surface number i is a number assigned to each lens surface in order from the object side, and the surface distance D represents the lens thickness or air space between the next surface (unit is m).
m).

[0014]

[Table 1]

The symbol "*" shown in the column of radius of curvature represents an aspherical surface. Aspheric surface condition Z = ch ² / [1+ {1- (1 + K) c 2 h 2} 1/2 ]
+ Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰ . In the equation, c represents the reciprocal of the radius of curvature (= 1 / R), and h represents the height of the light beam from the optical axis. Table 2 shows the aspheric coefficient.

[0016]

[Table 2]

FIG. 2 shows aberration diagrams of the photographic lens of the first embodiment. In the drawing, (A) represents spherical aberration, (B) represents astigmatism, and (C) represents distortion. Symbols S and T in the astigmatism diagram (B) in the figure represent aberrations with respect to the spherical and meridional image planes, respectively.

[Second Embodiment] FIG. 3 shows a second embodiment of the photographic lens of the present invention. The reference numerals in FIG. 3 are used in common with the photographic lens 10 shown in FIG. In the photographic lens of the second embodiment, the sixth lens group 16 is constituted by a biconcave lens.

The specifications of the photographic lens of the second embodiment are as follows. f = 36.05mm F _NO = 1.73

Table 3 shows the lens data of the photographic lens of the second embodiment, and Table 4 shows the aspheric coefficient.

[0021]

[Table 3]

[0022]

[Table 4]

FIG. 4 shows aberration diagrams of the photographic lens of the second embodiment.

[Third Embodiment] FIG. 5 shows a third embodiment of the photographic lens of the present invention. The reference numerals in FIG. 5 are used in common with the photographic lens 10 shown in FIG. In the photographic lens of the third embodiment, the second lens group 12 is composed of a meniscus positive lens having a convex surface facing the object side, and the fourth lens group 1
Reference numeral 4 denotes a cemented lens of a biconcave lens 24a on the object side and a positive meniscus lens 24b on the image side.
The sixth lens group 16 is constituted by a negative meniscus lens, as in the first embodiment.

The specifications of the photographic lens of the third embodiment are as follows. f = 35.42 mm F _NO = 1.75

Table 5 shows the lens data of the photographic lens of the third embodiment, and Table 6 shows the aspheric coefficient.

[0027]

[Table 5]

[0028]

[Table 6]

FIG. 6 shows aberration diagrams of the photographic lens of the third embodiment.

[0030]

As described above, according to the photographic lens of the present invention, the first lens group is composed of six groups having negative, positive, positive, negative, positive, and negative power in order from the object side. By forming a biconcave lens and forming the object-side lens surface of the negative lens constituting the sixth lens group into an aspherical shape, the spherical aberration can be kept in a good state without increasing the lens diameter. In addition, it is possible to suppress deterioration of field curvature.

The third lens group is constituted by a cemented lens of a biconvex lens and a negative meniscus lens.
By forming the fourth lens group with a cemented lens of a biconcave lens and a biconvex lens, it is possible to suppress the occurrence of chromatic aberration and astigmatism, and to maintain a good balance of various aberrations.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram showing a first embodiment of a photographic lens of the present invention.

FIG. 2 is an aberration diagram of the photographic lens shown in FIG. 1;
(A) represents spherical aberration, (B) represents astigmatism, and (C) represents distortion.

FIG. 3 is a lens configuration diagram showing a second embodiment of the photographic lens of the present invention.

4 is an aberration diagram of the photographic lens shown in FIG.

FIG. 5 is a lens configuration diagram showing a third embodiment of the photographic lens of the present invention.

6 is an aberration diagram of the photographic lens shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 photographic lens 11 first lens group 12 second lens group 13 third lens group 14 fourth lens group 15 fifth lens group 16 sixth lens group 17 aperture

Claims (3)

[Claims] 1. A photographic lens having a photographic angle of view of 60 ° or more, a six-group configuration, and a stop provided between a third group and a fourth group, wherein each lens group has a negative order in order from the object side. , Positive, positive, negative, positive,
A photographic lens having negative power, wherein the first lens group comprises a biconcave lens, and the sixth lens group has a concave surface comprising an aspheric surface facing the object side. 2. The photographic lens according to claim 1, wherein said third lens group comprises a cemented lens, and said cemented lens comprises a biconvex lens on the object side and a negative meniscus lens on the image plane side. 3. The photographic lens according to claim 2, wherein said fourth lens group comprises a cemented lens, and said cemented lens comprises a biconcave lens on the object side and a biconvex lens on the image plane side.