JPH08110465A - Photographing lens - Google Patents

Abstract

PURPOSE: To provide a photographing lens composed of two spherical lenses and can be used by the viewing angle of a standard lens having a half viewing angle of 15 deg.-30 deg.. CONSTITUTION: This lens is composed of two spherical lenses arranging a negative meniscus lens 11 whose convex surface confronts the side of an object surface 13 in the front and a positive convex lens 12 in the rear. By representing the radii of curvature of the front and the rear surfaces of the meniscus lens 11 by r1 , r2 , the radius of curvature of the rear surface of the convex lens 12 by r4 , the distance of air gap between two lenses by d2 and the focal distance of two lens system by (f), the conditions: 0.8<|r1 /r2 |<2.0, 0.6<|r1 /r4 |<2.0, 0.2<|d2 /f|<1.0 are satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a photographic lens having a structure of two spherical lenses, and relates to a photographic lens suitable for use in a photographic device such as a television camera, a video camera and a photographic camera.

[0002]

2. Description of the Related Art If a photographic lens provided in a photographic device such as a television camera is composed of a spherical lens, at least three lenses are required.

In other words, in the construction of one or two spherical lenses, the curvature radius of the lens, the lens surface interval, the parameters of the glass material, etc. are insufficient, so that each aberration correction (correction of Seidel 5 aberration and chromatic aberration) is required. It becomes insufficient and it is not possible to obtain a high-performance taking lens.

Therefore, in a taking lens having a lens structure of two or less, each aberration is corrected by using at least one lens as an aspherical lens.

For example, a taking lens having a two-lens structure in which a concave meniscus lens having a negative power from the object side and a biconvex lens having a positive power are sequentially arranged from the object side has been proposed. This taking lens is one in which one surface or both surfaces of the biconvex lens is formed as an aspherical surface.
(See Japanese Patent Laid-Open No. 2-77712)

[0006]

As described above, a photographing lens having a two-lens structure having an aspherical lens has already been proposed. However, since this photographing lens has an aspherical lens, it is costly. It becomes a high taking lens.

As widely known, aspherical lenses include those made of plastic and those made of glass. Since the plastic aspherical lens is produced by molding, the cost of the mold is high, and the cost of the lens itself is high. The lens performance of this aspherical lens is likely to change due to changes in temperature and humidity, which limits the usage environment.

[0008] The glass aspherical lens may be produced by molding or grinding, but the molding is expensive due to the die cost as mentioned above, and the grinding aspherical lens is used. Items are even more expensive due to the increased processing time and labor.

Since the price of the aspherical lens itself is high as described above, the production cost of the taking lens equipped with this lens is inevitably high, and it is practically preferable as a compact taking lens having a two-lens structure. There wasn't.

The present invention was developed in view of the above-mentioned situation, and its purpose is to reduce the production cost and mass-produce it by using a two-lens configuration of a spherical lens, and further, to achieve a standard half field angle of 15 to 30 degrees. An object of the present invention is to provide a taking lens that can be used at a lens angle of view.

[0011]

In order to achieve the above object, a taking lens according to the present invention has a negative meniscus lens with a convex surface facing the object side on the front side and a positive convex lens on the object side. It has an optical system structure composed of two spherical lenses arranged more sequentially.

The meniscus lens and the convex lens described above have a lens structure which satisfies the following conditions. (A) 0.8 <| r ₁ / r ₂ | <2.0 (b) 0.6 <| r ₁ / r ₄ | <2.0 (c) 0.2 <| d ₂ / f | < 1.0 where r _{1 is the} radius of curvature of the object side surface of the meniscus lens r _{2 is the} radius of curvature of the image side surface of the meniscus lens r _{4 is the} radius of curvature of the image side surface of the convex lens d _{2 is the} lens Air gap distance f: Focal length of two lens system

[0013]

The condition (a) is a condition for keeping the balance of the curvature of field, and if the radii of curvature r ₁ and r ₂ are out of this condition, the image plane tilts and astigmatism increases. Lens performance deteriorates.

Conditions (b) and (c) are conditions for keeping the spherical aberration balance and miniaturizing the entire lens system. If the curvature radii r ₁ and r ₄ are out of this condition, the spherical aberration becomes large. Also, it becomes difficult to downsize the entire lens system.

In particular, the condition (c) is that the half angle of view is 15 degrees to 3 degrees.
The condition is to reduce the F number at the angle of view of the standard lens of 0 degree.

By satisfying the above-mentioned conditions (a), (b) and (c), a small lens construction of two lenses can be obtained, and each aberration ( Seidel 5 aberration and chromatic aberration) can be corrected.

As a result, with practically sufficient lens performance,
Since a photographic lens having a small F number can be obtained with the two spherical lens structure, it is possible to provide a photographic lens which is extremely advantageous for cost reduction and mass production.

[0018]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows the arrangement of lenses, 11 is a negative meniscus lens, 12 is a positive convex lens, and these two lenses are spherical lenses.

The meniscus lens 11 has a convex surface on the object plane 1.
In the front lens disposed toward the side of _No. 3, the front surface has a radius of curvature of r ₁ (mm), the rear surface has a radius of curvature r ₂ (mm), and the lens surface distance d ₁ (mm).

The convex lens 12 is a rear lens disposed on the side of the image plane 14 with an air gap distance d ₂ (mm) between the convex lens 12 and the meniscus lens 11, and the radius of curvature of the front surface is r.
₃ (mm), radius of curvature of rear surface is r ₄ , distance between lens surfaces is d
_{It is 3} (mm).

Then, the respective radii of curvature r ₁ , r ₂ , r ₃ , r ₄ , the distances d ₁ , d ₂ , d ₃ and the focal lengths f of all the lenses 11, 12 were concretely determined and implemented. About.

First embodiment, f = 1.0 mm, FNo. = 2.8 radius of curvature r (mm) distance d (mm) refractive index n dispersion ν r ₁ 0.8608 d ₁ 0.40 1.84666 23.8 r ₂ 0.4877 d ₂ 0.27 r ₃ 9.1342 d ₃ 0.27 1.80420 46.5 r ₄ -0.5766

In the case of the first embodiment, | r ₁ / r ₂ | =
1.7650, | r ₁ / r ₄ | = 1.4928, | d ₂ /
f | = 0.27, and the above condition (a),
Satisfies (b) and (c). FIG. 2 shows the spherical aberration, chromatic aberration, distortion and field curvature obtained in this example. In addition, in FIG. 2 and FIGS. 3 to 6 shown below, c, d,
g represents three wavelengths of chromatic aberration, M represents a millideonal image plane, S represents a sagittal image plane, and ω / 2 represents a half field angle.

Second embodiment, f = 1.0 mm, FNo. = 2.8 radius of curvature r (mm) distance d (mm) refractive index n dispersion ν r ₁ 0.6024 d ₁ 0.35 1.84666 23.8 r ₂ 0.3162 d ₂ 0.24 r ₃ 8.0228 d ₃ 0.24 1.80420 46.5 r ₄ -0.5065

In the case of the second embodiment, | r ₁ / r ₂ | =
1.9051, | r ₁ / r ₄ | = 1.1893, | d ₂ /
f | = 0.24, which is the condition (a) described above.
Satisfies (b) and (c). FIG. 3 shows the spherical aberration, chromatic aberration, distortion, and field curvature obtained in this example.

Third embodiment, f = 1.0 mm, FNo. = 2.8 radius of curvature r (mm) distance d (mm) refractive index n dispersion ν r ₁ 0.4197 d ₁ 0.25 1.84666 23.8 r ₂ 0.2984 d ₂ 0.21 r ₃ 5.5892 d ₃ 0.16 1.80420 46.5 r ₄ -0.6225

In the case of the third embodiment, | r ₁ / r ₂ | =
1.4055, | r ₁ / r ₄ | = 0.6742, | d ₂ /
f | = 0.21, which is the condition (a) described above.
Satisfies (b) and (c). FIG. 4 shows the spherical aberration, chromatic aberration, distortion, and field curvature obtained in this example.

Fourth embodiment, f = 1.0 mm, FNo. = 2.8 radius of curvature r (mm) distance d (mm) refractive index n dispersion ν r ₁ 1.2014 d ₁ 0.70 1.84666 23.8 r ₂ 0.8543 d ₂ 0.47 r ₃ 16.0000 d ₃ 0.47 1.80420 46.5 r ₄ -0.6032

In the case of the fourth embodiment, | r ₁ / r ₂ | =
1.4063, | r ₁ / r ₄ | = 1.917, | d ₂ /
f | = 0.47, and the above condition (a),
Satisfies (b) and (c). FIG. 5 shows the spherical aberration, chromatic aberration, distortion and field curvature obtained in this example.

Fifth embodiment, f = 1.0 mm, FNo. = 2.8 radius of curvature r (mm) distance d (mm) refractive index n dispersion ν r ₁ 0.7254 d ₁ 0.42 1.84666 23.8 r ₂ 0.5158 d ₂ 0.29 r ₃ 9.6607 d ₃ 0.28 1.80420 46.5 r ₄ -0.6098

In the case of the fifth embodiment, | r ₁ / r ₂ | =
1.4064, | r ₁ / r ₄ | = 1.896, | d ₂ /
f | = 0.29, which is the condition (a) described above.
Satisfies (b) and (c). FIG. 6 shows the spherical aberration, chromatic aberration, distortion, and field curvature obtained in this example.

Although the respective embodiments have been described above, the rear-side convex lens 12 can be similarly implemented with the object side surface thereof being a flat surface or a concave surface, and the meniscus lens 11 and the convex lens are mainly glass spherical lenses. However, the present invention can also be implemented as a plastic spherical lens.

[0033]

As described above, according to the present invention, it is possible to provide a photographic lens in which each aberration is sufficiently corrected by the two-lens configuration using a spherical lens. Therefore, this type of photographic lens having an aspherical lens is provided. Compared with, the photographic lens is extremely advantageous for lowering production costs and mass production.

Further, according to the present invention, the angle of view of a standard lens having a half angle of view of 15 degrees to 30 degrees can be formed, and the F number can be made small, and the size of the photographing lens can be reduced. It becomes practical when mounted on a photographing device, and is particularly advantageous as a standard angle-of-view lens for a TV camera.

[Brief description of drawings]

FIG. 1 is a diagram showing a lens arrangement configuration example of a taking lens according to the present invention.

FIG. 2 is an aberration curve diagram for the first example.

FIG. 3 is an aberration curve diagram for Example 2.

FIG. 4 is an aberration curve diagram for the third example.

FIG. 5 is an aberration curve diagram for Example 4.

FIG. 6 is an aberration curve diagram for Example 5.

[Explanation of symbols]

11 Negative meniscus lens which is front lens 12 Positive convex lens which is rear lens 13 Object plane 14 Image plane r ₁ , r ₂ , r ₃ , r ₄ Radius of curvature d ₁ d ₃ Distance between lens surfaces d ₂ Between lenses Air gap distance

Claims (1)

[Claims] 1. A negative meniscus lens having a convex surface facing the object side is provided on the front side, and a positive convex lens is provided on the rear side, and two spherical lenses are sequentially arranged from the object side. Is r ₁ , the radius of curvature of the image-side surface of the lens is r ₂ , the radius of curvature of the image-side surface of the convex lens is r ₄ , and the air gap distance between the two lenses is d. ₂ , where f is the focal length of the two lens system, 0.8 <| r ₁ / r ₂ | <2.0 0.6 <| r ₁ / r ₄ | <2.0 0.2 < An imaging lens having a configuration satisfying the condition of | d ₂ / f | <1.0.