JPH06186475A - Photographing lens - Google Patents

Abstract

PURPOSE:To reduce the number of components, to simplify the assembling work and to reduce the price by constituting a single lens of an aspherical plano-convex lens and integrally providing a diaphragm on the plane of the aspherical piano-convex lens. CONSTITUTION:An aspherical piano-convex lens 1 and a diaphragm 2 are provided successively from the object side, a light beam from the aspherical piano- convex lens 1 is stopped down by means of the diaphragm 2 and the image is formed on the side surface 5 of an imaging device 4 such as a CCD through a protection glass 3. In such a case, the aspherical piano-convex lens 1 is made of plastic, arranged so that the convex surface faces the object side and the rear surface on the image plane side is formed on a plane 1a. The diaphragm 2 is integrally formed by printing, etc., on the plane 1a of the rear surface of the aspherical plano-convex lens 1 on the image plane side. A stepped projection part 1b is provided while protruding from the plane 1a so as to facilitate the printing of the diaphragm 2 on the location corresponding to the diaphragm 2 on the plane 1a of the aspherical piano-convex lens 1. The protection glass 3 protects the imaging device 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photographing lens used in a photographing device such as a surveillance camera.

[0002]

2. Description of the Related Art Conventionally, a photographing lens used in a video surveillance camera focuses a light flux from a subject on an image plane of an image pickup device such as a CCD. Such photographing lenses include a front diaphragm type and a rear diaphragm type, and in many cases, each of them is composed of a single lens made of plastic and a diaphragm. For example, a front diaphragm type photographing lens has a structure in which a diaphragm and a meniscus convex lens having a convex surface on the image side are arranged in order from the subject side.
In addition, the rear diaphragm type shooting lens, in order from the subject side,
It has a structure in which a convex meniscus lens with a convex surface on the subject side and a diaphragm are arranged.

[0003]

However, in this conventional taking lens, since the single lens is a meniscus convex lens, it is not possible to provide an aperture on the lens by printing or the like, and the single lens and the aperture are separate parts. Therefore, there is a problem that the number of parts is increased, the assembling work is complicated, and the manufacturing cost is increased. An object of the present invention is to provide a photographic lens that can secure sufficient performance, reduce the number of parts, and simplify the assembling work and reduce the cost.

[0004]

SUMMARY OF THE INVENTION According to the present invention, in a photographing lens having a single lens and a diaphragm, which forms a light flux from a subject on an image plane of an image sensor, the single lens is an aspheric plano-convex lens. However, a diaphragm is integrally provided on the plane of this aspherical plano-convex lens.

[0005]

According to the present invention, since the single lens is composed of an aspherical plano-convex lens, aberration correction is advantageous, sufficient performance can be obtained, and an aperture is formed on the plane of the aspherical plano-convex lens by printing or the like. It can be provided integrally, and the number of parts can be reduced. in this case,
When the paraxial radius of curvature of the aspherical plano-convex lens is R, its center thickness is D, its refractive index is Nd, and its focal length is f, (1) 0.9R <f (Nd- 1) <1.1R (2) R> 0, R <D <1.5R R <0, 0.7 | R | <D <| R | (3) 1.43 <Nd <1.55 For example, spherical aberration and coma are advantageous, and correction of off-axis aberration is also advantageous, so that a wide angle of view can be achieved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a taking lens of a video surveillance camera. This photographing lens is of a post diaphragm type and comprises an aspherical plano-convex lens 1 and a diaphragm 2 in that order from the subject side. The light flux from the aspherical plano-convex lens 1 is condensed by the diaphragm 2 and passed through the protective glass 3. An image is formed on the image plane 5 of the image pickup device 4 such as a CCD. In this case, the aspherical plano-convex lens 1 is made of plastic and is arranged with the convex surface facing the subject side, and the rear surface of the image side is formed as a flat surface 1a. The diaphragm 2 is integrally formed on the plane 1a on the image plane side of the aspherical plano-convex lens 1 by printing or the like. In this case, in order to easily print the diaphragm 2, a portion of the plane 1a of the aspherical plano-convex lens 1 corresponding to the diaphragm 2 is
The step convex portion 1b is provided so as to project from the flat surface 1a.
The protective glass 3 protects the image sensor 4.

Such a taking lens has the following formula: (1) 0.9R <f, where R is the paraxial radius of curvature of the aspherical plano-convex lens 1, D is its center thickness, Nd is its refractive index, and f is its focal length. (Nd-1) <1.1R (2) R> 0 and R <D <1.5R (3) 1.43 <Nd <1.55.

The conditions (1) to (3) will be described below. The condition (1) limits the contribution of the aspherical coefficient to the paraxial radius of curvature R of the aspherical surface of the aspherical plano-convex lens 1 to a small one. If this condition is not satisfied, there will be a disadvantage in correcting spherical aberration and coma. The condition (2) relates to the relationship between the central thickness D of the aspherical plano-convex lens 1 and the paraxial radius of curvature R when the convex surface of the aspherical plano-convex lens 1 faces the object side. If this condition is not satisfied, correction of off-axis aberration will be disadvantageous, and it will not be possible to achieve a wide angle of view. The condition (3) relates to the refractive index Nd of the aspherical plano-convex lens 1. The focal length f of the aspherical plano-convex lens 1 is determined by the refractive index Nd of the aspherical plano-convex lens 1, its paraxial radius of curvature R, and some aspherical coefficients. When the refractive index Nd is large, the paraxial radius of curvature R is small. When the refractive index Nd is small, the paraxial radius of curvature R becomes large. Therefore, when the paraxial radius of curvature R is small and the amount of aspherical surface at the peripheral portion of the lens surface is large, it is possible to widen the angle of view, and the refractive index Nd is higher than this condition.
Is large, it becomes impossible to widen the angle of view, and conversely, if the refractive index Nd is smaller than this condition, correction of spherical aberration becomes disadvantageous.

As described above, in this taking lens, since the single lens is composed of the aspherical plano-convex lens 1, aberration correction is advantageous, and sufficient performance can be obtained.
The diaphragm 2 can be integrally provided on the flat surface 1a of the aspherical plano-convex lens 1 by printing or the like, whereby the number of parts can be reduced, and the assembling work can be simplified and the cost can be reduced. Also, with this shooting lens,
By satisfying the condition (1), correction of spherical aberration and coma becomes advantageous, and by satisfying the condition (2), correction of off-axis aberration becomes advantageous, and a wide angle of view is achieved. By satisfying the condition (3), it becomes advantageous to correct the spherical aberration, which also makes it possible to widen the angle of view. Further, in this photographing lens, spherical aberration has an aberration curve as shown in FIG. 2 (a), and astigmatism has an aberration curve as shown in FIG. 2 (b). I understand. Therefore, even if the aperture of the lens is increased, sufficient performance can be ensured.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. The same parts as those in the first embodiment of FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. FIG. 3 shows a front diaphragm type photographing lens. This photographing lens is provided with a diaphragm 2 and an aspherical plano-convex lens 1 in order from the subject side. An image is formed on the image plane 5 of the image pickup device 4 via the image pickup device 3. In this case, the aspheric plano-convex lens 1
It is arranged with the flat surface 1a facing the subject side, and the rear surface of the image side is formed into an aspherical surface. The diaphragm 2 is integrally formed on the plane 1a on the object side of the aspherical plano-convex lens 1 by printing or the like as in the first embodiment.

In such a photographing lens, since the aspherical plano-convex lens 1 is arranged with the plane 1a facing the subject side, the condition (2) is different from the first embodiment, and (2) R <0 , 0.7 | R | <D <| R |, except that the structure satisfies the same conditions as the first embodiment. The condition (2) relates to the relationship between the central thickness D of the aspherical plano-convex lens 1 and the paraxial radius of curvature R, as in the first embodiment. If this condition is not satisfied, correction of off-axis aberrations is disadvantageous. It becomes impossible to achieve a wide angle of view.

In such a photographing lens, spherical aberration has an aberration curve as shown in FIG. 4A, and astigmatism has an aberration curve as shown in FIG. 4B, which is the same as in the first embodiment. In addition, the aberration characteristic is good and sufficient performance can be obtained. Further, since the plane 1a of the aspherical plano-convex lens 1 is directed to the subject side and the diaphragm 2 is provided on the plane 1a on the object side, the aspherical surface is formed by this diaphragm 2. Light rays incident from the peripheral portion of the plano-convex lens 1 can be blocked, and the number of parts can be further reduced.

In the above-described embodiment, the plane 1 of the aspherical plano-convex lens 1 is formed in order to facilitate the application of the diaphragm 2.
Although the step convex portion 1b is provided in a, the step convex portion 1b does not necessarily have to be provided.

[0014]

As described above, according to the present invention, since the single lens is composed of an aspherical plano-convex lens, aberration correction is advantageous and sufficient performance can be ensured, and this aspherical surface can be secured. A diaphragm can be integrally provided on the plane of the plano-convex lens, whereby the number of parts can be reduced, and the assembling work can be simplified and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a taking lens according to a first embodiment of the present invention.

2 shows the aberration characteristics of FIG. 1, (a) is a spherical aberration diagram,
(B) is an astigmatism diagram.

FIG. 3 is a configuration diagram of a taking lens according to a second embodiment of the present invention.

FIG. 4 shows the aberration characteristics of FIG. 3, (a) is a spherical aberration diagram,
(B) is an astigmatism diagram.

[Explanation of symbols]

 1 Aspheric plano-convex lens 2 Aperture

Claims (2)

[Claims] 1. A photographing lens comprising a single-lens lens and a diaphragm, which forms a light flux from a subject on an image plane of an image sensor, wherein the single-lens lens is composed of an aspherical plano-convex lens. A photographic lens characterized in that the diaphragm is integrally provided on the plane of. 2. In claim 1, where R is the paraxial radius of curvature of the aspherical plano-convex lens, D is its center thickness, Nd is its refractive index, and f is its focal length: (1) 0.9R <f (Nd-1) <1.1R (2) R> 0, R <D <1.5R When R <0, 0.7 | R | <D <| R | (3) 1.43 <Nd <1.55 A shooting lens characterized by satisfying.