JP2001208967A - Compact large-aperture wide-angle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact large-aperture wide-angle lens which is compact and has a wide viewing angle, which is bright to such an extent that its F value is about 1.0 to 1.1 while maintaining excellent optical performance and which is suitable for a monitor camera by arraying a 1st negative lens group, a diaphragm and a 2nd positive lens group from an object side and constituting the 1st lens group of six lenses having specified shape. SOLUTION: The 1st lens group G1 having negative refractive power, the diaphragm 2 and the 2nd lens group G2 having positive refractive power are arrayed in order from the object side. A filter part 2 such as an infrared cut filter is arranged on the image side of the 2nd lens group G2, and luminous flux made incident along an optical axis X from the object side is formed into an image at an image-forming position on the image pickup surface of a CCD. Then, this lens satisfies following conditional expressions (1) and (2). (1) 2.0<DS/f<4.0 and (2) 3.3<R2/f<4.5. Provided that (f) means the focal distance of a lens entire system, DS means the thickness of a combined lens in the 1st lens group and R2 means the radius of curvature of the surface on the image side of the lens nearest to the object side in the 1st lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized large-aperture wide-angle lens, and more particularly to a small-sized large-aperture wide-angle lens suitably used for a surveillance camera equipped with a CCD.

[0002]

2. Description of the Related Art Since lenses used for surveillance cameras and the like are mainly used indoors, bright large-diameter lenses are required. Further, in order to observe or photograph a wider range with one camera, a wide-angle lens system having a larger angle of view is required.

In general, a wide-angle lens generates negative distortion, and uses the effect of reducing the image around the angle of view due to the distortion. However, in the case of a wide-angle lens system having a larger angle of view, the occurrence of distortion becomes extremely large and may be a problem in practical use.Therefore, distortion is suppressed to a relatively small value, and the imaging aberration characteristics of the entire effective screen are reduced. There is a need for a corrected wide-angle lens system. Examples of such a wide-angle lens system include, for example, JP-A-9-80303 and JP-A-11-80303.
The one described in JP-A-64727 is known.

[0004]

However, the wide-angle lens system described in the former of the above publications requires improvement in terms of aberration correction. In particular, in surveillance cameras, in many cases, the cost of the lens is reduced in response to a request for a reduction in the cost. In this case, there is a possibility that color bleeding may occur in an image due to insufficient correction of chromatic aberration and the like.

Further, in order to increase the angle of view, the radius of curvature of the concave surface of the concave lens on the front side is smaller than the inner diameter of the lens, and the lens surface tends to have a shape close to a hemisphere. There is a problem that it becomes difficult.

On the other hand, in the latter wide-angle lens system in the above publication, the above-mentioned problems have been improved, and the angle of view has been increased to some extent.
The F number is about 1.2, and for surveillance cameras,
Since the use in darker places is required, F
There is a demand for a lens having a number as bright as about 1.0 to 1.1.

The present invention has been made in view of such circumstances, and has a small size, a wide angle of view, and an F value of about 1.0 to 1.1 while maintaining good optical performance. It is an object to provide a large-diameter lens.

[0008]

A small-diameter large-aperture lens according to the present invention comprises, in order from the object side, a first lens unit having a negative refractive power, a stop, and a second lens unit having a positive refractive power. The first lens group includes, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a lens having a positive refractive power having a convex surface facing the image side, and a negative meniscus having a positive refractive power facing the image side. A lens, two cemented lenses, and a lens having a positive refractive power are arranged;
The lens group is constituted by at least four lenses.

It is preferable to satisfy the following conditional expressions (1) and / or (2). _{2.0 <D S / f <4.0} (1) 3.3 <R 2 / f <4.5 (2) where, f: lens focal length D _S of: lens thickness of the cemented lens in the first lens group R _2: The radius of curvature of the image-side surface of the lens closest to the object in the first lens group

Further, it is preferable that the second lens group includes, in order from the object side, a positive lens having a convex surface facing the image side, a negative lens and a positive lens constituting a cemented lens, and a positive lens.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings and specific examples. FIG. 1 is a diagram showing a configuration of a small, large-aperture, wide-angle lens according to Example 1 which represents an embodiment of the present invention. As shown in the figure, the small-sized large-aperture wide-angle lens according to the present embodiment includes, in order from the object side, a first lens group G ₁ having a negative refractive power, a diaphragm 2 and a second lens group G ₂ having a positive refractive power. Are arranged. Further, the image side of the second lens group G ₂ is arranged a filter unit 2 such as an infrared cut filter, the optical axis X from the object side
The light beam incident along is formed at an image forming position on an image pickup surface (not shown) of a solid-state image pickup device (CCD).

The zoom lens according to the present embodiment is configured to satisfy the following conditional expressions (1) and (2). _{2.0 <D S / f <4.0} (1) 3.3 <R 2 / f <4.5 (2) where, f: lens focal length D _S of: lens thickness of the cemented lens in the first lens group R _2: The radius of curvature of the image-side surface of the lens closest to the object in the first lens group

Hereinafter, the significance of the conditional expressions (1) and (2) will be described. The above conditional expression (1) satisfies the first lens group G
₁ defines the thickness of the cemented lens. When the lens thickness of the cemented lens in the first lens group G ₁ exceeds the upper limit value becomes larger, the coma aberration is increased, the correction becomes difficult. On the other hand, when the lens thickness of the cemented lens in the first lens group G ₁ beyond the lower limit value is reduced, increased coma and curvature of field, the correction becomes difficult.

[0014] Condition (2) is a formula for achieving a balance of the optical performance and productivity, the curvature of the image side surface of the most object side lens in the first among lens group G ₁ radius R
₂ is specified.

[0015] Beyond this limit, the radius of curvature R ₂ increases, and increases coma aberration and curvature of field, the correction becomes difficult. On the other hand, the when than the lower limit value is the radius of curvature R ₂ decreases, the lens workability and lens assembly property is remarkably deteriorated, its production becomes difficult.

Hereinafter, the small-sized large-aperture wide-angle lens according to the present invention will be described in more detail with reference to specific examples.

<Embodiment 1> The configuration of a small, large-aperture, wide-angle lens according to Embodiment 1 is as shown in FIG. That is, the first lens group G ₁ is composed, in order from the object side, a first lens L ₁ composed of a negative meniscus lens having a convex surface directed toward the object side, the biconvex toward a surface with a stronger curvature on the image side 2
A lens L _2, a third lens L _3, which is a negative meniscus lens having a convex surface directed toward the object side, a fourth lens L ₄ biconvex toward a surface with a stronger curvature on the image side, a stronger curvature directed onto the object side A bi-concave fifth lens L ₅ facing the surface and a bi-convex sixth lens L ₆ are arranged. Note that the fourth lens L ₄ and the fifth lens L ₅ are bonded.

Further, the second lens group G ₂ includes, in order from the object side, a negative meniscus lens having a seventh lens L ₇ biconvex toward a surface with a stronger curvature on the image side, a concave surface on the image side the 8 lens L _8, a ninth lens L ₉ biconvex toward a surface with a stronger curvature on the object side, the tenth lens L ₁₀ and the array of positive meniscus lens having a convex surface directed toward the object side consisting of Be done. Note that the eighth lens L ₈ and the ninth lens L ₉ are cemented.

Hereinafter, specific data for the first embodiment will be shown. In the middle part of Table 1, the radius of curvature R of each lens surface, the distance between the axial upper surfaces of each lens (the center thickness of each lens and the air distance between each lens) D, and the refractive index N of each lens at d-line in Example 1 are shown. shows the _d and Abbe number ν _d. The upper part of Table 1 shows the focal length f and the F value. Further, the lower part of Table 1 shows values corresponding to the conditional expressions (1) and (2) in the present embodiment.

In Table 1 and the following Tables 2, 3, and 4, the numbers corresponding to the symbols are sequentially increased from the object side, and each value shown in the table is the focal length of the entire system. This is standardized by f.

[0021]

[Table 1]

FIG. 2 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the first embodiment. In these aberration diagrams and the following aberration diagrams, ω indicates a half angle of view. Also,
The astigmatism diagrams show aberrations on the sagittal image plane and the tangential image plane.

As shown in Table 1 and FIG. 2, the wide-angle lens of Example 1 satisfies all of the conditional expressions (1) and (2), has a bright F value of 1.05, and has an angle of view 2ω of 108. It is a high-performance, large-diameter wide-angle lens with a wide angle of 0.8 ° and capable of favorably correcting each aberration.

<Embodiment 2> The configuration of a small, large-aperture, wide-angle lens according to Embodiment 2 is as shown in FIG. Structure of a small retrofocus type wide-angle lens according to the second embodiment is basically the same as in Example 1, tenth lens L ₁₀ of the second lens group G ₂ with its surface with a stronger curvature on the object side The difference is that it is a biconvex lens.

Hereinafter, specific data of the second embodiment will be shown. In the middle part of Table 2, the radius of curvature R of each lens surface, the distance between the axial upper surfaces of each lens (the center thickness of each lens and the air distance between each lens) D, and the refractive index N of each lens at the d-line in Example 2 are shown. shows the _d and Abbe number ν _d. The upper part of Table 2 shows the focal length f and the F value. Further, the lower part of Table 2 shows values corresponding to the conditional expressions (1) and (2) in the present embodiment.

[0026]

[Table 2]

FIG. 4 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the second embodiment. In these aberration diagrams and the following aberration diagrams, ω indicates a half angle of view. Also,
The astigmatism diagrams show aberrations on the sagittal image plane and the tangential image plane.

As shown in Table 2 and FIG. 4, the wide-angle lens according to the second embodiment satisfies all of the conditional expressions (1) and (2), has a bright F value of 1.05, and has an angle of view 2ω of 108. It is a high-performance, large-diameter wide-angle lens with a wide angle of 0.8 ° and capable of favorably correcting each aberration.

<Embodiment 3> The configuration of a small-sized large-aperture wide-angle lens according to Embodiment 3 is as shown in FIG. The configuration of the small-sized large-aperture wide-angle lens according to the third embodiment is basically the same as that of the second embodiment.

Hereinafter, specific data for the third embodiment will be shown. In the middle part of Table 3, the radius of curvature R of each lens surface, the distance between the axial upper surfaces of each lens (the center thickness of each lens and the air distance between each lens) D, and the refractive index N of each lens at d line are shown in the middle part of Table 3. shows the _d and Abbe number ν _d. The upper part of Table 3 shows the focal length f and the F value. Further, the lower part of Table 3 shows values corresponding to the conditional expressions (1) and (2) in the present embodiment.

[0031]

[Table 3]

FIG. 5 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the third embodiment. In these aberration diagrams and the following aberration diagrams, ω indicates a half angle of view. Also,
The astigmatism diagrams show aberrations on the sagittal image plane and the tangential image plane.

As shown in Table 3 and FIG. 5, the wide-angle lens according to the third embodiment satisfies all of the conditional expressions (1) and (2), has a bright F value of 1.05, and has an angle of view 2ω of 108. It is a high-performance, large-diameter wide-angle lens with a wide angle of 0.8 ° and capable of favorably correcting each aberration.

<Embodiment 4> The configuration of a small, large-aperture, wide-angle lens according to Embodiment 4 is as shown in FIG. The configuration of the small-sized large-aperture wide-angle lens according to the fourth embodiment is basically the same as that of the second embodiment.

Hereinafter, specific data of the fourth embodiment will be shown. In the middle part of Table 4, the radius of curvature R of each lens surface, the distance between the axial upper surfaces of each lens (the center thickness of each lens and the air distance between each lens) D, and the refractive index N of each lens at d-line in Example 4 are shown. shows the _d and Abbe number ν _d. The upper part of Table 4 shows the focal length f and the F value. Further, the lower part of Table 4 shows values corresponding to the conditional expressions (1) and (2) in the present embodiment.

[0036]

[Table 4]

FIG. 8 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the fourth embodiment. In these aberration diagrams and the following aberration diagrams, ω indicates a half angle of view. Also,
The astigmatism diagrams show aberrations on the sagittal image plane and the tangential image plane.

As shown in Table 4 and FIG. 8, the wide-angle lens of Example 4 satisfies all of the conditional expressions (1) and (2), has a bright F-number of 1.05, and has an angle of view 2ω of 108. It is a high-performance small-diameter wide-angle lens with a wide angle of 0.8 ° and capable of favorably correcting each aberration.

It should be noted that the wide-angle lens of the present invention is not limited to the above-described embodiment, and various other modifications can be made. For example, the number and shape of the lenses constituting each lens group in each of the above-described embodiments can be appropriately changed. The small-sized large-aperture wide-angle lens of the present invention can be mounted on various optical devices other than the surveillance camera.

[0040]

As described above, according to the small-sized large-aperture wide-angle lens according to the present invention, the first negative lens unit, the stop, and the second positive lens unit are arranged from the object side, and By forming the first lens group located on the object side into a six-lens configuration having a predetermined shape including a thick cemented lens,
Small size and wide angle of view, while maintaining good optical performance,
Brightness having a value of about 1.0 to 1.1 can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a small-sized large-aperture wide-angle lens according to a first embodiment.

FIG. 2 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the first embodiment.

FIG. 3 is a diagram illustrating a configuration of a small-sized large-aperture wide-angle lens according to a second embodiment.

FIG. 4 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the second embodiment.

FIG. 5 is a diagram showing a configuration of a small-sized large-aperture wide-angle lens according to a third embodiment.

FIG. 6 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to the third embodiment.

FIG. 7 is a diagram illustrating a configuration of a small-sized large-aperture wide-angle lens according to a fourth embodiment.

8 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion) of the small-sized large-aperture wide-angle lens according to Example 4. FIG.

[EXPLANATION OF SYMBOLS] L ₁ ~L ₁₀ lens G ₁ ~G ₂ lens group X optical axis 1 stop 2 filter unit

Claims (4)

[Claims] 1. A first lens group having a negative refractive power, a stop, and a second lens group having a positive refractive power are arranged in order from the object side, and the first lens group is arranged in order from the object side. A negative meniscus lens with a convex surface facing the object side, a lens having a positive refractive power with a convex surface facing the image side, a negative meniscus lens with a convex surface facing the object side, two cemented lenses and a positive lens A small-sized large-aperture wide-angle lens, wherein lenses having a refractive power are arranged, and wherein the second lens group includes at least four lenses. 2. The small-sized large-aperture wide-angle lens according to claim 1, wherein the following conditional expression (1) is satisfied. _{2.0 <D S / f <4.0} (1) where, f: focal length of the entire lens system D _S: the lens thickness of the cemented lens in the first lens group 3. The small-sized large-aperture wide-angle lens according to claim 1, wherein the following conditional expression (2) is satisfied. _{3.3 <R 2 / f <4.5} (2) where, f: the entire lens system focal length R _2: radius of curvature of the image side surface of the most object side lens in the first lens group 4. The second lens group includes, in order from the object side,
A lens having a positive refractive power with a convex surface facing the image side, a lens having a negative refractive power and a lens having a positive refractive power, and a lens having a positive refractive power, which constitute a cemented lens, are arranged. The small-sized large-aperture wide-angle lens according to claim 1, wherein: