JP2006030581A - Large-diameter wide-angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large-diameter wide-angle lens with which various aberration over the entire distance of an object can be adequately corrected even though an F-number is approximately 1.4, assuring brightness, and an angle of view is approximately 60°or more, and which has optical performance ensuring high resolution and high contrast. <P>SOLUTION: In the large-diameter wide-angle lens, a first group G<SB>1</SB>of negative power and a second group G<SB>2</SB>of positive power are disposed in this order from the object side. The first group G<SB>1</SB>comprises in order from the object side: a first lens L<SB>1</SB>of positive power whose convex face is disposed on the object side, a second lens L<SB>2</SB>of negative power whose convex face is disposed on the object side; a third lens L<SB>3</SB>of negative power; and a fourth lens L<SB>4</SB>of positive power. The second group G<SB>2</SB>comprises in order from the object side: a fifth lens L<SB>5</SB>whose convex face is disposed on the image side; a sixth lens L<SB>6</SB>and a seventh lens L<SB>7</SB>, one having positive power and the other negative power, which compose a cemented lens; and an eighth lens L<SB>8</SB>and a ninth lens L<SB>9</SB>, one having positive power and the other negative power, which compose a cemented lens. The large-diameter wide-angle lens is focused by moving the second group G<SB>2</SB>on the optical axis. By satisfying prescribed conditional expressions, various aberrations (esp., coma aberration) are adequately corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a large-aperture wide-angle lens, and more particularly to a large-aperture wide-angle lens that is mounted on a surveillance camera or the like and has an F number of about 1.4 and an angle of view of about 60 degrees or more.

  Conventionally, since lenses used for surveillance cameras and the like are often used mainly indoors, they are required to be bright large-diameter lenses and have a wider angle of view for observing or photographing a wide range. A wide lens system is required.

  A lens described in Patent Document 1 is known as a lens used in such a surveillance camera. The lens system described in Patent Document 1 is a retro-focus type wide-angle lens, and performs focusing by moving only the rear group.

JP-A-9-212321

  However, the lens system described in Patent Document 1 has a dark F number of about 2.8 and is unsuitable for indoor use. Further, it has been difficult to say that various aberrations can be corrected well over the entire object distance.

  The present invention has been proposed in view of the above-described circumstances. The F number is as bright as about 1.4, the angle of view is about 60 degrees or more, and various aberrations can be corrected well over the entire object distance. An object of the present invention is to provide a large-aperture wide-angle lens having high resolution and high-contrast optical performance.

The large-aperture wide-angle lens of the present invention has been proposed in view of the above-described circumstances, and a first lens group having a negative refractive power and a second lens group having a positive refractive power are disposed in order from the object side. Being
The first lens group includes, in order from the object side, a first lens having a positive refractive power with a convex surface facing the object side, a second lens having a negative refractive power with a convex surface facing the object side, and a negative refractive power. And a fourth lens having a positive refractive power,
The second lens group includes, in order from the object side, a fifth lens having a positive refractive power with a convex surface facing the image side, one having a positive refractive power and the other having a negative refractive power, and a lens surface. Are joined together to form a cemented lens, and one of them has a positive refractive power and the other has a negative refractive power, and the lens surfaces are joined together to form a cemented lens. It consists of an eighth lens and a ninth lens,
Focusing is performed by moving the second lens group on the optical axis.

In addition to the above configuration, the large-aperture wide-angle lens of the present invention has a refractive index of the fifth lens of _NL5, and has a negative refractive power of two sets of cemented lenses that constitute the second lens group. It is preferable that the following conditional expressions (1) to (3) are satisfied when the refractive indexes of the lenses are N _LS1 and N _LS2 , respectively.
N _L5 > 1.75 (1)
N _LS1 > 1.75 (2)
N _LS2> 1.75 ··· (3)

Also, large-diameter wide-angle lens of the present invention, in addition to the arrangement, the focal length of the entire system is F, the focal length of the fifth lens when the F _L5, satisfies the following conditional expression (4) It is preferable.
3.0 <F _{L5 /F<4.4} (4)

In addition to the above configuration, the large-aperture wide-angle lens of the present invention has a radius of curvature of the object side surface of the fifth lens as _Ra and _a radius of curvature of the image side surface of the fifth lens as _Rb . It is preferable that the following conditional expression (5) is satisfied.
2.1 <(R _a + R _b ) / (R _a −R _b ) <3.1 (5)

  The large-aperture wide-angle lens of the present invention has the above-described configuration. In particular, since two sets of cemented lenses are used in the second lens group disposed on the image side, the F number is about 1.4. High-resolution and high-contrast optical performance that can correct various aberrations well over the entire object distance from a long distance to a close distance while having a wide field angle of about 60 degrees or more Can be demonstrated.

  Further, when the above conditional expressions are satisfied, particularly coma aberration can be corrected satisfactorily.

Hereinafter, embodiments of a large-aperture wide-angle lens according to the present invention will be described with reference to the drawings.
1 to 3 show a large-aperture wide-angle lens according to an embodiment of the present invention. FIG. 1 is a lens configuration diagram of the large-aperture wide-angle lens according to Example 1. FIG. 2 is a large-aperture wide-angle lens according to Example 2. FIG. 3 is a lens configuration diagram of a large aperture wide angle lens according to Example 3. FIG.

As shown in FIGS. 1 to 3, the large-aperture wide-angle lens according to the embodiment of the present invention has, in order from the object side, a first lens group G ₁ having a negative refractive power, a diaphragm 3, and a positive refractive power. the second lens group G ₂ is arranged, which is a second lens group G ₂ to perform focusing by moving on the optical axis.

Further, on the image side of the second lens group G ₂ includes, such as an infrared cut filter and the filter unit 2 is provided, the light flux incident along the optical axis X from the object side a solid-state imaging device (CCD), such as An image is formed at an imaging position on the imaging surface 1.

The first lens group G ₁ has, in order from the object side, a positive refractive power, a meniscus first lens L ₁ with a convex surface facing the object side, a negative refractive power, and a convex surface on the object side. A second meniscus lens L ₂ directed toward the surface, a third meniscus lens L ₃ having negative refractive power and having a convex surface directed toward the object side (a biconcave lens in the second embodiment), and a fourth lens having a biconvex shape. a lens _{L 4.}

The second lens group G ₂ has, in order from the object side, a positive refractive power, a meniscus fifth lens L ₅ having a convex surface facing the image side, a biconvex sixth lens L ₆ , and negative refraction. has a force, seventh lens L ₇ having a meniscus shape with a convex surface directed toward the image _side, the eighth lens L _{8 biconvex,} and becomes a bi-concave ninth lens L _9, a sixth lens L ₆ The seventh lens L ₇ , the eighth lens L _8, and the ninth lens L ₉ constitute a cemented lens whose lens surfaces are cemented with each other.

  Furthermore, the large-aperture wide-angle lens according to the embodiment of the present invention is configured to satisfy the following conditional expressions (1) to (5).

N _L5 > 1.75 (1)
N _LS1 > 1.75 (2)
N _LS2 > 1.75 (3)
3.0 <F _{L5 /F<4.4} (4)
2.1 <(R _a + R _b ) / (R _a −R _b ) <3.1 (5)
However,
N _L5 : Refractive index of the fifth lens N _LS1 , N _LS2 : Lens having negative refractive power out of two sets of cemented lenses constituting the second lens group (in the following examples, the seventh lens L ₇ and the seventh lens respectively) Refractive index of 9 lens L ₉ ) F: focal length of entire system F _L5 : focal length of 5th lens R _a : radius of curvature of object side surface of 5th lens (R _{10 in the following} examples)
R _b : radius of curvature of the image side surface of the fifth lens (R _{11 in the following} examples)

Next, the technical significance of each conditional expression will be described.
Condition (1) defines a refractive index N _L5 of the fifth lens L _5, the value of N _L5 is below the lower limit of the conditional expression (1), in particular coma correction increases It becomes difficult.

Conditional expressions (2) and (3) defines the refractive index N _LS1, N _LS2 of lenses having negative refractive power of the two cemented lenses of the second lens group G ₂ In the conditional expressions (2) and (3), if the values of N _LS1 and N _LS2 are lower than the lower limit, respectively, coma increases and it is difficult to correct.

Conditional expression (4) defines the ratio F _L5 / F of the focal length F _L5 of the fifth lens L _{5 and} the focal length F of the entire system. In this conditional expression (4), the value of F _L5 / F is Beyond the specified range, coma increases in particular, making correction difficult.

Conditional expression (5) is the ratio (R _a + R _b ) / (R _a ) of the sum and difference of the curvature radius R _a of the object side surface of the fifth lens L ₅ and the curvature radius R _b of the image side surface of the fifth lens L _5. −R _b ), and in this conditional expression (5), when the value of (R _a + R _b ) / (R _a −R _b ) exceeds the specified range, coma aberration increases. It becomes difficult to correct.

In addition, in terms of correcting coma aberration better,
N _L5 > 1.80
N _LS1 > 1.80
N _LS2 > 1.80
3.2 <F _{L5 /F<4.0}
2.4 <(R _a + R _b ) / (R _a −R _b ) <2.9
It is preferable that

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

<Example 1>
The lens configuration of the large-aperture wide-angle lens according to Example 1 is as shown in FIG.
Specific data for Example 1 will be shown below.
The upper part of Table 1 below shows the focal length f (mm) and the F number of the large-aperture wide-angle lens according to Example 1.

Further, in the middle of Table 1 below, the radius of curvature R (mm) of each lens surface of Example 1 and the axial top surface spacing of each lens (center thickness of each lens and air spacing between each lens; in Table 2 and Table 3) (Same) D (mm), refractive index N _d and Abbe number ν _d of each lens at the d-line. In Table 1 and Tables 2 and 3 below, the numbers corresponding to the respective symbols are sequentially increased from the object side.
Furthermore, each value of the conditional expressions (1) to (5) is shown in the lower part of Table 1 below.

  As is clear from the numerical values shown in the lower part of Table 1, the large-aperture wide-angle lens according to Example 1 satisfies all the conditional expressions (1) to (5).

  4 and 5 show various aberrations of the large-aperture wide-angle lens according to Example 1. FIG. 4 shows various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at an infinite object distance. FIG. 5 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at a focal length of 100 mm. In these aberration diagrams and the aberration diagrams shown in FIGS. 6 to 9, ω represents a half angle of view. Each aberration diagram of astigmatism shows aberrations on the sagittal image surface and the tangential image surface.

  As is clear from FIGS. 4 and 5, the large-aperture wide-angle lens according to Example 1 has high performance capable of satisfactorily correcting each aberration (particularly coma aberration).

<Example 2>
The lens configuration of the large-aperture wide-angle lens according to Example 2 is as shown in FIG. Note that the large aperture lens according to Example 1, the third lens L ₃ is different in that there is a biconcave lens.
Specific data for Example 2 will be shown below.

The upper part of Table 2 below shows the focal length f (mm) and the F number of the large-aperture wide-angle lens according to Example 2.
Further, in the middle of Table 2 below, the curvature radius R (mm) of each lens surface of Example 2, the axial distance D (mm) of each lens, the refractive index N _d of each lens at the d-line, and the Abbe number ν _d Indicates.
Furthermore, each value of the conditional expressions (1) to (5) is shown in the lower part of Table 2 below.

  As is clear from the numerical values shown in the lower part of Table 2, the large-aperture wide-angle lens according to Example 2 satisfies all the conditional expressions (1) to (5).

  6 and 7 show various aberrations of the large-aperture wide-angle lens according to Example 2. FIG. 6 shows various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at an infinite object distance. FIG. 7 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at a focal length of 100 mm.

  As is clear from FIGS. 6 and 7, the large-aperture wide-angle lens according to Example 2 has high performance capable of satisfactorily correcting each aberration (particularly coma aberration).

<Example 3>
The lens configuration of the large-aperture wide-angle lens according to Example 3 is as shown in FIG.
Specific data for Example 3 will be shown below.

The upper part of Table 3 below shows the focal length f (mm) and the F number of the large-aperture wide-angle lens according to Example 3.
Further, in the middle of Table 3 below, the curvature radius R (mm) of each lens surface of Example 3, the axial distance D (mm) of each lens, the refractive index N _d and the Abbe number ν _{d of} each lens at the d-line. Indicates.
Furthermore, the lower part of Table 3 below shows the values of the conditional expressions (1) to (5).

  As is clear from the numerical values shown in the lower part of Table 3, the large-aperture wide-angle lens according to Example 3 satisfies all the conditional expressions (1) to (5).

  8 and 9 show various aberrations of the large-aperture wide-angle lens according to Example 3. FIG. 8 shows various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at an infinite object distance. FIG. 9 is an aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at a focal length of 100 mm.

  As is clear from FIGS. 8 and 9, the large-aperture wide-angle lens according to Example 3 has high performance capable of satisfactorily correcting each aberration (particularly coma aberration).

<Other embodiments>
The large-aperture wide-angle lens of the present invention is not limited to those in the above embodiments, and various other modifications can be made. For example, the shape of the lens constituting each lens of each of the above embodiments can be changed as appropriate. In addition to the surveillance camera, the large-aperture wide-angle lens of the present invention can be mounted on various optical devices such as a general video camera and a digital camera.

1 is a lens configuration diagram of a large-aperture wide-angle lens according to Example 1 of the present invention. Lens configuration diagram of a large aperture wide angle lens according to Example 2 of the present invention Lens configuration diagram of a large aperture wide angle lens according to Example 3 of the present invention Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at an infinite object distance of the large-aperture wide-angle lens according to Example 1 of the present invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at a focal length of 100 mm of the large-aperture wide-angle lens according to Example 1 of the present invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at an infinite object distance of the large-aperture wide-angle lens according to Example 2 of the present invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at a focal length of 100 mm of the large-aperture wide-angle lens according to Example 2 of the present invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at an infinite object distance of the large-aperture wide-angle lens according to Example 3 of the present invention. Aberration diagram showing various aberrations (spherical aberration, astigmatism, distortion, coma aberration) at a focal length of 100 mm of the large aperture wide angle lens according to Example 3 of the present invention.

Explanation of symbols

1 imaging plane 2 filter unit 3 diaphragm G ₁ ~G ₂ lens group L ₁ ~L ₉ lens X optical axis

Claims (4)

In order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power are disposed.
The first lens group includes, in order from the object side, a first lens having a positive refractive power with a convex surface facing the object side, a second lens having a negative refractive power with a convex surface facing the object side, and a negative refractive power. And a fourth lens having a positive refractive power,
The second lens group includes, in order from the object side, a fifth lens having a positive refractive power with a convex surface facing the image side, one having a positive refractive power and the other having a negative refractive power, and a lens surface. Are joined together to form a cemented lens, and one of them has a positive refractive power and the other has a negative refractive power, and the lens surfaces are joined together to form a cemented lens. It consists of an eighth lens and a ninth lens,
A large-aperture wide-angle lens characterized in that focusing is performed by moving the second lens group on the optical axis. When the refractive index of the fifth lens is N _L5 and the refractive indexes of the lenses having negative refractive power among the two cemented lenses constituting the second lens group are N _LS1 and N _LS2 , respectively. The large-aperture wide-angle lens according to claim 1, wherein the following conditional expressions (1) to (3) are satisfied.
N _L5 > 1.75 (1)
N _LS1 > 1.75 (2)
N _LS2 > 1.75 (3) 3. The large-aperture wide-angle lens according to claim 1, wherein the following conditional expression (4) is satisfied when the focal length of the entire system is F and the focal length of the fifth lens is _FL5 .
3.0 <F _{L5 /F<4.4} (4) 2. The following conditional expression (5) is satisfied, where R _a is _a curvature radius of the object side surface of the fifth lens and R _b is a curvature radius of the image side surface of the fifth lens. The large-aperture wide-angle lens according to any one of?
2.1 <(R _a + R _b ) / (R _a −R _b ) <3.1 (5)

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