JP2008040033A - Wide-angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a compact wide-angle lens having optical performance which can cope with a large-sized imaging device, and also, capable of suppressing the angle of a light beam made incident on the imaging device. <P>SOLUTION: The wide-angle lens includes: in order from an object side, a first lens group G1 having negative refractive power; a second lens group G2 having negative refractive power; a third lens group G3 having positive refractive power; a fourth lens group G4 having negative refractive power; and a fifth lens group G5 having positive refractive power; wherein the fourth lens group G4 is constituted by cementing a biconcave lens L1 having negative refractive power and a biconvex lens L2 having positive refractive power, and the cemented lens is obtained by cementing aspherical lenses. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wide-angle lens used for a digital camera, a video camera, and the like.

Japanese Patent Application Laid-Open No. 2004-245893 discloses that a wide-angle lens used in a digital camera or a video camera has excellent optical performance that can cope with, for example, an image pickup device that has been reduced in size and increased in number of pixels, and achieves a sufficiently compact size. Japanese Patent Laid-Open No. 2002-228925 discloses that the lens has good telecentricity, has a back focus that is sufficient and does not become too large, sufficiently wides the angle, and realizes high imaging performance and low price. Are known.
JP 2004-245893 A JP 2002-228925 A

  The wide-angle lens described in the above Japanese Patent Application Laid-Open No. 2004-245893 has a small size and an optical performance that can cope with an image sensor with an increased number of pixels, but is used for a digital camera equipped with a large image sensor. However, the optical performance for extracting the performance of the image sensor cannot be obtained. In addition, the wide-angle lens described in JP-A-2002-228925 has good telecentricity, but when used for a digital camera equipped with a large image sensor, it has good telecentricity. It becomes difficult to maintain.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a compact wide-angle lens that has optical performance compatible with a large image sensor and can suppress the angle of light incident on the image sensor.

  In order to solve the above problems, in the wide-angle lens of the present invention, in order from the object side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, The lens unit includes a fourth lens unit having a negative refractive power and a fifth lens unit having a positive refractive power. The fourth lens unit includes a biconcave lens having a negative refractive power and a biconvex lens having a positive refractive power. The cemented lens is a cemented aspherical lens.

According to a preferred aspect of the present invention, the curvature radius on the object side of the first lens group is r1f, the curvature radius on the image side is r1b, the curvature radius on the object side of the second lens group is r2f, and the curvature on the image plane side. When the radius is r2b, the following conditions are satisfied.
(1) 1.5 <r1f / r1b <2.0
(2) 1.8 <r2f / r2b <2.3
Where r1f: radius of curvature on the object side of the first lens group r1b: radius of curvature on the image side of the first lens group r2f: radius of curvature on the object side of the second lens group r2b: radius of curvature on the image side of the second lens group curvature radius

Further, the inner thickness of the fourth lens group is d4, the maximum principal ray height of the surface on the image plane side of the fifth lens group is h5b, the air space from the fifth lens group to the image plane in the entire photographing region is Bf, When the diagonal length of the image plane is Is, the following conditions are satisfied.
(3) (Is−h5b) /Bf≦0.39
(4) 2.0 <Is / d4 <2.5
However, d4: Medium thickness of the fourth lens group h5b: Maximum principal ray height of the image side surface of the fifth lens group Bf: Air distance from the fifth lens group to the image plane in the entire imaging region Is: Image Diagonal length of face

Further, when the imaging magnification of the fifth lens group is β5, the following condition is satisfied.
(5) 0.7 <β5 <0.9
Where β5: imaging magnification of the fifth lens group

  According to the present invention, in order from the object side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power. , And a fifth lens group having a positive refractive power, and the fourth lens group is formed by bonding a biconcave lens having a negative refractive power and a biconvex lens having a positive refractive power. By joining with an aspherical lens, it is possible to achieve optical performance that can be used for a large image sensor, and to suppress the angle of light rays incident on the image sensor, thereby achieving a compact wide-angle lens.

  Conditional expression (1) defines the curvature radius ratio of the first lens group G1. When the lower limit of conditional expression (1) is exceeded, astigmatism becomes overcorrected. In addition, since the refractive power of the first lens group G1 becomes small, it is difficult to ensure the back focus. Furthermore, since it is necessary to relatively increase the refractive power of the second lens group G2 in order to maintain the focal length and back focus conditions of the entire system, it becomes difficult to correct negative distortion. If the upper limit of conditional expression (1) is exceeded, the sag amount of the first lens group G1 becomes large, and compactness cannot be achieved.

  Conditional expression (2) defines the curvature radius ratio of the second lens group G2. When the lower limit of conditional expression (2) is exceeded, astigmatism becomes overcorrected. In addition, since the refractive power of the second lens group G2 becomes small, it is difficult to ensure the back focus. Furthermore, since it is necessary to relatively increase the refractive power of the first lens group G1 in order to maintain the focal length and back focus conditions of the entire system, it is difficult to correct negative distortion. If the upper limit of conditional expression (2) is exceeded, the sag amount of the second lens group G2 becomes large, and compactness cannot be achieved.

  In recent years, digital cameras using CCDs and CMOSs as the image sensor have become mainstream, and shading becomes a problem when the incident angle to the image sensor becomes large. It has been demanded.

  Conditional expression (3) defines the maximum principal ray height and exit angle of the image side surface of the fifth lens group G5. If the range of the conditional expression (3) is exceeded, the emission angle of the maximum principal ray of the surface on the image plane side of the fifth lens group G5 becomes large, and the incident angle of the light ray to the image sensor used in the digital camera becomes large. Shading is a problem.

  Conditional expression (4) defines the thickness of the fourth lens group G4. If the lower limit of conditional expression (4) is exceeded, the refractive power of the biconcave lens L1 and the biconvex lens L2 constituting the fourth lens group G4 will be small and a sufficient achromatic effect will not be obtained, making it difficult to correct lateral chromatic aberration. If the upper limit of conditional expression (4) is exceeded, the thickness of the fourth lens group G4 will increase, making it impossible to achieve compactness.

  Conditional expression (5) defines the imaging magnification of the fifth lens group G5. If the lower limit of conditional expression (5) is exceeded, aberration fluctuations during focusing increase, and good optical performance cannot be maintained. When the upper limit of conditional expression (5) is exceeded, aberration fluctuations during focusing can be reduced and good optical performance can be maintained, but the amount of focusing movement increases and compactness cannot be achieved.

  In the fourth lens group G4, which is a cemented lens of the present invention, it is desirable to make the convex lens side aspherical, but the same effect can be obtained on the concave lens side.

  Examples 1 and 2 of the wide-angle lens of the present invention are shown below. Here (in the overall specifications), f is a focal length, Fno is an F number, and 2ω is an angle of view. In (lens specifications), the number indicates the lens surface number in order from the object side, r indicates the radius of curvature of the lens surface, d indicates the distance between the lens surfaces, n indicates the refractive index of the d-line, and ν indicates the Abbe number. Bf represents the back focus, and Obj represents the distance from the subject to the first lens surface.

Further, the shape of the aspheric surface is expressed by the following formula. Here, the radius of curvature at the center of the lens surface is r, the height from the optical axis is h, the conic coefficient is A, and A ₂ , A ₄ , A ₆ , A ₈ , A ₁₀ are the aspheric coefficients. To do.

(Overall specifications)
f = 16.67 mm
Fno = 4.02
2ω = 73.7 °

(Lens specifications)
Number r d n ν
[1] 22.0500 1.3500 1.58144 40.9
[2] 11.6500 3.0900
[3] 24.0000 1.0000 1.48749 70.4
[4] 11.6500 14.8800
[5] 13.5200 2.8000 1.74100 52.6
[6] -54.1400 1.2000
[7] Aperture 5.2000
[8] -13.0800 1.3000 1.76182 26.6
[9] 16.1500 4.3000 1.77227 47.1
[10] −18.9700 d10
[11] 64.6400 2.3900 1.58913 61.2
[12] -1000.00000 Bf

(10 aspherical coefficients)
A = 2.5919
A ₂ = 0.0
A ₄ = 0.16110D-03
A ₆ = 0.1009D-05
A ₈ = 0.17690D-07
A ₁₀ = 0.10340D-09

(Variable interval)
Obj ∞ 243.7497
d10 5.0000 1.4104
Bf 13.7403 17.3299

(Condition value)
(1) | r1f / r1b | = 1.89
(2) | r2f / r2b | = 2.06
(3) | (Is−h5b) /Bf|=0.38 (at a finite distance)
(4) | Is / d4 | = 2.23
(5) | β5 | = 0.833

(Overall specifications)
f = 15.6414 mm
Fno = 3.78
2ω = 77.3 °

(Lens specifications)
Number r d n ν
[1] 18.4700 1.0400 1.80450 39.6
[2] 11.7000 2.8600
[3] 23.8700 0.8200 1.51680 64.2
[4] 11.7000 15.0200
[5] 13.1800 2.5300 1.77250 49.6
[6] -65.0000 1.5200
[7] Aperture 4.9500
[8] -12.0500 0.8000 1.76182 26.6
[9] 12.9300 4.7000 1.77377 47.2
[10] -18.5600 d10
[11] 65.9600 1.9700 1.80420 46.5
[12] -597.7100 Bf

(10 aspherical coefficients)
A = 3.5369
A ₂ = 0.0
A ₄ = 0.19000D-03
A ₆ = 0.15830D-05
A ₈ = 0.14450D-07
A ₁₀ = 0.13370D-09

(Variable interval)
Obj ∞ 245.6557
d10 3.8900 1.4868
Bf 14.2443 16.6475

(Condition value)
(1) | r1f / r1b | = 1.58
(2) | r2f / r2b | = 2.04
(3) | (Is−h5b) /Bf|=0.39 (at finite distance)
(4) | Is / d4 | = 2.27
(5) | β5 | = 0.794

  Since the angle of the light beam incident on the image sensor can be suppressed and the optical performance is compatible with a large image sensor, it can be applied to a digital camera using a large CCD or CMOS image sensor.

2 is a lens cross-sectional view of Example 1. FIG. FIG. 6 is a diagram illustrating various aberrations at the time of shooting at infinity according to Example 1. FIG. 6 is a diagram illustrating various aberrations during finite object distance imaging in Example 1. 6 is a lens cross-sectional view of Example 2. FIG. FIG. 6 is a diagram illustrating various aberrations at the time of shooting at infinity according to Example 2. FIG. 6 is a diagram illustrating various aberrations during finite object distance imaging in Example 2.

Explanation of symbols

G1 1st lens group G2 2nd lens group G3 3rd lens group G4 4th lens group G5 5th lens group L1 Biconcave lens L2 Biconvex lens

Claims (4)

  In order from the object side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a positive refractive power The fourth lens group is composed of a birefringent lens having negative refractive power and a biconvex lens having positive refractive power, which are cemented with an aspherical lens. Wide-angle lens characterized by being. When the curvature radius on the object side of the first lens group is r1f, the curvature radius on the image plane side is r1b, the curvature radius on the object side of the second lens group is r2f, and the curvature radius on the image plane side is r2b, The wide-angle lens according to claim 1, wherein the following condition is satisfied.
(1) 1.5 <r1f / r1b <2.0
(2) 1.8 <r2f / r2b <2.3
Where r1f: radius of curvature on the object side of the first lens group r1b: radius of curvature on the image side of the first lens group r2f: radius of curvature on the object side of the second lens group r2b: radius of curvature on the image side of the second lens group curvature radius The inner thickness of the fourth lens group is d4, the maximum principal ray height of the surface on the image plane side of the fifth lens group is h5b, the air space from the fifth lens group to the image plane in the entire photographing region is Bf, and the image 3. The wide angle lens according to claim 1, wherein the following condition is satisfied when the diagonal length of the surface is Is.
(3) (Is−h5b) /Bf≦0.39
(4) 2.0 <Is / d4 <2.5
However, d4: Medium thickness of the fourth lens group h5b: Maximum principal ray height of the image side surface of the fifth lens group Bf: Air distance from the fifth lens group to the image plane in the entire imaging region Is: Image Diagonal length of face The wide-angle lens according to any one of claims 1 to 3, wherein the following condition is satisfied when the imaging magnification of the fifth lens group is β5.
(5) 0.7 <β5 <0.9
Where β5: imaging magnification of the fifth lens group

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