JP2005173276A - Super-wide angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens system which is compact and less in aberration fluctuations, caused by a focusing, while being a super-wide angle lens whose photographic viewing angle exceeds 110 degrees. <P>SOLUTION: The super-wide angle lens has a 1st lens group G1, having negative refractive power and a 2nd lens group G2 having positive refractive power, in this order starting from an object side, with the 1st lens group G1 includes a lens unit L1, constituted of a negative meniscus lens turning its convex surface to the object side; a negative meniscus lens L2 using an aspherical surface and turning its convex surface to the object side; a doublet L3, having negative power as a whole and having positive power and negative power; and a lens unit L4, having positive power as a whole in order from the object side. When focusing, the 1st lens group is moved to the object side, and the super-wide angle lens is set to satisfy a fixed condition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a super-wide-angle lens suitable for a single-lens reflex camera, an electronic still camera, a video camera, or the like whose angle of view exceeds 110 degrees.

Conventionally, as a retrofocus type super wide-angle lens having an angle of view exceeding 110 degrees, for example, a convex lens is used for a lens having a large effective beam diameter known in Japanese Patent Publication No. 62-50808, Japanese Patent No. 3118030, and the like. Therefore, there is a lens type that corrects distortion and adopts a rear focus type as a focusing method. In this retrofocus type super-wide-angle lens, in order to correct distortion, a configuration in which a convex lens is used as a lens having a large effective beam diameter from the first lens to the third lens in the front group having a strong negative power is generally used. It was the target.
Japanese Examined Patent Publication No. 62-50808 Japanese Patent No. 3118030

  However, if a convex lens is used for these lenses, the power of the concave lens unit becomes strong, and therefore there is a problem that the entire first group unit is enlarged and it is difficult to make it compact.

  In order to make the first lens group compact, it is effective to make the surface close to the object surface aspherical, such as the first lens, for example, but making a large diameter lens aspherical This is not desirable because it causes a significant increase in cost and a decrease in mass productivity.

  Therefore, by appropriately arranging the configuration of the first lens group, it is a problem to realize a lightweight and compact super wide-angle lens while performing sufficient aberration correction with a small configuration without using a large-aperture aspheric lens. It becomes.

  Furthermore, in recent years, electronic still cameras using CCD or CMOS as an image sensor are becoming mainstream, and there is a demand for a telecentric optical system in which the emission angle of peripheral luminous flux becomes gentle. There is a tendency that the exit angle becomes tighter. Furthermore, in AF systems that require rapid focusing, a rear focus system that moves a rear group unit, which is a small and light lens system, is the mainstream during focusing. However, if the emission angle of the off-axis light beam is made loose, the lens diameter of the second lens group becomes large. Therefore, there is no space for a mechanism for moving a large lens unit due to restrictions on the lens mount diameter during focusing. Further, as the lens diameter increases, the ray height of the peripheral luminous flux increases, so that it becomes difficult to correct astigmatism variation due to focusing. As a result, there is a demand for a system that can perform focusing with a simple structure without using the rear group unit.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a lens system in which the system has a compact size and less aberration fluctuation due to focusing, while the super wide-angle lens has a field angle of view exceeding 110 degrees.

The present invention includes a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side, and the first lens group has a convex surface directed toward the object side in order from the object side. A lens unit L1 composed of a negative meniscus lens, a negative meniscus lens L2 having a convex surface facing the object side using an aspherical surface, a cemented lens L3 having negative power as a whole, positive power and negative power, and the whole The first lens unit is moved to the object side during focusing, and satisfies the following conditions.
(1) 0.5 <| f ₁ /f|<2.0
(2) 0.5 × (r ₂ × h ₂ ) / f <d ₂ <2.0 × (r ₂ × h ₂ ) / f
However,
f: focal length of all optical systems f ₁ : focal length of first lens unit d ₂ : distance from first lens unit L2 second surface to L3 first surface r ₂ : curvature of first lens unit L2 second surface Radius h ₂ : Ray height from the optical axis of the second surface of the first lens unit L2

  The present invention includes a first lens group G1 having a negative refractive power and a second lens group G2 having a positive refractive power, and the first lens group G1 has a convex surface directed toward the object side in order from the object side. A lens unit L1 composed of a negative meniscus lens, a negative meniscus lens L2 having a convex surface facing the object side using an aspheric surface, a cemented lens L3 having negative power as a whole, positive power and negative power, as a whole By using the lens unit L4 having a positive power, focusing can be performed with a simple structure without using the rear group unit.

  In addition, the lens unit L1 can be simplified in configuration by including only a negative meniscus lens having a convex power on the object side. Further, by dividing the negative meniscus lens into a plurality of parts, the refractive power of the lens unit L1 can be increased without deteriorating various aberrations, so that the effective diameter of the negative meniscus lens L2 using an aspherical surface is reduced. can do.

Condition (1) is obtained by defining the ratio of the focal length f ₁ of the focal length f and the first lens group G1 of the entire system. If the lower limit of conditional expression (1) is exceeded, the negative refractive power of the first lens group G1 becomes strong, which is advantageous for downsizing, but it becomes difficult to correct distortion, and aberration fluctuations due to focusing also increase. . Exceeding the upper limit of conditional expression (1) is advantageous for aberration correction, but it is difficult to ensure back focus.

  Conditional expression (2) indicates that the distance from the second surface of the negative meniscus lens L2 to the first surface of the cemented lens L3, the radius of curvature of the second surface of the negative meniscus lens L2, the height of light from the optical axis, and the focal length of the entire system. If the lower limit of conditional expression (2) is exceeded, the distance from the second surface of the negative meniscus lens L2 to the first surface of the cemented lens L3 becomes too short, and the distance from the second surface of the negative meniscus lens L2 Since the exit angle becomes tight, it becomes difficult to correct astigmatism and distortion of the peripheral light flux. If the upper limit of conditional expression (2) is exceeded, the distance from the second surface of the negative meniscus lens L2 to the first surface of the cemented lens L3 increases, the effective beam diameter of the negative meniscus lens L2 using an aspheric surface increases, and the lens weight At the same time, manufacturing becomes difficult.

  According to the present invention, an ultra wide-angle lens having an angle of view exceeding 110 degrees can be configured in a compact system.

の式で表される。 Hereinafter, Numerical Example 1 and Numerical Example 2 of the super wide-angle lens according to the present invention will be described. Here, f is a focal length, _fNO is an F number, and _2ω is an angle of view. r is the radius of curvature of the i-th lens surface in order from the object side, d is the i-th lens thickness and air spacing in order from the object side, and n is the d-line (λ = 587) in order from the object side. .6 nm) Refractive index, v is the Abbe number of the i-th lens in order from the object side.
The expression representing the aspherical shape is as follows: when the optical axis is x, the height perpendicular to the optical axis is H, the radius of curvature is r, and the nth-order aspherical coefficient is An.

It is expressed by the following formula.

(Overall specifications)
f = 10.30
f _NO = 4.64
2 _ω = 111.2 °
(Lens specifications)
Number r d n v
[1] 34.1800 1.6000 1.80420 46.5
[2] 15.95570 4.8780
[3] 34.0840 1.5000 1.69350 53.2
[4] 16.6210 21.7530
[5] 147.1310 2.5000 1.64769 33.8
[6] -12.4940 0.8500 1.80420 46.5
[7] 32.7500 0.5460
[8] -29.0380 1.6680 1.48749 70.4
[9] -12.1520 3.7470
[10] 124.9570 2.9770 1.67270 32.2
[11] -60420 0.8500 1.77250 49.6
[12] 102.2500 1.7180
[13] 59.6220 1.9400 1.48749 70.4
[14] -91.8870 7.1200
[15] 1936.6120 5.4030 1.48749 70.2
[16] -15.8030 0.1000 1.51840 52.1
[17] -14.5060 0.1500
[18] 475.6900 0.8500 1.84666 23.8
[19] 28.8880 8.6160 1.49700 81.6
[20] -28.8880
r3
A ₄ = 4.2943346 × 10 ⁻⁵
A ₆ = −1.70332134 × 10 ⁻⁷
A ₈ = 1.8289499 × 10 ⁻⁹
A ₁₀ = −8.1142272 × 10 ⁻¹²
A ₁₂ = 1.6659290 × 10 ⁻¹⁴
r17
A ₄ = 3.8218463 × 10 ⁻⁵
A ₆ = 2.66948535 × 10 ⁻⁸
A ₈ = 5.7004833 × 10 ⁻¹⁰
A ₁₀ = −1.4100303 × 10 ⁻¹²

(Overall specifications)
f = 10.30
f _NO = 3.88
2 _ω = 10.6 °
(Lens specifications)
Number r d n v
[1] 34.7050 1.8000 1.77250 49.6
[2] 194640 3.4440
[3] 22.7130 1.5000 1.77250 49.6
[4] 16.3683 5.3420
[5] 41.0150 1.3000 1.743330 49.3
[6] 19.2750 23.5810
[7] 102.0730 2.7860 1.584144 40.9
[8]-17.7360 0.8500 1.80420 46.5
[9] 72.2530 0.8280
[10] -22.1700 1.6720 1.48749 70.4
[11]-13.1790 4.1860
[12] 30.3850 3.6980 1.695 30.0
[13] -7.3610 0.8500 1.80420 46.5
[14] 23.1870 1.5420
[15] 26.2150 1.8400 1.48749 70.4
[16] -105.4280 9.2850
[17] 0.0 4.6380 1.48749 70.4
[18] -16.9680 0.1000 1.5840 52.1
[19] -15.740 0.1500
[20] 1000.0000 0.8500 1.84666 23.8
[21] 21.0690 8.0260 1.49700 81.6
[22] -21.0690
(Aspheric coefficient)
r5
A ₄ = 3.3727675 × 10 ⁻⁵
A ₆ = −6.7206139 × 10 ⁻⁸
A ₈ = 8.612684 × 10 ⁻¹⁰
A ₁₀ = −4.1034933 × 10 ⁻¹²
A ₁₂ = 9.5076296 × 10 ⁻¹⁵
r19
A ₄ = 3.1037101 × 10 ⁻⁵
A ₆ = 3.5356814 × 10 ⁻⁸
A ₈ = −2.1356409 × 10 ⁻¹⁰
A ₁₀ = 2.3731519 × 10 ⁻¹²

The values of the conditional expressions of the present invention for the examples are as follows.
Conditional Example Example 1 Example 2
(1) f ₁ / f 1.567 1.808
(2) d ₂ 21.753 23.581
0.5 × (r ₂ × h ₂ ) / f 10.473 12.753
2.0 × (r ₂ × h ₂ ) / f 41.891 51.013

1 is a configuration diagram of Example 1. FIG. FIG. 5 is a diagram illustrating all aberrations of Example 1. FIG. 6 is a configuration diagram of Example 2. FIG. 6 is a diagram illustrating all aberrations of Example 2.

Explanation of symbols

G1 first lens group L1 lens unit L2 negative meniscus lens L3 cemented lens L4 lens unit G2 second lens group

Claims (1)

A negative meniscus having a first lens group having a negative refractive power and a second lens group having a positive refractive power in order from the object side, and further having a convex surface facing the object side in order from the object side. L1 lens unit composed of a lens, a negative meniscus lens L2 having a convex surface facing the object side using an aspherical surface, a cemented lens L3 having negative power as a whole and positive power and negative power as a whole, positive An ultra-wide-angle lens that is configured by a lens unit L4 having power and moves the first lens unit toward the object side during focusing and satisfies the following conditions.
(1) 0.5 <| f ₁ /f|<2.0
(2) 0.5 × (r ₂ × h ₂ ) / f <d ₂ <2.0 × (r ₂ × h ₂ ) / f
However,
f: focal length of all optical systems f ₁ : focal length of first lens unit d ₂ : distance from first lens unit L2 second surface to L3 first surface r ₂ : curvature of first lens unit L2 second surface Radius h ₂ : Ray height from the optical axis of the second surface of the first lens unit L2

Images