JPH09127413A - Large aperture ultra wide angle lens system - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a high-performance ultra-wide-angle lens with a very large aperture of F 0.8 to 0.95 and a half angle of view of about 60 ° for small TV cameras. [Arrangement] A front lens group having negative power, an aperture stop, and a rear lens group having positive power are arranged in this order from the object side, and the front lens group has negative power at the maximum lens interval position. The first-a lens unit and the first lens having negative power
The following conditional expressions (1) to (4)
A large aperture super wide-angle lens system that satisfies the requirements. (1) -0.5 <f / f _F <-0.2 (2) -0.2 <f / f _1a <-0.07 (3) 3 <d _ab / f <7 (4) 10 < Σd _{F + S} / f <15 where f: focal length of the entire system, f _F : focal length of the front lens group, f _1a : focal length of the 1a lens group, d _ab : 1a lens group and 1b lens Group spacing, Σd _{F + S} : Sum of front group lens thickness and front and rear group lens spacing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a large-diameter ultra-wide-angle lens applicable to a small television camera such as a CCTV camera.

[0002]

2. Description of the Related Art In a small television camera, the screen size is shifting from 1/2 "(inch) to 1/3" as the image pickup device is downsized and the resolution is increased. For this reason, a large-diameter image pickup lens having a small F number is required, but in the past, it was about F1.0 to 1.2.

[0003]

An object of the present invention is to reduce the screen size of an image sensor to 1 /
It can be used for small TV cameras of about 3 ", F
Very large aperture of 0.8 to 0.95 and half angle of view 60
The aim is to obtain a super wide-angle lens of about °.

[0004]

SUMMARY OF THE INVENTION A large aperture super wide-angle lens system according to the present invention comprises, in order from the object side, a front lens group having negative power; a diaphragm; and a rear lens group having positive power; Is characterized in that it is divided into a first-a lens group having negative power and a first-b lens group having negative power at the maximum lens interval position, and satisfies the following conditional expressions (1) to (4). There is. (1) -0.5 <f / f _F <-0.2 (2) -0.2 <f / f _1a <-0.07 (3) 3 <d _ab / f <7 (4) 10 < Σd _{F + S} / f <15 where f: focal length of the entire system, f _F : focal length of the front lens group, f _1a : focal length of the 1a lens group, d _ab : 1a lens group and 1b lens Group spacing, Σd _{F + S} : Sum of the thickness of the front group lens and the front and rear group lens spacing.

The rear lens group of the large-diameter ultra-wide-angle lens system of the present invention specifically has, in order from the object side, a positive lens having a convex surface on the image surface side and a cemented cemented surface on the image surface side. It is composed of a cemented lens of a negative lens and a positive lens, and three groups of four lenses of a positive lens having a convex surface on the object side. At least one surface of these lenses is provided with a divergent aspherical surface, and the following conditional expression ( It is preferable that 5) and (6) are satisfied. (5) −3.0 <ΔI _ASP <−0.5 (6) 5.0 <Σd _R /f<10.0 where ΔI _{ASP is the} aspherical term of the third-order spherical aberration coefficient of the aspherical lens. Aberration coefficient (aberration coefficient when focal length is converted to 1.0), Σd _R : thickness of rear group lens.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The large aperture wide-angle lens system of the present invention comprises
It is intended for a two-lens configuration including a negative lens group, a diaphragm, and a positive lens group. In this negative and positive two-group wide-angle lens system, the screen size of the image pickup device of the small TV camera is 1/2 "to 1/3".
When the focal length becomes shorter as the size becomes smaller,
In order to secure the same back focus (f _B ) as in the case of "/ 2", the negative power of the front group is more necessary.
It is also necessary to devise the power allocation for all systems in the front group. Conditional expression (1) relates to the negative power of the front lens group, and if the upper limit is exceeded, the back focus becomes too small to be mounted on a small TV camera. When the value goes below the lower limit, the aberration generated in the front lens group becomes large, and it becomes difficult to correct the aberration.

Conditional expression (2) is a condition relating to the power of the 1a lens group. If the upper limit of conditional expression (2) is exceeded,
If sufficient back focus cannot be obtained and the lower limit is exceeded, the negative power of the 1a lens group becomes large, the radius of curvature of the concave surface becomes small, and the ratio of the lens diameter to the radius of curvature becomes large, making manufacturing difficult. Becomes

Conditional expression (3) is defined by the first lens group a and the first lens group b.
This is a condition regarding the distance between lens groups. As shown in the conditional expression (3), by setting a large distance between the first-a lens group and the first-b lens group, aberration correction is further improved,
The back focus can be increased. When the upper limit of conditional expression (3) is exceeded, the diameter of the front lens group increases, and when the lower limit is exceeded, sufficient back focus cannot be obtained.

Further, since the present invention covers a super wide angle of about half the field angle of 60 °, the diameter of the 1a lens group, which is farther from the stop, becomes considerably larger than the diameter of the 1b lens group. Therefore, when the value goes below the lower limit, the distance between the diaphragm and the first-a lens group becomes small, which causes a problem that the first-a lens group and the diaphragm mechanism interfere with each other. The lower limit of the conditional expression (3) is necessary in order not to interfere with the diaphragm mechanism.

The power of the 1a lens group in the front lens group is 0.3 <f with respect to the power of the entire front lens group.
_It is preferable to set _F / f _1a <0.5. When the lower limit is exceeded and the power of the first-a lens unit is small, it is difficult to obtain a sufficient back focus, and when the upper limit is exceeded, the first-a lens unit is too weak.
If the power of the lens group is large (that is, if the power of the 1a lens group is more than half the power of the entire front lens group), the ratio of the lens diameter to the radius of curvature becomes large, which makes manufacturing difficult.

Conditional expression (4) is a condition relating to the sum of the lens thickness of the front lens group and the front and rear lens group distance. If the upper limit of conditional expression (4) is exceeded, not only the total lens length will increase, but also the diameter of the front lens group will increase, and if the lower limit is exceeded,
It becomes difficult to increase the back focus, or in order to increase the back focus, the negative power of the front lens group increases, and it becomes difficult to correct the aberration.

Conditional expression (5) is provided in the rear lens group,
It relates to an aspherical surface exhibiting divergence. An aspherical surface is a surface formed by adding an aspherical surface onto a paraxial spherical surface (base spherical surface), and "divergent aspherical surface" gives divergence to the surface refractive power of the base spherical surface. It means aspherical surface. If the upper limit of conditional expression (5) is exceeded, the effect of the aspherical surface will be small, and spherical aberration and coma will be insufficiently corrected. Conversely, if the lower limit is exceeded, these aberrations will be overcorrected.

Conditional expression (6) relates to the lens thickness of the rear lens group, and is a condition for increasing the aperture. If the upper limit of conditional expression (6) is exceeded, the total lens length and the diameter of the rear lens group will increase, and if the lower limit is exceeded, the peripheral thickness of the lens will become small, and a wide-angle ultra-wide angle of about F0.8 to 0.95 I can't get the lens.

Next, the relationship between the aspherical surface coefficient and the aberration coefficient will be shown. 1. The aspheric shape is defined by the following equation. x = cy ² / {1+ [1- (1 + K) c ² y ² ] ^1/2 } + A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰ +
(Where x: aspherical shape, c: curvature, y: height from the optical axis, K: conical coefficient) In this equation, for obtaining the aberration coefficient, converted to K = 0 (when the _{K = 0, B i = A} i) ^{for, B4 = A4 + Kc 3/} 8, B6 = A6 + (K 2 + 2K) When ^{c 5/16, B8 = A8} + 5 (K 3 + 3K 2 + 3K) c 7/128 B10 = A10 + 7 (K 4 + 4K 3 + 6K 2 + 4K) c 9/256, x = cy ² / {1+ [1-c ² y ² ] ^1/2 } + B4y ⁴ + B6y ⁶ + B8y ⁸ + B10y ¹⁰ +. 3. Furthermore, to convert to f = 1.0, X = x / f, Y = y / f, C = f ・ c, α4 = f ³ B4, α6 = f ⁵ B6, α8 = f ⁷ B8,
If α10 = f ⁹ B10, then X = CY ² / {1+ [1-C ² Y ² ] ^1/2 } + α4Y ⁴ + α6Y ⁶ + α8Y ⁸ + α10Y ¹⁰ + ・ ・
・ It becomes. 4. Defined by Φ = 8 (N'-N) α4, the third-order aberration coefficient is I: spherical aberration coefficient, II: coma aberration coefficient, III: astigmatism coefficient, IV: aspheric surface curvature coefficient, V : Distortion aberration coefficient, and the influence of the 4th-order aspherical surface coefficient (α4) of each aberration coefficient is ΔI = h ⁴ Φ ΔII = h ³ kΦ ΔIII = h ² k ² Φ ΔIV = h ² k ² Φ ΔV = hk ³ Φ (where, h: height of paraxial ray passing through, k: height of paraxial ray passing through the center of the pupil N ′: refractive index of aspherical rear side,
N: refractive index on the front side of the aspherical surface).

Next, the present invention will be described with reference to specific examples. 1, 3, and 5 show Embodiments 1, 2, and 3, respectively.
2 is a lens configuration diagram of FIG. In each of the examples, a front lens group 11, an aperture stop S, and a rear lens group 12 are arranged in this order from the object side. The front lens group 11 has a maximum lens distance (lens distance d ₂ ). 1a lens group 11a and 1st
It is divided into b lens group 11b. 1a lens group 1
1a is a meniscus single lens with a convex surface facing the object side (surface N
o. 1, 2), and the 1b-th lens group 11b is composed of 3 elements in 2 groups (surface Nos. 3 to 7). Rear lens group 12
Consists of a biconvex positive lens 12a, a negative lens 12b having a concave surface on the image side, a biconvex positive lens 12c, and a biconvex positive lens 12d. The negative lens 12b and the positive lens 12
c is pasted together. The curvature of the image-side surface (surface No. 9) of the biconvex positive lens 12a is larger than that of the object-side surface (surface No. 8), and the negative lens 12b and the positive lens 12c are bonded together. The curvature of the surface (surface No.11) is larger than that of the other surfaces (surface No.10, 12). Biconvex positive lens 12
The curvature of the object-side surface (surface No. 13) of d is the image-side surface (surface No. 1).
Greater than the curvature of 4). Surface Nos. 15 and 16 are CCD cover glasses 13. The cover glass 13 is a combination of the cover glass and the filter.
Hereinafter, it is abbreviated as a cover glass.

[Embodiment 1] FIG. 1 is a lens configuration diagram of Embodiment 1 of a large aperture ultra wide-angle lens system of the present invention. Numerical data of this lens system is shown in Table 1, and various aberrations in this lens system are shown in FIG. In the various aberration diagrams, SA is spherical aberration, SC is sine condition, d line, g line, and c line are chromatic aberrations indicated by spherical aberration at respective wavelengths, S is sagittal,
M indicates meridional.

In the tables and drawings, F _NO is an F number, F is a focal length, ω is a half angle of view, and f _B is a back focus (the distance from the image side of the final lens to the image pickup surface of the CCD including the cover glass 13). In the embodiment, the second surface of the cover glass is used as the image pickup surface), r _i is the radius of curvature of each surface of the lens, and d _i
Is the lens thickness or lens spacing, N is the refractive index of the d-line, ν
Indicates the Abbe number of the d line.

[0018]

[Table 1] F _NO = 1: 0.8 F = 2.88 ω = 62.3 f _B = d ₁₄ + d ₁₅ = 9.40 surface No. rd N ν 1 46.431 1.50 1.77250 49.6 2 12.480 13.92--3 49.884 1.22 1.83481 42.7 4 7.548 2.23 --5 -25.288 1.20 1.80023 29.2 6 7.403 4.65 1.84666 23.8 7 -15.916 5.94--Aperture ∞ 4.87--8 55.036 3.84 1.74320 49.3 9 -29.471 2.11--10 -506.763 1.20 1.84666 23.8 11 8.976 7.00 1.76400 49.0 12 -31.908 0.96 --13 * 11.969 5.70 1.66625 55.2 14 -46.478 3.70--15 ∞ 5.70 1.49782 66.8 16 ∞---* is rotationally symmetric aspherical aspherical surface data No.13: K = 0.0, A4 = -0.38860 × 10 ^-4 , A6 = -0.76296 x 1
0 ^-6 , A8 = 0.48918 × 10 ^-8 , A10 = -0.94415 × 10 ^-11 , A12 = 0.0 However, the rotationally symmetric aspherical surface is defined by the following equation. x = cy ² / {1+ [1- (1 + K) c ² y ² ] ^1/2 } + A4y ⁴ + A6y ⁶ + A8y ⁸ + ... (c is the curvature (1 / r), y is (Height from the optical axis, K is the cone coefficient)

[Embodiment 2] FIG. 3 is a lens configuration diagram of Embodiment 2 of the large-diameter super wide-angle lens system of the present invention. Numerical data of this lens system are shown in Table 2 and various aberrations thereof are shown in FIG.

[0020]

[Table 2] F _NO = 1: 0.95 F = 2.88 ω = 62.4 f _B = d ₁₄ + d ₁₅ = 9.41 No. rd N ν 1 50.120 1.50 1.77250 49.6 2 12.787 14.39--3 35.382 1.22 1.83481 42.7 4 7.839 2.73 --5 -24.006 1.20 1.80440 39.6 6 10.344 4.65 1.84666 23.8 7 -17.118 5.97--Aperture ∞ 4.90--8 * 49.867 3.84 1.74320 49.3 9 -26.962 1.05--10 629.935 1.20 1.84666 23.8 11 8.165 7.00 1.78800 47.4 12 -24.988 1.55 --13 13.656 4.24 1.66625 55.2 14 -153.130 3.71--15 ∞ 5.70 1.49782 66.8 16 ∞---* is rotationally symmetric aspherical aspherical surface data No.8: K = 0.0, A4 = -0.39338 × 10 ^-4 , A6 = 0.25604 × 1
0 ^-7 , A8 = 0.95540 × 10 ^-9 , A10 = 0.20021 × 10 ^-10 , A12 = 0.0

[Embodiment 3] FIG. 5 is a lens configuration diagram of Embodiment 3 of the large-diameter super wide-angle lens system of the present invention. Numerical data of this lens system are shown in Table 3, and various aberrations thereof are shown in FIG.

[0022]

[Table 3] F _NO = 1: 0.95 F = 2.88 ω = 62.6 f _B = d ₁₄ + d ₁₅ = 9.40 No. rd N ν 1 52.182 1.50 1.77250 49.6 2 12.800 15.11--3 42.110 1.22 1.83481 42.7 4 7.500 2.02 --5 -25.702 1.20 1.80440 39.6 6 9.260 4.65 1.84666 23.8 7 -16.160 5.24--Aperture ∞ 4.17--8 44.850 3.84 1.74320 49.3 9 -31.408 0.77--10 -2275.000 1.20 1.84666 23.8 11 8.233 7.00 1.78800 47.4 12 -26.975 0.50 --13 * 13.765 5.70 1.66625 55.2 14 -51.786 3.70--15 ∞ 5.70 1.49782 66.8 16 ∞---* is rotationally symmetric aspherical aspherical surface data No.13: K = 0.0, A4 = -0.39130 × 10 ^-4 , A6 = -0.41090 x 1
0 ^-6 , A8 = 0.41830 × 10 ^-8 , A10 = -0.35520 × 10 ^-10 , A12 = 0.0

Table 4 shows the values corresponding to the conditional expressions of Examples 1 to 3.

[Table 4]

As is clear from Table 4, the first to third embodiments all satisfy the conditional expressions (1) to (6). Further, in each embodiment, as indicated by the value of f _F / f _1a , the power of the first-a lens unit is less than half the power of the entire front lens unit. As shown in each aberration diagram, various aberrations are well corrected.

[0025]

According to the large-aperture ultra-wide-angle lens system of the present invention, the ultra-wide-angle lens has a very large aperture of about F 0.8 to 0.95 for a small TV camera and a high-performance ultra-wide angle of about 60 °. You can get a nice lens.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram showing a first embodiment of a large-diameter ultra-wide-angle lens system according to the present invention.

FIG. 2 is a diagram illustrating various aberrations of the lens system in FIG. 1;

FIG. 3 is a lens configuration diagram showing a second embodiment of a large-diameter ultra-wide-angle lens system according to the present invention.

FIG. 4 is a diagram illustrating various aberrations of the lens system in FIG. 3;

FIG. 5 is a lens configuration diagram showing a third embodiment of a large-diameter ultra-wide-angle lens system according to the present invention.

FIG. 6 is a diagram illustrating various aberrations of the lens system in FIG. 5;

Claims (2)

[Claims] 1. A front lens group having a negative power; an aperture; and a rear lens group having a positive power, in order from the object side, wherein the front lens group has a negative lens power at a maximum lens interval position. 1a lens group having a power and 1b lens having a negative power
A large aperture super wide-angle lens system that is divided into a lens group and satisfies the following conditional expressions (1) to (4). (1) -0.5 <f / f _F <-0.2 (2) -0.2 <f / f _1a <-0.07 (3) 3 <d _ab / f <7 (4) 10 < Σd _{F + S} / f <15 where f: focal length of the entire system, f _F : focal length of the front lens group, f _1a : focal length of the 1a lens group, d _ab : 1a lens group and 1b lens Group spacing, Σd _{F + S} : Sum of front group lens thickness and front and rear group lens spacing. 2. The rear lens group according to claim 1, wherein in order from the object side, a positive lens having a convex surface on the image surface side, and a negative lens and a positive lens having a concave bonding surface on the image surface side are cemented together. A lens and a positive lens having a convex surface on the object side, composed of 4 elements in 3 groups. At least one surface of these lenses has a divergent aspherical surface, and the following conditional expressions (5) and (6) are satisfied. Satisfactory large aperture super wide-angle lens system. (5) −3.0 <ΔI _ASP <−0.5 (6) 5.0 <Σd _R /f<10.0 where ΔI _{ASP is the} aspherical term of the third-order spherical aberration coefficient of the aspherical lens. Aberration coefficient (aberration coefficient when focal length is converted to 1.0), Σd _R : thickness of rear group lens.