JP3397446B2 - Large aperture lens system - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In this type of compact television camera, a compact and high-resolution image pickup device having a small size of one pixel is generally used. Therefore, a large-aperture photographic lens having a small F number is required. However, conventionally, F1.0 to 1.
It was about 2.

[0003]

An object of the present invention is to obtain a standard lens system having a very large aperture of about F0.8 and a large back focus.

[0004]

SUMMARY OF THE INVENTION A large-diameter lens of the present invention comprises, in order from the object side, a front lens group having negative power, an aperture stop, and a rear lens group having positive power, and the rear lens group is arranged in order from the object side. ,
The positive lens closest to the object, consisting of positive, positive, and positive lens groups
The group consists of a negative lens with a large curvature whose cemented surface is convex toward the object side and a positive lens.
It consists of a cemented lens and the following conditional expression
It is characterized by satisfying (1) to (7) . (1) -0.5 <f / f _F <-0.2 (2) 1.0 <Σd _{F + S} /f<3.0 (3) 1.5 <Σd _R /f<3.0 ( 4) 0.6 <Σd _{R1 + 2 /} f < 1.5 (5) 1.75 <N _R1 (6) 1.7 <N _R2 (7) 1.0 <r _RC /f<2.5 , F: focal length of the entire system, f _F : focal length of the front lens group, Σd _{F + S} : sum of the thickness of the front lens group and the distance between the front and rear lens groups, Σd _R : the thickness of the rear lens group. Σd _{R1 + 2} : Lens of the cemented lens on the object side of the rear lens group
Thickness, N _R1 : of the negative lens of the cemented lens on the object side of the rear lens group
Refractive index, N _R2 : of the positive lens of the cemented lens on the object side of the rear lens group
Refractive index, r _RC : of the cemented surface of the cemented lens on the object side of the rear lens group
The radius of curvature is.

[0005]

It is preferable that the rear lens group further has a divergent aspherical surface satisfying the following conditional expressions (8) and (9). _{(8) -0.9 <△ I ASP} <0 (9) I SP / △ I ASP <0.2 where, [Delta] I _ASP: 3 order spherical aberration coefficients (in terms of focal length 1.0 aspheric lens Is the aberration coefficient of the aspherical term of the aberration coefficient), I _{SP is the} aberration coefficient of the spherical term of the third-order spherical aberration coefficient of the aspherical lens.

On the other hand, the front lens group has at least positive, negative, negative, negative, positive, negative, depending on the specific lens system.
It is possible to have two lens configurations of positive and negative.

In the case of the above, the front lens group is composed of four positive, negative, negative and negative four lens groups, the third lens is a negative lens having a concave surface with a large curvature, and the fourth lens is The negative meniscus lens has a concave surface with a large curvature and satisfies the following conditional expressions (10) and (11). (10) 0.5 <r _3-2 /f<1.0 (11) -1.0 <r _4-1 /f<-0.5 where r _3-2 is the third negative of the front lens group. The radius of curvature of the lens on the image plane side, r _4-1 : The radius of curvature of the fourth negative lens of the front group lens on the object side.

In the above case, the front lens group is composed of four positive, negative, positive, and negative four lenses in order from the object side, and the second lens is a lens having a concave surface with a large curvature on the image side. The fourth lens is a negative meniscus lens having a concave surface with a large curvature, and satisfies the following conditional expressions (12) and (13). (12) 0.5 <r _2-2 /f<1.0 (13) -1.0 <r _4-1 /f<-0.5 where r _2-2 is the second negative of the front lens group. The radius of curvature of the lens on the image plane side is.

[0010]

Embodiments of the large-diameter lens of the present invention will be described below. Conventionally, a large-diameter standard lens is often a modified Gaussian type of a symmetrical system, but the large-diameter standard lens system of the present invention has a negative front lens group in order from the object side in order to increase the back focus. This is a so-called retrofocus-type asymmetric lens system composed of a lens and a positive rear lens group.

Regarding the diaphragm position, it is provided between the front and rear lens groups divided so as to satisfy the conditional expression (1).
There is an advantage that it is mechanically easy and the lens diameters of the front lens group and the rear lens group can be reduced in a well-balanced manner. Further, as compared with the case where a diaphragm is provided in the front lens group or the rear lens group, performance deterioration due to manufacturing errors such as eccentricity between lens groups divided by the diaphragm can be reduced.

Further, although this type of television camera may include an ND filter near the diaphragm, the conditional expression (1)
In connection with this, the position of the diaphragm is also good in order to reduce the ghost due to reflection on the surface of the ND filter and the image pickup device.

Conditional expression (1) relates to the power of the front lens group, and when the value exceeds the upper limit, the back focus becomes small and the mounting on the camera is hindered. When the value goes below the lower limit, the total length of the lens increases, the diameter of the rear lens group increases, and the power of each group increases, so that higher-order aberrations occur.

Conditional expression (2) relates to the sum of the lens thickness of the front lens group and the distance between the front and rear lens groups, and is a condition for increasing the back focus and increasing the aperture. If the upper limit is exceeded, not only will the total lens length increase, but
If the diameter of the front lens group becomes large and exceeds the lower limit, it becomes difficult to increase the back focus or correct the aberration.

Conditional expression (3) relates to the lens thickness of the rear lens group, and is a condition for increasing the aperture. If the upper limit is exceeded, the total lens length and the diameter of the rear lens group increase, and if the lower limit is exceeded, a large aperture lens with a large back focus cannot be obtained.

Conditional expressions (4) to (7) relate to the rear lens group. Conditional expression (4) is a condition for the lens thickness of the cemented lens of the positive lens group on the object side of the rear lens group. When the upper limit is exceeded, the lens size becomes large, and when the lower limit is exceeded, the back focus becomes large, and the front lens group It becomes difficult to correct the spherical aberration and the coma that occur inside.

Conditional expressions (5) and (6) are conditions relating to the refractive index of the negative lens and the positive lens of the cemented lens.
It is desirable to use a high-refractive-index glass having a lower limit or more. If the value goes below the lower limit, the edge thickness (peripheral thickness) of the lens tends to be small, and the radius of curvature of the surface is small, so that higher-order aberrations occur. Here, the reason why the refractive index of the negative lens is larger than that of the positive lens is to correct chromatic aberration and spherical aberration in the rear lens group.

Conditional expression (7) is related to conditional expressions (5) and (6) on the condition of the radius of curvature of the bonding surface. If the upper limit is exceeded, chromatic aberration and spherical aberration in the rear lens group can be corrected. Run out,
When the value goes below the lower limit, high-order spherical aberration occurs. Further, it is difficult to secure the peripheral thickness of the positive lens.

Conditional expressions (8) and (9) relate to an aspherical surface. If a divergent aspherical surface is provided in the rear lens group having a large axial light beam diameter, spherical aberration, coma aberration and astigmatism will be reduced. It can be corrected better. The divergent aspherical surface means a surface shape in which the curvature decreases (the radius of curvature increases) toward the peripheral edge when the convex surface is an aspherical surface, and the peripheral edge when the concave surface is an aspherical surface. A surface shape that has a larger curvature (smaller radius of curvature).

If the upper limit of conditional expression (8) is exceeded, the effect of the aspherical surface will be small, and if the lower limit is exceeded, overcorrection will occur.

Conditional expression (9) relates to the selection of the location of the aspherical surface. It is preferable to provide the aspherical surface on a surface where the value of the spherical term of the aspherical aberration coefficient is smaller than the upper limit of this conditional expression because performance deterioration due to manufacturing errors of the aspherical surface is small.

For a negative front group lens, at least
Positive, negative, negative, and negative lens configurations, or positive, negative, positive, and negative lens configurations can be considered in order from the object side. The positive lens in the negative front lens group is effective in correcting distortion.
In each of the positive, negative, negative, and negative lens configurations and the positive, negative, positive, and negative lens configurations, the surface of the front lens group having the largest curvature that is concave on the image side is expressed by the conditional expression (10 ), (12)
Is good to be satisfied.

When the upper limits of conditional expressions (10) and (12) are exceeded,
It becomes difficult to correct astigmatism and field curvature, and if the lower limit is exceeded, negative surface power will increase, spherical aberration and coma will be overcorrected, and higher-order aberrations will likely occur.

Conditional expression (11) relates to the final lens of the front lens group in the case of positive, negative, negative, and negative lens configurations, and conditional expression (13) is positive, negative, positive, negative. The present invention relates to the final lens of the front lens group when it has a lens configuration. By arranging a negative meniscus lens with a concave surface facing the object side as the final lens of the front lens group, in relation to the negative lens having a concave surface on the image side that satisfies conditional expressions (10) and (12), It is effective in correcting point aberration and field curvature. If the upper limits of conditional expressions (11) and (13) are exceeded, the negative surface power of the final lens in the front group will become large, and spherical aberration and coma will be overcorrected. On the other hand, when the value goes below the lower limit, the negative surface power becomes small, and astigmatism and field curvature are insufficiently corrected.

Next, the relationship between the aspherical surface coefficient and the aberration coefficient will be shown. 1. The aspherical 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 +
... 2. 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 3 + 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,
When α10 = f ⁹ B10, X = CY ² / {1+ [c ² y ² ] ^1/2 } + α4Y ⁴ + α6Y ⁶ + α8Y ⁸ + α10Y ¹⁰ + ... 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, VI: 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).

[Embodiment 1] FIG. 1 is a lens configuration diagram of Embodiment 1 of a large-diameter lens system of the present invention. No. I in front of aperture S
The lens unit is composed of first to fourth lenses, and the second lens unit after the stop S is composed of fifth to eighth lenses. The fifth lens and the sixth lens are cemented lenses. 8th
A plane parallel plate is located at the rear of the lens.

Specific numerical data of this lens system are shown in Table 1, and various aberrations are shown in FIG. SA in the aberration diagrams
Is a spherical aberration, SC is a sine condition, d-line, g-line, and C-line are chromatic aberration and chromatic aberration of magnification indicated by spherical aberration at respective wavelengths, S is sagittal, and M is meridional.

In the table and drawings, F _NO is the F number, F is the focal length, ω is the half angle of view, F _B is the back focus, r _i is the radius of curvature of each lens surface, d _i is the lens thickness or lens spacing, N represents the refractive index, and ν represents the Abbe number.

[0029]

[Table 1] F _NO = 1: 0.82 F = 12.30 ω = 19.2 F _B ＝ d ₁₅ + d ₁₆ (glass) = 11.92 surface No. rd N ν 1 21.238 6.10 1.83400 37.2 2 -671.565 0.39 3 60.867 1.90 1.51762 68.4 4 38.279 1.38 5 -531.905 1.50 1.50000 59.1 6 8.193 5.54 7 -7.297 2.27 1.84666 23.9 8 -11.221 3.18 9 -80.165 4.46 1.84666 23.9 10 18.391 7.55 1.77249 50.7 11 -20.710 0.10 12 27.669 5.64 1.51634 65.2 13 14-40717 4 0.22 50.7 15 44.354 5.92 16 ∞ 6.00 1.49782 66.8 17 ∞

[Embodiment 2] FIG. 3 is a lens configuration diagram of Embodiment 2 of the large-diameter lens system of the present invention. Table 2 shows specific numerical data of this lens system, and FIG. 4 shows various aberrations thereof.

[0031]

[Table 2] F _NO = 1: 0.82 F = 1.30 ω = 19.3 F _B ＝ d ₁₅ + d ₁₆ (glass) = 12.26 surface No. r d N ν 1 21.907 5.40 1.83400 37.2 2 -285.740 0.35 3 64.604 1.90 1.50000 72.2 4 40.142 1.60 5 -68.464 1.50 1.50000 56.5 6 8.523 6.15 7 -8.209 2.00 1.84666 23.9 8 -11.874 3.02 9 -141.119 6.81 1.84666 23.9 10 17.702 7.87 1.77250 50.7 11 -23.085 0.10 12 26.152 6.09 1.50000 67.1 -13 -39.173 0.10 46.6 15 32.932 6.26 16 ∞ 6.00 1.49782 66.8 17 ∞

[Embodiment 3] FIG. 5 is a lens configuration diagram of Embodiment 3 of the large-diameter lens system of the present invention. Table 3 shows specific numerical data of this lens system, and FIG. 6 shows various aberrations thereof.

[0033]

[Table 3] F _NO = 1: 0.82 F = 1.30 ω = 19.1 F _B ＝ d ₁₅ + d ₁₆ (glass) = 11.00 No. r d N ν 1 20.568 5.52 1.83400 37.2 2 -793.963 0.42 3 68.425 2.05 1.48749 70.2 4 22.481 1.73 5 -2053.281 2.48 1.51633 64.1 6 8.157 4.12 7 -7.569 2.97 1.84666 23.9 8 -11.432 4.04 9 -42.945 2.00 1.84666 23.9 10 17.629 8.62 1.74100 52.7 -11 -19.861 0.10 12 15.682 10.00 1.51633 64.1 13 -285.637 2.0 6.1 1.59015 61.4 15 -99.641 5.00 16 ∞ 6.00 1.49782 66.8 17 ∞ * is aspherical surface No.14; K = 0.0, A4 = -0.47153 × 10 ^-4 , A6 = -0.39021 × 10
^-6 , A8 = 0.61389 × 10 ^-9 , A10 = -0.41184 × 10 ^-10 , A12 = 0.0

[Embodiment 4] FIG. 7 is a lens configuration diagram of Embodiment 4 of the large-diameter lens system of the present invention. Table 4 shows specific numerical data of this lens system, and FIG. 8 shows various aberrations thereof.

[0035]

[Table 4] F _NO = 1: 0.82 F = 1.30 ω = 18.8 F _B ＝ d ₁₅ + d ₁₆ (glass) = 11.00 surface No. r d N ν 1 17.420 6.86 1.83400 37.2 2 166.090 0.30 3 31.253 1.90 1.56732 42.8 4 13.785 1.79 5 21515.462 2.13 1.51742 52.4 6 7.087 4.34 7 -5.881 2.51 1.84666 23.8 8 -7.952 3.25 9 -42.846 1.50 1.84666 23.8 10 16.143 7.59 1.74100 52.7 11 -18.975 0.71 12 14.937 8.03 1.48749 70.2 13 -147.15 4.75 1.590 * 18. 15 -37.278 5.00 16 ∞ 6.00 1.49782 66.8 17 ∞ * is aspherical No. 14; K = 0.0, A4 = -0.73070 × 10 ^-4 , A6 = -0.48150 × 10
^-6 , A8 = -0.84666 × 10 ^-9 , A10 = -0.36606 × 10 ^-10 ,
A12 = 0.0

[Embodiment 5] FIG. 9 is a lens configuration diagram of Embodiment 5 of the large-diameter lens system of the present invention. Table 5 shows specific numerical data of this lens system, and FIG. 10 shows various aberrations thereof.

[0037]

[Table 5] F _NO = 1: 0.82 F = 12.30 ω = 18.7 F _B ＝ d ₁₅ + d ₁₆ (glass) = 11.73 surface No. r d N ν 1 18.706 3.76 1.84700 23.9 2 80.543 0.10 3 35.124 2.25 1.48750 67.9 4 7.700 3.23 5 -52.624 3.34 1.84700 42.3 6 -16.644 1.26 7 7 -10.517 1.50 1.83337 24.3 8 -46.334 4.34 9 -24.549 1.50 1.84700 23.9 10 20.449 8.72 1.80400 46.6 11 -17.571 0.10 129.24 24.372 7.49 1.63569 59.1 149 -14.638. 1.66910 55.4 15 39.925 5.73 16 ∞ 6.00 1.49782 66.8 17 ∞ * is aspheric No. 14; K = 0.0, A4 = -0.85653 × 10 ^-5 , A6 = -0.17691 × 10
^-6 , A8 = 0.17690 × 10 ^-8 , A10 = -0.17354 × 10 ^-10 , A12 = 0.0

Table 6 shows the values corresponding to the conditional expressions of Examples 1 to 5.

[Table 6]                   Example 1 Example 2 Example 3 Example 4 Example 5                                                                              Conditional expression (1) -0.35 -0.35 -0.37 -0.35 -0.30     Conditional expression (2) 1.81 1.78 1.90 1.88 1.61     Conditional expression (3) 1.94 2.17 2.35 2.12 1.98     Conditional expression (4) 0.98 1.19 0.86 0.74 0.83     Conditional expression (5) 1.847 1.847 1.847 1.847 1.847     Conditional expression (6) 1.772 1.772 1.741 1.741 1.804     Conditional expression (7) 1.50 1.44 1.43 1.31 1.66     Conditional expression (8)---0.46 -0.50 -0.15     Conditional expression (9)--0.018 0.005 0.015     Conditional expression (10) 0.67 0.69 0.66 0.58-     Conditional expression (11) -0.59 -0.67 -0.62 -0.65-     Conditional expression (12)----0.63     Conditional expression (13)-----0.86

As is clear from Table 6, the numerical values of Examples 1 to 5 all satisfy the conditional expressions (1) to (13). The large aperture lens system of the present invention has an F0.8
The front and rear are bright and have a large aperture, and the various aberrations are well corrected as shown in the various aberration diagrams.

[0040]

According to the large-aperture lens system of the present invention, in the lens system having the front lens group, the diaphragm, and the rear lens group, the conditional expressions described in the claims are satisfied.
A lens having a large aperture of about F0.8 can be obtained.

[Brief description of drawings]

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

FIG. 2 is a diagram of various types of aberration of the lens system in FIG.

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

FIG. 4 is a diagram of various types of aberration of the lens system in FIG.

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

FIG. 6 is a diagram of various types of aberration of the lens system in FIG.

FIG. 7 is a lens configuration diagram showing a fourth embodiment of the large-diameter lens system according to the present invention.

FIG. 8 is a diagram of various types of aberration of the lens system in FIG.

FIG. 9 is a lens configuration diagram showing a fifth embodiment of the large-diameter lens system according to the present invention.

FIG. 10 is a diagram of various types of aberration of the lens system in FIG.

[Explanation of symbols]

F: Front group lens R: Rear lens group S: Aperture

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP 61-208020 (JP, A) JP 63-81309 (JP, A) JP 59-78316 (JP, A) JP 57- 10111 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 13/18 G02B 13/04

Claims (4)

(57) [Claims] From 1. A object side, it comprises a front lens group of negative power, a stop, and a rear lens group of positive power, the rear group
The lenses are, in order from the object side, positive, positive, positive lens group
In the positive lens group closest to the object side, the bonding surface is on the object side.
From a cemented lens consisting of a negative lens and a positive lens with a large convex curvature
A large-diameter lens system which is configured and satisfies the following conditional expressions (1) to (7) . (1) -0.5 <f / f _F <-0.2 (2) 1.0 <Σd _{F + S} /f<3.0 (3) 1.5 <Σd _R /f<3.0 ( 4) 0.6 <Σd _{R1 + 2 /} f < 1.5 (5) 1.75 <N _R1 (6) 1.7 <N _R2 (7) 1.0 <r _RC /f<2.5 , F: focal length of the entire system, f _F : focal length of the front lens group, Σd _{F + S} : sum of the thickness of the front lens group and the distance between the front and rear lens groups, Σd _R : the thickness of the rear lens group. Σd _{R1 + 2} : Lens of the cemented lens on the object side of the rear lens group
Thickness, N _R1 : of the negative lens of the cemented lens on the object side of the rear lens group
Refractive index, N _R2 : of the positive lens of the cemented lens on the object side of the rear lens group
Refractive index, r _RC : of the cemented surface of the cemented lens on the object side of the rear lens group
curvature radius. 2. The large-aperture lens system according to claim 1.
The rear lens group is a large-diameter lens system having a divergent aspherical surface that satisfies the following conditional expressions (8) and (9). _{(8) -0.9 <△ I ASP} <0 (9) I SP / △ I ASP <0.2 where, [Delta] I _ASP: 3 order spherical aberration coefficients (in terms of focal length 1.0 aspheric lens Aberration coefficient of the aspherical surface term of the aberration coefficient), I _SP : Aberration coefficient of the spherical term of the third-order spherical aberration coefficient of the aspherical lens. 3. The large-aperture lens system according to claim 1.
The front lens group is composed of four positive, negative, negative, and negative four groups in order from the object side, and the third lens is a negative lens having a concave surface with a large curvature on the image side. The lens is a negative meniscus lens having a concave surface with a large curvature, and a large-diameter lens system that satisfies the following conditional expressions (10) and (11). (10) 0.5 <r _3-2 /f<1.0 (11) -1.0 <r _4-1 /f<-0.5 where r _3-2 is the third negative of the front lens group. Curvature radius on the image side of the lens, r _4-1 : Curvature radius on the object side of the fourth negative lens in the front lens group. 4. The large-diameter lens system according to claim 1.
The front lens group is composed of four positive, negative, positive, and negative four lenses in order from the object side, and the second lens is a lens having a concave surface with a large curvature on the image side. Is a negative meniscus lens having a concave surface with a large curvature, and a large-diameter lens system that satisfies the following conditional expressions (12) and (13). (12) 0.5 <r _2-2 /f<1.0 (13) -1.0 <r _4-1 /f<-0.5 where r _2-2 is the second negative of the front lens group. The radius of curvature on the image side of the lens.