JP3144130B2 - Zoom lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens having an F number of 1.6 to 1.9, a large aperture ratio, a high zoom ratio of about 13 and an aspherical lens surface near the stop. The present invention relates to a small zoom lens having a short overall lens length and suitable for a television camera, a photographic camera, a video camera, and the like having good optical performance over the entire zoom range by using the zoom lens.

[0002]

2. Description of the Related Art Conventionally, television cameras, photographic cameras,
For a video camera or the like, there is a demand for a small zoom lens having a large diameter, high zoom ratio, and high optical performance and a small overall lens system.

[0003] Of these, in recent television cameras for broadcasting, there has been a demand for further downsizing of the camera head in accordance with high image quality and high density of a solid-state imaging device (CCD).

In particular, operability and mobility are emphasized in a color television camera for broadcasting, and in response to the demand, an image pickup device has recently become a small CCD of 2/3 inch or 1/2 inch.
(Solid-state imaging device) is becoming mainstream.

[0005] Since this CCD has a substantially uniform resolution over the entire imaging range, a zoom lens using the CCD is required to have a substantially uniform resolution from the center of the screen to the periphery of the screen.

As a zoom lens having a relatively high zoom ratio and a large aperture ratio for a television camera for broadcasting, a first lens unit having a positive refractive power for focusing and a negative lens having a negative refractive power for zooming in order from the object side. The second group,
A third group for correcting the image plane changed by the magnification change, and a fourth group for making the light flux from the third group an afocal light flux.
Group, and a fourth group of four lenses for imaging,
There is a so-called four-group zoom lens.
No. 042, and Japanese Patent Application Laid-Open No. 54-23556.

[0007]

In general, in the above-described four-unit zoom lens, it is necessary to maintain a high optical performance while reducing the overall length of the lens, to achieve a large aperture ratio, and to achieve a high zoom ratio. It is important to appropriately set the optical constants of the lens group.

In particular, in order to reduce the size of the entire lens system and increase the magnification, the power (refraction) of a variator (magnification lens group) must be achieved because a predetermined magnification ratio must be achieved within a short lens movement interval. Force) inevitably increases, and the divergence angle of the light beam incident on the imaging system (relay system) increases.

Generally, a method of dividing a relay system into two groups, a front group and a rear group (fourth and fifth groups), in order to correct aberrations of off-axis light beams and to secure an interval for inserting a built-in type extender. Has been taken.

At this time, the excessive spherical aberration occurring in the third lens group is reduced by the small number of lenses to the relay front lens group (the fourth lens group).
In the case of correcting by the group, a convex lens having a strong power is required, and as a result, the influence of a higher-order aberration coefficient cannot be ignored.

Therefore, since the lens must be formed of a convex lens having a weak power, it is emitted as divergent light from the front group of the relay, causing an increase in the diameter of the rear group. In addition, a large number of lenses is required to emit convergent light from the rear group (fifth group) while maintaining good aberration, which causes a problem that the optical system becomes large.

Further, when an extender is inserted into a divergent light beam, a gap error at the time of manufacture or a fall of an optical system adversely affects the optical performance, causing a problem that manufacturing becomes difficult.

Accordingly, it is necessary to emit a substantially afocal light beam from the front group of the relay.

If an attempt is made to emit substantially afocal rays from the front group of the relay while maintaining good aberration, a plurality of low power convex lenses are required, which hinders miniaturization of the optical system.

Further, as the center thickness of the optical system increases, the exit pupil becomes shorter, and the off-axis principal ray enters the image sensor as a strong divergent or convergent ray.

For example, when a dichroic film composed of a dielectric multilayer film arranged at an angle on the optical axis is used as a means for color separation as in a multi-panel color camera, the off-axis main body reaching the upper and lower portions of the screen is used. Since the incident angle of the light beam on the dichroic film is different, the spectral characteristics change, and there is a problem that color shading occurs.

The present invention relates to a so-called five-group zoom lens,
Reducing the aberration correction load on the relay system consisting of the fourth and fifth lens groups, which is caused by increasing the aperture, increasing the magnification, and reducing the size, while appropriately setting the refractive power and F-number of each lens group. In order to achieve this, an aspheric surface is provided at an appropriate position in the relay system, and in particular, by correcting spherical aberration, the front group of the relay (4th
It is an object of the present invention to provide a zoom lens that emits a more afocal light from the lens group and has good optical performance over the entire zoom range.

[0018]

A zoom lens according to the present invention sequentially changes from the object side to a first group of positive refractive power for focusing, a second group of negative refractive power having a variable power function, and variable power. A third group having a negative refractive power for correcting an image plane to be projected, and a fourth group having a positive refractive power for emitting a light beam from the third group as a substantially afocal light beam.
A fifth lens group having a positive refractive power and a fifth lens group having an image-forming action, and having an aperture stop in front of or in the fourth group; The object-side lens 41 is composed of a positive lens whose material has a refractive index of 1.7 or less, with the convex surface having a strong refractive power facing the image plane, and the image-side lens of the fourth group is strong on the object side. At least one lens surface in the fourth group is composed of an aspherical surface having a positive refractive power that increases toward the periphery of the lens, and the third group is composed of an object side. A cemented lens in which a negative lens 31 and a positive lens 32 are joined in this order. The focal lengths of the first system and the entire system at the telephoto end are respectively f1, fT,
The F number of the whole system at the group and at the telephoto end are FN3 and FN respectively
T, the lateral magnification of the fourth unit is β4, the effective diameter of the lens 41 is EA, and the image point of the first, second, and third units is
FN3 <2.2 (1) 5 <| β4 | (2) LD / EA <1.9 (3) f1 × FNT / fT <1.5 ... (4) The following condition is satisfied.

[0019]

1 and 2 are lens cross-sectional views of Numerical Embodiments 1 and 2 of the present invention, FIGS. 3 to 5 show Numerical Embodiment 1 of the present invention, and FIGS. FIG. 10 is a diagram illustrating various aberrations of Numerical Example 2. 3 and 6 show the wide-angle end, FIGS. 4 and 7 show the intermediate positions, and FIGS. 5 and 8 show the telephoto end.

In the drawing, L1 is the first positive refractive power for focusing.
Group L2 is a second group of negative refractive power that moves in minor for zooming;
L3 is a third group of negative refractive power for correcting an image plane that fluctuates with zooming, L4 is a fourth group of positive refractive power that emits a light beam from the third group L3 as a substantially afocal light beam, L5
Denotes a fifth lens unit having a positive refractive power and exhibits a fixed imaging action, and SP denotes a stop, which is disposed in front of or in the fourth lens unit.

G is a parallel plane plate such as a color separation optical system (3P prism), a face plate, and a filter. Second
The group and the third group constitute a variable power system, and the fourth and fifth groups constitute a relay system.

In this embodiment, the zooming from the wide-angle end to the telephoto end is performed by monotonously moving the second lens unit to the image plane side, and the third lens unit has a locus convex toward the object side. Is reciprocated so as to be located on the image plane side.

The refractive index and lens shape of the material of the lens on the object side and the image plane side of the fourth group, the shape of the aspheric surface used for at least one lens surface of the fourth group, and the optical properties of each lens group Constants and the like are set as described above.

As a result, a zoom lens having a high optical performance over the entire zoom range and an F-number of 1.6 and a zoom ratio of about 13 is obtained while reducing the size of the entire lens system.

In particular, by providing at least one lens surface near the stop of the fourth group having a positive refractive power with an aspherical surface having a shape such that the positive refractive power becomes stronger toward the periphery of the lens, the third surface is obtained.
The remaining positive spherical aberration is satisfactorily corrected by increasing the negative refractive power of the lens group and downsizing the entire lens system.

Next, the technical meaning of each of the above conditional expressions will be described.

Conditional expression (1) sets the F-number of the third lens group for correcting the image plane fluctuation accompanying zooming to be bright, appropriately controls the divergence angle of the luminous flux emitted from the third lens group, and Group and third
This is for facilitating a large aperture ratio while reducing the size of the zoom system composed of groups. If conditional expression (1) is not satisfied, it becomes difficult to increase the F-number while reducing the size of the entire lens system. Conditional expression (2) relates to the imaging magnification of the fourth lens unit, and is mainly for emitting the divergent light beam from the third lens unit as a substantially parallel light beam.

If conditional expression (2) is not satisfied, the degree of divergence and convergence of the luminous flux emitted from the fourth lens unit increases, and the outer diameter of the fifth lens unit (rear group) increases. The number of lenses in the group increases. Further, the influence of manufacturing errors when inserting and removing the built-in extender between the fourth group and the fifth group increases, which is not good.

Conditional expression (3) indicates that the lens 41 on the object side of the fourth group is located from the image point of the object formed by the first, second and third groups.
The ratio between the distance LD to the object-side lens surface and the effective diameter EA of the lens 41 is appropriately set, the F-number is maintained bright mainly at the wide-angle end, and the lens outer diameter of the fourth and fifth groups This is to reduce the size of the device.

If the condition (3) is not satisfied, the divergence angle of the light beam emitted from the third lens unit becomes loose, making it difficult to increase the aperture ratio and reduce the size.

Conditional expression (4) sets the focal length f1 of the first lens unit, the focal length fT of the entire system at the telephoto end and the F-number FNT appropriately, and mainly adjusts the F-number at the telephoto end to a constant brightness. This is for properly correcting various aberrations such as spherical aberration while maintaining them.

If conditional expression (4) is not satisfied, it becomes difficult to correct various aberrations such as spherical aberration and coma in a well-balanced manner while maintaining the F-number at the telephoto end at a predetermined brightness.

The zoom lens aimed at by the present invention can be achieved by satisfying the above conditions. In order to satisfactorily correct the fluctuation of aberration at the time of zooming, particularly the fluctuation of field curvature and chromatic aberration. When the refractive index and Abbe number of the material of the negative lens 31 are N31 and v31, and the refractive index and Abbe number of the material of the positive lens 32 are N31 and v31, respectively,

[0034]

(Equation 1) It is better to satisfy the following conditions.

Conditional expressions (5) and (6) are to obtain a predetermined zoom ratio effectively while increasing the refractive power of the third lens unit and to reduce the amount of movement accompanying zooming, and to obtain the chromatic aberration and zooming caused by zooming. This is for reducing aberration fluctuation such as curvature of field.

If conditional expressions (5) and (6) are not satisfied, it becomes difficult to satisfactorily correct aberration fluctuations such as chromatic aberration and curvature of field with zooming.

In the present invention, in order to satisfactorily correct the residual aberration caused by the first to third lens groups and to allow substantially parallel light beams to enter the fifth lens group, the fourth lens group must be sequentially moved from the object side to the image side. One or two positive lenses having a convex surface with a strong refractive power, a positive lens with both lens surfaces being convex, and a negative lens with a concave surface having a strong refractive power facing the object side are preferred.

Further, the light beam from the fourth group is efficiently collected,
In order to maintain good optical performance of the entire screen, the fifth lens unit is composed of a positive lens having a convex surface facing the image surface side, a cemented lens in which a negative lens and a positive lens are joined, and a cemented lens in which a positive lens and a negative lens are joined. It is preferable to form a compound lens and a positive lens whose both lens surfaces are convex.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R represents a paraxial radius of curvature, and A, B, C, D, and E represent aspherical shapes. Assuming spherical coefficients,

[0041]

(Equation 2) It is represented by the following expression.

<Numerical Example 1> F = 9.0 to 114 FNO = 1: 1.6 to 1.92 ω = 62.9 ° to 5.52 ° R 1 = 5008.06 D 1 = 2.42 N 1 = 1.81265 ν 1 = 25.4 R 2 = 99.77 D 2 = 5.81 R 3 = 5008.06 D 3 = 7.39 N 2 = 1.43496 ν 2 = 95.1 R 4 = -111.62 D 4 = 0.15 R 5 = 85.65 D 5 = 11.75 N 3 = 1.49845 ν 3 = 81.6 R 6 = -161.29 D 6 = 0.15 R 7 = 51.07 D 7 = 8.45 N 4 = 1.69979 ν 4 = 55.5 R 8 = 135.08 D 8 = Variable R 9 = 59.13 D 9 = 0.97 N 5 = 1.88814 ν 5 = 40.8 R10 = 18.16 D10 = 3.68 R11 = -61.91 D11 = 0.77 N 6 = 1.80811 ν 6 = 46.6 R12 = 79.67 D12 = 3.64 R13 = -15.62 D13 = 0.77 N 7 = 1.77621 ν 7 = 49.6 R14 = 297.56 D14 = 3.10 N 8 = 1.93306 ν 8 = 21.3 R15 = -27.94 D15 = Variable R16 = -25.35 D16 = 0.87 N 9 = 1.77621 ν 9 = 49.6 R17 = 28.33 D17 = 3.58 N10 = 1.81265 ν10 = 25.4 R18 = -760.77 D18 = Variable R19 = (Aperture) D19 = 2.23 R20 = 6570.48 D20 = 3.86 N11 = 1.72793 ν11 = 38.0 * R21 = -46.00 D21 = 0.19 R22 = 441.93 D22 = 3.68 N12 = 1.62032 ν12 = 63.4 R23 = -81.33 D23 = 0.19 R24 = 52.05 D24 = 7.77 N13 = 1.48915 ν13 = 70.2 R25 = -31.06 D25 = 1.61 N14 = 1.83932 ν14 = 37.2 R26 = -148.13 D26 = 19.14 R27 = -174 .02 D27 = 3.73 N15 = 1.50349 ν15 = 56.4 R28 = -46.40 D28 = 0.19 R29 = 369.23 D29 = 1.35 N16 = 1.83932 ν16 = 37.2 R30 = 20.19 D30 = 8.71 N17 = 1.50349 ν17 = 56.4 R31 = -115.02 D31 = 0.19 R32 = 112.58 D32 = 8.70 N18 = 1.51825 ν18 = 64.2 R33 = -22.05 D33 = 1.35 N19 = 1.80811 ν19 = 46.6 R34 = -86.09 D34 = 0.29 R35 = 76.09 D35 = 7.85 N20 = 1.48915 ν20 = 70.2 R36 = -30.16 D36 = 5.00 R37 = ∞D37 = 55.50 N21 = 1.51825 ν21 = 64.2 R38 = ∞ R21 is an aspheric surface FN3 = 1.54 | β4 | = 22.7 LD / EA = 1.34 f1 × FNT / fT = 1.07

[0043]

[Table 1] Aspherical coefficients, shift amount of the _{A 3 = 3.74158 × 10 -10 A} 4 = -8.05298 × 10 -12 A 5 = 2.14133 × 10 -14 reference sphere, the effective diameter 10 percent: -2.59Myuemu effective diameter 9 %: -1.28 μm Effective diameter 70%: -0.15 μm <Numerical example 2> F = 9.0 to 114 FNO = 1: 1.6 to 1.92 ω = 62.9 ° to 5.52 ° R 1 = 5008.06 D 1 = 2.42 N 1 = 1.81265 ν 1 = 25.4 R 2 = 99.77 D 2 = 5.81 R 3 = 5008.06 D 3 = 7.39 N 2 = 1.43496 ν 2 = 95.1 R 4 = -111.62 D 4 = 0.15 R 5 = 85.65 D 5 = 11.75 N 3 = 1.49845 ν 3 = 81.6 R 6 = -161.29 D 6 = 0.15 R 7 = 51.07 D 7 = 8.45 N 4 = 1.69979 ν 4 = 55.5 R 8 = 135.08 D 8 = Variable R 9 = 59.13 D 9 = 0.97 N 5 = 1.88814 ν 5 = 40.8 R10 = 18.16 D10 = 3.68 R11 = -61.91 D11 = 0.77 N 6 = 1.80811 ν 6 = 46.6 R12 = 79.67 D12 = 3.64 R13 = -15.62 D13 = 0.77 N 7 = 1.77621 ν 7 = 49.6 R14 = 297.56 D14 = 3.10 N 8 = 1.93306 ν 8 = 21.3 R15 = -27.94 D15 = Variable R16 = -25.35 D16 = 0.87 N 9 = 1.77621 ν 9 = 49.6 R17 = 28.33 D17 = 3.58 N10 = 1.81265 ν10 = 25.4 R18 = -760.77 D18 = Variable R19 = (Aperture) D19 = 2.23 R20 = 528.98 D20 = 5.05 N11 = 1.70557 ν11 = 41.2 R21 = -33.52 D21 = 0.15 * R22 = 36.94 D22 = 9.26 N12 = 1.48915 ν12 = 70.2 R23 = -26.53 D23 = 1.26 N13 = 1.83932 ν13 = 37.2 R24 = -149.62 D24 = 29.03 R25 = -2055.74 D25 = 5.37 N14 = 1.50349 ν14 = 56.4 R26 = -35.74 D26 = 0.15 R27 = -69.95 D27 = 1.35 N15 = 1.88814 ν15 = 40.8 R28 = 24.81 D28 = 9.18 N16 = 1.48915 ν16 = 70.2 R29 = -50.40 D29 = 0.15 R30 = 43.39 D30 = 8.19 N17 = 1.51825 ν17 = 64.2 R31 = -37.63 D31 = 1.94 N18 = 1.88814 ν18 = 40.8 R32 = -278.71 D32 = 0.15 R33 = 53.54 D33 = 6.99 N19 = 1.51977 ν19 = 52.4 R34 = -49.21 D34 = 5.00 R35 = ∞ D35 = 55.50 N20 = 1.51825 ν20 = 64.2 R36 = ∞ R22 is an aspheric surface FN3 = 1.54 | β4 | = 37 LD / EA = 1.34 f1 × FNT / fT = 1.07

[0044]

[Table 2] The aspherical surface coefficient is A ₃ = 5.77517 × 10 _-10 A ₄ = 1.92570 × 10 _-12 A ₅ = -1.54747 × 10 _{-14 The} amount of deviation from the reference sphere is effective diameter 100%: 34.01 μm effective diameter 90% : 15.62μm Effective diameter 70%: 2.43μm

[0045]

As described above, according to the present invention, in a so-called five-unit zoom lens, the refracting power, the F-number, etc. of each lens unit are appropriately set, and a large aperture, a high zoom ratio, and a compact size are realized. In order to reduce the aberration correction burden on the relay system composed of the fourth and fifth groups, which occurs when the above-described method is adopted, an aspherical surface is provided at an appropriate position of the relay system, and in particular, the spherical aberration is corrected so that the front group of the relay system From the (fourth group), it is possible to achieve a zoom lens that emits a light beam that is closer to afocal and has good optical performance over the entire zoom range.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 3 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 4 is an intermediate aberration diagram of the numerical example 1 of the present invention.

FIG. 5 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention.

FIG. 6 is an aberration diagram at a wide angle end according to Numerical Example 2 of the present invention.

FIG. 7 is an intermediate aberration diagram of the numerical example 2 of the present invention.

FIG. 8 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit L5 Fifth lens unit SP Stop G Glass block ΔS Sagittal image plane ΔM Meridional image plane

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (4)

(57) [Claims] 1. A first group of positive refractive power for focusing, a second group of negative refractive power having a zooming function, and a negative refractive power for correcting an image plane which fluctuates by zooming, in order from the object side. The third group of the third
A fourth lens group having a positive refractive power that emits a light beam from the group as a substantially afocal light beam; and a fifth lens group having a positive refractive power having an image forming function. Alternatively, an aperture stop is provided in the fourth group, and the object-side lens 41 of the fourth group has a convex surface having a strong refractive power directed toward the image plane side, and has a refractive index of 1.7 or less. The lens on the image plane side of the fourth group is a negative lens having a concave surface having a strong refractive power directed toward the object side, and at least one lens surface in the fourth group is positive as it goes to the lens periphery. The third group is composed of an aspheric surface having a shape in which the refractive power of
Affixing the negative lens 31 and the positive lens 32 in order from the side
A focal length of the first lens unit and the focal length of the entire system at the telephoto end are respectively f1 and fT, and an F number of the third lens unit and the entire system at the telephoto end.
The numbers are FN3 and FNT, respectively, and the lateral magnification of the fourth group is β
4. The effective diameter of the lens 41 is EA, the first, second, third
When the distance from the image point of the group to the lens surface of the lens 41 on the object side is LD, FN3 <2.25 <| β4 | LD / EA <1.9 f1 × FNT / fT <1.5 A zoom lens that satisfies the conditions. Wherein said negative lens 31 of material of refractive index and Abbe number, respectively N31, Nyu31, the material of the refractive index and Abbe number, respectively the N32 of the positive lens 32, when the ν32, ν32 <ν31 1.75 2. The zoom lens according to claim 1, wherein a condition of <N31 1.75 <N32 is satisfied. 3. The fourth group is composed of one or two positive lenses each having a convex surface facing the image surface side in order from the object side, a positive lens having both lens surfaces convex, and a negative lens having a concave surface facing the object side. The zoom lens according to claim 1 , wherein the zoom lens comprises: 4. The fifth group is composed of a positive lens whose convex surface faces the image surface side in order from the object side, a cemented lens in which a negative lens and a positive lens are joined, and a cemented lens in which a positive lens and a negative lens are joined.
Structure from Align lens and a positive lens of both lens surfaces is convex,
Claim, characterized in that formed, two or three of the zoom lens.