JPS60260912A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a small-sized zoom lens bright and excellent in aberration correction, by constituting the optical system of the zoom lens of four lens groups having a positive, negative, negative, and positive refractive indexes from the object side, and making the optical system satisfy a prescribed condition. CONSTITUTION:The 4th lens group consists of the 41-th lens group IV1 and 42-th lens group IV2. The lens group IV1 is composed of the 411-th and 412-th lenses having positive refracting powers, 413-th lens having a negative refracting power, and 414-th lens having a positive refracting power and the lens group IV2 composed of the 421-th lens having a negative refracting power, 422-th lens having a positive refracting power, and 423-th lens having a positive refracting power. The optical system is made to satisfy the conditions of formulas I -VII. The RIIi of the formula represents the radius of curvature of the i-th lens surface from the object side of the 2nd lens group II and the RIVi1 and RIVi2 respectively represent radii of curvature of the lens surface at the object side and image side of the i-th lens counting from the object side of the 4th lens group IV1 and IV2. The Di-i+1 represents the interval between the i-th and (i+1)-th lenses and the fW represents the focal length of the entire system at the zoom position of the wide angle end.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and particularly to a zoom lens suitable for a color video camera.

2. Description of the Related Art Photographic lenses for video cameras have traditionally been required to be as bright as possible because the sensitivity of an image sensor is relatively low. Furthermore, in order to make video cameras smaller and lighter, there is a need for a photographic lens with a short overall lens length. Furthermore, in color video cameras that use stripe filters such as single-tube color image pickup tubes and OO and D image pickup plates, the light rays incident on the stripe filter are shortened to prevent color mixture. It is required that the optical system be a so-called telecentric Y-link optical system in which the light is incident perpendicularly, and that the optical system has a high resolution. As described above, various requirements are required of photographic lenses used in video cameras. Generally, when trying to satisfy the above-mentioned requirements using a zoom lens, it becomes difficult to properly correct aberrations. In particular, when trying to downsize a zoom lens, it becomes difficult to satisfactorily correct distortion, bispherical aberration, coma, and the like, which results in a reduction in image contrast.

An object of the present invention is to provide a compact zoom lens in which the entire lens system is substantially telecentric, has a brightness of Fl.4, has a large aperture, and achieves good aberration correction.

The main features of the zoom lens for achieving the purpose of the present invention are, in order from the object side, a lens group with a positive refractive power for focusing, a second lens group with a negative refractive power for zooming, and a lens group with a negative refractive power for zooming. It has four lens groups: a sixth lens group with negative refractive power for correcting a changing image plane, and a fourth lens group with positive refractive power for image formation. The second lens group has a meniscus-shaped second lens with a negative refractive power with a concave surface facing the image side, and a laminated lens of negative and positive refractive power lenses with a laminated surface with a convex surface facing the object side. However, the fourth lens group has two lens groups: a fourth lens group with positive refractive power and a 42nd lens group with positive refractive power, and the fourth lens group is A 41st lens in which both lens surfaces are convex, with the lens surface on the image side having stronger refractive power (hereinafter referred to as "stronger refractive power on the image side"), and the lens surface on the object side compared to the lens surface on the image side. has a stronger refractive power (hereinafter referred to as “
"strong refractive power on the object side." ), the 412th lens has a negative refractive power and has a strong refractive power on the object side, and the 414th lens has a strong refractive power on the object side and has both convex lens surfaces. The 42nd lens group includes a 42nd lens with both concave lens surfaces having a strong refractive power on the image side, a 422nd lens with both lens surfaces having a convex surface and a strong refractive power on the image side, and an object. The fourth lens has both convex lens surfaces with strong refractive power on the side.
The radius of curvature of the second lens surface counting from the object side of the second lens group is R1.
(, the radius of curvature of the object-side and image-side lens surfaces of the th lens counting from the object side of the fourth lens group is R
i1. R■i2, when the distance between the 1st lens and the +1st lens is Di -1-4-1, and the focal length at the wide-angle end zoom position of the entire system is fw, 0.79
<IRII2/ Ru5t<0.85 (However, Jn2>
o, Ru3<a)・Φ・(1)t5<l RIV
21/RNslK 1.7 (However, Ru21>0.
Ru31〈0)...(2)1.6 <Rya1/
fw < 1.8...(3) 11 < RV52/
fw< 1.5 @@@(4>t 1 < l R■6
2/ Ru711<1.4 (However, Ru62<O,
Ru71>O)...(5)t1<RNy1/
fw < 1.4 *” (6) 0.15〈Dy2~5＜
0.2 @...(7) 0.95<Dy4~5<1.2
...(8) must be satisfied.

In this way, the present invention particularly provides a compact zoom lens with excellent aberration correction by setting the lens configurations of the second lens group for variable power and the fourth lens group for imaging as described above. Achieved. Among these, by setting the refractive power of the image side lens surface of the second lens of the second lens group and the object side lens surface of the 22nd lens within a predetermined range, aberration fluctuations due to zooming can be reduced. Furthermore, by setting the shape and refractive power of each lens in the fourth lens group as described above, a bright and telecentric optical system is successfully achieved, and aberrations are well corrected over the entire zoom range.

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

Conditional expression (1) is intended to obtain a predetermined zoom ratio while minimizing the amount of movement of the second lens group, and to reduce fluctuations in aberrations, particularly fluctuations in spherical aberration and coma aberration, over the entire zoom range. If the upper limit is exceeded and the refractive power of the lens surface on the image side of the second lens becomes smaller than the refractive power of the lens surface on the object side of the second lens, introverted coma aberration occurs;
If the lower limit is exceeded, the spherical aberration at the telephoto zoom position becomes overcorrected.

Conditional expression (2) relates to the refractive power ratio of the object-side lens surfaces of the 412th lens and the 413th lens, and is particularly intended to appropriately correct spherical aberration over the entire zoom range. If the upper limit is exceeded, the spherical aberration will be over-corrected, and if the lower limit is exceeded, the spherical aberration will be under-corrected.

Conditional expression (3) is intended to appropriately set the refractive power of the object-side lens surface of the 414th lens, to minimize the amount of spherical aberration, and to efficiently converge the light beam. If the upper limit is exceeded, it will be difficult to sufficiently converge the light beam, and it will be difficult to reduce the overall lens diameter of the rear 42nd lens group.If the lower limit is exceeded, the overall length of the lens will be shortened, making it difficult to downsize the zoom lens. Although this can be achieved, it is not preferable because a large amount of spherical aberration occurs.

Conditional expression (4) relates to the refractive power of the lens surface on the image side of the 42nd lens in order to minimize the occurrence of coma aberration and make the entire lens system a good telecentric optical system.

If the upper limit is exceeded, it will be difficult to obtain a good telescopic link optical system, and if the lower limit is exceeded, extroverted coma aberration will occur frequently in the middle of the screen, and the extroverted coma at this time will be transferred to other lens surfaces. This makes it difficult to correct.

Conditional expressions (5) and (6) relate to the refractive power of the image-side lens surface of the 422nd lens and the object-side lens surface of the 423rd lens. This is to reduce the overall curvature of field. Conditional expression (
If the upper limit of conditional expression (5) and the lower limit of conditional expression (6) are exceeded, the 42nd
It becomes difficult to satisfactorily correct the one-extroverted coma aberration that occurs in the lens, and the curvature of field also increases. Conditional expression (5
) and the upper limit of conditional expression (6) are exceeded, spherical aberration becomes overcorrected over the entire zoom range, and more coma aberration occurs.

Conditional Expression (The force is used to properly maintain the air distance between the 412th lens and the 413th lens and properly correct spherical aberration and comatic aberration of the entire screen. If the upper limit is exceeded, spherical aberration will be overcorrected, Furthermore, the occurrence of coma aberration increases.Also,
If the lower limit is exceeded, spherical aberration will be insufficiently corrected.

Conditional expression (8) sets the distance between the 414th lens and the 42nd lens appropriately, that is, the distance between the 4th lens group and the 42nd lens group, and corrects comatic aberration and off-axis chromatic aberration of the entire screen in a well-balanced manner. , and to achieve a good telecentric optical system. If the upper limit value is exceeded, outward comatic aberration will occur more often, and off-axis chromatic aberration will tend to be over-corrected.If the lower limit value is exceeded, off-axis chromatic aberration will be under-corrected, and a good telecentric optical system will not be possible. difficult to achieve.

As explained above, in the present invention, by satisfying the above-mentioned conditions, it is possible to achieve a compact zoom lens with a large aperture, well-corrected aberrations, and a good telecentric optical system. .

In addition, in the present invention, by configuring the sixth lens group with a single meniscus lens with a convex surface facing the image plane side, the overall length of the lens can be shortened and aberration fluctuations due to zooming can be reduced. There is.

Next, numerical examples of the present invention will be shown. In numerical examples,
Ri is the radius of curvature of the th lens surface in order from the object side,
Di is the thickness and air gap of the first lens from the object side, and Ni and νt are the refractive index and Abbe number of the glass of the second lens from the object side, respectively.

R30 in Numerical Examples 1 and 2. R31, 12B in Numerical Examples 6 and 4, R29 is a face plate,
Glass blocks such as low-pass filters and near-infrared cut filters, R15 in Numerical Examples 1 and 2. R16
is the actual value of the finder light flux and the light flux for automatic focus detection Example 1 F-1 ~ 5.7 FNO-1: 1.42ω-492'-
8,7°R17-Aperture Dl7-0.1667 b, f-0,595 Lens total length-10,35,0 Numerical example 2 F-1~5.7 FNO-1F1.42ω-492°~
8.7゜R17-Aperture Dl 7-0.1667b, f
-0,549 Lens total length -10,285 Numerical example 6 F-1~5.7 FNO-1:i, 42ω-492°~
8.7゜R1-9,2544D I-0,1627N
1-1.80518ν1-25.4R2-5A925D
2-0.6507 N 2-1.60511 C 2-6
0.7R5--10,4139D 3-0.0121R
4-2,8656D 4-0.4349N 3-1.
69680ν3-55.5R5-12 Near 675 D
5-Variable R6-22,8612D 6-0.0815 N 4-
1.77250ν4-49.6R7-1, 1808D
7-0.5091R8--14607D B=0.08
13 N 5-1.69680ν5-55.5R9-1
4920D 9-0.2603 N 6-1.8466
6shi6-23.9R10--31,5074Dlo-Variable R11--18871Dll-0,0815N 7-
169680 sear 55.5R12=18.3046
D12-variable R13-7, 8584D13-0.414
8 N 8-1.77250ν8-49.6R14--
2159D14-0.305 (lR15-Aperture D15
-0.1667 R16-5,0984D16-0.3498 N 9-
1.69/)80ν9-55.5R17--9,189
1D17-0.1864R18--19654D18-
α0976 N10-1.84666 10-23.9
R19--10,5125D1? -0,0122R20
-1,7462D20-0.4880 N11-151
633shi11-64. lR21--8, 1420D21
-1.0564R22--4,5097D22-0.0
813 N12-1.83400ν12-37.2R2
5-1,3115D25-0130R24-4,129
4D24-0.5254 N13-1.51633si1
3-64.1R25--1,6847D25-0.01
22R26-1, 2905D26-0.4067 N1
4-1.57135shi14-53.0R27--12.
5351 D27-0.1627R28-* D28-
0.7906 N15-1.51633 15-64.
1R29-substitute, f-0,5772 Lens total length-9831 Numerical example 4 F=1~5.7 FNO-1,: 1.42ω-492°
~8.7゜R1-9,4373D I-0,1627N
1-1.80518ν1-25.4R2-3,218
2D 2-06507 N 2-1.60511 C 2-
60.7R5--10,1451D 5-0.0115
R4-2,8535D 4-0.4298 N 3-1
．． 69680ν5-55.5R5-12, 3999D
5-Variable R6-20,6618D 6-0.081! l N 4
-1.77250ν4-49.6R7-1,1880D
7-0.3109R8--14575D 8-0.0
813 N 5-1.69680ν5-55.5R9-
1,50! +7 D 9-0.2603N 6-1.8
4666shi6-23.9R10--37,1497I)
10-Variable R11--1,8819Dll-0,081
3N 7-1.69680 sear 55.5R12--1
7,8?162 D12-variable R13-7,8552D
15-0.4148 N 8-1.77250ν8-4
9.6R14--2,1140D14-0.3009R
15-Aperture D15-0.1667 R16-5, 1345DI6-0.3497 N 9-
1.69680ν9-55.5R17--9,0919
D17-0.1877R1B--1,9516D18-
0.0976 N10-1.84666 10-23.
9R19---9,9099D19-0.0122R2
0-1,7583D20-0.4880 N11-1.
51653S1l-S4. lR21--7,73<S9
D21-1.0564R22--4,3587D22
-0.0813 N12-1.83400ν12-37
．． 2R25-1, 3268D23-0.1119R24
-4,3082D24-0.3253 N13-1.5
1633shi 13-64. lR25--1,6552D2
5-0.0122R26-1, 2909D26-0.4
067 N14-1.57135shi14-53.0R2
7--13.7234 D27-0.17527R28
-o=D28-0.7906N15=1.51633
C15-64. I29-00 b, f-0,577 Lens total length -9831 Next, Table 1 shows the correspondence between the above-mentioned conditions and numerical examples of the present invention.

Relationship between Table 11n conditions and numerical examples of the present invention

[Brief explanation of the drawing]

1st. Second. Third. Figure 4 shows numerical example 1 of the present invention.
, 2, 3.4 lens sectional view, Fig. 5 (~. (b) + (') + Fig. 6 (a), (b), (C),
Figure 7 (a), (b), (C), Figure 8 (a), (b)
). (0) are various aberration diagrams of numerical examples 1, 2, and 5.4 of the present invention, and in the figures, (a), (b), and (C) are respectively at the wide-angle end.Zoom at the intermediate and telephoto end. Various aberration diagrams at various positions, 696 planes, Δ
M is the meridional image plane, and ■, ...+"+■1+■2 are the 1st, 2nd, 3rd, 41st, and 42nd lens groups, respectively. Patent applicant Canon Co., Ltd. 1 Figure 2 3 Fig. 4 Fig. 5 Same time) Mao 5 Residence cb> No. S Encircle..., Fig. 6, ., Fig. 6 2 (b) Notebook 6 Fig.,..., 7th concave (2) Fig. 7 (1) )) Section 71c.

Claims (1)

[Claims] In order from the object side, a first lens group with positive refractive power for focusing, a second lens group with negative refractive power for zooming, and a negative lens group for correcting the image plane that changes due to zooming. It has four lens groups: a third lens group with refractive power and a fourth lens group with positive refractive power that performs an imaging function, and the second lens group has a meniscus-shaped negative lens group with a concave surface facing the image plane The fourth lens group includes a second lens with a refractive power, and a laminated lens of a lens with a negative and positive refractive power having a laminated surface with a convex surface facing the object side, and the fourth lens group includes a fourth lun with a positive refractive power. The fourth lens group includes a 41st lens whose both lens surfaces are convex and has a strong refractive power on the image side, and both lenses have a strong refractive power on the object side. A 412th lens with a convex surface, a 413rd lens with a negative refractive power having a strong refractive power on the object side, and a 41st lens with both lens surfaces convex and having a strong refractive power on the object side.
The 42nd lens group has four lenses, and the 42nd lens group has a strong refractive power on the image side and both lens surfaces are concave.
The 422nd lens has both convex lens surfaces and has strong refractive power on the image side - ゛ And the 4th lens has both convex lens surfaces and has strong refractive power on the object side
The radius of curvature of the second lens surface counting from the object side of the second lens group is RI.
[i1 The radius of curvature of the object-side and image-side lens surfaces of the th lens counting from the object side of the fourth lens group is R, respectively.
1vi1°RIvi2, when the distance between the 1st lens and the 1st+1st lens is Di-1+1, and the focal length at the wide-angle end zoom position of the entire system is fW, 0.7
9< lRI[2/ RI[31<0.85 (however, R
1[2>O, RII3<0) 1,'5 (lR■21/
R ■ 511 (1, 7 (however - R ■ 21 > O, RIvSl
<0)1.6<RIV41/fw<1.81.
1 < RIV52 / fw < 1.51.1 and IR■62/R■71 l < 1.4 (However, R■
62〈0. R ■71〉0)1.1 <RNy+ /
A zoom lens that satisfies the following condition: fw<1.40.15<DN2~S<02 0.95<Dy4~5<1.2.