JP2917567B2 - Rear focus 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 rear focus type zoom lens, and more particularly to a large aperture ratio of about 8 to 10 and an F number of about 2.0 used for a photographic camera, a video camera, a broadcast camera and the like. The present invention relates to a rear focus type zoom lens suitable for a zoom lens having a high zoom ratio.

[0002]

2. Description of the Related Art Conventionally, various types of zoom lenses such as a photographic camera and a video camera adopting a so-called rear focus system in which a lens group other than the first group on the object side is moved to perform focusing is proposed. ing.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which moves and focuses the first lens group, so that the entire lens system can be easily miniaturized, and close-up photographing can be performed. In particular, extremely close-up photographing is facilitated, and since the relatively small and light lens group is moved, the driving force of the lens group is small and quick focusing can be performed.

For example, Japanese Patent Application Laid-Open No. 63-44614 discloses a rear focus type zoom lens having a first lens unit having a positive refractive power, a second lens unit having a negative refractive power for zooming, and a zoom lens. In a so-called four-unit zoom lens composed of four lens units, a third unit having a negative refractive power and a fourth unit having a positive refractive power, for correcting an image plane variation caused by magnification, the third unit is moved. The focus is on. However, in this zoom lens, the moving space of the third lens group must be secured, and the overall length of the lens tends to increase.

In Japanese Patent Application Laid-Open No. 58-136012, a zooming unit is composed of three or more lens groups, and focusing is performed by moving some of the lens groups.

In JP-A-63-247316, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and
It has four lens groups, a third group having a positive refractive power and a fourth group having a positive refractive power. The second group is moved to perform zooming, and the fourth group is moved to accompany zooming. Performs image plane fluctuation and focus.

In JP-A-58-160913, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and
The zoom lens has four lens groups, a third lens group having a positive refractive power and a fourth lens group having a positive refractive power. The first and second groups are moved to perform zooming, and the image plane varies with zooming. Is performed by moving the fourth group. Then, focusing is performed by moving one or more of these lens groups.

In JP-A-58-129404 and JP-A-61-258217, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power are arranged in order from the object side.
In a five-unit zoom lens including five lens units, a fourth unit having a positive refractive power, and a fifth unit having a negative refractive power, the fifth unit or a plurality of lens units including the fifth unit is moved. Focus. Japanese Patent Application Laid-Open No. 60-6914 discloses a five-unit zoom lens similar to that described above, in which the position of the focus lens unit on the optical axis with respect to a specific finite distance object is constant regardless of zooming. Has been proposed.

[0009]

Generally, when a rear focus system is employed in a zoom lens, the overall lens system can be reduced in size and quick focusing becomes possible as described above, and further advantages such as close-up photographing can be easily obtained. .

[0010] On the other hand, however, aberration fluctuations during focusing become large, and it becomes very difficult to obtain high optical performance while reducing the size of the entire lens system over the entire object distance from an object at infinity to a close object. A point arises.

In particular, a zoom lens having a large aperture ratio and a high zoom ratio has a problem that it is very difficult to obtain high optical performance over the entire zoom range and over the entire object distance.

The present invention employs a rear focus method to achieve a large aperture ratio and a high zoom ratio, while preventing the entire lens system from being enlarged, and covering the entire zoom range from the wide-angle end to the telephoto end. Another object of the present invention is to provide a rear-focus type zoom lens having a simple configuration and excellent optical performance over the entire object distance from an object at infinity to an object at a short distance.

[0013]

A rear focus type zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. A fourth lens group having a positive refractive power and a fifth lens group having a negative refractive power. The first lens group is moved to the object side, and the second lens group is moved to the image plane side, and the wide-angle end From the zoom lens to the telephoto end, and corrects the image plane variation caused by the zooming by moving the fourth lens unit, and focuses by moving the fourth lens unit, so that the focal length of the i-th lens unit is fi, When the focal lengths of the entire system at the wide-angle end and the telephoto end are respectively fw and fT, and the imaging magnification of the fifth unit is β5.

[0014]

(Equation 3) It is characterized by satisfying certain conditions.

[0015]

FIG. 1 is a schematic view of an embodiment showing a paraxial refractive power arrangement of a rear focus type zoom lens according to the present invention. 2 and 3 are lens cross-sectional views of Numerical Examples 1 and 2 of the present invention described later, and FIGS. 4 to 6 are aberration diagrams at a wide angle end, a middle position, and a telephoto end of Numerical Embodiment 1 of the present invention. is there. FIG.
FIG. 9 is a view illustrating a wide-angle end, a middle position, and a numerical value according to a second embodiment of the present invention described later.
FIG. 7 is a diagram illustrating various aberrations at the telephoto end. 10 to 12 are graphs showing various aberrations at the wide-angle end, a middle position, and a telephoto end in a numerical example 3 described later of the present invention. 13 to 15 are graphs showing various aberrations at the wide-angle end, a middle position, and a telephoto end of a numerical example 4 described later of the present invention.

In the figure, 1 is a first group having a positive refractive power, 2 is a second group having a negative refractive power, 3 is a third group having a positive refractive power, 4 is a fourth group having a positive refractive power, Reference numeral 5 denotes a fifth lens unit having a negative refractive power. SP denotes an aperture stop, which is arranged in front of the third lens unit 3.

At the time of zooming from the wide-angle end to the telephoto end, the first lens unit is moved to the object side as shown by the arrow, and the second lens unit is moved to the image plane side. Has been corrected.

Also, a rear focus system is employed in which the fourth unit is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The third and fifth units are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane fluctuation accompanying zooming, and the fourth lens unit is moved to perform focusing. In particular, curve 4 in FIG.
When zooming from the wide-angle end to the telephoto end, the lens is moved so as to have a convex trajectory toward the object side as shown in FIGS.
Thereby, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as indicated by a straight line 4c in FIG.

In the present embodiment, the effective lens diameter of the first group is increased by adopting the rear focus method as described above in comparison with a conventional four-group zoom lens in which the first group is extended and focused. Prevention.

By arranging the aperture stop immediately before the third lens unit, aberration fluctuations caused by the movable lens unit can be reduced, and the distance between the lens units in front of the aperture stop can be reduced to reduce the diameter of the front lens. Achieved easily.

By specifying the optical constants of each lens unit as described above, a zoom lens having a high zoom ratio having good optical performance over the entire zoom range and over the entire object distance is obtained.

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

The conditional expression (1) is for effectively obtaining a predetermined zoom ratio while reducing aberration fluctuations caused by zooming with respect to the refractive power of the second lens unit. If the refractive power of the second lens unit becomes too strong beyond the lower limit, the size of the entire lens system can be easily reduced. However, the Petzval sum increases in the negative direction, the field curvature increases, and the aberration variation accompanying zooming increases. Is getting bigger.
If the refractive power of the second lens unit becomes excessively weaker than the upper limit, aberration fluctuations associated with zooming will decrease, but the amount of movement of the second lens unit to obtain a predetermined zooming ratio will increase, and the overall length of the lens will increase. It ’s not good because it ’s getting better.

Conditional expression (2) relates to the imaging magnification of the fifth lens unit.
This is mainly for maintaining good optical performance over the entire screen while shortening the entire length of the lens. If the imaging magnification of the fifth unit is too small below the lower limit, the reduction of the overall length of the lens becomes insufficient. On the other hand, if the imaging magnification is too large beyond the upper limit, the overall length of the lens will be short, but it will be difficult to obtain a predetermined back focus, and the distance from the exit pupil to the image plane will be short.

Conditional expression (3) relates to the ratio between the refractive powers of the third and fourth units, and is mainly for shortening the total length of the lenses of the third and subsequent units while maintaining good optical performance of the entire screen. is there. If the refractive power of the third lens unit becomes too strong beyond the lower limit, the overall length of the lens will be short, but it will be difficult to satisfactorily correct spherical aberration and coma, and it will be difficult to secure a predetermined back focus. . On the other hand, if the refractive power of the third lens unit becomes too weak beyond the upper limit, the reduction of the overall length of the lens becomes insufficient.

The rear focus type zoom lens which is the object of the present invention can be achieved by satisfying the above-mentioned conditions, but further reduces aberration fluctuations accompanying zooming, and is high over the entire zooming range. In order to obtain optical performance, the following conditions should be satisfied.

The zoom ratio is z, the imaging magnification of the second unit at the telephoto end is β2T, and the moving amounts of the first and second units at zooming from the wide-angle end to the telephoto end are V1 and V2, respectively. In this case, however, the amount of movement is positive when measured on the image plane side, and negative when the opposite.

[0030]

(Equation 4) Satisfying the following conditions.

Conditional expression (4) relates to the ratio of the amount of movement between the first lens unit and the second lens unit at the time of zooming from the wide-angle end to the telephoto end, while favorably correcting aberration fluctuations during zooming. This is for achieving both a reduction in the diameter of the front lens and a reduction in the overall length of the lens in a well-balanced manner. If the amount of movement of the first lens unit is too small below the lower limit, it is difficult to effectively shorten the overall lens length at the wide-angle end, and if the amount of movement of the first lens unit is too large beyond the upper limit. It is not good because the diameter of the front lens for securing off-axis light flux in the zoom range from the middle to the telephoto end increases.

Condition (5) relates to the imaging magnification at the telephoto end of the second lens unit with respect to the zoom ratio. If the imaging magnification becomes too small below the lower limit, the amount of movement of the second unit for obtaining a predetermined zoom ratio increases, and the overall length of the lens increases. Conversely, if the imaging magnification becomes too large beyond the upper limit, the overall length of the lens will be shortened, but the moving trajectory of the fourth group near the telephoto end of an infinite object will change abruptly, and driving means such as a motor Is not good because the load on

In the present invention, it is particularly preferable that the zoom lens satisfy the following condition: 1.8 <| f5 / f3 | <2.6２ (6)

Conditional expression (6) relates to the refractive powers of the fifth unit and the third unit, and is for obtaining good optical performance while shortening the lens length of the third and subsequent units. If the refractive power of the fifth lens unit becomes too strong beyond the lower limit of conditional expression (6), the negative Petzval sum increases, and it becomes difficult to correct the field curvature.
Conversely, if the refractive power of the fifth group is too weak beyond the upper limit, a sufficient effect of shortening the entire length cannot be obtained.

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.

Note that R19 and R19 in Numerical Examples 1 and 3
20, R20 and R21 in Numerical Examples 2 and 4 are glass materials such as a face plate.

The aspherical surface 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 ₀ is a paraxial radius of curvature, and B, C, D, and E are aspherical coefficients, respectively. And when

[0038]

(Equation 5) Table 1 shows the relationship with each conditional expression in each numerical example. Numerical Example 1 F = 1 to 9.51 FNO = 1: 2.05 to 2.88 2ω = 56.1 ° to 6.4 ° R 1 = 9.167 D 1 = 0.166 N 1 = 1.80518 ν 1 = 25.4 R 2 = 3.363 D 2 = 0.658 N 2 = 1.51633 ν 2 = 64.1 R 3 = -38.490 D 3 = 0.025 R 4 = 3.548 D 4 = 0.475 N 3 = 1.80400 ν 3 = 46.6 R 5 = 17.348 D 5 = Variable R 6 = 24.092 D 6 = 0.083 N 4 = 1.83400 ν 4 = 37.2 R 7 = 0.749 D 7 = 0.275 R 8 = -1.352 D 8 = 0.083 N 5 = 1.51742 ν 5 = 52.4 R 9 = 0.988 D 9 = 0.325 N 6 = 1.80518 ν 6 = 25.4 R10 = -16.201 D10 = Variable R11 = Aperture D11 = 0.170 R12 = Aspherical surface D12 = 0.450 N 7 = 1.58913 ν 7 = 61.2 R13 = -18.788 D13 = Variable R14 = 2.200 D14 = 0.083 N 8 = 1.80518 ν 8 = 25.4 R15 = 0.980 D15 = 0.566 N 9 = 1.58313 ν 9 = 59.4 R16 = Aspherical D16 = Variable R17 = -32.161 D17 = 0.083 N10 = 1.76182 ν10 = 26.5 R18 = Aspherical D18 = 0.500 R19 = ∞ D19 = 0.933 N11 = 1.51633 ν11 = 64.1 R20 =

[0039]

[Table 1]R12 surface R₀=  1.552  B = -4.528 × 10^-2 C = -1.663 × 10^-2D = 6.660 × 10^-3 R16 surface R₀= -2.505  B = 6.627 × 10^-2 C = -5.766 × 10^-2D = 4.475 × 10^-2 R18 surface R₀=  4.493  B = 7.893 × 10^-Four C = 1.279 × 10^-1D = -8.642 × 10^-2 Numerical example 2 F = 1 to 9.51 FNO = 1: 2.05 to 2.88 2ω = 56.1 ° to 6.4 ° R 1 = 9.165 D 1 = 0.166 N 1 = 1.80518 ν 1 = 25.4 R 2 = 3.363 D 2 = 0.650 N 2 = 1.51633 ν 2 = 64.1 R 3 = -39.307 D 3 = 0.025 R 4 = 3.567 D 4 = 0.483 N 3 = 1.80400 ν 3 = 46.6 R 5 = 17.872 D 5 = Variable R 6 = 21.503 D 6 = 0.083 N 4 = 1.83400 ν 4 = 37.2 R 7 = 0.749 D 7 = 0.275 R 8 = -1.346 D 8 = 0.083 N 5 = 1.51742 ν 5 = 52.4 R 9 = 0.990 D 9 = 0.333 N 6 = 1.80518 ν 6 = 25.4 R10 = -16.474 D10 = Variable R11 = Aperture D11 = 0.170 R12 = Aspherical surface D12 = 0.450 N 7 = 1.60311 ν 7 = 60.7 R13 = -48.791 D13 = Variable R14 = 2.337 D14 = 0.083 N 8 = 1.84666 ν 8 = 23.8 R15 = 1.102 D15 = 0.025 R16 = 1.167 D16 = 0.516 N 9 = 1.58313 ν 9 = 59.4 R17 = Aspherical surface D17 = Variable R18 = -10.862 D18 = 0.083 N10 = 1.78472 ν10 = 25.7 R19 = Aspherical surface D19 = 0.500 R20 = ∞ D20 = 0.933 N11 = 1.51633 ν11 = 64.1 R21 = ∞

[0040]

[Table 2]R12 surface R₀=  1.498  B = -4.890 × 10^-2 C = -1.704 × 10^-2D = 4.439 × 10^-3 R16 surface R₀= -2.200  B = 6.534 × 10^-2 C = -5.194 × 10^-2D = 2.196 × 10^-2 R19 surface R₀=  7.340  B = -2.842 × 10^-3 C = 1.017 × 10^-1D = -4.738 × 10^-2 Numerical example 3 F = 1 to 7.59 FNO = 1: 2.05 to 2.88 2ω = 52.4 ° to 7.4 ° R 1 = 6.162 D 1 = 0.138 N 1 = 1.80518 ν 1 = 25.4 R 2 = 2.524 D 2 = 0.568 N 2 = 1.51633 ν 2 = 64.1 R 3 = 106.969 D 3 = 0.023 R 4 = 2.827 D 4 = 0.422 N 3 = 1.80400 ν 3 = 46.6 R 5 = 15.628 D 5 = Variable R 6 = 17.783 D 6 = 0.076 N 4 = 1.83400 ν 4 = 37.2 R 7 = 0.637 D 7 = 0.238 R 8 = -0.973 D 8 = 0.076 N 5 = 1.51742 ν 5 = 52.4 R 9 = 0.917 D 9 = 0.294 N 6 = 1.80518 ν 6 = 25.4 R10 = -6.370 D10 = Variable R11 = Aperture D11 = 0.150 R12 = Aspherical surface D12 = 0.437 N 7 = 1.58913 ν 7 = 61.2 R13 = -6.246 D13 = Variable R14 = 2.108 D14 = 0.092 N 8 = 1.80518 ν 8 = 25.4 R15 = 0.874 D15 = 0.537 N 9 = 1.58313 ν 9 = 59.4 R16 = Aspherical D16 = Variable R17 = -55.890 D17 = 0.076 N10 = 1.78472 ν10 = 25.7 R18 = Aspherical D18 = 0.460 R19 = ∞ D19 = 0.860 N11 = 1.51633 ν11 = 64.1 R20 =

[0041]

[Table 3]R12 surface R₀=  1.409  B = -7.693 × 10^-2 C = -1.925 × 10^-2D = 6.623 × 10^-3 R16 surface R₀= -2.145  B = 8.329 × 10^-2 C = -7.255 × 10^-2D = 4.399 × 10^-2 R18 surface R₀=  3.563  B = 1.052 × 10^-2 C = 2.346 × 10^-1D = -2.470 × 10^-1 Numerical example 4 F = 1 to 7.59 FNO = 1: 2.05 to 2.88 2ω = 52.4 ° to 7.4 ° R 1 = 6.342 D 1 = 0.138 N 1 = 1.80518 ν 1 = 25.4 R 2 = 2.527 D 2 = 0.568 N 2 = 1.51633 ν 2 = 64.1 R 3 = 101.290 D 3 = 0.023 R 4 = 2.873 D 4 = 0.414 N 3 = 1.80400 ν 3 = 46.6 R 5 = 17.266 D 5 = Variable R 6 = 21.863 D 6 = 0.076 N 4 = 1.88300 ν 4 = 40.8 R 7 = 0.686 D 7 = 0.238 R 8 = -1.103 D 8 = 0.076 N 5 = 1.51742 ν 5 = 52.4 R 9 = 0.931 D 9 = 0.276 N 6 = 1.80518 ν 6 = 25.4 R10 = -7.556 D10 = Variable R11 = Aperture D11 = 0.150 R12 = Aspherical D12 = 0.4147 N 7 = 1.60311 ν 7 = 60.7 R13 = -14.337 D13 = Variable R14 = 2.361 D14 = 0.092 N 8 = 1.84666 ν 8 = 23.8 R15 = 1.017 D15 = 0.023 R16 = 1.103 D16 = 0.483 N 9 = 1.60311 ν 9 = 60.7 R17 = Aspherical surface D17 = Variable R18 = -17.020 D18 = 0.076 N10 = 1.78472 ν10 = 25.7 R19 = 5.079 D19 = 0.460 R20 = ∞ D20 = 0.860 N11 = 1.51633 ν11 = 64.1 R21 = ∞

[0042]

[Table 4]R12 surface R₀=  1.318  B = -8.866 × 10^-2 C = -1.146 × 10^-2D = -1.061 × 10^-2 R17 surface R₀= -1.903  B = 6.518 × 10^-2 C = -1.462 × 10^-2D = -8.315 × 10^-2 R19 surface R₀=  5.079 B = 2.412 × 10^-3 C = 2.134 × 10^-1D = -2.856 × 10^-1 Table 1

[0043]

[Table 5]

[0044]

According to the present invention, as described above, the lens configuration for setting the refractive power of the five lens units and the moving conditions of the first and second units in zooming and moving the fourth unit during focusing. By adopting the optical system, it is possible to reduce the size of the entire lens system, achieve good aberration correction over the entire zoom range of about 8 to 10, and achieve high optical performance with little aberration fluctuation during focusing. Thus, a rear focus zoom lens having an F number of 2.0 and a large aperture ratio can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an embodiment showing a paraxial refractive power arrangement of the present invention.

FIG. 2 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 3 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 4 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 5 is a diagram showing various aberrations in the middle of Numerical Example 1 of the present invention.

FIG. 6 is a diagram illustrating various aberrations at the telephoto end according to Numerical Embodiment 1 of the present invention.

FIG. 7 is a diagram showing various aberrations at the wide-angle end according to Numerical Example 2 of the present invention;

FIG. 8 is a diagram showing various aberrations in the middle of Numerical Example 2 of the present invention.

FIG. 9 is a diagram showing various aberrations at the telephoto end according to Numerical Example 2 of the present invention.

FIG. 10 is a diagram showing various aberrations at the wide-angle end according to Numerical Example 3 of the present invention.

FIG. 11 is a diagram showing various aberrations in the intermediate state of Numerical Example 3 of the present invention.

FIG. 12 is a diagram illustrating various aberrations at the telephoto end according to Numerical Example 3 of the present invention.

FIG. 13 is a diagram illustrating various aberrations at the wide-angle end according to Numerical Example 4 of the present invention.

FIG. 14 is a diagram showing various aberrations in the middle of the numerical example 4 of the present invention;

FIG. 15 is a diagram illustrating various aberrations at the telephoto end according to Numerical Example 4 of the present invention.

[Explanation of symbols]

 Reference Signs List 1 1st group 2 2nd group 3 3rd group 4 4th group 5 5th group d d-line g g-line ΔM Meridional image plane ΔS Sagittal image plane SP diaphragm

Claims (3)

(57) [Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a negative lens having a negative refractive power in order from the object side. The fifth lens unit includes five lens units. The first unit is moved to the object side, and the second unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end. The fourth group is moved to correct the surface fluctuation, and the fourth group is moved to perform focusing. The focal length of the i-th group is set to fi,
The focal lengths at the wide-angle end and the telephoto end of the entire system are fw and f, respectively.
T, when the imaging magnification of the fifth group is β5 A rear focus zoom lens that satisfies certain conditions. 2. The zoom ratio is z, the imaging magnification of the second unit at the telephoto end is β2T, and the moving amounts of the first and second units during zooming from the wide-angle end to the telephoto end are V1 and V2, respectively. [Equation 2] 2. The rear focus type zoom lens according to claim 1, wherein the following condition is satisfied. 3. The rear focus type zoom lens according to claim 2, wherein the following condition is satisfied: 1.8 <| f5 / f3 | <2.6.