JPH05313066A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide a zoom lens having a wide angle of view and a high variable power ratio by arranging five lens groups as a whole, and setting moving conditions of respective lens groups properly according to refracting powers or variable powers of the respective lens groups. CONSTITUTION:Five lens groups of the first group L1 having a negative refracting power, the second group L2 having a negative refracting power, the third group L3 having a positive refracting power, the fourth group L4 having a negative refracting power and the fifth group L5 having a positive refracting power are arranged in this order from the object side, and when a power variation is carried out from a wide angle end to a telescopic end, at least the first L1, the second L2, the third L3 and the fifth group L5 are moved so that a distance between the second group L2 and the third group L3 is decreased and a distance between the third group L3 and the fourth group L4 is increased and a distance between the fourth group L4 and the fifth group L5 is decreased, and the first group L1 and the second group L2 are moved on different loci.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens suitable for a photographic camera for 35 mm film, a video camera for electronic recording, an SV camera and the like. A wide angle of view with high optical performance over the entire zoom range by having the lens groups and appropriately setting the movement conditions associated with zooming of these five lens groups, the refractive power of each lens group, and the lens configuration. The present invention relates to a zoom lens including a range.

[0002]

2. Description of the Related Art So-called negative lead type zoom lenses, in which a lens unit having a negative refracting power precedes, are relatively easy to widen the field angle, and are therefore often used in zoom lenses for wide field angles. .. For example, in Japanese Examined Patent Publication No. 49-23912 and Japanese Unexamined Patent Publication No. 57-163213, the first group having negative refracting power, the second group having positive refracting power, the third group having negative refracting power, and It has four lens groups of the fourth lens group of positive refractive power, and when zooming from the wide-angle end to the telephoto end, the first group is moved to the image side, and the second and fourth groups are moved to the object side. Move
A zoom lens in which the third group is fixed or moved has been proposed.

A negative lead type zoom lens, which is preceded by such a lens unit having a negative refractive power, is characterized in that it is relatively easy to widen the angle of view and that the close-up distance is shortened.

However, if the refracting power of each lens unit is strengthened in order to reduce the size of the entire lens system while achieving a high zoom ratio, various aberrations will occur and the optical performance will be greatly deteriorated. Further, if an attempt is made to increase the aperture, the diameter of the diaphragm will increase, and the size of the entire lens system will increase.

A zoom lens which has been improved in view of these drawbacks, and which has been made compact and has a high zoom ratio, is disclosed in, for example, Japanese Patent Publication No. 55-14403 and Japanese Patent Publication No. 63-241511. It is proposed in the official gazette.

In each of these publications, a zoom lens is composed of four lens groups in order from the object side, negative, positive, negative, and positive, and the predetermined lens group is appropriately moved. I am changing the magnification.

In addition, in Japanese Laid-Open Patent Publication No. 2-201310, in a zoom lens having a similar structure, a relatively lightweight part of the first lens group is moved along the optical axis to perform focusing, for example, autofocusing. We have proposed a zoom lens that facilitates the focus operation when performing.

[0008]

In recent years, a standard zoom lens used for a single-lens reflex camera, a video camera, etc. is required to have a wide field angle and a high zoom ratio.
For example, in a single-lens reflex camera for 35 mm film, a zoom lens having a wide field angle with a focal length of about 35 mm to 70 mm has already been used as a standard zoom lens.

Generally, if it is attempted to secure an aperture ratio of an F number of about 2.8 with such a shooting angle of view, the lens structure becomes complicated and it becomes difficult to satisfactorily correct the optical performance over the entire zoom range. .. In general, such a zoom lens often has a large lens outer diameter and a large weight on the object side.

For this reason, for example, in a power focus type camera for electrically focusing such as autofocus, if the first group of heavy weight is moved during focusing, a driving means such as a large motor is required, and power consumption and space are reduced. Therefore, there is a problem that the size of the entire camera becomes large.

According to the present invention, the zoom lens is composed of five lens groups as a whole, and by appropriately setting the refracting power of each lens group and the moving condition of each lens group due to zooming,
An object of the present invention is to provide a zoom lens having a short overall lens length, a large aperture ratio, a relatively wide angle of view, and high optical performance over the entire zoom range.

In addition to this, the present invention adopts an inner focus system in which focusing is performed by a lens group other than the first group,
An object of the present invention is to provide a zoom lens having a wide angle of view, which is suitable for, for example, an autofocus camera and the like, which facilitates focus operation.

[0013]

A zoom lens according to the present invention comprises a first lens unit having a negative refractive power and a second lens unit having a negative refractive power in order from the object side.
There are five lens groups, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power, and the second lens group upon zooming from the wide-angle end to the telephoto end. The distance between the third group and the third group is decreased, the distance between the third group and the fourth group is increased, and the fourth group is increased.
At least the first, second, third, and fifth groups are moved so as to reduce the distance between the group and the fifth group, and the first group and the second group are moved on different trajectories. It has a feature.

In particular, the present invention is characterized in that the first lens unit is moved in one direction during zooming and that the second lens unit is moved for focusing.

[0015]

1 to 3 are lens cross-sectional views at the wide-angle end in Numerical Embodiments 1 to 3 of the present invention.

In the figure, L1 is the first group of negative refractive power, L2 is the second group of negative refractive power, L3 is the third group of positive refractive power, L4 is the fourth group of negative refractive power, and L5. Is a fifth group of positive refractive power. SP is a diaphragm. The arrows show the movement loci of the respective lens groups when zooming from the wide-angle end to the telephoto end.

In the present embodiment, as shown in the figure, when zooming from the wide-angle end to the telephoto end, the distance between the second group and the third group is decreased, and the distance between the third group and the fourth group is increased. , A predetermined lens group is moved so as to reduce the distance between the fourth group and the fifth group, and the first group and the second group are moved on different trajectories.

Of these, in Numerical Example 1 of FIG. 1, all five lens groups are moved. In the numerical examples 2 and 3 of FIGS. 2 and 3, the first, second, third and fifth groups are moved to move the fourth group.
The group is fixed. In each of the embodiments shown in FIGS. 1 to 3, focusing is performed by moving the second group.

In the zoom lens according to the present invention, at the wide-angle end, the first lens unit and the second lens unit, both of which have negative refractive power, are arranged with the third lens unit having positive refractive power spaced apart (far apart) from each other on the optical axis. Further, a fourth group having a negative refractive power is arranged close to the third group, and a fifth group having a positive refractive power is arranged apart from the fourth group. As a result, the entire lens system has a retro-type lens structure, and a predetermined back focus can be easily obtained while achieving a wide angle of view.

When zooming from the wide-angle end to the telephoto end, at the telephoto end, the third lens unit having a positive refractive power is brought closer to the first lens unit and the second lens unit having a negative refractive power, The distance between the group and the fourth group having a negative refracting power should be wide,
A predetermined lens unit is moved so that the fifth lens unit having a positive refractive power approaches the lens unit to perform zooming, so that the entire lens system has a telephoto type lens configuration.

This allows each lens group to effectively share the variable power, and reduces the moving amount of each lens group during the variable power,
The entire lens system is being downsized while ensuring a predetermined zoom ratio.

In Numerical Embodiment 1 of FIG. 1, during zooming from the wide-angle end to the telephoto end, the first and fourth groups are moved linearly toward the image plane side, and the third group is moved linearly toward the object side. To the object side so as to have a convex locus, and the second group to the image side so as to have a convex locus. In Numerical Examples 2 and 3 of FIGS. 2 and 3, the fourth group is fixed, the fifth group moves linearly toward the object side, and the other lens groups are the same as Numerical Example 1.

According to the present invention, at this time, the moving speed of the first lens unit does not suddenly change during zooming, and the moving direction does not reverse during zooming. It enables the construction of a strong lens barrel.

In particular, the first lens group is linearly moved to strengthen it against an impact on the camera, and a cam groove is not required in the lens barrel structure, so that the lens barrel structure is simplified. In addition, by using the so-called inner focus method, in which focusing is performed by moving the second group, which has a relatively small lens weight, on the optical axis, it is possible to facilitate the focusing operation when applied to an autofocus camera, for example, and to perform high-speed focusing operation. It is possible.

Further, by adopting such an inner focus system, the structure of the lens barrel in which the first lens unit does not rotate at the time of zooming and focusing becomes possible, and simplification of the structure is facilitated.

In the zoom lens according to the present invention, the first lens group is provided with a meniscus negative lens having a concave surface having a strong refractive power facing the image side. As a result, the off-axis light beam is gradually refracted to facilitate retro-type conversion of the entire lens system at the wide-angle end, and the negative distortion aberration on the wide-angle side that occurs when widening the angle of view is satisfactorily corrected. There is.

In the present invention, it is preferable to satisfy the following conditions in order to obtain a high optical performance with a small variation in aberration over the entire zoom range while shortening the total lens length and widening the angle of view.

The second lens group has a negative 21st lens having a concave surface facing the image side and a positive 22nd lens having a convex surface facing the object side. The radius of curvature of the lens surface is R2a, the radius of curvature of the object side lens surface of the 22nd lens is R2b, the focal length of the i-th group is fi, and the combined focal length of the first and second groups at the wide-angle end. F
1 and 2, assuming that the focal length of the entire system at the telephoto end is fT 0.35 <| f1,2 | / fT <0.9 (1) 0.75 <f1 / f2 <3.0 (2) 0.7 <R2a / R2b <1.2 (3) The condition is satisfied.

Conditional expression (1) appropriately sets the combined refracting power of the first group and the second group at the wide-angle end, mainly correcting the outer diameter of the lens and correcting various aberrations in a balanced manner. It is for the purpose.

When the upper limit of conditional expression (1) is exceeded and the combined refracting power of the first group and the second group becomes too weak, the refracting action of the off-axis light beam becomes weak on the wide-angle side, and a predetermined amount of off-axis light beam is obtained. In order to ensure the above, it becomes necessary to increase the lens outer diameters of the first and second groups. If the combined refractive power of the first group and the second group becomes too strong below the lower limit, the lens outer diameters of the first group and the second group become small, but the distortion aberrations occurring in the first group and the second group. And off-axis aberrations such as astigmatism become large, and it becomes difficult to correct these various aberrations by other lens groups.

The conditional expression (2) is based on the conditional expression (1), in which the ratio of the refracting powers of the first group and the second group is appropriately set, and the total length of the lens is shortened, while the second group is designed. This is for reducing aberration fluctuations when focusing.

If the upper limit of conditional expression (2) is exceeded and the refracting power of the second lens unit becomes too strong, the amount of movement for focusing by the second lens unit becomes small, which is advantageous for shortening the total lens length. However, the amount of fluctuation in aberration during focusing becomes large, and it becomes difficult to maintain good optical performance over the entire object distance. If the lower limit is exceeded and the refractive power of the second lens unit becomes too weak, the amount of movement during focusing increases, the overall lens length increases, and the distance between the first lens unit and the aperture increases, ensuring an off-axis light beam. This is not good because the outer diameter of the lens of the first lens group for increasing the diameter increases.

Conditional expression (3) is defined by the second negative value which constitutes the second group.
The curvature radius Ra of the lens surface on the image side of one lens and the positive second
This is for appropriately setting the ratio of the radius of curvature Rb of the lens surface of the two lenses on the object side, and favorably correcting the spherical aberration mainly generated in the first group.

The radius of curvature R is exceeded by exceeding the upper limit of conditional expression (3).
If 2a becomes too large compared with the radius of curvature R2b, the spherical aberration will be corrected well, but the negative refracting power of the entire second lens group will weaken, and if this is burdened by another lens surface, coma aberration etc. The amount of various aberrations increases.

If the radius of curvature R2a becomes smaller than the radius of curvature R2b below the lower limit, the amount of positive spherical aberration will increase, which may occur on other lens surfaces, for example, the 22nd lens.
It becomes difficult to correct with the lens surface on the object side of the lens.

In addition, in the present invention, the following conditions are preferably satisfied in order to correct various aberrations in a balanced manner over the entire zoom range while ensuring a predetermined zoom ratio.

When the third lens unit has at least one negative lens and at least two positive lenses, the focal length of the third lens unit is f3, and the focal length of the entire system at the telephoto end is fT. The condition is 0.28 <f3 / fT <0.85 (4).

Conditional expression (4) relates to the ratio of the focal length of the third lens group to the focal length of the entire system at the telephoto end.

When the upper limit of conditional expression (4) is exceeded and the refractive power of the third lens unit becomes too weak, the amount of movement of each lens unit accompanying zooming for ensuring a predetermined zoom ratio increases. However, this is not good because the total lens length increases and the lens outer diameter increases. If the lower limit is exceeded and the refractive power of the third lens group becomes too strong, the entire lens system will become smaller, but various aberrations such as spherical aberration will increase from the third lens group, and this will be corrected by other lens groups. Becomes difficult.

According to the present invention, the conditional expression (4) is satisfied, and the third lens unit is constructed so as to have at least one negative lens and at least two positive lenses, whereby chromatic aberration is satisfactorily corrected and spherical aberration is achieved. The generation amount of is reduced.

Next, numerical examples of the present invention will be shown. 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 gap from the object side, and Ni and νi are the values of the i-th lens in order from the object side, respectively. The refractive index of glass and the Abbe number.

The aspherical shape has an X axis in the optical axis direction, an H axis in the direction perpendicular to the optical axis, a positive light traveling direction, and R as a paraxial radius of curvature.
When A, B, C, D, and E are aspherical coefficients, respectively

[0043]

[Equation 1] It is expressed by Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. Numerical Example 1 F = 36.5 to 77.4 FNO = 1: 2.9 2 ω = 62.2 ° to 31.1 ° R 1 = 69.33 D 1 = 2.20 N 1 = 1.77250 ν 1 = 49.6 (aspherical surface) R 2 = 38.49 D 2 = variable R 3 = -79.11 D 3 = 1.80 N 2 = 1.88300 ν 2 = 40.8 R 4 = 54.47 D 4 = 0.50 R 5 = 56.11 D 5 = 4.50 N 3 = 1.84666 ν 3 = 23.8 R 6 = 5045.30 D 6 = variable R 7 = 89.26 D 7 = 1.50 N 4 = 1.84666 ν 4 = 23.8 R 8 = 37.81 D 8 = 8.00 N 5 = 1.65160 ν 5 = 58.5 R 9 = -103.33 D 9 = 0.15 R10 = 74.97 D10 = 4.00 N 6 = 1.69680 ν 6 = 55.5 R11 = 1307.60 D11 = 0.15 R12 = 51.67 D12 = 5.00 N 7 = 1.69680 ν 7 = 55.5 R13 = 3317.12 D13 = Variable R14 = (Aperture) D14 = 2.00 R15 = -93.73 D15 = 3.30 N 8 = 1.80518 ν 8 = 25.4 R16 = -31.23 D16 = 1.30 N 9 = 1.63930 ν 9 = 44.9 R17 = 77.19 D17 = 1.40 R18 = -162.57 D18 = 1.30 N10 = 1.60323 ν10 = 42.3 R19 = -7621.93 D19 = variable R20 = 245.95 D20 = 1.30 N11 = 1.84666 ν11 = 23.8 R21 = 35.85 D21 = 2.70 R22 = 871.81 D22 = 3.00 N12 = 1.69680 ν12 = 55.5 R23 = -46.11 D23 = 0.15 R24 = 41.75 D24 = 2.80 N13 = 1.77250 ν13 = 49.6 R25 = 81.22 Aspheric surface number B = 2.01734 × 10 ^-7 C = 1.456 ^{7 × 10 -10 D = 6.76429 ×} 10 -14 E = -3.01424 × 10 -16

[0044]

[Table 1] Numerical Example 2 F = 35.9 to 77.8 FNO = 1: 2.9 2 ω = 62.2 ° to 31.1 ° R 1 = 684.66 D 1 = 2.62 N 1 = 1.80518 ν 1 = 25.4 R 2 = -1055.76 D 2 = 0.20 R 3 = 149.76 D 3 = 2.10 N 2 = 1.71300 ν 2 = 53.8 R 4 = 53.30 D 4 = Variable R 5 = -488.25 D 5 = 2.00 N 3 = 1.77250 ν 3 = 49.6 R 6 = 44.81 D 6 = 0.53 R 7 = 43.27 D 7 = 3.50 N 4 = 1.84666 ν 4 = 23.9 R 8 = 78.34 D 8 = Variable R 9 = 84.43 D 9 = 1.20 N 5 = 1.84666 ν 5 = 23.8 R10 = 30.98 D10 = 7.20 N 6 = 1.55963 ν 6 = 61.2 R11 = -1529.08 D11 = 0.15 R12 = 50.67 D12 = 6.00 N 7 = 1.65160 ν 7 = 58.5 R13 = -110.42 D13 = 0.15 R14 = 40.57 D14 = 3.30 N 8 = 1.65160 ν 8 = 58.5 R15 = 71.98 D15 = variable R16 = ( Aperture) D16 = 1.50 R17 = -145.10 D17 = 3.00 N 9 = 1.84666 ν 9 = 23.8 R18 = -34.13 D18 = 1.20 N10 = 1.60311 ν10 = 60.7 R19 = 112.83 D19 = 2.00 R20 = -42.83 D20 = 1.40 N11 = 1.60311 ν11 = 60.7 R21 = 66.44 D21 = Variable R22 = 347.07 D22 = 5.00 N12 = 1.55963 ν12 = 61.2 R23 = -26.27 D23 = 1.50 N13 = 1.80518 ν13 = 25.4 R24 = -35.22 D24 = 0.15 R25 = 104.39 D25 = 5.00 N14 = 1.71300 ν14 = 53.8 R26 = -51.25 D26 = 5.44 R27 = -30.94 D27 = 1.35 N15 = 1.84666 15 = 23.8 R28 = -84.63

[Table 2] Numerical Example 3 F = 35.8 to 77.6 FNO = 1: 2.9 2 ω = 62.3 ° to 31.2 ° R 1 = 791.76 D 1 = 2.62 N 1 = 1.80518 ν 1 = 25.4 R 2 -1937.16 D 2 = 0.20 R 3 = 112.86 D 3 = 2.10 N 2 = 1.71300 ν 2 = 53.8 R 4 = 51.40 D 4 = Variable R 5 = -317.21 D 5 = 2.00 N 3 = 1.77250 ν 3 = 49.6 R 6 = 44.52 D 6 = 0.60 R 7 = 43.29 D 7 = 3.50 N 4 = 1.84666 ν 4 = 23.9 R 8 = 75.72 D 8 = Variable R 9 = 78.89 D 9 = 1.20 N 5 = 1.84666 ν 5 = 23.8 R10 = 31.34 D10 = 7.20 N 6 = 1.55963 ν 6 = 61.2 R11 = -78204.10 D11 = 0.15 R12 = 52.30 D12 = 6.00 N 7 = 1.65160 ν 7 = 58.5 R13 = -104.66 D13 = 0.15 R14 = 43.06 D14 = 3.30 N 8 = 1.65160 ν 8 = 58.5 R15 = 95.40 D15 = Variable R16 = (Aperture ) D16 = 1.50 R17 = -134.01 D17 = 3.00 N 9 = 1.84666 ν 9 = 23.8 R18 = -33.45 D18 = 1.20 N10 = 1.60311 ν10 = 60.7 R19 = 102.01 D19 = 2.00 R20 = -44.08 D20 = 1.40 N11 = 1.60311 ν11 = 60.7 R21 = 63.77 D21 = Variable R22 = 723.38 D22 = 5.30 N12 = 1.55963 ν12 = 61.2 R23 = -26.94 D23 = 1.50 N13 = 1.80518 ν13 = 25.4 R24 = -31.98 D24 = 0.15 R25 = 97.49 D25 = 5.00 N14 = 1.71300 ν14 = 53.8 R26 = -48.30 D26 = 2.50 R27 = -32.10 D27 = 1.35 N15 = 1.84666 15 = 23.8 R28 = -125.97

[Table 3]

[0045]

[Table 4]

[0046]

According to the present invention, as described above, the total lens length can be shortened and the lens barrel structure can be realized by specifying the refractive powers of the five lens groups and the moving conditions of each lens group due to the zooming. It is possible to achieve a zoom lens having a relatively wide angle of view and a high optical performance over the entire zooming range with a high zooming ratio while being simple.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a diagram showing various types of aberration at the wide-angle end zoom position according to Numerical Example 1 of the present invention.

FIG. 5 is a diagram showing various types of aberration at an intermediate zoom position in Numerical Example 1 of the present invention.

FIG. 6 is a diagram of various types of aberration at the zoom position at the telephoto end according to Numerical Example 1 of the present invention.

FIG. 7 is a diagram of various types of aberration at the wide-angle end zoom position according to Numerical Example 2 of the present invention.

FIG. 8 is a diagram of various types of aberration at a middle zoom position of Numerical Example 2 of the present invention.

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

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

FIG. 11 is a diagram of various types of aberration at a middle zoom position in Numerical Example 3 of the present invention.

FIG. 12 is a diagram showing various types of aberration at the zoom position at the telephoto end according to Numerical Example 3 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group L5 5th group SP Aperture S Sagittal image surface M Meridional image surface d d line g g line

Claims (5)

[Claims] 1. A first group of negative refracting power, a second group of negative refracting power, a third group of positive refracting power, a fourth group of negative refracting power, and a positive refracting power It has five lens units, the fifth lens unit, and the second lens unit and the third lens unit when zooming from the wide-angle end to the telephoto end.
At least the first, second, third, and third groups so as to reduce the distance between the groups, increase the distance between the third group and the fourth group, and decrease the distance between the fourth group and the fifth group. A zoom lens characterized in that the fifth lens unit is moved and the first lens unit and the second lens unit are moved along different trajectories. 2. The zoom lens according to claim 1, wherein the first lens unit moves in one direction during zooming. 3. The zoom lens according to claim 1, wherein the second lens unit is moved for focusing. 4. The second lens group includes a negative 21st lens having a concave surface facing the image surface side and a positive 22nd lens having a convex surface facing the object side, and the image surface of the 21st lens. R2a, the radius of curvature of the object side lens surface of the 22nd lens is R2b, the focal length of the i-th group is fi, and the combination of the first and second groups at the wide-angle end is Focal length f
1 and 2, when the focal length of the entire system at the telephoto end is fT: 0.35 <| f1,2 | / fT <0.9 0.75 <f1 / f2 <3.0 0.7 <R2a / R2b The zoom lens according to claim 1, wherein the condition <1.2 is satisfied. 5. The third lens unit has at least one negative lens and at least two positive lenses, the focal length of the third lens unit is f3, and the focal length of the entire system at the telephoto end is fT.
The zoom lens according to claim 1, wherein the condition 0.28 <f3 / fT <0.85 is satisfied.