JPH0593858A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To provide the lens which is compact and has a high power variation ratio and also has respective aberrations corrected with good balance, and can be mounted on a compact camera by making the back focus at the wide- angle end shorter than 58% of the diagonal length of a picture plane. CONSTITUTION:This zoom lens is a zoom lens which has a 1st lens group with negative refracting power and a 2nd lens group with positive refracting power and is varied in power by varying the interval between both the lens group; and the 2nd lens group consists of a front-side unit with positive refracting power and a rear-side unit with negative refracting power in order from an object side and the back focus at the wide-angle end is set shorter than 58% of the picture plane diagonal length. Consequently, the zoom lens is obtained which includes a >=32 deg. wide half field angle and an about X3 high power variation ratio and also has respective aberrations corrected with good balance and is suitably mounted on a compact camera.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens used for a lens shutter camera or the like, and more particularly to a zoom lens having a high zoom ratio including a wide zoom range.

[0002]

2. Description of the Related Art Conventionally, as a zoom lens for a lens shutter camera, a zoom lens having a zoom ratio of about 2 includes a front group having a positive refractive power and a rear group having a negative refractive power in order from the object side. A two-group zoom system is generally used (for example, see JP-A-56-128911). The feature of this system is that the entire system has a telephoto configuration, and the back focus and the total lens length are short.

On the other hand, recent trends in lens shutter cameras include two directions: high zoom ratio and wide angle.
Among these, as the high zoom lens, a three-group zoom system (for example, see Japanese Patent Laid-Open No. 63-153511) or
A large number of group zoom systems (for example, see JP-A-63-43115) have been proposed. Further, as a wide-angle zoom lens having a zoom ratio of about 2, Japanese Patent Laid-Open No. 2-284109, which uses a two-group zoom system in which a positive lens group precedes, is known. Even if the two requirements of high zoom ratio and wide angle are satisfied, there are disclosed in Japanese Patent Laid-Open No. 2-238417 and Japanese Patent Laid-Open No. 2-238417.
No. 37317 is known. These are all 3
It is a group zoom system, and is disadvantageous as compared with the two-group zoom system for a lens shutter camera that requires compactness.

Therefore, it is conceivable that a high zoom ratio and a wide angle can be obtained by a two-group zoom system in which a positive lens group precedes as in the above-mentioned Japanese Patent Laid-Open No. 2-284109. If the back focus is secured and the focal length on the telephoto side is extended, the refracting power of each lens group becomes strong, and it becomes extremely difficult to correct monochromatic aberration and chromatic aberration. On the other hand, as a zoom lens for a lens shutter camera preceded by a negative lens group, Japanese Patent Laid-Open No. 62-507 has been proposed.
No. 18 is publicly known, but all the zoom lenses shown here have a zoom ratio of less than 2 times and a focal length range only within the standard range, and the zoom range has a high zoom ratio including a wide angle. It was not applicable to zoom lenses. Moreover, the back focus of each of these zoom lenses is quite long, and the advantages of being used for lens shutter cameras have not been fully utilized.

[0005]

The object of the present invention is suitable for a lens shutter camera or the like which has two requirements of high zoom ratio and wide angle at the same time while adopting the simplest structure of the two-group zoom system. To provide a compact zoom lens.

[0006]

To achieve the above object, a zoom lens according to the present invention has a first lens group having a negative refractive power and a second lens group having a positive refractive power, and an interval between both lens groups. In the zoom lens for changing the magnification by changing the zoom ratio, the second lens group is composed of a front unit having a positive refracting power and a rear unit having a negative refracting power in order from the object side. The zoom lens is configured to be shorter than 58% of the diagonal length of the screen.

Further, it is desirable that this zoom lens satisfies the following conditions. 0.75 <| φ ₂ b | / φ ₂ a <1.20, where φ ₂ a: the refractive power of the positive front unit in the second group φ ₂ b: after the negative in the second group Refractive power of side unit

[0008]

First, it will be explained paraxially that the negative group preceding type is advantageous in terms of performance in order to obtain a wide-angle zoom lens having a high zoom ratio by using the two-group zoom system. If the refracting powers of the first and second lens groups are φ ₁ and φ ₂ , respectively, and the refracting powers of the entire system at the wide-angle end and the telephoto end are φw and φt, respectively, and the back focus as a thin-walled system at the wide-angle end is fbw. , Φ ₁ and φ ₂ can be obtained using the following equation. φ ₁ = φw−fbw · φw · φ ₂ φ ₁ = φt−φ ₂ However, the lens group spacing at the telephoto end is set to zero for simplicity. That is, as shown in FIG. 1, when φ ₂ is taken on the horizontal axis and φ ₁ is taken on the vertical axis, the coordinates of the intersections of the equations and the straight lines corresponding to the equations show the values of φ ₁ and φ ₂ at this time. There is. First, when φw and φt are given as lens specifications, the equation is determined as a straight line, and the equation becomes a straight line passing through (0, φw) and (1 / fbw, 0). By giving fbw, the coordinates of the intersection point are It is determined. When 1 / fbw> φw, the equation is a straight line −
Therefore, the intersection point Pa exists in the regions of φ ₁ > 0 and φ ₂ <0. Further, when 1 / fbw <φw, the equation becomes a straight line −b, and the intersection point Pb exists in the region of φ ₁ <0, φ ₂ > 0. 1
There is also a solution of φ ₁ > 0 and φ ₂ > 0 corresponding to / fbw <φt, but the scaling factor φ ₁ · φ _{2 with} respect to the change in the lens group interval
Since the value of becomes small, it is not considered here.

On the straight line -a, if fw is kept at an appropriate value and φw is increased to widen the angle, and if φt is decreased to attain high zooming, the intersection point Pa moves to the upper left. Both φ ₁ and | φ ₂ | have large values, making it difficult to correct aberrations. On the other hand, if an attempt is made to widen the angle and increase the magnification while keeping φ ₁ and φ ₂ at appropriate values, 1 / fbw becomes large, that is, fbw becomes too small, which causes a problem in practical use.

On the other hand, if 1 / fbw <φw, then φw
Is larger or φt is smaller, φt <1
The intersection can be found in the range of / fbw <φw,
The values of φ ₁ and φ ₂ can also be kept in an appropriate range.

As described above, in the two-group zoom system, the negative group preceding type is advantageous in performance, but there is a problem that the total lens length becomes large because the back focus is long. As described above, in the lens shutter camera, there is no limitation on the back focus except when the lens shutter camera is extremely short. Therefore, the positive second lens group is made into a telephoto type, and the back focus can be shortened to achieve miniaturization. .. That is, the second group of positive refracting power is divided into a front unit of positive refracting power and a rear unit of negative refracting power in order from the object side, and the back focus at the wide-angle end is 58% of the screen diagonal length. Configure the zoom lens so that

The effect of making the positive second group telephoto type as described above can be explained as follows. Two thin lens groups G with refractive powers φ ₁ (<0) and φ ₂ (> 0)
The total length L of the lens system composed of ₁ and G ₂ is represented by L = (1 / φ) + t {1- (φ ₁ / φ)} where t is the lens group distance and φ is the combined refractive power. From this, it can be seen that it is effective to reduce t in order to reduce L. In the two-group zoom method, the variable power efficiency | φ ₁ · φ ₂ | cannot be increased due to aberration correction and manufacturing restrictions, and it is difficult to reduce the lens group interval change Δt. Therefore, reducing the total length L in the entire zoom range depends on how small the lens group interval tt at the telephoto end where both lenses are closest to each other can be reduced. When obtaining the outline of the power allocation in FIG. 1, there was no problem even if tt = 0.
Actually, tt often takes a positive value due to the lens thickness. In the present invention, the second group is of the telephoto type to reduce tt. That is, as shown in FIG. 2, the second group G ₂ is divided into a front unit G ₂ a having a positive refractive power and a rear unit G ₂ b having a negative refractive power, and the object-side principal point H ₂ of the second group is , G ₂ a so as to be closer to the object side, the interval t between principal points is made shorter than the lens interval l. Tt at the telephoto end
That is, the distance between the image-side principal point of the first group and the object-side principal point of the second group may take a negative value (the reference numeral indicates that the second-group principal point is on the image side of the first-group principal point). If the case is positive). By making the second group a telephoto type in this way, the interval t
Also, the total length L can be reduced, and the actual back focus Fbw at the wide-angle end can be as short as 58% or less of the diagonal length of the screen.

In the present invention, the effect of making the above-mentioned positive second lens unit a telephoto type lens becomes larger by satisfying the conditions. This condition relates to the refractive power of the front and rear units in the positive second group,
If | φ ₂ b | becomes smaller than the lower limit, the effect of the telephoto type becomes small and the back focus cannot be shortened. If | φ ₂ b | becomes larger than the upper limit, it becomes difficult to correct distortion and lateral chromatic aberration at the wide-angle end.
By satisfying this condition, the interval tt between principal points at the telephoto end can take a small value of tt <-1.0.

As described above, the present invention is effective in widening the angle of view of the zoom lens, but for that purpose, it is desirable to satisfy the following conditions. 1.36 <(1-φ ₁ · tw) <1.70 where tw is the distance between the image-side principal point of the first lens group and the object-side principal point of the second lens group at the wide-angle end, where tw is Since it is transformed into φ ₁ = φw−fbw · φw · φ ₂ = φw− (1−φ ₁ · tw) φ ₂ , the equation (1−φ ₁ · tw)
Indicates the magnitude of inclination of the straight line −b in FIG.
If the slope becomes less than the lower limit of the equation, in order to increase φw and achieve a wide angle, both | φ ₁ | and φ ₂ must take large values, and aberration correction becomes difficult. Further, if the inclination becomes larger than the upper limit, fbw increases and the compactness is lost.

In the zoom lens according to the present invention, focusing is usually performed by the first group, but if there is no mechanical limitation, the second group can be moved simultaneously.

Examples of the zoom lens of the present invention will be shown below. In the table, f is the focal length, F is the F number, ω is the half angle of view, r is the paraxial radius of curvature, d is the axial upper surface spacing, nd is the refractive index for the d line, and νd is the Abbe number. In addition, the symbol * indicates an aspherical surface, and its shape is a vertex coordinate of the origin, the vertex of the surface is the origin, the vertex curvature is c, the conic coefficient is K, and the aspherical surface coefficient is Ai (i. = 4, 6) and expressed by the following mathematical formula 1.

[0017]

[Equation 1]

Example 1 f = 28.77 to 78.09 F4.0 to 7.8 2ω = 75.1 to 30.4 ° Surface number rd nd νd 1 66.031 1.20 1.77250 49.6 2 19.256 4.12 3 71.475 1.00 1.79952 42.2 4 27.180 2.94 5 24.724 3.50 1.80518 25.4 6 58.222 d ₆ 7 * 17.339 5.75 1.48749 70.2 8 -17.979 1.00 1.80518 25.4 9 -39.009 0.50 10 ∞ 10.69 11 1302.0 3.80 1.70154 41.2 12 * -38.285 13.25 13 -16.855 1.20 1.71300 53.9 14 -131.44 f 28.77 49.79 78.09 d ₆ 21.61 7.50 0.50 Aspheric coefficient 7th surface 12th surface K = -0.27870 K = -0.46771 A ₄ = -0.87027 × 10 ⁻⁵ A ₄ = 0.18572 × 10 ^{− Four} A ₆ = 0.25793 × 10 ^-7 A ₆ = 0.12651 × 10 ^-6 _{Fbw = 15.57 | φ 2 b |} / φ 2 a = 0.93 tt = -3.22 1-φ 1 · tw = 1.45

Example 2 f = 28.82 to 87.80 F4.0 to 8.7 2ω = 75.5 to 27.3 ° Surface number rd nd νd 1 59.891 1.20 1.77250 49.6 2 19.222 4.12 3 67.142 1.00 1.79952 42.2 4 25.944 3.12 5 24.316 3.50 1.80518 25.4 6 53.980 d ₆ 7 * 20.521 3.00 1.51633 64.1 8 402.53 0.30 9 50.203 3.50 1.48749 70.2 10 -23.085 1.00 1.80518 25.4 11 -95.898 0.50 12 ∞ 11.09 13 309.56 3.30 1.70154 41.2 14 * -39.667 14.13 15 -17.369 1.20 1.71300 53.9 16 -111.48 f 28.82 54.78 87.80 d ₆ 23.59 7.30 0.50 aspherical coefficient seventh surface fourteenth surface _{K = -0.37499 K = -0.20230 A 4} = -0.88645 × 10 -6 A ₄ = 0.16116 x 10 ^-4 A ₆ = 0.87785 × 10 ^-8 A ₆ = 0.84753 × 10 ^-7 _{Fbw = 15.85 | φ 2 b |} / φ 2 a = 0.91 tt = -3.25 1-φ 1 · tw = 1.50

In each of the above-mentioned two embodiments, the positive front unit in the second unit is composed of a positive lens unit including a diaphragm, and an aspherical surface arranged with an air space on the image side. The positive lens group is divided into two. The shape of this aspherical surface is selected so that the curvature becomes weak off-axis, and it is effective for correction of coma on the long focus side. The negative rear unit in the second group is composed of one lens. In this embodiment, the screen diagonal length is 43.27 in all cases.

[0021]

As described above, the zoom lens of the present invention is compact and has a half angle of view of 32 ° or more, although it has a simple structure of two groups as shown in the examples and each aberration diagram. It has a high zoom ratio of about 3 times, including the wide angle, and each aberration is well-balanced, making it suitable for mounting on a compact camera.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a power determination method for a two-group zoom lens according to the present invention.

FIG. 2 is an explanatory diagram of the configuration and action of a second lens group.

FIG. 3 is a sectional view of a first group of the second group zoom lens according to the present invention.

FIG. 4 is a sectional view of a second group zoom lens according to a second embodiment of the present invention.

FIG. 5 is an aberration diagram at the wide-angle end of Embodiment 1 of the second group zoom lens according to the present invention.

FIG. 6 is an aberration diagram in the intermediate portion of Example 1 of the two-group zoom lens according to the present invention.

FIG. 7 is an aberration diagram at the telephoto end of Embodiment 1 of the second group zoom lens according to the present invention.

FIG. 8 is an aberration diagram at the wide-angle end of Embodiment 2 of the second group zoom lens according to the present invention.

FIG. 9 is an aberration diagram in the intermediate portion of Example 2 of the two-group zoom lens according to the present invention.

FIG. 10 is an aberration diagram of Example 2 of the two-group zoom lens according to the present invention at the telephoto end.

[Explanation of symbols]

In the figure, “d” and “g” are spherical aberrations at the d-line and the g-line, “ΔS” and “ΔM” are the sagittal image planes, respectively.
It represents the meridional image plane.

Claims (2)

[Claims] 1. A zoom lens comprising, in order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, wherein zooming is performed by changing an interval between both lens groups. The second lens group is composed of a front unit having a positive refractive power and a rear unit having a negative refractive power in order from the object side, and the back focus at the wide-angle end is shorter than 58% of the diagonal length of the screen. Small zoom lens 2. The compact zoom lens according to claim 1, wherein the following condition is satisfied: 0.75 <| φ ₂ b | / φ ₂ a <1.20, where φ ₂ a: second Refractive power of the positive front unit in the group φ ₂ b: Refractive power of the negative rear unit in the second group