JPH0498212A - Compact wide angle zoom lens - Google Patents

Abstract

PURPOSE:To simultaneously attain a wide picture angle and a high zoom rate by using a zoom lens constituted of two positive and negative groups satisfying specific conditions. CONSTITUTION:The zoom lens is constituted of the 1st lens group G1 having positive refractive power and consisting of a front group GF and a rear group GR and the 2nd lens group G2 having negative refractive power successively arranged from the object side. When it is defined that the focal distance of the 1st lens group G1 is F1, the focal distance of the 2nd lens group G2 is F2, maximum image height on an image face is Y, and the image formation power of the 2nd lens group G2 at a wide angle end is beta2w, the optimum focal distance of the 1st lens group G1 is regulated by conditional expression I. The range of the optimum focal distance of the 2nd lens group G2 at the time of shortening the focal distance is regulated by conditional expression II and the optimul image formation power of the 2nd lens group G2 at the wide angle end is regulated by conditional expression III. At the time of moving a focusing position from an infinite object to a near object in order to secure effective image formation per group GF and the rear group GR are respectively defined as fF and fR.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a zoom lens suitable for a lens-shutter type compact camera, which has a wide angle of view of about 64°, and has an angle of 2.5°.
The present invention relates to a zoom lens having a zoom ratio of approximately 2 times.

[Conventional technology]

Recently, lens specifications have become more sophisticated in the field of zoom lenses for compact cameras, and lenses with zoom ratios exceeding 2x have been proposed. For example, JP-A-1
JP-A-191114 proposes a zoom lens with a maximum angle of view of 60° and a zoom ratio of 2.2 times.

[Problem to be solved by the invention]

In recent years, there has been an increasing demand for zoom lenses for compact cameras to have a wide angle of view in addition to a high zoom ratio. In other words, it is desired that the camera not only be able to take larger pictures of distant objects, but also be able to take pictures of objects with a wide angle of view.

The zoom lens disclosed in Japanese Patent Application Laid-open No. 1-191114 mentioned above can meet the former requirement of photographing distant objects even larger, but it does not fully meet the latter requirement of photographing objects with a wider angle of view. I couldn't.

Therefore, in order to meet the above requirements, the present invention has been developed to meet the above requirements.
The object of the present invention is to provide a high-performance zoom lens suitable for a compact camera, which has a zoom ratio of about 2.5 times and a wide angle of view of about 2.5 times.

[Means to solve the problem]

In order to achieve the above object, the present invention has a first lens group G1 having a positive refractive power and a second lens group G2 having a negative refractive power, as shown in FIG. In a zoom lens that performs magnification by changing the distance between the groups, the first lens group G1 includes, in order from the object side, a front group G having a positive refractive power, and a rear group having a positive refractive power. G, and the front group GF has a positive refractive second lens component L1 formed in a meniscus lens shape with a convex surface facing the object side, and a negative refractive lens component L1 with a stronger concave surface facing the object side. a second lens component L2 with a positive refractive power, a third lens component L3 with a positive refractive power, and a fourth lens component with a positive refractive power, and the rear group GR has a fifth lens component L5 with a positive refractive power. The second lens group G2 includes a positive refractive sixth lens component L6 formed in a meniscus shape with a convex surface facing the image side, and a negative refractive lens component L6 formed in a meniscus shape with a convex surface facing the image side. It has a seventh lens component L7 with a strong refractive power and an eighth lens component L8 with a negative refractive power formed in a meniscus shape with a convex surface facing the image side, and further satisfies the following conditions. .

(1) 1.14<fl/Y<1.19(2)
1.0<l f2/Yl<1.09. f2<
0(3) 1.21<β2Vl<1.32 However, fI: Focal length of the first lens group G1, f2: Focal length of the second lens group G2, Y: Maximum image height at the image plane, β2w : The imaging magnification of the second lens group G2 at the wide-angle end.

In addition, in order to ensure good imaging performance from infinity to short distances, when focusing from an object at infinity to a short distance object, the front group CF is moved toward the object side, and the focal length of the front group G is When f is the focal length of the rear group GR, and fR is the focal length of the rear group GR, (4) 3.5<fR/f, <t.

It is desirable to satisfy the following.

[For production]

In a zoom lens with a positive and negative two-group configuration as in the present invention, when trying to simultaneously achieve a wide angle of view and high magnification (high zoom ratio), refraction between the first lens group G1 and the second lens group G2 There is a need to distribute power appropriately.

First, condition (1) defines an appropriate focal length of the first lens group G.

In the present invention, by configuring the first lens group G1 to have a short focal length, it is possible to reduce the focal length at the wide-angle end.

If the upper limit of condition (1) is exceeded, it becomes difficult to obtain a wide angle of view. That is, the first lens group G1 and the second lens group G2
In order to reduce the combined focal length of the lens, it is necessary to increase the distance between the first lens group G1 and the second lens group G2. As a result, the back focus is extremely reduced, and it becomes necessary to increase the diameter of the lens closest to the image side. Therefore,
It is extremely difficult to make the entire camera compact, making it unsuitable as a zoom lens for compact cameras.

On the other hand, if the lower limit of condition (1) is exceeded, it is suitable for obtaining a large back focus while reducing the composite focal length at the wide-angle end, but on the other hand, the power borne by the first lens group G1 becomes excessive. Since it becomes difficult to correct various aberrations including spherical aberration, good imaging performance cannot be obtained.

Now, in a zoom lens having two positive and negative lens groups as in the present invention, zooming is performed by changing the distance between the two lens groups. At this time, at the wide-angle end, the distance between both lens groups becomes maximum, and at the telephoto end, the distance between both lens groups becomes minimum.

Here, with a certain zoom ratio obtained, the distance between the first lens group G1 and the second lens group G2 at the wide-angle end (air distance), and the distance between the first lens group G1 and the second lens group G1 at the telephoto end. Second
If the difference between the lens group G2 and the group spacing (air spacing) is small, the air spacing between the first lens group G and the second lens group G2 at the telephoto end can be ensured.

Therefore, both lens groups can be moved for zooming to the extent that they do not interfere mechanically.
A higher zoom ratio can be obtained.

At this time, in order to reduce the amount of change in the air distance between the first lens group G1 and the second lens group G2 and to perform zooming efficiently, it is more advantageous to have a shorter focal length of the second lens group G2.

Therefore, the present invention provides the second lens group G2 under condition (2).
This defines the range of optimal focal lengths when the focal length is shortened.

If the upper limit of condition (2) is exceeded, the focal length of the second lens group G2 becomes too long, and in order to obtain a large zoom ratio, the lens distance between the first lens group G+ and the second lens group G2 at the wide-angle end must be adjusted. must be made larger.

This results in an increase in the size of the lens system.

On the other hand, exceeding the lower limit of condition (2) is preferable for obtaining a high zoom ratio, but the negative refractive power (power) of the second lens group G2 becomes excessive, making it difficult to correct distortion and Petzval sum.

Condition (3) defines the optimal imaging magnification of the second lens group at the wide-angle end, and the relative arrangement of the first lens group G1 and the second lens group G2 that is optimal for widening the angle of view. It shows the relationship.

If the lower limit of condition (3) is exceeded, the back focus at the wide-angle end becomes extremely short and the diameter of the image-side lens in the second lens group becomes large, making it impossible to achieve compactness.

On the other hand, if the upper limit of condition (3) is exceeded, the focal length of the first lens group G1 must be made too short in order to widen the angle of view, making it difficult to correct various aberrations including spherical aberration. It becomes difficult.

In the present invention, based on the basic configuration of each group as described above,
The first lens group G is a second lens component L having a positive refractive power formed in a meniscus lens shape with a convex surface facing the object side.
1, and a second lens with negative refractive power with a stronger concave surface facing the object side.
A configuration including a front group G having a lens component L2, a third lens component L3, a fourth lens component L4 having a positive refractive power, and a rear group having a fifth lens component L6 having a positive refractive power. The second lens group G2 includes a sixth lens component with positive refractive power formed in a meniscus shape with a convex surface facing the image side.
, a seventh lens component L7 with a negative refractive power formed in a meniscus shape with a convex surface facing the image side, and an eighth lens component L7 with negative refractive power also formed in a meniscus shape with a convex surface facing the image side. The configuration has the following features.

With the above-described specific lens configuration, the present invention enables excellent aberration correction even when achieving a wide angle of view and a high zoom ratio at the same time.

In particular, the positive meniscus component in the first lens group has its convex surface facing the object side, and the positive meniscus component LI1 and negative meniscus lens components L7 and L8 in the second lens group have their convex surfaces facing the image side, The shape is such that it cannot be turned against off-axis rays.

As a result, the angle of incidence of off-axis rays with respect to the normal to the lens surface when passing through each lens surface of these meniscus lenses becomes small, and since these off-axis rays pass through each lens without being significantly refracted, This can effectively correct coma and distortion at the wide-angle end.

In addition, in the wide-angle zoom lens of the present invention, in order to ensure good close-range focusing performance, the first lens group G1 is divided into a front group G and a rear group GR, so that focusing from infinity to close distance is possible. During focusing, it is preferable to move only the front group toward the object. This makes it possible to suppress fluctuations in astigmatism and field curvature, which tend to occur excessively in the negative direction when focusing on short distances.

At this time, it is more preferable to satisfy the following conditions.

(4) 3.5 < f R / f F < 10 However, f,: focal length of front group G, fR: focal length of rear group GR, It is.

Condition (4) defines appropriate refractive power distribution between the front group G and the rear group in the first lens group.

When the upper limit of condition (4) is exceeded, the positive refractive power borne by the rear group GR becomes smaller, which has the effect of suppressing fluctuations in astigmatism and field curvature that tend to occur excessively in the negative direction during focusing. It becomes smaller and its short-range performance deteriorates significantly.

On the other hand, if the lower limit of condition (4) is exceeded, astigmatism and field curvature will excessively occur in the positive direction during focusing, and the fluctuations in these aberrations will become large.

Further, in order to achieve better correction of various aberrations in the wide-angle zoom lens of the present invention, it is desirable that the following conditions be satisfied.

(5) 1.7 <ft, /fp <3.8 (6)
0.6 < l fL2/f, l < t, 3,
ft2<0(7) 0.6<fi4/fP<1.
9(8) t, o < l fLs/f21 <2.
0, fLe>0(9) 0.7 <fL7/f2 <
1.5 (10) 0.8 < f L8/ f 2
<2.5(11) 40 <ν, <60 (12) 18<shi, 8-shiL8<26(13)
15<Sh, 8-ShL7<28 However, fl,: Focal length of the first lens component L1 in the first lens group, f L2: Focal length of the second lens component L2 in the first lens group, f L4 Focal length of the fourth lens component L4 in the first lens group, fhs Focal length of the sixth lens component L6 in the second lens group, fw Focal length of the seventh lens component L7 in the second lens group, ft8: th Focal length of the 8th lens component 8 in the 2nd lens group, f: Focal length of the front group G in the 1st lens group, f2:
The focal length of the second lens group G2 is 1. : Atsube number of the first lens component L1 in the first lens group, ν, 6 Atsube number of the sixth lens component L6 in the second lens group, νL7・Atsube number of the seventh lens component L7 in the second lens group , LB=Abbe number of the eighth lens component L8 in the second lens group.

Here, each of the above conditions will be explained.

Condition (5) defines the optimal focal length of the second lens component in the first lens group in order to correct coma aberration in a well-balanced manner. In particular, this condition (5) is for correcting inward coma aberration occurring on the object side of the second lens component L2 on the wide-angle side in a well-balanced manner.

When the upper limit of condition (5) is exceeded, the refractive power of the second lens component L1 in the first lens group becomes small, and the second lens component L2
cannot fully correct the inward coma aberration that occurs on the side of the object.

On the other hand, if the lower limit of condition (5) is exceeded, a large amount of external coma aberration occurs in the second lens component in the first lens group.

In addition, the principal point of the entire first lens group moves toward the object with respect to the most image side surface (final surface) of the first lens group G1, and the air gap between the first lens group G1 and the second lens group G2 becomes narrower. Become. For this reason, changing the magnification toward the telephoto side is restricted, making it impossible to obtain a large zoom ratio.

Condition (6) defines the optimum focal length of the second lens component L2 in the first lens group in order to satisfactorily correct distortion aberration.

In a zoom lens having two positive and negative lens groups as in the present invention, a larger amount of positive distortion occurs at the wide-angle end than in the second lens group G2. This tendency becomes particularly noticeable when trying to obtain a wide angle of view at the wide-angle end.

Therefore, in order to correct this positive distortion, the refractive power of the second lens component L2 having negative refractive power in the first lens group is increased to generate negative distortion, and the second lens component A good balance is achieved with the positive distortion generated by G2.

When the upper limit of condition (6) is exceeded, the negative refractive power of the second lens component L2 in the first lens group becomes small, and the negative distortion generated in this second lens component L2 becomes insufficient, and the second lens component
It is only possible to cancel out the positive distortion that occurs in the lens group G2.

On the other hand, if the lower limit of condition (6) is exceeded, the negative refractive power of the second lens component L2 in the first lens group becomes excessive, which leads to deterioration of various aberrations including coma, which is not preferable.

Condition (7) defines the optimal focal length of the fourth lens component L4 in the first lens group in order to obtain a large zoom ratio while satisfactorily correcting spherical aberration.

When the upper limit of condition (7) is exceeded, the positive refractive power of the fourth lens component L4 in the first lens group becomes small, and the principal point of the entire first lens group becomes the closest to the image side (the final surface) of the first lens group G1. ) in the object direction, and the air gap between the first lens group G1 and the second lens group G2 becomes narrower. For this reason, changing the magnification toward the telephoto side is restricted, making it impossible to obtain a large zoom ratio.

On the other hand, if the lower limit of condition (7) is exceeded, the positive refractive power of the fourth lens component in the first lens group becomes excessively large, making it difficult to correct spherical aberration, resulting in poor imaging performance.

Condition (8) defines the focal length of the sixth lens component L6 in the second lens group in order to satisfactorily correct spherical aberration over the entire zoom range.

In order to properly correct spherical aberration over the entire zoom range, it is preferable that spherical aberration be corrected independently in each of the first lens group G and second lens group G2.

Here, since the second lens group G2 has a positive/negative/negative configuration, the seventh lens component L7 and the eighth lens component L7 each have a negative refractive power.
It is desirable to correct the positive spherical aberration generated in the lens component L8 in a well-balanced manner with the negative spherical aberration generated in the sixth lens component L6 having positive refractive power.

Therefore, in condition (8), the sixth lens component in the second lens group. In order to appropriately generate spherical aberration, the second
An appropriate focal length ratio of the sixth lens component L6 to the lens group G2 is defined.

If the upper limit of condition (8) is exceeded, the positive refractive power of the sixth lens component L6 becomes small, and positive spherical aberration remains in the second lens group as a whole, which is not preferable.

On the other hand, if the lower limit of condition (8) is exceeded, the sixth lens component L
The positive refractive power of No. 6 becomes excessive, and in order to ensure an appropriate negative refractive power in the second lens group G2, it becomes necessary to increase the negative refractive power of each of the No. 7 and 8 lens components. As a result, spherical aberration, comatic aberration, etc. are worsened, which is not preferable.

In conditions (9) and (10), in order to better correct distortion aberration, the seventh lens components L7 . The optimum focal length ratio of the eighth lens component L8 is defined.

When the upper limit of condition (9) is exceeded, the negative refractive power of the seventh lens component 7 becomes small, and the negative refractive power shared by the eighth lens component becomes excessive. As a result, the eighth lens component L8
This is not preferable because the positive distortion that occurs at the wide-angle end becomes noticeable.

On the other hand, if the lower limit of condition (9) is exceeded, the seventh lens component L7
This is not preferable because the negative refractive power shared by the lens becomes excessive and the positive distortion at the wide-angle end becomes enormous.

Condition (10) is not preferable because the positive distortion at the wide-angle end becomes significant even if either the upper limit or the lower limit of this condition is exceeded.

Condition (11), condition (12), and condition (13) are for appropriately correcting chromatic aberration.

Condition (11) defines the Abbe number of the first lens component L1. If either the upper limit or the lower limit of condition (11) is exceeded, it becomes difficult to correct both longitudinal chromatic aberration and lateral chromatic aberration in a well-balanced manner.

Condition (12) defines an appropriate difference in Abbe number between the sixth lens component L8 and the eighth lens component L8 in the second lens group.

If the upper limit of condition (12) is exceeded, the chromatic aberration within the second lens group will be overcorrected, and fluctuations in longitudinal chromatic aberration and lateral chromatic aberration during zooming will become large, which is not preferable.

If the lower limit of condition (12) is exceeded, the chromatic aberration within the second lens group will be insufficiently corrected, and fluctuations in longitudinal chromatic aberration and lateral chromatic aberration during zooming will become large, which is not preferable.

Condition (13) defines an appropriate difference in Abbe number between the seventh lens component L7 and the eighth lens component L8 in the second lens group.

In the zoom lens of the present invention, out of the negative seventh lens component L7 and the negative eighth lens component L8, the eighth lens component L8, which is closer to the image plane, has relatively low dispersion. The chromatic aberration of magnification that tends to occur is suppressed to a minimum, and fluctuations in chromatic aberration of magnification during zooming are minimized.

When the lower limit of condition (13) is exceeded, the difference in Atsube number between the seventh lens component L7 and the eighth lens component L7 becomes small, making it difficult to construct the eighth lens component L8 from a glass material with sufficiently low dispersion. Become. As a result, fluctuations in lateral chromatic aberration during zooming increase, which is undesirable.

On the other hand, if the upper limit of condition (13) is exceeded, the 8th
The lens component L8 must be made of a glass material with a low refractive index,
This is undesirable because it leads to higher-order curvature of chromatic aberration of magnification and an increase in positive distortion at the wide-angle end.

〔Example〕

FIG. 1 and FIG. 3 respectively show Example 1. A lens configuration diagram of Example 2 is shown, and each example according to the present invention will be described with reference to this diagram.

Common to each embodiment, the first lens group G1 includes a first lens component L1 having a positive refractive power formed in a meniscus lens shape with a convex surface facing the object side, and a negative lens component L1 having a stronger concave surface facing the object side. a front group G consisting of a second lens component L2 having a refractive power, a third lens component L3, and a fourth lens component L4 having a positive refractive power, and a rear group consisting of a fifth lens component L6 having a positive refractive power. It is composed of group GR. The second lens group G2 includes a sixth lens component with a positive refractive power formed in a meniscus shape with a convex surface facing the image side, and a negative lens component formed with a meniscus shape with a convex surface facing the image side. It consists of a seventh lens component L7 with refractive power and an eighth lens component with negative refractive power, which is also formed in a meniscus shape with a convex surface facing the image side.

In each embodiment, when changing the magnification from the wide-angle end to the telephoto end, each lens group moves toward the object side so that the air gap formed between the first lens group G1 and the second lens group G2 is reduced. Moving.

Furthermore, when focusing from an object at infinity to an object at a short distance, the front group GF in the first lens group moves toward the object side and moves so that the aperture space is expanded.

In each embodiment, the aperture S is arranged between the front group G and the rear group GR.

Next, the characteristic configuration of each embodiment of the present invention will be explained in more detail.

Example 1. In both cases, the second lens component L2 is composed of a meniscus-shaped cemented lens with a convex surface facing the image side as a whole, which is cemented with a biconcave negative lens and a biconvex positive lens, and the third lens component Lll is constituted by a positive lens having a convex surface with a stronger curvature facing the object side. The fourth lens component L4 is composed of a positive lens with a convex surface facing the image side and a negative meniscus lens with a concave surface facing the object side, and has a positive refractive power as a whole. There is. In the case of this configuration, it is desirable to configure it so that the following conditions are satisfied in order to satisfactorily correct spherical aberration.

(14) 0.2 < n 14n n L2D(1
5) 0.27< n L411 1 L4p However, nL2□ = refractive index of the negative lens in the second lens component L2, nt2p: refractive index of the positive lens in the second lens component L2, np<a: fourth lens The refractive index of the negative lens in the component L4, n+, 4p: the refractive index of the positive lens in the fourth lens component L4.

Further, the lens system of this embodiment is preferably configured to satisfy the following conditions in order to correct both longitudinal chromatic aberration and lateral chromatic aberration in a well-balanced manner.

(16)-3<shi, 2. ．． -shiL2. <7 (17) 2
5<νL4D −νL4□<35However, νL2. ．． - Atsube number of the negative lens in the second lens component L2, shi L29. Atsube number of the positive lens in the second lens component L2, SI L4. : Atsube number of the positive lens in the fourth lens component L4, Si1. n: Atsube number of the negative lens in the fourth lens component.

Furthermore, in order to simultaneously achieve compactness and wide angle in this embodiment, it is more preferable to satisfy the following conditions.

(18) 3<qL2<6 (19) 1.1<q+, v<3(20) 0.
25<DLa/ f w<Q, 4, q,2: shape factor of the second lens component L2 in the first lens group, =24 qL7: shape factor of the seventh lens component L7 in the second lens group, DL2: axial thickness of the second lens component in the first lens group, fw: focal length at the wide-angle end of the zoom lens.

Here, the shape factor Qt,l of the i-th lens component is
When the radius of curvature of the lens component closest to the object side is r, and the radius of curvature of the lens component closest to the image side is rl, it is defined as rb ra L rb rll .

Condition (18) relates to correction of distortion at the wide-angle end. By forming the second lens component L2 in the first lens group into a meniscus shape with a concave surface facing the object side, the curvature on the object side can be made stronger, so that negative distortion can be prevented by the concave surface on the object side. is generated more effectively. Thereby, the positive distortion generated in the second lens group G is corrected in a well-balanced manner, making it possible to widen the angle of view.

Condition (19), together with the above-mentioned condition (18), relates to correction of distortion at the wide-angle end, and is a condition for suppressing positive distortion generated in the second lens group 62.

By making the negative lens component L7 in the second lens group have a meniscus shape with a convex surface facing the image side, the incident angle with respect to the normal to the lens surface when the chief ray at the wide-angle end passes through this negative lens component L7 and the exit angle can both be made smaller. Thereby, the occurrence of positive distortion and coma aberration at the wide-angle end can be suppressed to a minimum.

Condition (20), together with conditions (18) and (19) above, relates to correction of distortion at the wide-angle end and compactization of the first lens group G1.

In order to effectively generate negative distortion at the object side of the second lens component L2 in the first lens group, it is preferable to configure the optical path length from the object side of the second lens component L2 to the aperture to be long. . At this time, compared to the case where a predetermined optical path length is obtained by widening the air gap between the second lens component L2 and the third lens component L3, the second lens component L has a higher refractive power than air.
It is better to increase the axial thickness of 2 to obtain a predetermined optical path length.
The axial thickness of the entire first lens group can be reduced.

Therefore, it is possible to make the lens system more compact.

Now, Tables 1 and 2 below list the specifications of each embodiment of the present invention.

In Table 1.2 below, the leftmost numbers represent the order from the object side, r is the radius of curvature, d is the distance between lens surfaces, ν is Atsube's number, n is the refractive index at the d-line (λ = 587.6 nm), f represents the focal length of the entire system, F No represents the F number, and 2ω represents the angle of view.

Further, Table 3 lists numerical values corresponding to conditions for each embodiment according to the present invention. However, the maximum image height Y in Table 3 is 21.6.

Table 1 (Example 1) f=32. ll-830, F No = 3. IiO~912. 2 ω-647~2936 24.667 45.566 29.557 14.000 46.563 32.361 +0.957 17.338 112.757 34.837 13.537 12.910 37, Go.

14. Go.

73.452 3.30 511.8 1.658442.00
43.3 1.84042B, 80 40.
7 1.581441.80 45.0 1
．． 744003.60 53.5 1.5473
9+, 70 23.0 1.86074 (dlo
) 1.20230 (d12) 1.86074 (B, f) 1.67003 1.802111 ■ 32.8015 3.2387 12.3786 4.9876 50.0033 3.2387 6.2070 20.8571 83.0080 3 .2387 1.5278 51.3055 f=32.8~830, F No=3.60~9 12. 2 ωz650~294 21.988 41.04B 31.447 14.000 51.410 31.859 10.723 17.246 3.30 54.0 2.00 43.3 g, 60 40.7 0.60 1 .80 45.0 0.50 3.6G 53.5 1.70 23.0 (dlo) 1.84042 1.58144 1.54739 112.757 1.20 23.0 (d12) 24.842 14.883 13.811 54.817 14.000 29.539 2.50 1.20 1.30 (B, f) 1.80411 1.59319 32.8017 2.2978 12.7273 3.1636 50.003B 2.2978 6.5557 19.0333 83.0090 2.2978 1.8785 49.4822 From the values of the specifications of each example above, 64°
It can be seen that even though the angle of view has been widened to a certain degree, a zoom ratio as high as 2.5, which is higher than that of conventional lenses, has been achieved.

Now, FIG. 2 and FIG. 4 respectively show Example 1 according to the present invention.
．． 3 shows various aberration diagrams of Example 2. FIG.

In each aberration diagram, (A) shows various aberrations in the shortest focal length state at the wide-angle end, (B) in the intermediate focal length state, and (C) in the longest focal length state at the telephoto end.

Here, in each aberration diagram, d is the d-line (λ587, 6nm
), and g is the aberration due to g-line (λ435, 8n
m). Regarding astigmatism in each aberration diagram, the dotted line M indicates a meridional image surface, and the solid line S indicates a sagittal image surface.

Comparison of each aberration diagram shows that each example has excellent imaging performance in all magnification ranges, even though a wide angle of view and high magnification (zoom ratio) have been achieved at the same time. It is clear that there are

In particular, it can be seen that astigmatism and distortion, which tend to worsen, are extremely well corrected at the wide-angle end.

In this embodiment, the lens system is composed of spherical lenses, but it goes without saying that an aspherical lens may be used as appropriate.

〔Effect of the invention〕

As described above, according to this embodiment, it is possible to achieve a compact wide-angle zoom lens that simultaneously achieves a wide angle and a high zoom ratio, and has extremely good imaging performance in all zoom ranges.

[Brief explanation of drawings]

FIG. 1 and FIG. 3 are lens configuration diagrams of Example 1 and Example 2 of the present invention, respectively. FIG. 2 and FIG. 4 are diagrams of various aberrations of Example 1 and Example 2 according to the present invention, respectively. (Explanation of symbols of main parts) S--One stop

Claims (1)

[Claims] 1) It has a first lens group G_1 having a positive refractive power and a second lens group G_2 having a negative refractive power, and magnification can be changed by changing the distance between the two groups. The first lens group G_1 includes, in order from the object side, a front group G_F with positive refractive power and a rear group G_R with positive refractive power; The first lens component L_ has a positive refractive power and is formed in a meniscus lens shape with a convex surface facing the side.
1, and a second lens with negative refractive power with a stronger concave surface facing the object side.
The rear group G_R includes a lens component L_2, a third lens component L_3, and a fourth lens component L_4 having a positive refractive power.
has a fifth lens component L_5 with positive refractive power, and the second lens group G_2 has a sixth lens component L_5 with positive refractive power formed in a meniscus shape with a convex surface facing the image side.
6, a seventh lens component L_7 with a negative refractive power formed in a meniscus shape with a convex surface facing the image side, and an eighth lens component L_7 with negative refractive power formed in a meniscus shape with a convex surface facing the image side. A compact wide-angle zoom lens having an L_8 and satisfying the following conditions. (1) 1.14<f_1/Y<1.19 (2) 1.0<|f_2/Y|<1.09, f_2<0
(3) 1.21<β_2_w<1.32 However, f_1: Focal length of the first lens group G_1, f_2:
Focal length of the second lens group G_2, Y: maximum image height on the image plane, β_2_w: imaging magnification of the second lens group G_2 at the wide-angle end. 2) A compact wide-angle zoom according to claim 1, characterized in that when focusing from an object at infinity to an object at a short distance, the front group G_F moves toward the object side and satisfies the following conditions. lens. (4) 3.5<f_R/f_F<10 where f_F: focal length of the front group G_F, f_R: focal length of the rear group G_R.