JP3492336B2 - Zoom lens and optical device using the same - Google Patents

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 digital still camera, a video camera, a film camera and the like and an optical apparatus using the zoom lens, and particularly, while reducing the variation of the exit pupil position during zooming. The present invention relates to a zoom lens which is excellent in portability and which has a wide shooting angle of view and a short overall lens length, and an optical device using the zoom lens.

[0002]

2. Description of the Related Art Recently, as cameras (optical devices) such as video cameras, digital cameras, electronic still cameras, etc., which use a solid-state image sensor have become highly functional, the optical system used for them has both high optical performance and miniaturization. Is required.

Generally, a zoom lens used in a photographing device (optical device) using a CCD such as a video camera has a lens group closest to the object side fixed during zooming.
Lens types of 3 to 5 groups starting with lens groups of positive, negative, and positive refractive power are often used.

For example, in Japanese Patent Laid-Open No. 63-81313, there are four lens groups having positive, negative, positive and positive refractive powers,
A zoom lens with a zoom ratio of about 3 has been proposed.
Further, as a zoom lens having a high zoom ratio, for example, Japanese Unexamined Patent Publication No.
In Japanese Patent Publication No. 296706, positive, negative, positive, and positive refractive powers of 4
A zoom lens having one lens group and a zoom ratio of about 10 has been proposed.

On the other hand, a still image is taken using a CCD,
As a zoom lens for electronic still cameras, the overall lens length is extremely short, and due to the characteristics of still images, it has a wide angle of view.
Further, there is a demand for an optical system having higher optical performance than a zoom lens used for a moving image video camera.

A zoom ratio of 2.5 to 3 times and a relatively low zoom ratio, which includes a wide angle range and is bright and has high performance, is disclosed in Japanese Examined Patent Publication No. 6-66808. Proposes a zoom lens which has two lens groups having negative and positive refracting powers and which varies its magnification depending on a change in air distance between the lens groups.

In Japanese Unexamined Patent Publication No. 7-52256, negative,
There has been proposed a zoom lens which has three lens groups having positive and positive refracting powers and which widens the distance between the second group and the third group during zooming from the wide-angle end to the telephoto end.

In US Pat. No. 5,434,710, a negative,
There is disclosed a zoom lens having three lens groups having positive and positive refracting powers, in which the distance between the second group and the third group is reduced during zooming from the wide-angle end to the telephoto end.

In Japanese Patent Laid-Open No. 60-31110, negative,
It has four lens groups of positive, positive and positive refracting power, and during zooming from the wide-angle end to the telephoto end, the distance between the second and third groups decreases, and the fourth group is fixed during zooming. A lens has been proposed.

In Japanese Patent Laid-Open No. 10-104520,
A zoom lens having a four-group configuration of lens groups having negative, positive, positive, and positive refractive powers is disclosed.

In Japanese Unexamined Patent Application Publication No. 11-84242, negative,
A zoom lens that is compact, has a zoom ratio of about 3 times, and has a relatively small variation in the exit pupil during zooming is proposed for a zoom lens of a four-group type having positive, positive, and positive refractive power lens groups. There is.

[0012]

In recent years, the number of pixels of the solid-state image pickup device has been increased, and accordingly, a taking lens having higher optical performance than that of the conventional one has been required.

In particular, it has a telecentric characteristic (the exit pupil position is located farther from the image plane (infinity if possible)) necessary for reducing shading for a solid-state image pickup element, and the total lens length is shortened to be compact. Therefore, a zoom lens having a high zoom ratio is desired.

A zoom lens having a large variation in the exit pupil of the lens system during zooming is not a problem as a zoom lens for a silver halide camera, but when used in an electronic still camera using a CCD, there is a restriction on the power arrangement in design. Therefore, the entire lens system tends to increase in size.

It is an object of the present invention to provide a compact zoom lens having a small number of constituent lenses and excellent optical performance, and an optical apparatus using the same.

In addition, the present invention reduces the number of lenses in the entire system by optimally setting the lens configuration of each lens group and the moving method of each lens group during zooming, and by appropriately using an aspherical surface. A zoom lens suitable for digital still cameras, video cameras, etc. that has a desired zoom ratio, is bright, has high optical performance, and has a wide angle range while achieving a reduction in overall lens length. The purpose is to provide the used optical equipment.

[0017]

According to another aspect of the present invention, there is provided a zoom lens having a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a second lens group having a positive refractive power in order from the object side. It has three lens groups and a fourth lens group having a positive refractive power, and the distance between the first lens group and the second lens group at the telephoto end is small with respect to the wide angle end, and the distance between the second lens group and the third lens group is small. Is small, third
In a zoom lens that performs zooming by moving at least the second and third lens groups toward the object side so that the distance between the lens group and the fourth lens group becomes large, a negative lens is located closest to the object side of the first lens group. The second lens group has two or more positive lenses and one or more aspherical surfaces, and is located at the wide-angle end.
The focal length of the entire system is fw, and the focal length of the entire system at the telephoto end
Ft is the distance, and the distance from the image plane at the wide-angle end to the exit pupil is
tkw, the distance from the image plane at the telephoto end to the exit pupil is t
When it is kt,

[Equation 1] It is characterized by satisfying the conditional expression of .

The invention of claim 2 is the same as the invention of claim 1.
The focal length of the entire system at the wide-angle end is fw, and at the telephoto end
The focal length of the entire system is ft, and the back focal length at the wide angle end is
When the curve is bfw,

[Formula 2] It is characterized by satisfying the conditional expression of .

The invention of claim 3 is based on the invention of claim 1 or 2.
Second lens group and third lens group at the wide-angle end in Ming
Of the second lens group and the third lens at the telephoto end.
When the distance between the lens groups is d2t, the conditional expression of 0.1 <d2t / d2w <0.7 is satisfied .

The invention of claim 4 is the invention of claims 1 to 3.
In the invention of item 1, the second lens group is on the object side.
In order from the positive lens, the positive lens, the negative lens
It is characterized by having a gap.

The invention of claim 5 is the invention of claims 1 to 4.
In the invention of item 1, the first lens group is composed of two negative lenses.
It is characterized by having a lens and one positive lens .

The invention of claim 6 is the invention of claims 1 to 5.
In the invention of item 1, the first lens group has one or more surfaces.
It is characterized by having an aspherical surface .

The invention of claim 7 relates to any one of claims 1 to 6.
In the invention of item 1, there is a diaphragm in the second lens group.
And the aperture is moved together with the second lens group during zooming.
It is characterized by moving .

The invention of claim 8 is the same as claims 1 to 7.
In the invention of item 1, the first lens group is a wide-angle end.
Moves to the image side when zooming to a more intermediate zoom position
During zooming from the middle zoom position to the telephoto end.
It is characterized by moving to the object side.

The invention of claim 9 is the same as claims 1 to 8.
In the invention of item 1, the first lens group is a zoom lens.
It is characterized by moving throughout the entire group.

The invention of claim 10 is the same as that of claims 1 to 9.
An image is formed on a solid-state image sensor according to any one of the inventions
It is characterized by doing.

The optical device of the invention of claim 11 is the optical device of claim 1.
To the zoom lens of any one of
Solid-state image sensor that receives the image formed by the lens
It is characterized by having.

The invention of claim 12 is the invention of claim 11
Note that the optical device is a digital camera.
It is a sign.

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

1 is a lens sectional view of a zoom lens according to Numerical Example 1 of the present invention, which will be described later. 2 to 4
[Fig. 4] is an aberration diagram at a wide-angle end, a middle zoom position, and a telephoto end of the zoom lens according to Numerical Example 1 of the present invention.

FIG. 5 is a lens sectional view of a zoom lens according to Numerical Example 2 of the present invention, which will be described later. 6 to 8 are aberration diagrams of the zoom lens of Numerical Example 2 of the present invention at the wide-angle end, the intermediate zoom position, and the telephoto end.

FIG. 9 is a lens cross-sectional view of a zoom lens according to Numerical Example 3 of the present invention, which will be described later. 10 to 12 are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to Numerical Embodiment 3 of the present invention.

In the lens sectional views of the zoom lens of each numerical example shown in FIGS. 1, 5 and 9, L1 is the first lens group (first lens group) having a negative refractive power, and L2 is the first lens group having a positive refractive power. Second group (second lens group), L3 is a third group (third lens group) having a positive refractive power, L4 is a fourth group (fourth lens group) having a positive refractive power, SP is an aperture stop, and IP is The image plane. G is a glass block corresponding to a filter, a color separation prism or the like.

The zoom lens of this embodiment has, in order from the object side, a first lens unit L1 having a negative refractive power and a second lens unit L having a positive refractive power.
2, third group L3 having positive refractive power, fourth group L4 having positive refractive power
And the first group L1 and the second group L at the telephoto end with respect to the wide-angle end.
2 is small, the distance between the second lens unit L2 and the third lens unit L3 is small, and the distance between the third lens unit L3 and the fourth lens unit L4 is large. ,
The first lens unit L1, the second lens unit and the third lens unit are moved as indicated by the arrows. The fourth group is fixed upon zooming.

A negative lens (a lens having a negative refractive power) is located closest to the object side in the first lens group.

The first lens group has two negative lenses and a positive lens which are adjacent to each other. The second lens group has two or more positive lenses and one or more aspherical surfaces. The third lens group has at least one positive lens unit composed of a single lens or a cemented lens.

The fourth lens group has at least one positive lens unit composed of a single lens or a cemented lens.

Focusing is performed by moving out the third group or the fourth group.

Next, specific lens configurations of Numerical Examples 1 to 3 will be described.

The first lens unit having a negative refractive power is a meniscus negative lens having a convex surface facing the object side (a lens having a negative refractive power), a meniscus negative lens having a convex surface facing the object side, and the object side. It is made up of three meniscus-shaped positive lenses (lenses having positive refractive power) having convex surfaces facing each other. The second lens unit having a positive refractive power is composed of three lenses: a positive lens, and a cemented lens having a positive lens having a convex surface facing the object side and a negative lens having a concave surface facing the image side.

The third lens unit having a positive refractive power is composed of a single or cemented positive lens unit having a convex surface directed toward the object side.

The fourth lens unit having a positive refractive power is composed of a single or cemented positive lens unit having a convex surface directed toward the object side.

In the present embodiment, as described above, the lens configuration of each lens group, the position of the aspherical surface, the method of moving each lens group during zooming, etc. are optimally arranged to reduce the number of lenses,
A zoom lens suitable for digital still cameras, etc., which has a wide zoom range and has a very high optical performance while having a zoom ratio of about 3x despite achieving a reduction in overall lens length. Has been achieved.

The zoom lens of the present invention achieves the initial object by the above-mentioned constitution, but in order to obtain further better optical performance or to reduce the size of the entire lens system,
It is preferable to satisfy at least one of the following conditions.

The focal length of the entire system at the wide-angle end is fw,
When the focal length of the entire system at the telephoto end is ft, the distance from the image plane at the wide-angle end to the exit pupil is tkw, and the distance from the image plane at the telephoto end to the exit pupil is tkt

[0061]

[Equation 9]

To satisfy the above condition.

Conditional expression (1) relates to the variation of the exit pupil during zooming (magnification) from the wide-angle end to the telephoto end and the focal length in the middle of the zoom, and satisfies conditional expression (2) that defines the magnification ratio. It is a desirable numerical value range to be satisfied in the zoom ratio of about 3 times (the numerical value range of the conditional expression (2)).

When the upper limit of conditional expression (1) is exceeded and the variation of the exit pupil during zooming becomes too large, the image quality is deteriorated due to shading, which is not good.

In a configuration in which the lower limit of conditional expression (1) is exceeded and the variation of the exit pupil is reduced more than necessary, the overall lens length in the wide-angle range becomes long and the front lens diameter also increases, which is not preferable. .

Conditional expression (2) relates to the variable power ratio, and is to obtain good optical performance over the entire variable power range under the conditional expression (1) by appropriately setting the variable power ratio. .
Unless the conditional expressions (1) and (2) are satisfied at the same time, the technical effect of the conditional expression (1) cannot be obtained.

It is more preferable that conditional expressions (1) and (2) are satisfied.
It is good to set the numerical range of as follows.

[0068]

[Equation 10]

The back focus at the wide-angle end is bf
when w

[0070]

[Equation 11]

It is to satisfy.

Here, the back focus bfw is the air-equivalent length from the final lens surface to the image surface.

Therefore, when there is a low-pass filter, an optical filter, or the like between the final lens surface and the image plane, the thickness (t) is replaced by the refractive index (n) instead of the thickness (t).
The value (t / n) divided by is used as the length when the length of the back focus is obtained.

Conditional expression (3) relates to the back focus at the wide-angle end and the intermediate focal length.

If the back focus becomes too long beyond the upper limit of conditional expression (3), the total lens length at the wide-angle end becomes long, and the front lens diameter increases, which is not preferable.

If the lower limit of conditional expression (3) is exceeded and the back focus becomes too short, the space into which a low-pass filter, IR cut filter, etc. can be inserted becomes small, which is not preferable.

More preferably, the numerical range of conditional expression (3) should be defined as the following term.

[0078]

[Equation 12]

When the distance between the second lens group and the third lens group at the wide-angle end is d2w and the distance between the second lens group and the third lens group at the telephoto end is d2t, 0.1 <d2t / d2w <0. 7 ... (4) is satisfied.

Conditional expression (4) relates to the ratio of the air distance between the wide-angle end and the telephoto end of the second lens unit and the third lens unit.

If the upper limit of conditional expression (4) is exceeded and the distance between the second group and the third group at the wide-angle end becomes small, the exit pupil position at the wide-angle end becomes short, which is not good.

If the distance between the second lens group and the third lens group at the wide-angle end becomes too large beyond the lower limit of conditional expression (4), the overall length at the wide-angle end will increase, which is not preferable.

More preferably, the numerical range of conditional expression (4) is set as follows.

0.19 <d2t / d2w <0.5 (4a) Numerical examples of the present invention will be shown below. In each numerical example, i indicates the order of the surfaces from the object side, Ri is the radius of curvature of each surface, Di is the member wall thickness or air gap between the i-th surface and the (i + 1) -th surface, and Ni and νi are The refractive index and Abbe number for the d-line are shown respectively. Further, the two surfaces closest to the image are glass blocks G corresponding to a crystal low-pass filter, an infrared cut filter, and the like. The aspherical shape is such that when the displacement in the optical axis direction at the position of height H from the optical axis is x with reference to the surface vertex,

[0085]

[Equation 13]

It is represented by However, R is a radius of curvature, K is a conic constant, and A, B, C, D, and E are aspherical coefficients.

[E−X] means “× 10 ^−X ”.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

[0089]

[Outer 1]

[0090]

[Outside 2]

[0091]

[Outside 3]

[0092]

[Table 1]

Next, an embodiment of a digital camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG.

In FIG. 13, 10 is a camera body and 11
Is a photographing optical system configured by the zoom lens of the present invention, 12 is a strobe built into the camera body, 13 is an external viewfinder, and 14 is a shutter button.

By thus applying the zoom lens of the present invention to an optical device such as a digital camera, an optical device having a small size and high optical performance is realized.

[0096]

According to the present invention, it is possible to achieve a compact zoom lens having a small number of constituent lenses and excellent optical performance, and an optical apparatus using the same.

In addition, according to the present invention, by appropriately setting the lens configuration of each lens group and the moving method of each lens group during zooming, and appropriately using an aspherical surface,
While reducing the total number of lenses in the entire system and achieving a reduction in the total lens length, it has a desired zoom ratio, is bright, has high optical performance, and has a wide-angle range. It is possible to achieve a zoom lens suitable for, for example, an optical device using the same.

[Brief description of drawings]

FIG. 1 is an optical cross-sectional view of Numerical Example 1.

FIG. 2 is an aberration diagram at the wide-angle end according to Numerical Example 1.

FIG. 3 is an aberration diagram at an intermediate zoom position of Numerical Example 1.

FIG. 4 is an aberration diagram at a telephoto end according to Numerical Example 1.

5 is an optical cross-sectional view of Numerical Example 2. FIG.

FIG. 6 is an aberration diagram at the wide-angle end according to Numerical Example 2.

FIG. 7 is an aberration diagram at an intermediate zoom position in Numerical Example 2.

FIG. 8 is an aberration diagram at a telephoto end according to Numerical Example 2.

FIG. 9 is an optical cross-sectional view of Numerical Example 3.

FIG. 10 is an aberration diagram at a wide-angle end according to Numerical Example 3.

FIG. 11 is an aberration diagram at an intermediate zoom position in Numerical Example 3.

FIG. 12 is an aberration diagram at a telephoto end according to Numerical Example 3.

FIG. 13 is a schematic view of an optical device of the present invention.

[Explanation of symbols]

L1 first group L2 second group L3 third group L4 4th group SP aperture IP image plane d d line g g line ΔS sagittal image plane ΔM meridional image plane

Claims (12)

(57) [Claims] 1. A first lens unit having a negative refracting power, a second lens unit having a positive refracting power, a third lens unit having a positive refracting power, and a fourth lens unit having a positive refracting power in order from the object side. The distance between the first lens group and the second lens group at the telephoto end is small with respect to the wide-angle end, the distance between the second lens group and the third lens group is small, and
In a zoom lens that performs zooming by moving at least the second and third lens groups toward the object side so that the distance between the lens group and the fourth lens group becomes large, a negative lens is located closest to the object side in the first lens group. Located, second
The lens group has two or more positive lenses and one or more aspherical surfaces, the focal length of the entire system at the wide-angle end is fw, the focal length of the entire system at the telephoto end is ft, from the image plane at the wide-angle end to the exit pupil. Is tkw, and the distance from the image plane at the telephoto end to the exit pupil is tkt.
When, A zoom lens that satisfies the conditional expression of . Wherein when the focal length of the entire system at the wide angle end fw, the focal length of the entire system at the telephoto end ft, the bfw the back focus at the wide-angle end, Equation 2] The zoom lens according to claim 1 , wherein the conditional expression is satisfied. 3. When the distance between the second lens group and the third lens group at the wide-angle end is d2w and the distance between the second lens group and the third lens group at the telephoto end is d2t , 0.1 <d2t / d2w < The zoom lens according to claim 1 , wherein the conditional expression of 0.7 is satisfied. 4. The second lens group , in order from the object side,
Has three lenses, a positive lens, a positive lens, and a negative lens
The zoom lens according to any one of claims 1 to 3, characterized in that. 5. The first lens group includes two negative lenses and one negative lens.
4 claims 1, characterized in that it comprises a single positive lens
The zoom lens according to any one of 1 . Wherein said first lens group zoom lens according to claim 1, any one of 5, characterized in that it has at least one aspherical surface. 7. A any one of claims 1 to 6, characterized in <br/> that aperture in the second lens group that moves integrally with the second lens group arranged the narrowed zooming The described zoom lens. Wherein said first lens group moves toward the image side during zooming to the intermediate zoom position from the wide angle end, characterized in that moves during zooming to the telephoto end than the intermediate zoom position to the object side Any one of claims 1 to 7.
The zoom lens according to item. 9. A zoom lens according to any one of claims 1-8, wherein the first lens group that moves during zooming. 10. The zoom lens according to claim 1 , wherein an image is formed on a solid-state image sensor. 11. An optical apparatus comprising: the zoom lens according to claim 1 ; and a solid-state image sensor that receives an image formed by the zoom lens. 12. The optical apparatus, optical apparatus according to claim 1 1, characterized in that a digital camera.