JPH0843737A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide an extremely compact photographing lens whose field angle is about 73.5 deg. at a wide angle end and which has a high power variable magnification of a variable power rate of about 3.5, and high performance over the entire area of zooming. CONSTITUTION:As for this lens which has a first group 1 having negative refracting power, a second group 2 having positive refracting power, a third group 3 having positive refracting power, and a fourth group 4 having negative refracting power set from an object side in this order and performs variable power by changing air intervals between respective groups; each group is moved so that the air interval between the group 1 and the group 2 is enlarged, the air interval between the group 2 and the group 3 is enlarged, and the air interval between the group 3 and the group 4 is decreased in the case of performing zooming from the wide angle end to the telephone end.

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 having a high zoom ratio and a wide angle of view, which is suitable for a lens shutter camera, a video camera, etc. The present invention relates to a zoom lens for photographing which is excellent in portability and has a shortened distance from one lens surface to an image surface.

[0002]

2. Description of the Related Art Recently, in a lens shutter camera, a video camera, etc., a compact zoom lens having a short total lens length has been demanded as the camera becomes smaller.

In particular, the lens shutter camera is becoming smaller and smaller due to the development of peripheral technologies such as an electric circuit for zoom driving, and a photographing lens provided therein is required to have a high zoom ratio and a compact zoom lens. Has been done.

Conventionally, as a zoom lens for a lens shutter, a so-called two-group zoom lens composed of two lens groups having positive and negative refracting powers has been mainly used. Since the two-group zoom lens has a simple lens structure and a moving mechanism at the time of zooming, it has advantages such as downsizing of the camera and relatively low cost.

However, since the zooming action must be performed by only one lens group, the zooming ratio is 1.6 to
It is about 2 times, and forcibly enlarging the zoom ratio leads to an increase in the size of the lens system, and at the same time, it becomes difficult to maintain high optical performance.

On the basis of a two-group zoom lens, the first group is divided into two lens groups having a positive refractive power, and the whole group is positive,
A three-group zoom lens aiming at a high zoom ratio as a three-group configuration of positive and negative refracting power is disclosed in, for example, JP-A-3-282409, JP-A-4-37810, and JP-A-4-7651.
It is proposed in Japanese Patent Publication No. 1 and the like.

However, if an attempt is made to achieve a wide-angle zoom lens system having a half angle of view of 35 ° or more with this lens group configuration, the change in the entrance pupil position during zooming becomes large. For this reason, it becomes very difficult to suppress aberration variation due to zooming when achieving high zooming.

In addition to this, a zoom lens having a wide field angle and a high zoom ratio with a wide field end having a half field angle of about 38 ° and a zoom ratio of about 3.5 due to the formation of a multi-lens group, For example, Japanese Patent Application Laid-Open No. 2
-72316 and Japanese Patent Laid-Open No. 3-249614.

However, these zoom lens systems have a large front lens diameter and a large overall lens length, and are not always sufficient as a taking lens for a compact camera.

Particularly when applied to a camera using an external viewfinder, there is a problem that the lens barrel obstructs the field of view of the viewfinder at the wide image end. Further, as a result, there arises a problem that the viewfinder arrangement and the camera form are restricted.

On the other hand, as a conventional example of a zoom lens having four groups of negative, positive, negative, and US Pat. No. 4,787,718.
No. 4,756,609, No. 5,111,338, No. 5,270,865, No. 5,274,504, JP-A No.
No. 15610 and Japanese Patent Laid-Open No. 4-237090, both of which move such that the distance between the first and second lens groups decreases with zooming from the wide-angle end to the telephoto end.

At this time, US Pat. No. 4,787,718
No. 4 has a variable power ratio of about 2 times, and US Pat.
No. 756609, No. 5270865, No. 5274
In the lens system described in JP-A No. 504 and JP-A-4-15610, the widening of the angle was about 3 times and the angle of view was insufficient.

In US Pat. No. 5,111,338 and Japanese Unexamined Patent Publication No. 4-237090, a wide angle and a high zoom ratio are achieved, but the number of lenses is extremely large and the diameter of the front lens becomes too large for practical use. ing.

[0014]

Generally, in a zoom lens, if the refractive power of each lens group is increased, the amount of movement of each lens group for obtaining a predetermined zoom ratio is reduced, and the total lens length is shortened. High zoom ratio is possible. However, if the refracting power of each lens unit is simply increased, the aberration variation due to zooming becomes large, and it is difficult to obtain good optical performance over the entire zooming range, especially when achieving high zooming and widening the angle of view. There is a problem that it will become.

It is an object of the present invention to enlarge the angle of view at the wide-angle end while increasing good zoom ratio, increase the zoom ratio, and further reduce the size of the entire system. Incidentally, in a numerical example to be described later, a zoom lens having a photographing field angle of about 73.5 degrees and a zoom ratio of about 3.5 is realized.

As problems subordinate to the above problems, (1) high zooming and good aberration correction are achieved, (2) aberration variation due to focusing is excellently suppressed, and (3) the number of lenses in each lens group is reduced. Nevertheless, good aberration, correction,
(4) Shortening the total optical length at the wide-angle end, (5) facilitating aberration correction in the middle region of zooming, (6) ensuring a sufficient zoom ratio, (7) the first lens group is fourth The conditions for moving to correct the chromatic aberration of the lens group, and (8) shortening of the total length at telephoto are mentioned.

[0017]

[Means for solving the problem]

1. 4 from the first group having negative refractive power, the second group having positive refractive power, the third group having positive refractive power, and the fourth group having negative refractive power in order from the object side.
In a zoom lens that has two lens groups and performs zooming by changing the air spacing between each group, when zooming from the wide-angle end to the telephoto end, the air spacing between the first and second groups is Each group is moved so as to increase, the air gap between the second group and the third group increases, and the air gap between the third group and the fourth group decreases. The above configuration also relates to the subordinate issue (1).

2. The first group having negative refractive power in order from the object side,
It has four lens groups, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, and the magnification is changed by changing the air space between the respective lens groups. In the zoom lens to be used, when zooming from the wide-angle end to the telephoto end, the air gap between the first and second groups increases, and the air gap between the third and fourth groups decreases. And move the third
Focus on the group. The above configuration is also related to the subordinate issue (2).

3. The first group having negative refractive power in order from the object side,
It has four lens groups, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, and the magnification is changed by changing the air space between the respective lens groups. In the zoom lens to be used, when zooming from the wide-angle end to the telephoto end, the air gap between the first and second groups increases, and the air gap between the third and fourth groups decreases. While moving, focus on one body in all groups. The above configuration is also related to the subordinate issue (2).

4. The first group having negative refractive power in order from the object side,
It has four lens groups, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, and the magnification is changed by changing the air space between the respective lens groups. In the zoom lens to be used, when zooming from the wide-angle end to the telephoto end, the air gap between the first and second groups increases, and the air gap between the third and fourth groups decreases. While moving the 4th
It has at least one aspherical surface in the group.

With the above configuration, the main problem and the dependent problem (3)
In addition, the angle of view characteristics in a wide angle of view and the coma aberration due to zooming are corrected well.

5. The first group having negative refractive power in order from the object side,
It has four lens groups, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power, and the magnification is changed by changing the air space between the respective lens groups. In the zoom lens to be used, when zooming from the wide-angle end to the telephoto end, the air space between the first and second groups increases, and the air space between the third and fourth groups decreases. And move the third
It has at least one positive lens having an aspherical surface and at least one negative lens in the group. With the above configuration, the main task and the subordinate task (3) are fulfilled.

6. It is even better if the following conditions are satisfied.

In the lens system, at least one aspherical surface should be included in the third lens group.

In the lens system, the first to fourth groups should move to the object side during zooming.

In the lens system, an aperture is provided in the third lens group.

In the lens system, the lens closest to the object in the fourth group is a negative lens.

In the lens system, the fourth lens unit should be composed of a negative single lens having an aspherical surface on the object side where the negative refractive power is weakened in the periphery.

7. In the lens system, it is preferable that the following conditional expression is satisfied.

[0030] _{^{-3 × 10 -2 <hh 3t /}} (f t -f w) <2 × 10 -2 ... (1) f w; of the entire system at the telephoto end focal length f _t of the entire system at the wide angle end Focal length hh _3t ; principal point distance between the 3rd and 4th lens groups at the telephoto end

In the above lens system, it is desirable that the following conditional expression be satisfied.

[0032] _{0.1 <(d 1t -d 1w)} / f w <0.9 ... (2) d iw; i-th group at the telephoto end; i-th group and the i + 1 group of the air gap d _it in the wide-angle end the air gap of the i + 1 group _{^{3.0 × 10 -3 <d 1w /}} f w <0.2 ... (3) 3 <d 1t / d 1w <50 ... (4) 2 <d 2t / d 2w <10 (4) In the lens system, it is preferable that the following conditional expression is satisfied.

[0033] _{-90 <f 1 / f w <} -3 ... (6) f 1; focal length of the first group _{-0.8 <f 4 / f w <} -0.3 ... (7) f 4; the Focal length of 4 groups

In the above lens system, it is desirable that the following conditional expression be satisfied.

2.0 <Beta4t / Beta4w <5.0 (8) Beta4w: Magnification of fourth group at wide-angle end Beta4t: Magnification of fourth group at telephoto end More preferably, (1) to (8)
All the conditional expressions of are satisfied.

The above-mentioned lens system preferably has a configuration in which an off-axis ray in a wide-angle range passing through each lens surface passes through the highest position on the lens surface closest to the image side, while from the wide-angle end to the telephoto end of zooming. Each lens group moves to the object side.

[0037]

As described above, there has been a zoom lens having a positive / negative type two-group zoom lens as a basic type and having a structure of four groups of negative, positive, negative, and negative in the past.
When a high magnification equal to or more than 2 times is implemented, it becomes difficult to ignore the aberration variation due to the movement of the lens group, which is mainly responsible for the magnification variation. Therefore, it is necessary to increase the number of lenses in those lens groups to perform aberration correction.

That is, when the refractive power of the lens group is strengthened to reduce the total length, the aberration can be suppressed by increasing the number of lenses, but the increase in the number of lenses makes it difficult to retract the taking lens into the camera body to some extent. ing.

The main feature of the present invention is that the distance between the first group and the second group is increased during zooming from the wide angle to the telephoto in the negative, positive, positive, and negative four-group configuration. This allows
Since the first group can correct the variation of the chromatic aberration generated in the fourth group, which is mainly responsible for zooming, the burden on the aberration correction of the fourth group is reduced, and a large increase in the number of lenses can be prevented.

Next, each conditional expression and the meaning of the extreme value will be described.

Equation (1) relates to the distance between the principal points of the third and fourth lens units at the telephoto end and the focal lengths on the telephoto and wide-angle sides. If the distance between the principal points of the third group and the fourth group exceeds the upper limit of equation (1) and it becomes too large, it becomes difficult to obtain a predetermined zoom ratio, and if the power that forcibly secures the predetermined zoom ratio is obtained. If it is arranged, the total length at the telephoto end becomes long.
If the principal point spacing becomes too small below the lower limit of equation (1), it becomes difficult to secure the actual spacing between the third and fourth groups, and there is a risk of collision between the two groups due to manufacturing errors or the like. There is.

The equation (2) relates to the telephoto distance between the first lens group and the second lens group, the air distance at wide angle, and the focal length at the wide angle end.
If the distance between the first and second lens units at the telephoto end becomes too large beyond the upper limit of the equation, the total lens length at the telephoto end becomes too long, which is not good. If the lower limit of expression (2) is exceeded,
When the distance between the second lens group and the telephoto lens at the wide-angle is too small, it becomes difficult for the first lens group to cancel the aberration variation occurring in the fourth lens group, and thus it becomes difficult to obtain good aberrations as a whole.

Equation (3) relates to the distance between the first and second lens units at wide angle and the focal length at wide angle. (3)
If the distance between the first and second groups at the wide-angle end becomes too large beyond the upper limit of the formula, the length of the entire system and the front lens diameter at the wide-angle end increase. If the distance between the first and second groups becomes too small below the lower limit of the expression (3), there is a risk of collision between the two groups due to manufacturing errors or the like.

Equation (4) relates to the distance ratio between the first and second lens groups at the telephoto and wide angle. If the distance between the first and second groups in the telephoto state becomes too large beyond the upper limit of the equation (4), the total length in the telephoto state becomes long, which is inconvenient.
If the distance between the first and second lens groups at the telephoto position becomes too small below the lower limit of the expression (4), it becomes difficult to correct chromatic aberration due to zooming.

The equation (5) relates to the distance ratio between the second and third lens units at the telephoto and wide angle. If the distance between the second and third lens groups in the telephoto state becomes too large beyond the upper limit of the equation (5), the total length in the telephoto state becomes an undesired length. If the distance between the second and third lens units at the telephoto position becomes too small below the lower limit of the expression (5), it becomes difficult to correct variations in various aberrations during zooming.

Equation (6) relates to the ratio of the focal length of the first lens unit to the focal length of the entire system at the wide-angle end. If the focal length of the first lens unit becomes too short beyond the upper limit of the expression (6), the retro ratio at the telephoto end becomes large, and the total length at the telephoto end becomes an undesired length. If the focal length of the first lens unit becomes too long beyond the lower limit of the expression (6), the field angle characteristic on the wide angle side deteriorates, and it becomes difficult to correct the off-axis aberration at the wide angle.

Equation (7) relates to the ratio of the focal length of the fourth lens unit to the focal length at the telephoto end. If the focal length of the fourth lens unit is too short beyond the upper limit of the expression (7), it becomes difficult to correct coma flare near the wide angle end. If the focal length of the fourth lens unit becomes too long below the lower limit of equation (7),
The movement stroke of the fourth group for zooming increases,
The total length at the telephoto end is undesirably long.

The expression (8) relates to the ratio of magnifications of the fourth lens unit at the telephoto position and at the wide angle position. If the magnification ratio of the fourth lens unit becomes too large beyond the upper limit of the equation (8), it becomes difficult to correct the variation of various aberrations due to zooming. If the lower limit of the expression (8) is exceeded and the magnification ratio of the fourth lens unit becomes too small, it becomes necessary to secure a variable power ratio in other parts, which is not preferable because the entire lens system tends to become large.

It is preferable to reduce the upper limit value or the lower limit value or both of the conditional expressions (1) to (8) according to the following extreme values in order to enhance the action.

[0050] _{^{-5 × 10 -3 <hh 3t /}} (f t -f w) <8 × 10 -3 ... (1) '0.3 <(d 1t -d 1w) / f w <0.6 ... ^{(2) '1 × 10 -2} <d 1w / f w <6 × 10 -2 ... (3)' 10 <d 1t / d 1w <35 ... (4) '3.5 <d 2t / d 2w < 7 ... (5) '-25 < f 1 / f w <-4 ... (6)' -0.7 <f 4 / f w <-0.45 ... (7) '2.5 <β 4t / β _4w <3.5 ... (8) '

1 to 4 are sectional views of zoom lenses corresponding to Numerical Embodiments 1 to 4, respectively. (A) is a wide-angle end, (B) is an intermediate angle of view, and (C) is a telephoto end. Is shown. In the figure, 1 is a first group, 2 is a second group, 3 is a third group, and 4 is a fourth group. When zooming from the wide-angle end to the telephoto end,
Each lens group moves to the object side, and the first group and the second group 2
The air gap between the second group 2 and the third group 3 increases, and the air gap between the third group 3 and the fourth group 4 decreases. Focusing is performed by moving the third group 3 or the entire system as a unit.

In the zoom lens shown in FIGS. 1 to 3, the first group 1 is constructed such that the curvature of the image-side lens surface is tighter than that of the other surface and the biconvex lens and the object-side concave lens surface have refractive powers of the other surface. It is a two-lens structure with a stronger negative lens.

In the zoom lens of FIG. 4, the first lens group is composed of only one negative lens element having an aspherical surface on the image side.

In the zoom lens of FIGS. 1 to 4, the second lens unit has a positive meniscus lens 1 having a convex surface on the object side.
It consists of only one sheet.

In the zoom lens of FIG. 1 and FIG.
The configuration of the group is composed of a negative meniscus lens having a concave surface on the object side and a positive meniscus lens having an image-side lens surface whose curvature is tighter than that of the other surface, for a total of three lenses. ing.

In FIGS. 3 and 4, the third lens unit has a diaphragm arranged closest to the object side and has a negative meniscus lens having a concave surface on the object side and an image-side lens surface whose curvature is greater than that of the other lens surface. It consists of two biconvex lenses.

Both the zoom lenses of FIGS. 1 to 4 have an aspherical surface on the lens surface closest to the image side of the third lens unit.

In FIGS. 1 to 4, the fourth lens unit is composed of only one negative lens whose lens surface on the object side is concave more tightly than the other and has an aspherical surface.

Numerical examples will be described below.

Ri is the radius of curvature, Di is the lens surface distance, N
i is the refractive index and νi is the Abbe number.

The aspherical surface is

[0062]

[Outside 1] , And A to E are coefficients. Also, e + i is × 10 ⁱ
, ^Ei represents ^x10 -e.

The aberration curve diagrams of FIGS. 5 to 8 correspond to Numerical Examples 1 to 4 in order. (A) is a wide-angle end, (B) is an intermediate angle of view, and (C) is a telephoto end.

[0064]

[Outside 2]

[0065]

[Outside 3]

[0066]

[Outside 4]

[0067]

[Outside 5] The values calculated for the numerical examples according to the conditional expressions are shown.

[0068]

[Table 1]

[0069]

As described above, according to the present invention, an extremely wide angle of view, for example, a shooting angle of view of 73.5 degrees and a high zoom ratio, for example, 3.5 to 4 are achieved, and the entire zoom range is achieved. (EN) Provided is a zoom lens which realizes extremely high optical performance and is extremely compact.

[Brief description of drawings]

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

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

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

FIG. 4 is a lens cross-sectional view of Numerical Example 4.

FIG. 5 is a diagram of various types of aberration of Numerical example 1.

FIG. 6 is a diagram of various types of aberration in Numerical example 2.

FIG. 7 is a diagram of various types of aberration in Numerical example 3.

FIG. 8 is a diagram of various types of aberration of Numerical example 4.

[Explanation of Codes] 1 first group (first lens group) 2 2nd group (2nd lens group) 3 3rd group (3rd lens group) 4 4th group (4th lens group) S sagittal surface M meridional Surface d d line g g line

Claims (19)

[Claims] 1. A four-lens group consisting of a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a negative refractive power in order from the object side. In a zoom lens that has a zoom ratio that varies by changing the air space between each group, the air space between the first group and the second group increases during zooming from the wide-angle end to the telephoto end. A zoom lens, wherein each group is moved so that an air gap between the third group and the third group increases and an air gap between the third group and the fourth group decreases. 2. A four-lens group having a negative refractive power first group, a positive refractive power second group, a positive refractive power third group, and a negative refractive power fourth group in order from the object side. In a zoom lens that has a variable magnification by changing the air space between each group,
When zooming from the wide-angle end to the telephoto end, the first group and the second group
A zoom lens characterized in that each group is moved so that the air gap between the groups increases and the air gap between the third group and the fourth group decreases, and focusing is performed by the third group. 3. A four-lens group having a negative refractive power first group, a positive refractive power second group, a positive refractive power third group, and a negative refractive power fourth group in order from the object side. In a zoom lens that has a variable magnification by changing the air space between each group,
When zooming from the wide-angle end to the telephoto end, the first group and the second group
A zoom lens characterized in that each group is moved so that the air gap between the groups is increased and the air gap between the third group and the fourth group is reduced, and focusing is carried out as a whole. 4. A four-lens group consisting of a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a negative refractive power in order from the object side. In a zoom lens that has a variable magnification by changing the air space between each group,
When zooming from the wide-angle end to the telephoto end, the first group and the second group
Each group is moved so that the air space between the groups increases and the air space between the third group and the fourth group decreases, and at least one aspherical surface is included in the fourth group. And a zoom lens. 5. A four-lens group consisting of a first group having a negative refractive power, a second group having a positive refractive power, a third group having a positive refractive power, and a fourth group having a negative refractive power in order from the object side. In a zoom lens that has a variable magnification by changing the air space between each group,
When zooming from the wide-angle end to the telephoto end, the first group and the second group
A positive lens having at least one aspherical surface in the third group while moving each group such that the air distance between the groups increases and the air distance between the third group and the fourth group decreases. A zoom lens having at least one negative lens. 6. The zoom lens according to claim 1, wherein at least one aspherical surface is included in the third lens unit. 7. The first group to the fourth group move toward the object side together with the fourth group during zooming.
The zoom lens described in the item. 8. The zoom lens according to claim 1, further comprising an aperture in the third lens unit. 9. The zoom lens according to claim 1, wherein the lens closest to the object side in the fourth group is a negative lens. 10. The zoom lens according to claim 4, wherein the fourth lens unit is composed of a negative single lens having an aspherical surface on the object side where the negative refractive power is weakened in the periphery. 11. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. _{^{-3 × 10 -2 <hh 3t /}} (f t -f w) <2 × 10 -2 where f _w; telephoto focal length hh _3t of the entire system at the telephoto end focal length f _t of the entire system at the wide angle end Distance between principal points of the third and fourth groups at the edge 12. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. _{0.1 <(d 1t -d 1w)} / f w <0.9 where f _w; i-th group at the wide-angle end and the (i + 1) group of air spacing d _it;; telephoto focal length d _iw of the entire system at the wide-angle end Air gap between the i-th group and the i + 1-th group at the edge 13. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. _{^{3.0 × 10 -3 <d 1w /}} f w <0.2 where f _w; air gap of the i group and the (i + 1) group in a wide angle end focal length d _iw of the entire system at the wide-angle end 14. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. 3 <d _1t / d _1w <50 where d _iw ; air distance between the i-th group and the i + 1-th group at the wide-angle end d _it ; air distance between the i-th group and the i + 1-th group at the telephoto end 15. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. 2 <d _2t / d _2w <10 where d _iw ; air distance between the i-th group and the i + 1-th group at the wide-angle end d _it ; air distance between the i-th group and the i + 1-th group at the telephoto end 16. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. -90 <f ₁ / _fw <-3 where f ₁ ; focal length of first group _fw ; focal length of entire system at wide-angle end 17. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. Focal length of the entire system at the wide-angle _{end; -0.8 <f 4 / f w} <-0.3 where f _4; focal length f _w of the fourth group 18. The zoom lens according to claim 1, wherein the following conditional expression is satisfied in the zoom lens. 2.0 <Beta4t / Beta4w <5.0 where Beta4w; magnification of fourth group at wide-angle end Beta4t; magnification of fourth group at telephoto end 19. The zoom lens according to claim 1, wherein in the zoom lens, an off-axis ray in a wide angle range passes through the highest position on the image side lens surface.