JPH06250087A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To make the compactness of the zoom lens possible to be compatible with the lens performance having well compensated aberration by satisfying a prescribed condition for a number of lenses of respective lens groups. CONSTITUTION:This zoom lens comprizes the first lens group I having a positive refractive power, the second lens group II having a positive or negative refractive power, the third lens group III having a positive refractive power and the fourth lens group IV having a negative refractive power in order from the object side and zooming is performed by changing the spacing of each lens group. The first lens group I has at least one positive lens whose convex surface confronts the object side, the second lens group II is composed of two or less lenses, the third lens group III has at least one negative lens and a positive lens whose convex surface confronts the image plane side and the fourth lens group IV at least one positive lens whose convex surface confronts the image plane side and a negative lens whose concave surface confronts the object side. By representing a number of lenses of the ith group (a number of lenses in the separated state in the case of a combined lens) with Mi, the lens is composed under the condition: M2=M2=1 or 1<=M2<M1<=M4<=M3<=6.

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, and more particularly to a zoom lens suitable for a lens shutter camera and having a high zoom ratio.

[0002]

2. Description of the Related Art Conventionally, zoom lenses that are relatively compact are disclosed in Japanese Patent Application Laid-Open Nos. 56-128911 and 5-8.
As is known from Japanese Patent Publication No. 7-201213, a two-group zoom having positive and negative refractive powers from the object side, and Japanese Patent Publication No.
No. 16764 and JP-A-60-263113, a three-group zoom lens having positive, positive, and negative refracting powers from the object side, and further JP-A-61-50112 and JP-A-60-50112. As is known from Japanese Patent Laid-Open No. 4-67114, there is a four-group zoom having positive, negative, positive, and negative refracting powers from the object side. Further, as an interchangeable lens corresponding to a single-lens reflex camera that requires a relatively large back focus, positive, negative, positive, and negative four-group zoom from the object side are disclosed.
It is known from Japanese Patent No. 55314 and Japanese Patent Laid-Open No. 63-113410.

[0003]

However, in the above-described conventional example, when the zoom ratio exceeds 2 in the positive / negative two-group zoom, the zoom stroke of each lens group becomes large, and the zoom ratio is increased while the size is reduced. If it is attempted to obtain it, the sensitivity of the lens becomes high, and the manufacturing accuracy becomes strict.
In order to solve this drawback, various types of zoom lenses of positive, positive, negative three-group configuration and zoom lenses of positive, negative, positive, negative four-group configuration have been studied, but they do not combine lens performance and compactness. is the current situation.

In view of the above problems, it is an object of the present invention to provide a compact zoom lens which has a high zoom ratio of about 2.8.

[0005]

The features of the present invention are as follows. First, from the object side, a first lens group having a positive refractive power, a second lens group having a positive or negative refractive power, and a positive refractive power. Is a zoom lens which has a third lens group of 4 and a fourth lens group of negative refractive power, and performs zooming by changing the distance between the lens groups, wherein the first lens group is at least one object side. It has a positive lens having a convex surface, the second lens group is composed of two or less lenses, and the third lens group has at least one negative lens and a positive lens having a convex surface on the image side. However, the fourth lens group has at least one positive lens having a convex surface facing the image side and a negative lens having a concave surface facing the object side, and when Mi is the number of lenses in the i-th group (however, The number of lenses in the detached state,
M ₁ = M ₂ = 1 or 1 ≦ M ₂ <M ₁ ≦ M ₄ ≦ M ₃ ≦
It consisted of 6.

Alternatively, a first lens group having a positive refractive power, 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 are provided in order from the object side. A zoom lens that performs zooming by changing the distance between the lens groups, wherein the first lens group has at least one positive lens having a convex surface directed toward the object side, and the second lens group has the following: The third lens group has at least one negative lens and a positive lens having a convex surface facing the image side, and the fourth lens group has at least one lens. A positive lens having a convex surface directed to the image side and a negative lens having a concave surface directed to the object side.

[0007]

[Outside 5] However, R _2F , R _2R ... Curvature radii on the object side and image plane side of the second lens group f _W ... Focal length of the entire lens system at the wide end f ₂ ... Focal length of the second lens group

Alternatively, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, at least one positive lens and a negative lens are provided. Having the fourth lens group having a negative refracting power as a whole, zooming is performed by changing the distance between the lens groups, and the following conditional expression is satisfied.

[0009]

[Outside 6] ψi ... Refractive power of the i-th lens group ψ _W , f _W ... Composite refractive power and composite focal length of the entire lens system at the wide end Bi ... Length of the i-th lens group on the optical axis ω _W ... At the wide end Half angle of view of the entire lens system SK _W , TD _W ... Back focus and total lens length of the entire lens system at the wide end

Alternatively, in order from the object side, at least one positive lens is provided, the first lens group having a positive refractive power and at least one negative lens are provided, and the second lens having a negative refractive power as a whole. A third lens group having a lens group, at least one positive lens and a negative lens, and having a positive refracting power as a whole, and having at least one positive lens and a negative lens, being a fourth lens having a negative refracting power as a whole. The present invention is to have a lens group, perform zooming by changing the distance between the lens groups, and satisfy the following conditional expression.

[0011]

[Outside 7] However, f ₃ , f ₄ ... Focal length of each lens group of the 3rd and 4th lens groups f _W , f _T ... Focal length of each lens system at wide end and tele end ω _W ... Lens whole system at wide end Half angle of view d _2W , d _2T ... Lens spacing between the second and third lens groups at wide end and tele end d _3W , d _3T ... Third and fourth lens group spacing at wide end and tele end B ₃ ... Length of 3 lens groups on the optical axis

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A zoom lens according to the present invention will be described below with reference to the drawings. 1, FIG. 3, FIG. 5, FIG. 7, FIG. 9, FIG. 11, and FIG. 13 are lens cross-sectional views of a zoom lens according to the present invention. In the figure, I is a first lens group having a positive refracting power, and II is a second lens group, which has a positive refracting power in Numerical Examples 1 to 4 and a negative refracting power in Numerical Examples 5 to 7. is doing. III is a third lens group having a positive refractive power, IV is a fourth lens group having a negative refractive power,
S is a diaphragm fixed to the second lens group II. In the aberration diagrams, (A), (B), and (C) are various aberration diagrams at the wide-angle end, the middle, and the telephoto end, respectively. When zooming from the wide-angle side to the telephoto side, (A), (B),
As shown in the lens position of (C), each lens group moves to the object side, and the distance between the first lens group and the second lens group,
The second lens group and the third lens group are moved so that the distance between them is widened, while the distance between the third lens group and the fourth lens group is narrowed. The second lens group is located between the positive first lens group and the positive third lens group and has a small number of about 1 or 2 to achieve compactness and low cost, while eliminating aberrations generated in the second lens group. It is corrected by the first lens group or the third lens group. In addition, the third lens group,
It has the strongest positive refracting power in this zoom lens and is also responsible for the image forming action. Further, the fourth lens group mainly plays a zooming function in this zoom lens. For such a zoom lens, the above condition (M ₁ = M ₂ or 1
The total number of lenses is set so as to satisfy ≦ M ₂ <M ₁ ≦ M ₄ ≦ M ₃ ≦ 6), so that the total lens length is short and the cost is kept low.

Next, as shown in Numerical Examples 1 to 4, when the second lens group is composed of a single positive lens, a positive lens having a convex surface facing the object side is arranged in the first lens group. The occurrence of spherical aberration is suppressed.

Further, a single positive lens having a convex surface facing the image plane side is arranged in the second lens group to correct coma and spherical aberration in a well-balanced manner.

Further, by disposing at least a negative lens and a positive lens in the third lens group, good chromatic aberration can be corrected, and by making the positive lens a convex surface on the image side, the main point of the third lens group. The position can be relatively arranged on the fourth lens group side, and the distance between the principal points of the third lens group and the fourth lens group is shortened at the telephoto end to increase the zoom ratio. Furthermore, a positive lens having a convex surface facing the image side and a negative lens having a concave surface facing the object side are arranged in the fourth lens group to satisfactorily correct chromatic aberration, spherical aberration, and coma.

Then, by satisfying the conditional expression (1) which defines the lens shape of the second lens group, each aberration such as spherical aberration and distortion is favorably corrected. If the upper limit of conditional expression (1) is exceeded, the lens shape of the second lens group will be a lens shape convex toward the image side, and its refracting power will tend to be strong, and spherical aberration will be considerably underpreferable. On the other hand, when the value goes below the lower limit, the lens of the second lens group has a convex shape on the object side, and at the same time, its refracting power becomes strong, so that distortion tends to increase to the plus side on the wide side, which is not preferable.

Then, when each lens unit is constructed in the order of positive, positive, positive and negative from the object side, the conditional expressions (2) to (6) are satisfied to maintain good optical performance while maintaining good optical performance. We are trying to downsize the system.

Conditional expressions (2) and (3) are conditional expressions that regulate the refractive power of each lens unit. If both are above the upper limit, it is advantageous for compactness, but the power becomes too large and spherical aberration during zooming. However, the fluctuation of coma aberration increases, which is not preferable. On the contrary, if the lower limit is exceeded, it tends to be difficult to obtain a compact zoom.

Conditional expression (4) is a conditional expression that defines the thickness of each lens unit. When the upper limit of this conditional expression (4) is exceeded, the lens system becomes large, and when it exceeds the lower limit, axial aberration and off-axis aberrations occur. It becomes difficult to satisfactorily correct both. Further, for compactness, the upper limit value is preferably 1.01.

Conditional expression (5) is a conditional expression that regulates the back focus length with respect to the total lens length at the wide-angle end. If the upper limit of this conditional expression is exceeded, it is advantageous for compactness.
Since the total lens length is short, it becomes difficult to satisfactorily correct both the on-axis aberration and the off-axis aberration. Compactness will not be achieved if the lower limit is exceeded.

Conditional expression (6) is a condition for defining the length of the lens system, and if the upper limit of this conditional expression is exceeded, compactness will not be achieved. When the value goes below the lower limit, it becomes difficult to satisfactorily correct both the axial aberration and the off-axis aberration.

Further, it is preferable to set the zoom lens having positive, positive, positive and negative refractive powers in order from the object side so that the following conditions are satisfied.

[0023]

[Outside 8] dS _W ... Distance from the first surface to the diaphragm at the wide-angle end

Conditional expression (7) is a conditional expression relating to the position of the diaphragm. If the upper limit is exceeded, the diaphragm will be located considerably on the image plane side from the first surface, and the lens diameter on the most object side will increase, which is preferable. Absent. On the other hand, if the diaphragm position is located relatively close to the object side beyond the lower limit, it is advantageous for downsizing the lens diameter on the most object side, but off-axis aberrations, particularly distortion at the wide end, increase in the positive direction, which is preferable. Absent.

On the other hand, especially when the second lens unit is constructed with a negative refractive power, it is desirable to satisfy the following conditional expression.

[0026]

[Outside 9]

Conditional expression (8) relates to the ratio of the focal length of the entire system at the wide-angle end to the distance between the second and third lens groups with respect to the angle of view. When the upper limit is exceeded, the total lens length increases as the distance between the second and third lens groups increases. It becomes difficult to reduce both the lens diameter on the most object side and the lens diameter on the most image side regardless of the position of the stop in the entire lens system. On the other hand, when the value goes below the lower limit, when the distance between the second and third lens groups becomes small, the second lens group and the third lens group cause mechanical interference, which is not preferable.

The conditional expression (9) relates to the thickness of the third lens group, and if the thickness of the third lens group exceeds the upper limit, the lens system becomes large. When the thickness is less than the lower limit, it becomes difficult to correct axial aberration and off-axis aberration in a well-balanced manner. Furthermore, for compactness, it is desirable to set the upper limit to about 0.51.

If the upper limit of conditional expression (10) is exceeded, the lens of the second lens group will have a concave shape on the image side and its refracting power will tend to be strong, and distortion will increase to the plus side on the wide side, which is not desirable. On the other hand, when the value goes below the lower limit, the shape becomes concave on the object side and the refracting power becomes strong and spherical aberration is overcorrected, which is not preferable.

Next, the first lens group, the second lens group, and the third lens group each have a positive refractive power, and the fourth lens group
When the lens group has a negative refracting power, by satisfying the conditional expressions (11) to (15), good optical performance can be maintained and size reduction can be achieved.

Conditional expressions (11) and (12) are conditional expressions for defining the focal lengths of the third lens group and the fourth lens group, respectively, and if both are below the lower limits, it is advantageous for compactness.
Refractive power becomes too large and spherical aberration during zooming,
The fluctuation of coma becomes large, which is not preferable. On the contrary, if the upper limit is exceeded, it becomes difficult to obtain a compact zoom.

Conditional expression (13) relates to the ratio of the focal length of the entire system at the wide-angle end to the lens group interval of the second and third groups with respect to the angle of view. When the upper limit is exceeded, the total lens length becomes large. However, it becomes difficult to reduce both the lens diameter on the most object side and the lens diameter on the most image side in any position of the diaphragm in the entire lens system. On the other hand, when the value goes below the lower limit, when the distance between the second and third lens groups becomes small, the second lens group and the third lens group cause mechanical interference, which is not preferable.

Conditional expression (14) is based on the change of the interval between 2 and 3 groups and 3
As for the ratio of the change in the distance between the four groups, when the upper limit is exceeded, the change in the distance between the second and third groups becomes large, the distance between the second and third groups becomes large at the wide end, and the lens diameter increases. When the value goes below the lower limit, the distance between the second and third lens groups becomes large in the telephoto direction, the zoom movement amount of the first lens group increases, and when the high zoom ratio is attempted, the total telephoto length becomes long, which is not preferable.

Conditional expression (15) relates to the thickness of the third lens group, and if the thickness of the third lens group exceeds the upper limit, the lens system becomes large. When the thickness is less than the lower limit, it becomes difficult to correct axial aberration and off-axis aberration in a well-balanced manner. Furthermore, for compactness, it is desirable to set the upper limit to about 0.51.

Further, in all the numerical examples of the present invention, it is desirable to set various optical elements so as to satisfy the following conditional expressions.

[0036]

[Outside 10] However, ν _3N ... Abbe number of at least one negative lens in the third lens group ν _3P ... Abbe number of at least one positive lens in the third lens group ν _4P ... At least one lens in the fourth lens group Abbe number ν _4N of the positive lens of at least one negative lens in the fourth lens group R _iF … the lens curvature radius on the most object side in the i-th lens group R _iR … the most image surface in the i-th lens group Side lens curvature radius

When the lower limit of conditional expression (16) is exceeded and there is no difference in Abbe number, it becomes difficult to correct axial chromatic aberration in the third lens group.

When the lower limit of conditional expression (17) is exceeded and there is no difference in Abbe number, it becomes difficult to correct lateral chromatic aberration during zooming.

If the upper limit of conditional expression (18) is exceeded, the first surface becomes a strong convex surface on the object side, the back focus becomes short, and the lens diameter of the final lens becomes large. In addition, the distortion increases positively at the wide end. On the other hand, if the value goes below the lower limit, spherical aberration is overcorrected, which is not preferable.

When the upper limit of conditional expression (19) is exceeded, the positive refracting power on this surface disappears and the positive refraction of the other lens surface in the first lens group is made to have a predetermined focal length. The force must be increased, and it is necessary to increase the number of lenses in order to perform good aberration correction. If the lower limit is exceeded, spherical aberration will be undercorrected.

When the upper limit of conditional expression (20) is exceeded, the position of the front principal point of the fourth lens unit moves to the image plane side, and the distance between the principal points of the third and fourth lens units increases on the telescopic side, which is disadvantageous for high zooming. is there. If the value goes below the lower limit, the fluctuation of coma aberration during zooming becomes large. More preferably, the lower limit is set to about -1,10.

If the upper limit of conditional expression (21) is exceeded, the distortion at the wide end will be excessive, and if the lower limit is exceeded, the back focus will be short and the diameter of the final lens will be large.

More preferably, the number of lenses in each group is M
_It is preferable that ₁ <M ₄ or M ₄ <M ₃ , M ₃ ≦ 4.

Further, the diaphragm S may be arranged at the most object side of the third lens group or near the intermediate position in the third lens group.

Next, numerical examples of the present invention will be shown. In the numerical examples, R _i is the radius of curvature of the i-th lens surface in order from the object side, D _i is the i-th lens thickness and air gap from the object side, and N _i and ν _i are respectively in order from the object side. The refractive index and Abbe number of the glass of the th lens.

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

[0047]

[Outside 11] It is expressed by

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

[0049]

[Table 1]

[0050]

[Outside 12]

[0051]

[Outside 13]

[0052]

[Outside 14]

[0053]

[Outside 15]

[0054]

[Outside 16]

[0055]

[Outside 17]

[0056]

[Outside 18]

Finally, in this embodiment, the first lens group is composed of a negative lens and a positive lens in order, so that the degree of freedom in correcting chromatic aberration in the first lens group is increased, and the third lens group and the fourth lens are Aberration correction in the group becomes easy.

It is desirable that the second lens group be composed of a single lens, because it is very effective in making it compact.

The third lens group has an L _3N lens having a negative refracting power on the relatively object side, an L _3P lens having a positive refracting power on the relatively image side, and a negative lens on the object side of the L _3P lens. It is preferable that a positive lens is arranged between the L _3N lens and the L _3P lens by bonding.

Focusing is preferably performed by only one lens group among the first, third, and fourth groups because the mechanical mechanism is simple. However, although the mechanical mechanism is slightly complicated, it may be performed in combination with another group.

[0061]

As described above, according to the present invention, it is possible to achieve both compactness and excellent aberration-corrected lens performance at an extremely high level. I was able to provide a zoom lens.

[Brief description of drawings]

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

FIG. 2 is a diagram of various types of aberration of Numerical example 1 according to the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 2 according to the present invention.

FIG. 4 is a diagram of various types of aberration of Numerical example 2 according to the present invention.

FIG. 5 is a lens cross-sectional view of Numerical Example 3 according to the present invention.

FIG. 6 is a diagram of various types of aberration of Numerical example 3 according to the present invention.

FIG. 7 is a lens cross-sectional view of Numerical Example 4 according to the present invention.

FIG. 8 is a diagram of various types of aberration of Numerical example 4 according to the present invention.

FIG. 9 is a lens cross-sectional view of Numerical Example 5 according to the present invention.

FIG. 10 is a diagram of various types of aberration of Numerical example 5 according to the present invention.

FIG. 11 is a lens cross-sectional view of Numerical Example 6 according to the present invention.

FIG. 12 is a diagram of various types of aberration of Numerical example 6 according to the present invention.

FIG. 13 is a lens cross-sectional view of Numerical Example 7 according to the present invention.

FIG. 14 is a diagram of various types of aberration of Numerical example 7 according to the present invention.

[Explanation of symbols]

 S Sagittal image plane M Meridional image plane d d line g g line I 1st lens group II 2nd lens group III 3rd lens group IV 4th lens group S Aperture

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Makoto Misaka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeshi Koyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (5)

[Claims] 1. A first lens group having a positive refractive power, a second lens group having a positive or negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power in order from the object side. A zoom lens for zooming by changing the distance between the lens groups, wherein the first lens group has at least one positive lens having a convex surface on the object side, and the second lens group Is composed of two or less lenses, the third lens group has at least one negative lens and a positive lens having a convex surface facing the image plane side, and the fourth lens group has at least one image plane side. When a positive lens having a convex surface facing toward and a negative lens having a concave surface facing toward the object side are provided, and Mi is the number of lenses in the i-th group (however,
The cemented lens is counted in the peeled state. ), M ₁
= M ₂ = 1 or 1 ≦ M ₂ <M ₁ ≦ M ₄ ≦ M ₃ ≦ 6, which is a compact zoom lens. 2. A first lens group having a positive refractive power, 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 in order from the object side. A zoom lens that performs zooming by changing the distance between the lens groups, wherein the first lens group has at least one positive lens having a convex surface directed toward the object side, and the second lens group has the following: The third lens group has at least one negative lens and a positive lens having a convex surface facing the image plane side, and the fourth lens group has at least one negative lens. A compact zoom lens having a positive lens having a convex surface facing the image side and a negative lens having a concave surface facing the object side. [Outer 1] However, R _2F , R _2R ... Radius of curvature on the object side and the image side of the second lens group, respectively. f _W : Focal length of entire lens system at wide end f ₂ : Focal length of second lens group 3. A first lens group having a positive refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, at least one positive lens and a negative lens in order from the object side. A compact zoom lens having a fourth lens unit having a negative refracting power as a whole, zooming by changing the distance between the lens units, and satisfying the following conditional expression. [Outside 2] ψi ... Refractive power of the i-th lens group ψ _W , f _W ... Combined refractive power and combined focal length of the entire lens system at the wide end. Bi ... Length of optical axis of i-th lens group ω _W ... Half field angle of entire lens system at wide end SK _W , TD _W ... Back focus and total lens length of entire lens system at wide end 4. The zoom lens according to claim 1, wherein the second lens unit has a negative refractive power and satisfies the following conditional expression. [Outside 3] However, d _2W ... Lens spacing of the second and third groups at wide end f _W ... Composite focal length of entire system at wide end ω _W ... Half field angle of entire system at wide end B ₃ ... Optical axis of third lens group Upper length R _2F ... Radius of curvature of lens surface closest to object in second lens group R _2R ... Radius of curvature of lens surface closest to image surface in second lens group f ₂ ... Focal length of second lens group 5. A first lens group having at least one positive lens in order from the object side and having a positive refractive power as a whole, and a second lens group having at least one negative lens and having a negative refractive power as a whole. A lens group, a third lens group having at least one positive lens and a negative lens and having a positive refracting power as a whole, and a fourth lens group having at least one positive lens and a negative lens as a whole, having a negative refracting power A compact zoom lens that has the following, performs zooming by changing the distance between each lens group, and satisfies the following conditional expression. [Outside 4] However, f ₃ , f ₄ ... Focal length of each lens group of the 3rd and 4th lens groups f _W , f _T ... Focal length of each lens system at wide end and tele end ω _W ... Lens whole system at wide end Half angle of view d _2W , d _2T ... Lens spacing between second and third lens groups at wide end and tele end d _3W , d _3T ... Third and fourth lens group spacing at wide end and tele end B ₃ ... Length of 3 lens groups on the optical axis