JP2811943B2 - Zoom lens having flare stop and camera including the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a camera including a zoom lens having a flare stop suitable for a photographic camera, a video camera, and the like. The present invention relates to a camera including a zoom lens having a flare stop which is arranged in a lens system to block a part of an off-axis light beam so as to obtain good optical performance over the entire zoom range.

(Prior Art) Conventionally, there are three lens groups of a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power in order from the object side. The applicant of the present invention has disclosed a zoom lens in which zooming is performed by moving a lens group, for example, in Japanese Patent Laid-Open No.
No. 14, JP-A-64-72114, and the like.

This type of zoom lens is relatively widely used as a photographing system for a wide angle of view because it is relatively easy to widen the angle of view.

In this publication, the first, second, and third groups are moved under a certain condition to perform zooming, and the lens configuration of the three lens groups is specified to thereby correct aberration fluctuations accompanying zooming well. 8 with a zoom ratio of 2-3 times with optical performance
A relatively compact zoom lens having up to nine lenses, particularly suitable for a lens shutter camera, has been achieved.

(Problems to be Solved by the Invention) The zoom lenses proposed in the above-mentioned JP-A-63-271214 and JP-A-64-72114 each comprise two or more lenses in each lens group. For example, the chromatic aberration is corrected within each lens unit, and the refractive power of each lens unit is increased to shorten the overall optical length (the distance from the first lens surface to the imaging surface).

However, in general, if an attempt is made to reduce the number of lenses while maintaining a constant zoom ratio to reduce the size of the entire lens system, the amount of various aberrations such as spherical aberration, coma, halo, and flare increases, and these various aberrations increase. It becomes very difficult to correct the balance in a balanced manner.

The present invention utilizes the refractive power arrangement of the zoom lens proposed earlier by the present applicant, and provides a flare stop different from the aperture stop (F number stop) mainly for a part of the off-axis light beam that mainly causes flare. The objective is to propose a camera including a zoom lens having a flare stop suitable for a lens shutter camera with an F number of about 4.6, which shields light and has good optical performance over the entire zoom range with a zoom ratio of about 2. I do.

(Means for Solving the Problems) A zoom lens having a flare stop according to the present invention includes, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a zoom lens having a negative refractive power. The first lens group includes three lens groups, and the three lens groups are moved to perform zooming.
An aperture stop that moves integrally with the second lens unit during zooming between the second lens unit and the second lens unit is arranged, and the zoom lens is moved between the second lens unit and the third lens unit from the wide-angle end to the telephoto end. A flare stop which moves independently for each lens group by drawing a locus convex toward the image plane side is arranged, and the distance between the flare stop and the second group at the wide-angle end and the telephoto end is D5W, D5T, respectively. When It is characterized by satisfying certain conditions.

The camera including the zoom lens having the flare stop according to the present invention includes, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. These three lens groups are moved to perform zooming, and an aperture stop is arranged between the first group and the second group.
At the time of zooming from the wide-angle end to the telephoto end, a flare stop that moves independently of each lens group while drawing a locus convex toward the image plane during zooming from the wide-angle end to the telephoto end is disposed between the second group and the third group. The distance between the flare stop and the second group at the end and the telephoto end is D5
W, D5T, the focal length of the i-th group is Fi, the focal length at the wide-angle end of the entire system is Fw, and the principal point intervals at the wide-angle end and the telephoto end of the i-th and (i + 1) groups are EiW, EiT, respectively. The three lens groups are each composed of a single lens, the refractive index and Abbe number of the material of the lens of the i-th group are Ni and νi, respectively, and the aspherical surface is provided on the object-side lens surface of the first group. An aspherical surface is applied to the lens surface on the image plane side of the second lens unit, and an aspherical surface is applied to the lens surface on the object side of the third lens unit.
i, when the diagonal length of the effective screen is Y It is characterized by satisfying certain conditions.

(Embodiment) FIG. 1 is a schematic view of a main part of an optical system according to an embodiment of the present invention.

2 and 3 are lens cross-sectional views of Numerical Examples 1 and 2 of the present invention. 1 to 3, (A), (B),
(C) shows the zoom positions at the wide-angle end, the middle, and the telephoto end, respectively.

In the figure, I is a first group having a negative refractive power, and II is a second group having a positive refractive power.
The group III is a third group having a negative refractive power, and SA is an aperture stop (F number stop), which is disposed between the first group and the second group. SB is a flare stop, which is arranged between the second and third units. F is an image plane.

In this embodiment, zooming from the wide-angle end to the telephoto end is performed by moving the three lens groups independently toward the object side as indicated by arrows. At this time, the aperture stop SA is moved integrally with the second lens unit.

The flare stop SB is independently moved so as to draw a locus convex toward the image plane. At this time, the flare aperture SB and the second
The flare stop SB and the flare stop SB are set so that the distance from the lens group satisfies the conditional expression (1), that is, the distance between the lens group and the lens group is wider at the telephoto end (FIG. 1C) than at the wide-angle end (FIG. Two groups are moving properly.

As a result, the intermediate zoom position (first
From FIG. (B)), at the telephoto end zoom position (FIG. 1 (C)), the upper light flux of the off-axis light flux serving as the flare component is effectively blocked, and the optical performance is maintained satisfactorily.

In particular, the aperture stop SA is disposed closer to the object side than the second lens unit, the flare stop SB is disposed closer to the image plane than the second lens unit, and the conditional expression (1) is satisfied. The upper flare light beam of the light beam is effectively shielded.

If the distance between the flare stop SB and the second lens unit exceeds the upper limit of the conditional expression (1) due to zooming, and the amount of change during zooming becomes too small, the upper part of the off-axis light flux at the intermediate zoom position will become higher. It is not good, because the shading of the flare light beam is reduced.

Conversely, if the distance between the second lens unit and the flare stop becomes too wide on the telephoto side beyond the lower limit value of conditional expression (1), the flare stop and the third lens unit mechanically interfere with each other, which is not good.

When zooming from the wide-angle end to the telephoto end, the zoom lens according to the present embodiment moves all three lens groups independently in the object side direction as shown in each figure. In particular, a predetermined zoom ratio is effectively obtained by greatly changing the distance between the second and third lens units.

The zoom lens according to the present invention is composed of three lens units having negative, positive, and negative refractive power in order from the object side as shown in FIGS. 1, 2, and 3, that is, the second group having positive refractive power. The first and third units having negative refractive power are arranged on both sides of the lens so that the refractive power arrangement during zooming has a substantially symmetrical lens configuration. or,
The first group employs a high-refractive-index high-dispersion glass, and the second group employs a low-refractive-index low-dispersion glass.

By adopting such a substantially symmetrical lens arrangement and using glass of an appropriate material, it is possible to correct chromatic aberration in a well-balanced manner as a whole lens system without using a method of correcting chromatic aberration in each lens group as in the related art. Like that. That is, the three lens groups cancel each other out.

Further, the first group is a meniscus negative first lens having a convex surface facing the object side, and the second group is a positive second lens whose both lens surfaces having a strong refractive index on the image surface side are convex. Even if each lens group of the meniscus negative third lens having a convex surface facing the image plane side of the three groups is constituted by a single lens to shorten the entire length of the lens, chromatic aberration is included over the entire zoom range. The various aberrations can be corrected in a well-balanced manner, and a zoom lens with high optical performance can be obtained.

In the present invention, in order to further correct various aberrations in a well-balanced manner over the entire zoom range, the focal length of the i-th lens unit is set to F.
i, the focal length at the wide-angle end of the entire system is Fw, and the principal point intervals at the wide-angle end and the telephoto end of the i-th and (i + 1) -th groups are respectively
EiW, EiT It is better to satisfy the following conditions.

Conditional expression (2) appropriately sets the negative refractive power of the first group,
This is for properly correcting various aberrations.

If the refractive power of the first lens unit becomes too strong beyond the upper limit of conditional expression (2), it becomes difficult to correct various aberrations in a well-balanced manner over the entire zoom range. If the refractive power of the first lens unit is too weak below the lower limit, it becomes difficult to satisfactorily correct axial chromatic aberration on the wide-angle side.

Conditional expression (3) is for appropriately setting the distance between the principal points of the first unit and the second unit at the wide-angle end, and correcting various aberrations in a well-balanced manner while reducing the size of the entire lens system.

If the distance between the principal points of the first and second units is too long beyond the upper limit of conditional expression (3), the effective lens diameter of the first unit will increase, and the first unit and the second unit will exceed the lower limit. If the distance between the principal points of the two groups is too short, the symmetry of the entire lens system will be lost, and it will be difficult to correct various aberrations in a well-balanced manner.

Conditional expression (4) is for appropriately setting the ratio between the refractive powers of the second group and the third group to effectively obtain a predetermined zoom ratio.

If the upper limit of conditional expression (4) is exceeded and the refractive power of the third lens unit becomes too weak, the amount of movement of the third lens unit for securing a predetermined zoom ratio increases, and the overall length of the lens increases. If the refractive power of the third lens unit becomes too strong beyond the lower limit, it becomes difficult to satisfactorily correct off-axis aberrations such as field curvature.

Conditional expression (5) is the ratio of the amount of change in the principal point distance between the first and second units and the amount of change in the principal point distance between the second and third units during zooming from the wide-angle end to the telephoto end. Is set appropriately, and mainly to satisfactorily correct field curvature.

When the value exceeds the upper limit of conditional expression (5), the field curvature greatly changes in the negative direction when zooming from the wide-angle end to the telephoto end. On the other hand, if the value exceeds the lower limit, the field curvature greatly changes in the positive direction when zooming from the wide-angle end to the telephoto end, which is not good.

In addition, in order to favorably correct various aberrations while reducing the size of the entire lens system in the present invention, each of the three lens groups is constituted by a single lens, and the refractive index of the material of the lens of the i-th group and the Abbe's When the numbers are Ni and νi, respectively ν1 <ν3 <ν2 It is preferable to satisfy the following condition (7).

Conditional expression (6) is for appropriately setting the refractive index of the material of each lens group and mainly for favorably correcting the image surface characteristics.
Beyond the upper limit, the Petzval sum increases in the positive direction,
On the other hand, if the lower limit is exceeded, the Petzval sum increases in the negative direction, making it difficult to satisfactorily correct astigmatism in any case.

Conditional expression (7) is for appropriately setting the Abbe number of the material of each lens group and favorably correcting axial chromatic aberration and lateral chromatic aberration over the entire zoom range.

If conditional expression (7) is not satisfied, it becomes difficult to correct these chromatic aberrations with good balance over the entire zoom range.

In a camera including a zoom lens having a flare stop according to the present invention, in addition to the above-described conditional expressions (1) to (7), an aspherical surface is provided on the object-side lens surface of the first group. An aspherical surface on the image side lens surface of the second group, and an aspherical surface on the object side lens surface of the third group,
The aspherical coefficients of fourth-order aspheric first i group Bi, -15 when the diagonal length of the effective screen was ^{Y <B1 · Y 3 <-1} ...... (8) -7 <B2 · Y 3 <- 0.1 (9) | B3 · Y ³ | <2 (10) It is preferable to satisfy the following condition.

The conditional expressions (8) and (10) are mainly for favorably correcting the field curvature.

If the upper limit of conditional expression (8) or the lower limit of conditional expression (10) is exceeded, it becomes difficult to satisfactorily correct the field curvature. If the lower limit value of the conditional expression (8) or the upper limit value of the conditional expression (10) is exceeded, the aspherical effect becomes too strong, and the field curvature becomes excessively corrected.

If the upper limit of conditional expression (8) is exceeded, the aspherical effect will be too weak, making it difficult to satisfactorily correct spherical aberration. On the other hand, if the value exceeds the lower limit, spherical aberration will be overcorrected, which is not good.

Next, numerical examples of the present invention will be described. In numerical examples
Ri is the radius of curvature of the i-th lens surface in order from the object side,
Is the i-th lens thickness and air gap from the object side, Ni and ν
i is the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

The aspheric surface has an X-axis in the optical axis direction and H in the direction perpendicular to the optical axis.
The axis and the traveling direction of light are positive, and R is the paraxial radius of curvature, A, B,
When C, D, and E are aspheric coefficients It is represented by the following equation.

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

(Effects of the Invention) According to the present invention, in a zoom lens composed of three lens groups having a predetermined refractive power, the aperture stop and the flare stop are appropriately set as described above, and the refractive power and the lens configuration of the three lens groups are changed. By properly specifying, a part of the off-axis light beam that causes flare light is effectively shielded, and the entire lens system is reduced in size. A camera including a zoom lens having a flare stop capable of obtaining good optical performance can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an optical system according to an embodiment of the present invention, FIGS. 2 and 3 are lens cross-sectional views of Numerical Embodiments 1 and 2 of the present invention, and FIGS. Numerical examples 1 and 2 of the present invention, respectively
FIG. 4 is a diagram of various aberrations of FIG. I, II, III
In order of the first group, the second group, the third group, SA is the aperture stop, SB is the flare stop, and the arrows are the moving directions of each lens group during zooming from the wide-angle end to the telephoto end, and the lens cross-sectional views and aberration diagrams. (A), (B), and (C) show the wide-angle end, the middle, and the telephoto end, respectively. d is a d-line, g is a g-line, SC is a sine condition, S is a sagittal image plane, and M is a meridional image plane.

Claims (4)

(57) [Claims] 1. A lens system comprising: a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. Is moved to perform zooming, an aperture stop is arranged between the first and second units, and an image is formed between the second and third units when zooming from the wide-angle end to the telephoto end. A flare stop that moves independently for each lens group while drawing a convex locus toward the surface side is disposed, and the distance between the flare stop and the second group at the wide-angle end and the telephoto end is set to each.
When D5W, D5T A zoom lens having a flare stop, which satisfies certain conditions. 2. The focal length of the i-th lens unit is Fi, the focal length at the wide-angle end of the entire system is Fw, and the distance between principal points at the wide-angle end and the telephoto end of the i-th and (i + 1) -th units is EiW and EiT, respectively. And when 2. A zoom lens having a flare stop according to claim 1, wherein the following conditions are satisfied. 3. When the three lens groups are each composed of a single lens, and the refractive index and Abbe number of the material of the lens of the i-th group are Ni and νi, respectively. 3. A zoom lens having a flare stop according to claim 2, wherein the following conditions are satisfied. 4. A lens unit comprising: a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. Is moved to perform zooming, an aperture stop is arranged between the first and second units, and an image is formed between the second and third units when zooming from the wide-angle end to the telephoto end. A flare stop that moves independently of each lens group while drawing a locus convex toward the surface is arranged, and the distance between the flare stop and the second group at the wide-angle end and the telephoto end is set to each.
D5W, D5T, the focal length of the i-th unit is Fi, the focal length at the wide-angle end of the entire system is Fw, and the principal point intervals at the wide-angle end and the telephoto end of the i-th and (i + 1) th groups are EiW, EiT, respectively. The three lens groups are each composed of a single lens, and the refractive index and Abbe number of the material of the lens of the i-th group are Ni, νi, and the first lens, respectively.
An aspherical surface is formed on the object-side lens surface of the group, an aspherical surface is formed on the image-side lens surface of the second group, and an aspherical surface is formed on the object-side lens surface of the third group. The fourth order aspheric coefficient of
Bi, when the diagonal length of the effective screen is Y A camera including a zoom lens having a flare stop, characterized by satisfying the following conditions.