JP2842642B2 - Zoom lens for compact cameras covering a wide angle - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens suitable for a compact camera having a smaller back focus than that for a single-lens reflex camera, and more particularly, to a structurally simple zoom lens. Despite being a telephoto two-group zoom lens (hereinafter referred to as a two-group type), the half-angle of view on the short focal length side covers a wide angle of about 37 °, and the zoom ratio is about two-group type covering a wide angle. The present invention relates to a small zoom lens having a size as large as 2.5 times and its focusing method.

[Prior Art] As zoom lenses for compact cameras, there are (A) two-group type, (B) three-group type and four-group type.

The type (B) has a feature that the amount of movement is smaller than that of the two-group type, but has a large lens system and a complicated structure, and is clearly different from the two-group type as in the present invention. Details are omitted.

In comparison, the two-group type has a slightly larger travel distance,
The lens configuration and mechanical structure are simple, and miniaturization is easy.

Examples of such two-group type zoom lenses include: (A-1) JP-A-56-128911; JP-A-57-201213;
No. 48009, No. 60-170816, No. 60-191216 (A-2) JP-A Nos. 62-90611 and 64-57222 (A-3) JP-A Nos. 62-113120 and 62-264019 No. have been known.

In the present invention, the first lens is constituted by a negative lens. However, the first lens of the first lens group of the telephoto type two-unit zoom lens is described in JP-A-63-2760 assuming that the first lens is a negative lens.
There is No. 13.

Further, regarding focusing, see JP-A-Hei.
There is 189620.

"Problem to be Solved by the Invention" However, the camera of (A-1) has a problem that the camera as a whole cannot be made compact because the back focus is small and the rear lens diameter is large. There is also a problem that internal reflection and the like easily occur between the film surface and the final surface.

In order to solve such a problem, the applicant of the present application has proposed a two-group type zoom lens having a relatively large back focus for a compact camera (A-2).
With a zoom ratio of 1.5 to 1.6 times and a structure with 6 elements in 5 groups, (A-
3) The magnification ratio is about 1.7 to 2.5 times, the zoom ratio is about 1.5 to 1.6 times, and the zoom ratio is about 1.5 to 1.6 times. Has provided an eight-panel configuration, but the half-angle of view on the short focal length side is about 30 °, and it is not enough to meet the demand for wide-angle photography with a compact camera for landscape photography, etc. there were. In addition, there is a problem that the demand for a smaller and less expensive zoom lens for a compact camera cannot be satisfied.

In JP-A-63-276013, as in the present invention,
Although a negative lens is used as the first lens, since it uses a gradient index lens, it is still expensive in current technology, and it is difficult to reduce the cost. There were challenges. Moreover, the half angle of view is as small as 30 °.

On the other hand, as a problem of widening the angle, there is a problem of a peripheral light amount.
In the conventional two-group type, a focusing method is provided in which a diaphragm is provided between the first lens group and the second lens group, and at the time of focusing, the diaphragm and the second lens group are fixed, and only the first lens group is moved. Is the simplest, but the height of the marginal ray at the maximum angle of view passing through the aperture position is smaller,
There is a problem that an increase in the amount of peripheral light when the aperture is stopped cannot be expected.

Further, when focusing is performed by the entire first lens unit, there is also a problem that the amount of change in astigmatism at a short distance and under curvature of the image plane is large (see FIGS. 12 and 14).

As a prior example relating to such focusing, there is Japanese Patent Application Laid-Open No. 1-189620, but the half angle of view on the short focal length side is as small as about 30 °, and the first lens is a positive lens like other conventional examples. The desired wide angle cannot be achieved.

The present invention has been made to solve the above problems, and the present applicant has already assumed that the half angle of view is as wide as about 37 ° C.
Japanese Patent Application No. 1-110849, a group type with a zoom ratio of about 2.7 times,
Japanese Patent Application No. 1-272392, a 2-group type with a zoom ratio of about twice, approx.
The invention of Japanese Patent Application No. 1-302570, which is 2.5 times larger, achieves a wider angle by devising the structure of the first lens group and the aperture while keeping the simple system of the two-group type. It is another object of the present invention to provide a zoom lens for a compact camera having a small aberration variation from an infinite object to a short distance and a focusing method thereof by further increasing the magnification.

[Means for Solving the Problems] To achieve the above object, a zoom lens according to the present invention includes, in order from the object side, a first lens group having a positive focal length, and a second lens having a negative focal length. A first lens group having a positive focal length from the object side; and a first F lens group having a positive focal length from the object side. And a positive first R lens group having a small power behind the stop. The first lens of the first F lens group is a negative lens, and (1) −0.8 <f _1G / f ₁ <−0.1 (2) 0.05 <f _1G / f _1R <0.35 (3) 1.2 <f _S / f _1G <1.7 (4) 0.03 <d _1F-1R / f _S <0.15 where f _{1G is} the first lens Group focal length f ₁ : Focal length of first lens f _1R : Focal length of first R lens group f _S : Focal length of entire system on the short focal length side d _{1F to 1R} : Infinite object distance It is characterized by satisfying various conditions of the distance between the first F and first R lens groups in the first lens unit.

In the zoom lens having such characteristics, the first F lens group includes, from the object side, a 1a lens group including at least three lenses of two negative lenses (first and second lenses) and a positive lens; consists of a first 1b lens group having a large power, and _{(5) -1.5 <f 1G /} f 1,2 <-0.8 (6) 0.6 <f 1G / f 1b <0.9 However f _{1, 2:} first, The combined focal length of the two lenses, f _1b, is characterized by satisfying the following conditions: the focal length of the 1b lens group, and the 1a lens group is a negative lens having a concave surface with a large curvature from the object side. A first lens, a negative second lens having a concave object side surface and a large curvature, and a positive lens having a convex object side.
The 1b lens group includes a biconvex positive lens having a diverging cemented surface and a negative meniscus lens.

In addition, in the above-mentioned zoom lens, the condition of (7) −20 <ΔI _1a <0 where ΔI _1a : the amount of change of the third-order spherical aberration coefficient due to the aspherical surface in the first lens group is included in the first lens group. At least one aspherical surface having a divergent aspherical amount with respect to the paraxial radius of curvature satisfying the following condition.

Further, the zoom lens according to the present invention includes, in order from the object side, a first lens group having a positive focal length and a second lens group having a negative focal length, and a distance between the first and second lens groups. In the zoom lens that performs zooming by changing the power, the first lens group includes, from the object side, a first F lens group having a positive focal length, and a diaphragm disposed behind the first F lens group, and a small power behind the diaphragm. A positive first R lens group, wherein the first R lens group is made of plastic and is composed of only one positive meniscus lens having a convex surface facing the rear surface side; and (2) 0.05 <f _1G / f _1R <0.35 (8) (m _2L −m _1R · m _2L ) ² <0.8 where m _2L : the lateral magnification of the second lens group on the long focal length side m _1R : the lateral magnification of the first R lens group It is characterized by satisfaction.

Further, the first R lens group is such that: (9) -20 <ΔI _1R <0, where ΔI _{1R is} a paraxial axis satisfying a condition of a change amount of a third-order spherical aberration coefficient due to an aspheric surface in the first R lens group. It is characterized by having at least one aspheric surface having a divergent aspherical amount with respect to a radius of curvature, wherein the second lens group includes a positive meniscus lens having a convex surface facing the image side from the object side, and Consisting of two negative lenses with concave surfaces, and Here, ▲ ▼: d-li of two negative lenses in the second lens group
It satisfies the condition of average value of refractive index of ne.

The focusing method of the zoom lens according to the present invention includes, in order from the object side, a first lens group having a positive focal length and a second lens having a negative focal length. In a zoom lens that performs zooming by changing the group interval, the first lens group includes a first F lens group having a positive focal length from the object side, and a stop disposed behind the first F lens group. And the first lens of the first F lens group is a negative lens, and (1) −0.8 <f _1G / f ₁ <−0.1 (2) 0.05 <f _1G / f _1R <0.35 However, X _1R : the amount of movement of the first R lens group during focusing X _1F : the conditions of the amount of movement of the first F lens group during focusing, and the first F lens group and the first R lens during focusing Moving the first lens group toward the object side while increasing the group spacing, or
The lens group includes, from the object side, a first F lens group having a positive focal length, a stop disposed behind the first F lens group, and a positive first R lens group having a small power behind the stop. group, made of plastic, characterized in that it consists of only one positive meniscus lens convex on its image plane _{side, (2) 0.05 <f 1G} / f 1R <0.35 (8) (m 2L -m 1R・_{M 2L} ) ² <0.8 Is satisfied, and at the time of focusing, the first lens group is moved to the object side while increasing the distance between the first F lens group and the first R lens group.

In addition, in such a focusing method, the aperture and the first R lens group are fixed at the time of focusing.

[Operation and Effect of the Invention] The first lens of the conventional two-group type compact camera zoom lens is almost a positive lens.
In order to widen the half angle of view on the short focus side to about 37 ° and increase the back focus to some extent, basically (
The relationship between the second lens group is a telephoto type, while the positive first lens group is composed of a positive first F lens group and a low-power positive first R lens group. It has a unique lens configuration that has never existed before.

Further, by devising the aperture position and the focusing method, it is possible to easily achieve a small variation in aberration at a short distance and a large peripheral light amount when the aperture is stopped down.

Condition (1) relates to the power of the negative first lens. When the value exceeds the upper limit, the negative power decreases, and it is difficult to increase the back focus to some extent. When the value exceeds the lower limit, the negative power increases. This is not preferable for aberration correction.

The condition (2) relates to the power of the first R lens group. Most of the power of the first lens group is occupied by the first F lens group. The power of the first lens group becomes too large, which causes an increase in coma. To improve this, coma aberration can be obtained by disposing the first R lens group with small power at a small distance behind the first F lens group (conditional expression (4)) and reducing the load on the first F lens group. Is better corrected. If the upper limit is exceeded, the power becomes too large, and the coma of the first R lens group itself becomes large, and when the first F lens group is a focusing lens, there arises a problem that the amount of extension becomes large. Below the lower limit, the power of the first F lens group becomes too large, and the effect of disposing the first R lens group is lost.

Condition (3) relates to the power of the entire first lens unit. If the upper limit is exceeded, it is advantageous for miniaturization, but the back focus tends to be small, and the position error of each lens unit on the long focal length side is also large. The focus shift (hereinafter, referred to as focus sensitivity) with respect to the image sharply increases, and manufacturing becomes difficult. If the lower limit is exceeded, it is advantageous for aberration correction, but the amount of movement of each lens group (particularly, the second lens group) increases rapidly, which is against miniaturization.

Condition (4) relates to the distance between the first F lens group and the first R lens group. If the upper limit is exceeded, aberration correction becomes easy, but if the lens system does not become compact and the lower limit is exceeded,
Coma aberration increases, and a stop cannot be provided.

Further, in order to easily achieve a wide angle with respect to the first F lens group, from the object side, a 1a lens group including at least three lenses of two negative lenses and a positive lens, A large 1b lens group,
It is more preferable that the conditions (5) and (6) be satisfied.

The condition (5) relates to the power of the two negative lenses in the 1a-th lens unit, and is related to the condition (1). When the upper limit is exceeded, it is difficult to increase the back focus. The negative power increases, (1st
The lens group has a large positive power)
The 1b lens group is not preferable because the positive power becomes too large and high-order aberrations are easily generated.

Condition (6) relates to the power of the 1b lens group. The 1b lens group occupies most of the power of the 1st lens group, but when exceeding the upper limit, the power of the 1b lens group becomes too large. Therefore, high-order aberrations are liable to occur, and if the lower limit is exceeded, the power becomes small, which is against compactness.

Condition (7) relates to the aspheric surface of the 1a lens group. If the upper limit of the condition (7) is exceeded, the lens will not have a divergent aspheric surface, and it will be difficult to correct coma and astigmatism, especially on the short focal length side. If the lower limit is exceeded, the correction becomes excessive, high-order aberrations are likely to occur, and it is difficult to manufacture an aspherical surface.

Here, the amount of change of the third-order aberration coefficient due to the aspherical surface will be supplemented. The aspherical shape is generally represented as follows.

Converting this to a focal length f = 1.0, If you replace it with Becomes

The second term and below give the amount of the aspherical surface.
Factor A ₄ terms are related, such as the third-order aspheric coefficient φ follows.

φ = 8 (N′−N) A ₄ where N: refractive index before aspherical surface N ′: refractive index after aspherical surface Aspherical coefficient φ is next to third-order aberration coefficient in aberration theory Resulting in the indicated change.

^{ΔI = h 4 φ ΔII = h} 3 φ ΔIII = h 2 2 φ ΔIV = h 2 2 φ ΔV = h 3 φ However I: spherical aberration coefficient II: coma aberration coefficient III: astigmatism coefficient VI: Tamaketsuzo surface Curve coefficient V: Distortion aberration coefficient h: Height of the paraxial on-axis ray passing through each lens surface: Height of the paraxial off-axis ray passing through the center of the pupil passing through each lens surface. There are various expressions using conic coefficients and odd-order terms, but when y is smaller than the paraxial radius of curvature, only even-order terms can be sufficiently approximated. Therefore, simply changing the expression of the aspherical shape does not depart from the application of the present invention.

The conditions (2), (8), and (9) relate to the first R lens group, so that the first R lens group has relatively low power, so that plastic can be used. When using a lens, the focus movement and the change in performance with respect to temperature and humidity are small, the weight can be reduced, and if a plastic lens is used, the aspherical surface can be easily formed, so that the performance can be improved.

Here, a supplementary explanation will be given on the focus movement with respect to the temperature or humidity change of the plastic lens. The change in the coefficient of linear expansion or refractive index of plastic with respect to temperature or humidity is
It is about 10 times larger than ordinary glass, but the amount of change in the focal length of the lens is Δf, and the lateral magnification of the lens group behind it without the plastic lens is m ′. ) Assuming that the lateral magnification up to the rear lens group is m, the focus movement amount Δp is Δp = Δf (m′−m) ² .

Therefore, when the value exceeds the upper limit of the condition (8), the focus shift with respect to the temperature and the humidity increases, which is not suitable for a compact camera.

When the first R lens group having a small power is made of plastic, it is preferable to use a positive lens so as to satisfy the condition (2) in order to reduce a focus movement with respect to a temperature change. Because, when the temperature rises, the lens frame extends,
Since the distance between the second lens groups widens and the focus position tends to shift to the lens side, when the temperature of the plastic lens rises when the lens is a positive lens, the focus position is shifted so as to become farther from the lens. Is more appropriate, the focus movement due to the focus change due to the temperature change can be made smaller than that of the glassless lens.

In the case of a plastic lens, it is easier to make an aspheric surface than glass. However, the condition (9) relates to the aspheric surface of the first R lens. In other words, it becomes impossible to correct the under-aberration that occurs in the 1b lens group. If the lower-limit is exceeded, the correction will be excessive and higher-order aberrations will occur, and it will be difficult to manufacture an aspheric surface.

Condition (10) relates to the two negative lenses of the second lens group. If the lower limit of the condition (10) is exceeded, it becomes difficult to correct the image surface curvature particularly on the short focal length side.

Having described the lens configuration, the focusing method will be described below.

The focusing method according to the present invention uses the first lens group of the first lens group.
The lens group and the first R lens group are moved separately, and a stop is provided between the first F lens group and the first R lens group.

By providing an aperture between the first F and first R lens groups, an increase in the amount of peripheral light when the aperture is stopped can be expected.

In addition, if the first lens group is moved toward the object side while increasing the distance between the first F and first R lens groups, fluctuations in astigmatism and field curvature from infinity to a short distance can be suppressed.

The condition (11) is a condition relating to movement of the first F and first R lens units during focusing.
When the amount of movement of the R lens unit approaches, the focusing becomes closer to the entire first lens unit, and it becomes difficult to correct astigmatism and curvature of field. When the lower limit is exceeded, the first R lens unit moves to the image side. As a result, the image is curved, and the curvature of the image surface becomes excessive due to excessive correction. At this time, if the stop and the first R lens group are fixed, it is mechanically easy to manufacture.

FIGS. 3 and 9 show the cases where the first and second embodiments are moved only by focusing on the first F lens group, respectively, and FIG. 5 shows the first and the first R lens groups of the first embodiment moved by 1: 0.3. This is the case when it is performed.

"Examples" Hereinafter, Examples 1 and 2 of the present invention will be described. Where f
Focal length, omega denotes a half angle, f _B designates the back focal distance, r is the radius of curvature of each lens surface, d is the lens thickness or spacing between adjacent lens surfaces, N is the refractive index of the d-line of each lens, [nu each lens Is the Abbe number of Α ₄ , α ₅ , α ₈ are the fourth order, 6
These are the eighth and eighth order aspherical coefficients.

The following table shows values corresponding to the conditional expressions in the above embodiments.

Conditional expression EX.1 EX.2 (1) -0.55 -0.53 (2) 0.197 0.217 (3) 1.50 1.49 (4) 0.069 0.070 (5) -1.05 -1.10 (6) 0.74 0.69 (7) -7.7 -6.2 ( 8) 0.59 0.70 (9) -5.2 -6.4 (10) 1.820 1.817

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens system configuration when an infinite object distance on the short focus side according to the first embodiment of the present invention, and FIG. 2 is a diagram illustrating various aberrations at that time. FIG. 3 is a lens system configuration diagram when the distance between object images is 1 m when only the first F lens group is moved and focused in the first embodiment, and FIG. 4 is a diagram illustrating various aberrations at that time. FIG. 5 shows that the first F and first R lens groups in Example 1 are 1: 0.3
1m distance between objects when focusing by moving at the ratio of
FIG. 6 is a diagram of various aberrations at that time. FIG. 7 is a lens system configuration diagram when the infinite object distance on the short focal length side according to the second embodiment of the present invention, and FIG. 8 is a diagram illustrating various aberrations at that time. FIG. 9 is a diagram illustrating a lens system configuration when the distance between object images is 1 m when only the first F lens group is moved and focused in the second embodiment, and FIG. 10 is a diagram illustrating various aberrations at that time. FIG. 11 is a lens system configuration diagram when the distance between object images is 1 m when the entire first lens unit is moved by focusing in Example 1, and FIG. 12 is a diagram illustrating various aberrations at that time. FIG. 13 is a diagram showing a lens system configuration when the entire first lens group is moved by focusing in Example 2 and the object image distance is 1 m, and FIG. 14 is a diagram showing various aberrations at that time. A denotes an aperture, and in FIGS. 2, 4, 6, 8, 10, 12, and 14, various aberration diagrams
(A) shows the state on the short focal side, (b) shows the state on the intermediate side, and (c) shows the state on the long focal side.

Claims (11)

(57) [Claims] 1. A lens system comprising a first lens unit having a positive focal length and a second lens unit having a negative focal length in order from the object side, wherein the distance between the first and second lens units is changed. In the zoom lens that performs magnification, the first lens group includes, from the object side, a first F lens group having a positive focal length, and a stop disposed behind the first F lens group.
The first lens of the first F lens group is a negative lens, and (1) −8.8 <f _1G / f ₁ <−0.1 (2) 0.05 <f _1G / f _1R <0.35 _{(3) 1.2 <f S /} f 1G <1.7 (4) 0.03 <d 1F~1R / f S <0.15 However f _1G focal length f ₁ of the first lens group: the focal point of the first lens distance f _1R: No. Focal length of 1R lens group f _S : Focal length of the whole system on the short focal length side d 1F _{~ 1R} : Comprehensive wide angle characterized by satisfying various conditions of 1F and 1R distance between infinity object distance Zoom lens for compact cameras. 2. The lens system according to claim 1, wherein the first F lens group includes, from the object side, a 1a lens group including at least three negative lenses (first and second lenses) and a positive lens; It consists of a first 1b lens group having a large positive power, and _{(5) -1.5 <f 1G /} f 1,2 <-0.8 (6) 0.6 <f 1G / f 1b <0.9 However f _{1, 2:} first And a focal length _f1b : a focal length of the first lens unit. 3. The first lens unit according to claim 2, wherein the first lens group includes a first lens of a negative lens having a concave curvature on the rear surface side from the object side and a second lens of a negative lens having a concave curvature on the object side surface. A zoom lens for a compact camera having a wide angle, comprising a positive lens whose object side is convex. 4. A zoom lens for a wide-angle compact camera according to claim 2, wherein the first lens group comprises a biconvex positive lens having a diverging cemented surface and a negative meniscus lens. 5. The lens system according to claim 2, wherein: (7) −20 <ΔI _1a <0 where ΔI _1a is an amount of change of a third-order spherical aberration coefficient due to an aspheric surface in the first lens group. A wide-angle zoom lens for a compact camera, comprising at least one aspherical surface having a divergent aspherical amount with respect to a paraxial radius of curvature satisfying a condition. 6. A first lens group having a positive focal length and a second lens group having a negative focal length are arranged in order from the object side, and the distance between the first and second lens groups is changed. In the zoom lens that performs magnification, the first lens group includes, from the object side, a first F lens group having a positive focal length, and a stop disposed behind the first F lens group.
The first R lens group is made of plastic, and consists of only one positive meniscus lens having a convex surface facing the image surface side, and has a divergent aspherical amount with respect to the paraxial radius of curvature. (2) 0.05 <f _1G / f _1R <0.35 (8) (m _2L −m _1R · m _2L ) ² <0.8 (9) −20 <ΔI _1R <0 where m _2L : lateral magnification of the second lens group on the long focal length side m _1R : lateral magnification of the first R lens group ΔI _1R : change amount of the third order spherical aberration coefficient due to the aspheric surface in the first R lens group A wide-angle zoom lens for compact cameras that satisfies the conditions. 7. The first R lens group according to claim 1, wherein (9) -20 <ΔI _1R <0, where ΔI _1R is a condition of a change amount of a third-order spherical aberration coefficient due to an aspheric surface in the first R lens group. A zoom lens for a wide-angle compact camera, comprising at least one aspheric surface having a divergent aspheric amount with respect to a paraxial radius of curvature. 8. The lens system according to claim 1, wherein the second lens group includes, from the object side, a positive meniscus lens having a convex surface facing the image side, and two negative lenses having a concave surface facing the object side. and Here, ▲ ▼: d-li of two negative lenses in the second lens group
A wide-angle zoom lens for compact cameras that satisfies the condition of the average value of the refractive index of ne. 9. A lens system comprising: a first lens group having a positive focal length and a second lens group having a negative focal length in order from the object side, wherein the distance between the first and second lens groups is varied. In the zoom lens that performs magnification, the first lens group includes, from the object side, a first F lens group having a positive focal length, and a stop disposed behind the first F lens group.
A first lens group of the first F lens group is a negative lens, and (1) −0.8 <f _1G / f ₁ <−0.1 (2) 0.05 <f _1G / f _1R <0.35 (11 0 ≦ X _1R / X _1F <0.7 where X _1R : the amount of movement of the first R lens at the time of focusing X _1F : the amount of movement of the first F lens group at the time of focusing A zoom lens for a wide-angle compact camera, wherein at least the first F lens group is moved to the object side while increasing the distance between the first F lens group and the first R lens group. 10. The method according to claim 6, further comprising: (11) satisfying a condition of 0 ≦ X _1R / X _1F <0.7, and increasing a distance between the first F lens group and the first R lens group during focusing. A wide-angle zoom lens for a compact camera, wherein at least the first F lens group is moved to the object side. 11. A zoom lens for a wide-angle compact camera according to claim 9, wherein the aperture and the first R lens group are fixed during focusing.