JP2000089115A - Two-group zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized zoom lens capable of dealing with the zoom ratio >= about 2.5 and whose whole length is shortened when the lens is collapsed. SOLUTION: As for the two-group zoom lens which is moved to an object side at varying the power from a wide angle end to a telephoto end so that a distance between a 1st positive lens group; L1, L2 and L3 and a 2nd negative lens group; L4 and L5 may be reduced, the 1st lens group is constituted of a negative lens group and a positive lens group, and the negative lens group is constituted of a negative lens whose curvature on an image side is more stronger, and the positive lens group is constituted of a negative lens and a positive lens, and the 2nd lens group is constituted of at least one positive lens and one negative lens, and the following conditional expressions are satisfied; (1) 0.2<|f1N/D|<2.1, (2) 5<νdR-νdF<20, provided that f1N denotes the focal distance of the negative lens among the 1st lens group, D denotes the diagonal length of a photographic screen, νdR denotes Abbe's number of the negative lens positioned closest to the image side, and νdF denotes Abbe's number of the negative lens positioned closest to the object side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-unit zoom lens used for imaging, for example, a two-unit zoom lens used for a lens shutter camera or the like.

[0002]

2. Description of the Related Art In recent years, as a lens shutter camera, a camera provided with a zoom lens has been generally used. In particular, a camera having a zoom ratio exceeding 2 times has been desired. However, even if the zoom ratio of the photographic lens is high, it is desirable that the lens be small and lightweight, so by reducing the lens diameter and narrowing the air gap between adjacent zoom groups, The storage of the lens into the lens, that is, the shortening of the total length of the lens at the time of collapsing, is attempted. Further, shortening of the entire length of the lens at the time of collapsing is an important issue for the development of a lens system. Generally, in order to achieve miniaturization, a method of reducing the number of lenses by using an aspherical lens in a zoom lens is used.

[0003] As a zoom lens which achieves a zoom magnification ratio of 2.5 or more by reducing the size using an aspherical lens,
For example, there is a zoom lens disclosed in JP-A-8-304701.

Further, in order to manufacture an aspherical lens at low cost and to reduce the weight, an aspherical lens is also manufactured from plastic. As described above, as a zoom lens which achieves a zoom magnification ratio of 2 or more by measuring the size and weight with a plastic aspherical lens, for example, JP-A-6-130298, JP-A-7-261078, JP-A-9-152549, JP-A-9-56
There is a zoom lens disclosed in Japanese Patent Application Publication No. 27-27.

[0005]

However, when the aspherical lens is a plastic lens, there is a problem that the shape and the refractive index of the plastic lens change due to a change in temperature or humidity. That is, the focal length changes due to a change in the environment, and this causes a shift in the focal plane of the lens system. This problem becomes more apparent as the refractive power of the plastic lens increases and the number of plastic lenses increases.

In the zoom lenses described in JP-A-6-130298 and JP-A-9-5627, the refractive power of the plastic lens is reduced to reduce the influence of changes in temperature, humidity, and the like on the plastic lens. But,
At the telephoto end, the focal plane changes greatly, and the effects of changes in temperature, humidity, and the like cannot be completely eliminated. Also,
Since a plurality of plastic lenses are used, the lens is easily affected by temperature and humidity.

[0007] In the zoom lens described in Japanese Patent Application Laid-Open No. 7-261078, the plastic lens has a strong refractive power, and thus is susceptible to changes in temperature and humidity.
Further, the total length of the lenses on the optical axis of each zoom lens group is relatively long, and the thickness of the camera body when retracted is large.

In the zoom lens described in Japanese Patent Application Laid-Open No. 9-152549, the influence of changes in temperature, humidity, and the like on the plastic lens is reduced by reducing the refractive power of the plastic lens. The change is large, and the effects of changes in temperature, humidity, and the like cannot be completely eliminated. Further, the total length of the lenses on the optical axis of each zoom lens group is relatively long, and the thickness of the camera body when retracted is large.

On the other hand, Japanese Patent Application Laid-Open No. 8-304 discloses a zoom magnification ratio of 2.5 or more without using a plastic lens.
In the zoom lens described in Japanese Patent Publication No. 701, the total number of lenses in each lens group is large, so that the entire length of the lens on the optical axis is long, and the thickness of the camera body when collapsed is large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a small zoom lens which can cope with a zoom magnification ratio of about 2.5 times or more and can shorten the entire length of the lens when retracted. Is to provide a lens. Another object of the present invention is to provide a zoom lens in which the effect of temperature and humidity is very small and the size and weight can be reduced by effectively arranging a lens using a plastic material.

[0011]

In order to achieve the above object, a zoom lens according to the present invention employs a configuration described in detail below. (1) The first configuration according to the present invention includes, in order from the object side, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, and is arranged from the wide-angle end to the telephoto end. In a two-unit zoom lens in which each lens unit is moved to the object side so that the distance between the first lens unit and the second lens unit is reduced at the time of zooming, the first lens unit is arranged in order from the object side. , A negative lens group, and a positive lens group. The negative lens group in the first lens group is composed of a negative lens having a stronger curvature on the image side, and the positive lens group in the first lens group is negative. The second lens group includes a lens and a positive lens, and the second lens group includes at least one positive lens and a negative lens, and satisfies the following conditional expression. 0.2 <| f _1N /D|<2.1 (1) 5 <ν _d R−ν _d F <20 (2) where f _{1N is} the focal length of the negative lens in the first lens group,
D: diagonal length of the photographing screen, ν _d R: Abbe number of the negative lens closest to the image, ν _d F: Abbe number of the negative lens closest to the object.

In a first configuration of the present invention, the first lens group includes, in order from the object side, a lens group having a negative refractive power;
By using a retrofocus type lens unit having a positive refractive power, the principal point of the first lens unit can be positioned closer to the image plane, and a sufficient back focus can be ensured at the wide-angle end. Satisfactorily can be corrected.

The positive lens group of the first lens group is composed of a negative lens and a positive lens. When the negative lens group of the first lens group is composed of one negative lens, the negative lens group is used alone. Taking into account the inability to correct the chromatic aberration of
With this configuration, it is possible to satisfactorily correct chromatic aberration in the first lens group. Similarly, by configuring the second lens group with at least one positive lens and one negative lens,
Chromatic aberration can be favorably corrected in the lens group.

The reason why the negative lens unit of the first lens unit is constituted by a negative lens having a stronger curvature on the object side will be described below. In the case of a zoom system having a two-group configuration as in the present invention, good aberration performance cannot be obtained in the entire system at the time of zooming unless various aberrations are properly corrected by each lens group alone. In particular, since the first lens group has a positive refractive power, in a configuration like the present invention, the refractive power of the positive lens group is relatively strong. Therefore, the amount of negative spherical aberration and positive coma generated in the positive lens group increases.

Therefore, in order to satisfactorily correct various aberrations with respect to the positive lens unit, the negative lens unit disposed on the object side is a negative lens having a stronger curvature on the image side. That is,
By arranging a lens surface with a concave surface with a stronger curvature on the image side, a positive spherical aberration and a negative coma are generated on the surface, and the spherical aberration and the coma in the first lens group are relatively reduced. To cancel.

Conditional expression (1) is a condition for achieving a balance between miniaturization of the zoom lens and aberration performance, and defines the focal length of the negative lens in the first lens group.
Here, the negative lens in the first lens group may be a negative lens included in any of the positive lens group and the negative lens group, and when a plurality of negative lenses are included, each negative lens has a conditional expression ( 1) is satisfied.

When the refractive power of the negative lens in the first lens group is increased so as to satisfy the conditional expression (1), the refractive power of the positive lens group is also increased, and as a result, the refractive power of the negative lens in the first lens group is increased. . Then, the distance between the principal points of the negative lens unit and the positive lens unit is reduced, and the overall length of the first lens unit on the optical axis can be reduced. This leads to securing a sufficient back focus with the first lens group, so that the second lens group can be arranged closer to the object side, and the back focus in the entire system can be lengthened. Further, since the light flux passing through the outermost of the second lens group is reduced, the lens diameter of the second lens group can be reduced, and the lens frame diameter can be reduced.

As described above, by satisfying the conditional expression (1), the total length of the lens on the optical axis at the time of collapsing can be reduced, and the diameter of the lens barrel can be reduced. Therefore, the optical apparatus using the zoom lens according to the present invention. Can be reduced in size.

If the lower limit of conditional expression (1) is exceeded, it is advantageous for miniaturization, but negative spherical aberration and positive coma are largely generated in the first lens unit, so that the whole system is good. It becomes difficult to obtain a high aberration performance. Conversely, if the upper limit of conditional expression (1) is exceeded, it will be difficult to reduce the size of the optical device using the zoom lens according to the present invention.

Conditional expression (2) is a condition for favorably correcting lateral chromatic aberration in the entire zoom lens system. Focusing on the negative lenses of the first and second lens groups, with respect to axial chromatic aberration, each lens group generates the same negative chromatic aberration, but with respect to lateral chromatic aberration, each lens group cancels out each other. Chromatic aberration is generated to match. Therefore, the Abbe number of the outermost negative lens is defined by the conditional expression (2).

If the lower limit of the conditional expression (2) is exceeded, the chromatic aberration of magnification at the wide-angle end becomes excessively corrected, and the chromatic aberration of magnification at the telephoto end is large. It will not be taken. Conversely, if the upper limit of conditional expression (2) is exceeded, lateral chromatic aberration at the telephoto end will be overcorrected, and lateral chromatic aberration at the wide-angle end will be greatly increased. It will not be taken. (2) Further, another configuration according to the present invention is characterized in that, in the first configuration of the present invention, all lenses are formed of glass lenses. In the first configuration of the present invention, each lens group is composed of a lens having relatively high refractive power. Therefore, it is desirable that all lenses are formed of glass lenses so as not to be affected by temperature and humidity. (3) Still another configuration according to the present invention is characterized in that, in the first configuration of the present invention, the positive lens group in the first lens group includes a cemented lens.

In the present invention, which aims at miniaturization while achieving a high zoom ratio, it is necessary to increase the refractive power of each lens unit, and the refractive power of the negative lens in the negative second lens unit is relatively high. Becomes stronger. For this reason, strong positive chromatic aberration of magnification occurs. However, if the positive lens group of the first lens group is a cemented lens of a negative lens and a positive lens, the occurrence of positive chromatic aberration of magnification in the first lens group is reduced. It is possible to reduce the size and to suppress the occurrence of positive lateral chromatic aberration in the entire zoom lens system. (4) The second configuration according to the present invention comprises, in order from the object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power, from the wide-angle end to the telephoto end. In a two-unit zoom lens in which each lens unit is moved to the object side so that the distance between the first lens unit and the second lens unit is reduced at the time of zooming, the first lens unit is arranged in order from the object side. , A negative lens group, and a positive lens group, wherein the negative lens group in the first lens group is composed of a negative lens (L ₁ ), and the positive lens group in the first lens group has at least one lens. The second lens group includes a negative lens and a positive lens, and the second lens group includes at least one positive lens and a negative lens, and satisfies the following conditional expression. 0.2 <| f _1N /D|<2.1 (1) 5 <ν _d R−ν _d F <20 (2) −5.0 <(R ₂ + R ₁ ) / (R ₂ −R ₁ ) <−0.9 (3) where f _{1N is} the focal length of the negative lens in the first lens group,
D: diagonal length of the shooting screen, ν _d R: Abbe number of the negative lens closest to the image side, ν _d F: Abbe number of the negative lens closest to the object side, R ₁ : object of the negative lens (L ₁ ) Radius of curvature of the side,
R ₂ : radius of curvature of the negative lens (L ₁ ) on the image side.

In the second configuration of the present invention, similarly to the first configuration, the first lens group is divided into a lens group having a negative refractive power and a retrograde lens group having a positive refractive power in order from the object side. By using the focus type, it is possible to make the principal point position of the first lens group closer to the image plane, to secure a sufficient back focus at the wide-angle end, and to satisfactorily correct positive distortion. It is possible.

Since conditional expressions (1) and (2) are satisfied in the same manner as the first configuration, the size of the optical device using the zoom lens according to the present invention can be reduced, and excellent aberration correction can be achieved. I have.

Conditional expression (3) is a shaping factor of the negative lens (L ₁ ) of the negative lens unit in the first lens unit.
This defines the shape of the negative lens (L ₁ ). Conditional expression (3) specifies that the image-side surface of the negative lens (L ₁ ) has a larger curvature than the object-side surface. The amount of generation of spherical aberration and negative coma is increased so as to cancel the negative spherical aberration and positive coma generated in the positive lens unit.

If the upper limit of conditional expression (3) is exceeded, the amount of positive spherical aberration and negative coma generated by the negative lens unit will be small, and the negative spherical aberration and positive coma generated by the positive lens unit will be reduced. It cannot be countered. If the lower limit of conditional expression (3) is exceeded, the amount of positive spherical aberration and negative coma generated by the negative lens unit will increase, and the first lens unit will have positive spherical aberration,
Negative coma will remain.

From the viewpoint of chromatic aberration correction in the entire system, it is desirable that chromatic aberration is corrected to some extent in each zoom lens group. Since the negative lens group of the first lens group is composed of one negative lens, chromatic aberration cannot be corrected by the negative lens group alone. However, the positive lens group of the first lens group has at least one negative lens and one positive lens. Since it is constituted by a lens, it is possible to satisfactorily correct chromatic aberration alone in the first lens group. Further, since the second lens group includes at least one positive lens and one negative lens, chromatic aberration can be favorably corrected independently in the second lens group. (5) Further, according to another configuration of the present invention, in all the above-described configurations of the present invention, an aspheric surface is used for at least one surface of the negative lens unit in the first lens unit.

While achieving a magnification ratio of more than 2.5 times,
Reducing the overall length requires increasing the refractive power of each lens group. In this case, since the first lens group is a positive lens group, the refractive power of the positive lens group becomes relatively strong within the group, and the amount of negative spherical aberration and positive coma generated here is large. turn into. Further, since the refractive power of the negative lens group is not so strong as that of the positive lens group, it becomes difficult to relatively correct the refractive power within the group.

Therefore, in this configuration, by using an aspheric surface for at least one surface of the negative lens unit of the first lens unit, the amount of generation of positive spherical aberration and negative coma of the negative lens unit is increased. , And has a function of canceling out negative spherical aberration and positive coma of the positive lens unit. (6) Further, in another configuration according to the present invention, in any of the above-described configurations of the present invention, an aspherical layer obtained by coating and curing a transparent resin layer on one surface of the negative lens in the first lens group is provided. It is characterized by having.

In all of the above-described configurations of the present invention, the negative lens in the first lens unit satisfies the conditional expression (1) and has a certain refractive power. Therefore, when an aspheric surface is arranged on the negative lens in the first lens group, it is desirable to use a glass mold lens in order to prevent the lens from being adversely affected by temperature and humidity, but the glass mold lens is expensive. Costly.

Here, if a so-called hybrid lens is used as an aspherical lens in which a thin transparent resin layer is applied to a glass spherical lens and a cured aspherical layer is adhered to the glass spherical lens as in this configuration, it is relatively inexpensive. Can be manufactured. Besides,
The hybrid lens allows the resin layer to be formed very thin, and one side is in close contact with the glass lens.
It also has the effect of being hardly affected by temperature and humidity as compared with plastic aspheric lenses. (7) Still another configuration according to the invention is characterized in that, in the configuration of the above (6), the following conditional expression (5) is satisfied. 2.0 <| f _H | / D (5) where f _{H is} the paraxial focal length of the hybrid lens resin layer, and D is the diagonal length of the photographing screen.

By satisfying conditional expression (5), the resin layer becomes substantially uniform in thickness with respect to the glass surface that is in close contact, and the effects of temperature and humidity can be minimized. If the lower limit of conditional expression (5) is exceeded, the refractive power of the resin layer becomes strong, so that the influence of temperature and humidity increases. (8) The third configuration according to the present invention includes, in order from the object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power, and is arranged from the wide-angle end to the telephoto end. In a two-unit zoom lens in which each lens unit is moved to the object side so that the distance between the first lens unit and the second lens unit is reduced at the time of zooming, the first lens unit is arranged in order from the object side. , A negative lens group, and a positive lens group. The negative lens group in the first lens group includes, in order from the object side, a negative lens having a stronger curvature on the object side and a meniscus lens convex on the object side. The positive lens group in the first lens group includes at least one negative lens and a positive lens, and the second lens group includes at least one positive lens and a negative lens. Is satisfied. 0.2 <| f _1F /D|<2.1 (4) 5 <ν _d R−ν _d F <20 (2) where f _{1F is} the focal length of the negative lens group in the first lens group,
D: diagonal length of the photographing screen, ν _d R: Abbe number of the negative lens closest to the image, ν _d F: Abbe number of the negative lens closest to the object.

In a third configuration of the present invention, the first lens unit is a lens unit having a negative refractive power in order from the object side;
By using a retrofocus type lens unit having a positive refractive power, the principal point of the first lens unit can be positioned closer to the image plane, and a sufficient back focus can be ensured at the wide-angle end. Satisfactorily can be corrected.

Further, the positive lens group of the first lens group has at least one negative lens and a positive lens.
This takes into account that the chromatic aberration cannot be corrected by the negative lens group alone when the negative lens group of the lens group is composed of only the negative lens. With this configuration, the chromatic aberration in the first lens group is favorably corrected. be able to. Similarly, by configuring the second lens group with at least one positive lens and one negative lens, chromatic aberration can be favorably corrected in the second lens group.

Here, the reason why the negative lens unit of the first lens unit is composed of, in order from the object side, a negative lens having a stronger curvature on the object side and a meniscus lens convex on the object side will be described below. In the case of a two-group zoom system as in the present invention,
If various aberrations are not properly corrected by each lens group alone,
At the time of zooming, good aberration performance cannot be obtained in the entire system.
In particular, since the first lens group has a positive refractive power, in a configuration like the present invention, the refractive power of the positive lens group is relatively strong. Therefore, in this positive lens group, negative spherical aberration,
The amount of generation of astigmatism increases. Further, when the zoom ratio is about 2.5 times or more as in the zoom lens of the present invention, the amount of astigmatism generated particularly in the intermediate zoom state increases, and the imaging performance at the image peripheral portion is significantly reduced. Resulting in.
Such a problem becomes more prominent when the total length is shortened by increasing the refractive power of the group.

In order to satisfactorily correct various aberrations with respect to the positive lens group, first, regarding spherical aberration and coma aberration, a meniscus lens convex on the object side is provided in the negative lens group of the first lens group. In addition, a large amount of positive spherical aberration and negative coma are generated, and the amount of generated aberration is reduced as a whole by the canceling action. Regarding negative astigmatism generated in the positive lens group, by providing a negative lens having a shape whose curvature on the object side is stronger than that on the image side in the negative lens group of the first lens group, positive astigmatism can be obtained. Are generated, and the amount of aberration as a whole is reduced by the canceling action.

Further, regarding the arrangement of a negative lens having a stronger curvature on the object side and a meniscus lens convex on the object side,
A lens that generates large astigmatism is located at a position where off-axis rays are high, that is, disposed closer to the object side, and a lens with a large amount of spherical aberration and coma aberration has a relatively high on-axis ray, that is, It is desirable to adopt a configuration that is arranged closer to the image. With such a configuration, the first lens group has the most efficient arrangement for aberration correction.

Conditional expression (4) defines conditions for miniaturizing an optical apparatus using the zoom lens according to the present invention, and the focal length of the negative lens group in the first lens group is conditional. By satisfying (4), the overall length of the first lens unit on the optical axis can be reduced.

When the refractive power of the negative lens group in the first lens group is increased so as to satisfy the conditional expression (4), the refractive power of the positive lens group is also increased. As a result, the refractive power of the negative lens in the first lens group is increased. Strengthen. Then, the distance between the principal points of the negative lens unit and the positive lens unit is reduced, and the overall length of the first lens unit on the optical axis can be reduced. This means
Since a sufficient back focus can be ensured by the first lens group, the second lens group can be disposed closer to the object side, and the back focus in the entire system can be lengthened. Further, since the light flux passing through the outermost of the second lens group is reduced, the lens diameter of the second lens group can be reduced, and the lens frame diameter can be reduced.

As described above, by satisfying conditional expression (4), the total length of the lens on the optical axis at the time of collapsing can be reduced, and the diameter of the lens barrel can be reduced. Therefore, the optical apparatus using the zoom lens according to the present invention. Can be reduced in size.

If the lower limit of conditional expression (4) is exceeded, it is advantageous for miniaturization, but negative spherical aberration and positive coma are largely generated in the first lens unit, so that the whole system is good. It becomes difficult to obtain a high aberration performance. Conversely, if the upper limit of conditional expression (4) is exceeded, it will be difficult to reduce the size of the optical device using the zoom lens according to the present invention.

By satisfying conditional expression (2), the same function and effect as those of the first embodiment of the present invention are obtained, and excellent aberration performance is achieved. (9) Still another configuration according to the invention is characterized in that, in all of the above-described configurations of the invention, an aspheric surface is used for at least one surface of the second lens group.

Since the second lens group according to the present invention has a negative refractive power as a whole, if the refractive power of the group is increased to shorten the entire length of the lens, the refractive power of the negative lens is relatively large within the group. Becomes stronger. Therefore, in the negative lens in the second lens group, the amount of positive spherical aberration generated particularly at the telephoto end increases. Therefore, in the present configuration, by using an aspherical surface for at least one surface in the second lens group, a negative spherical aberration is generated, and an effect of relatively canceling this is provided. As a result, the overall length of the lens can be easily reduced, and the size of the camera can be reduced.

Further, since the lenses of the second lens group have a certain degree of refractive power in order to shorten the entire length of the lens, the aspherical surface in the second lens group of the present configuration has a glass mold lens or the aforementioned It is desirable to use an inexpensive hybrid lens. According to this structure, an effect of being hardly affected by temperature and humidity can be obtained as compared with the case where a plastic aspherical lens is used. (10) Further, in another configuration according to the present invention, in all of the above-described configurations of the present invention, in the second lens group, a transparent resin layer is coated and cured, and an aspherical layer is provided. I do.

If the hybrid lens is used as an aspherical lens, it can be manufactured relatively inexpensively. In addition, the hybrid lens allows the resin layer to be formed very thin, and has one side that is in close contact with the glass lens, so it is less affected by temperature and humidity than plastic aspherical lenses. Play.

When the aspherical surface is composed of a hybrid lens as in the present configuration, it is desirable that the above-mentioned conditional expression (5) is satisfied. By doing so, the resin layer becomes substantially uniform in thickness with respect to the glass surface that is in close contact, and the influence of changes in temperature and humidity can be minimized. (11) The fourth configuration according to the present invention includes, in order from the object side, a first lens group having a positive refractive power and a second lens group having a negative refractive power, and is arranged from the wide-angle end to the telephoto end. In a two-unit zoom lens system in which each lens unit is moved to the object side so that the distance between the first lens unit and the second lens unit is reduced during zooming, at least one of the first lens unit The second lens group has at least one negative lens and a positive lens, and a transparent resin layer is applied to one surface of the negative lens in the first lens group. It has a cured aspherical layer.

In the fourth configuration of the present invention, each zoom lens group is composed of at least one positive lens and one negative lens, so that each zoom lens group can correct chromatic aberration to some extent. This is good for good chromatic aberration correction in the entire system.

In order to shorten the overall length while achieving a zoom ratio exceeding 2.5, the refractive power of each lens unit must be increased to some extent. In that case, since the first lens group has a positive refractive power, the refractive power of the positive lens becomes relatively strong within the group, and negative spherical aberration generated here,
The amount of generation of positive coma becomes large. In addition, since the refractive power of the negative lens is not as strong as that of the positive lens, it becomes difficult to relatively correct the refractive power within the group.

In the fourth structure of the present invention, the amount of positive spherical aberration and negative coma generated by the negative lens is increased by using an aspheric surface for at least one surface of the negative lens in the first lens unit. Thus, it has the function of canceling out the negative spherical aberration and the positive coma of the positive lens.

Further, since the hybrid lens is used as an aspherical lens, it can be manufactured relatively inexpensively. In addition, the hybrid lens allows the resin layer to be formed very thin, and has one side that is in close contact with the glass lens, so it is less affected by temperature and humidity than plastic aspherical lenses. Play. (12) Still another configuration according to the invention is characterized in that, in the fourth configuration of the invention, at least one surface in the second lens group is an aspheric surface.

Since the second lens group of the present invention is a negative lens group as a whole, if the refractive power of the group is increased to shorten the entire length of the lens, the refractive power of the negative lens becomes relatively high within the group. . Therefore, the negative lens in the second lens group
Particularly, the amount of positive spherical aberration generated at the telephoto end increases. Therefore, by using an aspheric surface for at least one surface in the second lens group, a negative spherical aberration is generated, and an effect of relatively canceling this is provided. As a result, the overall length of the lens can be easily reduced, and the size of the camera can be reduced.

Here, as the negative lens having the aspherical surface, for example, in order to prevent the influence of temperature and humidity,
A glass mold lens may be used. (13) Still another configuration according to the invention is characterized in that, in the configuration of the above (12), the aspheric surface is formed by an aspherical layer obtained by applying and curing a transparent resin layer.

Since a glass mold lens is known to be expensive, in this construction, a thin transparent resin layer is applied to a glass spherical lens and cured as a means for manufacturing an aspherical lens at relatively low cost. A so-called hybrid lens having an aspherical layer adhered thereto is used.

The hybrid lens can be formed with a very thin resin layer. One side of the hybrid lens is in close contact with the glass lens.
Hardly affected by humidity. (14) Further, other configurations according to the present invention are as described in (11) and (1) above.
2) and (13), characterized by satisfying conditional expression (5).

If conditional expression (5) is satisfied, the resin layer of the hybrid lens has a substantially uniform thickness with respect to the glass surface in close contact with the hybrid lens, and the influence of changes in temperature and humidity can be minimized.

As described above, the present invention has been described. With respect to the conditional expression (1), the following conditional expressions (1-1) and (1-2)
Is more preferably satisfied. 0.2 <| f _1N /D|<1.9 (1-1) 0.2 <| f _1N /D|<1.7 (1-2) Also, regarding the conditional expression (2), the following condition is satisfied. Equation (2-
It is more preferable to satisfy 1) and (2-2). 5 <ν _d R−ν _d F <17 (2-1) 5 <ν _d R−ν _d F <14 (2-2) Further, regarding the conditional expression (3), the following conditional expression (3-
It is more preferable to satisfy 1) and (3-2). _{-3.8 <(R 2 + R 1} ) / (R 2 -R 1) <- 0.9 (3-1) -2.3 <(R 2 + R 1) / (R 2 -R 1) <- 0.9 (3-2) Also, regarding the conditional expression (4), the following conditional expression (4-
It is more preferable to satisfy 1) and (4-2). _{0.2 <| f 1F /D|<1.8 (4-1} ) 0.2 <| f 1F /D|<1.5 (4-2)

[0057]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 4, which are specific embodiments of the present invention, will be described below with reference to the drawings. 1 to 4 show the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) of the two-unit zoom lenses according to Examples 1 to 4.
FIG. 3 is a diagram showing a lens cross-sectional view of FIG. Embodiment 1 Embodiment 1 corresponds to the first and second configurations of the present invention. In order from the object side, a negative lens group (a negative meniscus lens L ₁ having a convex surface facing the object side) and a positive lens are arranged in order from the object side. lens first lens group is configured from a (negative meniscus lens L ₂ having a convex surface facing the object side biconvex positive lens L ₃ of the cemented lens), an aperture stop, and a positive meniscus lens having a concave surface facing the object (L ₄ ) and a second meniscus lens (L ₅ ) having a concave surface facing the object side.
Each lens group moves to the object side so that the lens group interval decreases.

In focusing, it is desirable that the first lens unit be moved toward the object side. An aspheric surface is the image side of the lens L _1, is used on the surface of the object side of the lens L _4, the lens L _1, lens L ₄ is a glass molded aspherical lens. [Example 2] Example 2 is intended to correspond to the first, second configuration of the present invention, in order from the object side, a negative lens group (negative meniscus lens L ₁ having a convex surface on the object side) positive lens first lens group is configured from a (negative meniscus lens L ₂ having a convex surface facing the object side biconvex positive lens L ₃ of the cemented lens), an aperture stop, and a positive meniscus lens having a concave surface facing the object is constituted by the second lens group composed of a negative meniscus lens L ₅ Metropolitan having a concave surface facing the L ₄ and object side,
At the time of zooming from the wide-angle end to the telephoto end, each lens unit moves toward the object side such that the distance between the first and second lens units decreases. In focusing, it is desirable that the first lens group be moved toward the object side.

[0059] An aspheric surface is the image side of the lens L _1, lens L ₄
Is used for the surface on the object side, a lens L ₁ is a glass molded aspherical lens, lens L ₄ is a hybrid aspheric lens is brought into close contact with the resin layer of the aspherical surface. A hybrid lens is a lens in which a thin transparent resin layer is applied to a glass spherical lens and then hardened with an aspherical layer.

When a hybrid lens is used, unlike an expensive glass molded lens, it can be manufactured relatively inexpensively, and since one side of the transparent resin layer is in close contact with the glass lens, a lens using a plastic material is used. However, the effects of temperature and humidity can be greatly reduced. [Embodiment 3] Embodiment 3 corresponds to the first, second, and fourth configurations of the present invention, and includes, in order from the object side, a negative lens group (a negative meniscus lens L ₁ having a convex surface facing the object side). ) And a positive lens group (negative meniscus lens L having a convex surface facing the object side)
₂ a biconvex positive lens L ₃ of the cemented lens) because the first lens group is configured, an aperture stop, and a negative meniscus lens with its concave surface facing the positive meniscus lens L ₄ and the object side with a concave surface facing the object side L ₅ when the zooming is performed from the wide-angle end to the telephoto end.
Each lens group moves to the object side so that the lens group interval decreases. In focusing, it is desirable that the first lens group be moved toward the object side.

[0061] An aspheric surface is the image side of the lens L _1, lens L ₄
The lens L ₁ and the lens L ₄ are hybrid aspherical lenses having an aspherical resin layer adhered thereto. Therefore, the lens system can be manufactured relatively inexpensively, and is a lens system made of a plastic material, but has very little influence of temperature and humidity. [Example 4] This example is intended to correspond to a third aspect of the present invention, in order from the object side, a negative meniscus lens L ₁ and the convex surface on the object side with a concave surface facing the negative lens group (object side A first lens group including a meniscus lens L _{2 having} no refractive power and a positive lens group (a cemented lens of a negative meniscus lens L ₃ having a convex surface facing the object side and a biconvex positive lens L ₄ ), and an aperture aperture, and is constructed by the second lens group composed of a negative meniscus lens L ₆ Metropolitan having a concave surface facing the positive meniscus lens L ₅ and the object side with a concave surface facing the object side,
At the time of zooming from the wide-angle end to the telephoto end, each lens unit moves toward the object side such that the distance between the first and second lens units decreases.

It is desirable to extend the first lens unit toward the object side during focusing. Aspherical surface at the object side-lens L _2, is used on the surface of the object side of the lens L _4,
Lens L ₁ is no refractive power plastic aspherical lens,
Lens L ₄ is a hybrid aspheric lens is brought into close contact with the resin layer of the aspherical surface. Therefore, the lens system can be manufactured relatively inexpensively, and is a lens system made of a plastic material, but has very little influence of temperature and humidity.

The embodiments have been described above.
The aspheric shape in the embodiment is such that the traveling direction of light on the optical axis is x,
When y is the direction perpendicular to the optical axis, it is expressed by the following equation.
You. x = (y^Two/ R) / [1+ ｛1- (1 + K) (y /
r)^Two｝^1/2] + A_Foury^Four+ A₆ y⁶+ A₈y⁸+ A_Teny
^Ten Where r is the paraxial radius of curvature, K is the conic coefficient, A_Four,
A₆, A₈, A_TenIs an aspheric coefficient.

The numerical data of each of the above embodiments is shown below. f is the focal length of the entire system, F _NO is the F number, 2ω is the angle of view, and f _B is the back focus. The leftmost numeral in the table of each embodiment represents the order of the lens surface from the object side, that is, the surface number, r is the radius of curvature of the lens surface, d is the lens surface interval, the refractive index n and the Abbe number ν are d This is the value for the line. In each of the tables, an aspherical lens surface is indicated by “*” as a surface number. Note that the diagonal length D of the photographing screen is assumed to be an APS camera (30.2 × 16.7) in the first to fourth embodiments, and D = 3 in each embodiment.
4.5. [Example 1] f = 29.04 ~47.33 ~78.50 F N0 = 4.6 ~7.5 ~12.5 2ω = 61.02 ~39.96 ~24.80 f B = 9.07263 ~26.40475~55.94007 r d n ν 1 108.3950 1.5000 1.80610 40.73 2 * 31.2134 2.7200 3 63.1750 1.2000 1.72342 37.95 4 12.8510 5.4800 1.58913 61.14 5 -9.3740 0.8000 6 ∞ (aperture) 8.6000 〜4.0000-1.1000 7 * -45.2526 2.1303 1.68893 31.16 8 -23.6851 3.8345 9 -8.1819 1.3000 1.75700 47.82 10 -39.5458 (back focus) 2nd surface K = 18.7934 A ₄ = 1.7083 × 10 ^-4 A ₆ = 6.6546 × 10 ^-6 A ₈ = -2.6797 × 10 ^-7 A ₁₀ = 1.0951 × 10 ^-8 7th surface K = 0.4556 A ₄ = 1.0912 × 10 ^-4 A ₆ = 1.4962 × 10 ^-6 A ₈ = -7.5156 × 10 ^-9 A ₁₀ = 1.5500 × 10 ^-10 [Example 2] f = 29.06 to 47.36 to 78.74 F _N0 = 4.6 to 7.5 to 12.5 2ω = 61.00 _{~39.92 ~24.72 f B = 8.97909 ~26.23582~55.83008 r} d n ν 1 109.9819 1.5000 1.80610 40.73 2 * 31.3706 2.7229 3 63.3271 1.2000 1.72342 37.95 4 12.8633 5.47 81 1.58913 61.14 5 -9.3805 0.8000 6 ∞ (aperture) 8.5827 〜4.0000-1.1000 7 * -44.4226 0.2500 1.52540 51.81 8 -66.3064 1.8331 1.61293 36.99 9 -23.6902 3.8960 10 -8.0849 1.3000 1.74100 52.64 11 -38.1219 Non-spherical surface Second surface K = 14.1468 A ₄ = 1.9033 × 10 ^-4 A ₆ = 6.9992 × 10 ^-6 A ₈ = -2.6338 × 10 ^-7 A ₁₀ = 1.1120 × 10 ^-8 Surface 7 K = -22.2132 A ₄ = 1.1104 × 10 ⁻⁴ A ₆ = 2.1749 × 10 ⁻⁶ A ₈ = −9.3544 × 10 ⁻⁹ A ₁₀ = 1.2157 × 10 ⁻¹⁰ [Example 3] f = 29.00 to 47.42 to 78.68 F _N0 = 4.6 to 7.6 to 12.5 2Ω _{= 61.52 ~40.02 ~24.78 f B = 9.11641} ~26.88080~57.02632 r d n ν 1 263.9190 1.3500 1.79952 42.22 2 30.5668 0.1500 1.52540 51.81 3 * 43.0132 2.5161 4 72.4020 1.2000 1.72342 37.95 5 12.4790 5.6274 1.60311 60.64 6 -9.4997 0.8000 7 ∞ ( aperture ) 8.6357 〜4.0000-1.1000 8 * -33.3500 0.2500 1.52540 51.81 9 -44.5032 1.8000 1.61293 36.99 10 -20.6465 3.8446 11 -7.9658 1.3000 1.7 4100 52.64 12 -32.9097 (back focus) aspherical coefficients third surface _{K = 38.8850 A 4 = 3.2185 ×} 10 -4 A 6 = 1.0117 × 10 -5 A 8 = -4.2093 × 10 -7 A 10 = 1.9157 × 10 - ^8th surface K = -97.0910 A ₄ = -1.5964 × 10 ^-4 A ₆ = 1.1607 × 10 ^-5 A ₈ = -2.1807 × 10 ^-7 A ₁₀ = 2.2890 × 10 ^-9 [Example 4] f = 28.67 _{~47.20 ~78.86 F N0 = 4.6 ~7.6 ~12.7} 2ω = 62.72 ~40.44 ~24.80 f B = 8.31243 ~26.89056~58.62645 r d n ν 1 -37.6299 1.2000 1.79952 42.22 2 1394.2381 0.2000 3 * 22.9698 1.5000 1.52542 55.78 4 22.4541 3.4401 5 28.6292 1.2000 1.72342 37.95 6 11.0958 3.1401 1.58913 61.14 7 -11.0958 0.9500 8 ∞ (Aperture) 9.5127 -4.2000-0.900 9 * -28.5717 0.3000 1.52540 51.81 10 -39.3868 2.0847 1.57501 41.50 11 -17.5385 3.5974 12 -7.9193 1.3000 1.729 -54 back focus) aspherical coefficients third surface _{K = 0.0 A 4 = -2.4953 ×} 10 -4 A 6 = -4.3594 × 10 -6 A 8 = -1.0576 × 10 -9 The ninth surface _{K = -2.1815 A 4 = 1.3309 ×} 10 -4 A 6 = 1.6863 × 10 -6 A 8 = 1.0558 × 10 -8 5-8, each wide-angle end of the above Examples 1 to 4 (a) FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the intermediate focal length (b) and the telephoto end (c).

The conditional expressions (1) in Examples 1 to 4 above were satisfied.
The following table shows values corresponding to the conditional expression (5).

[0066]

[Table 1]

The two-group zoom lens according to the present invention as described above is used, for example, as a photographic objective lens of a compact camera having a configuration as shown in a perspective view in FIG. 9 and a sectional view in FIG. In these figures, L _b is taking optical path, L _e denotes an optical path finder, photographing optical path L _b and the finder optical path L _e are arranged in parallel, the image of the object, the finder The image is observed by a finder including an objective lens, an image erecting prism, an aperture, and an eyepiece, and formed on a film by a photographing objective lens.

[0068]

As described above, the two-unit zoom lens according to the present invention has a zoom magnification ratio of about 2.5 or more.
An object of the present invention is to provide a compact zoom lens having a short overall lens length when retracted. In addition, by effectively arranging a lens using a plastic material, the lens system is very less affected by temperature and humidity.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a cross-sectional view of a two-unit zoom lens according to a first embodiment at a wide-angle end (a), an intermediate focal length (b), and a telephoto end (c).

FIG. 2 is a diagram illustrating a lens cross-sectional view of a two-unit zoom lens according to Example 2 at a wide-angle end (a), an intermediate focal length (b), and a telephoto end (c).

FIG. 3 is a diagram showing a lens cross-sectional view of a two-unit zoom lens according to Example 3 at a wide-angle end (a), an intermediate focal length (b), and a telephoto end (c).

FIG. 4 is a diagram showing lens cross-sectional views of a two-unit zoom lens according to Example 4 at a wide-angle end (a), an intermediate focal length (b), and a telephoto end (c).

FIG. 5 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) of Example 1.

FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) in Example 2.

FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) of the third embodiment.

FIG. 8 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the wide-angle end (a), an intermediate focal length (b), and a telephoto end (c) in Example 4.

FIG. 9 is a perspective view illustrating a configuration of a compact camera.

FIG. 10 is a cross-sectional view illustrating a configuration of a compact camera.

Claims (14)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
Each lens is composed of a lens group and a second lens group having a negative refractive power, such that the distance between the first lens group and the second lens group is reduced during zooming from the wide-angle end to the telephoto end. In the two-unit zoom lens for moving the group to the object side, the first group
The lens group includes, in order from the object side, a negative lens group and a positive lens group. The negative lens group in the first lens group includes a negative lens having a stronger curvature on the image side, and the first lens group. The second positive lens group includes a negative lens and a positive lens, and the second lens group includes at least one positive lens and a negative lens, and satisfies the following conditional expression. Zoom lens. 0.2 <| f _1N /D|<2.1 (1) 5 <ν _d R−ν _d F <20 (2) where f _{1N is} the focal length of the negative lens in the first lens group,
D: diagonal length of the photographing screen, ν _d R: Abbe number of the negative lens closest to the image, ν _d F: Abbe number of the negative lens closest to the object. 2. The two-unit zoom lens according to claim 1, wherein all the lenses are glass lenses. 3. The two-unit zoom lens according to claim 1, wherein the positive lens group in the first lens group is a cemented lens. 4. A first lens having a positive refractive power in order from the object side.
Consisting of a lens group and a second lens group having negative refractive power
When zooming from the wide-angle end to the telephoto end, the first lens group
So that the distance between the lens units and the second lens unit is reduced.
In the two-unit zoom lens that moves to the object side,
The lens group consists of a negative lens group and a positive lens group in order from the object side.
And the negative lens group in the first lens group is a negative lens group.
A positive lens group in the first lens group, comprising a lens
Is composed of at least one negative lens and one positive lens.
The second lens group includes at least one positive lens.
Consisting of a negative lens and satisfying the following conditional expression:
Characteristic two-group zoom lens. 0.2 <| f_1N/D|<2.1 (1) 5 <ν_dR-ν_dF <20 (2) −5.0 <(R_Two+ R₁) / (R_Two-R₁) <-0.9 (3) where f_1N: Focal length of the negative lens in the first lens group,
D: length of diagonal of shooting screen, ν_dR: negative lens closest to image side
Abbe number of ν_dF: Abbe of the negative lens closest to the object side
Number, R₁: Negative lens of the negative lens group in the first lens group
Body side radius of curvature, R _Two: Of the negative lens group in the first lens group
The radius of curvature on the image side of the negative lens. 5. The two-unit zoom lens according to claim 1, wherein an aspheric surface is used for at least one surface of the negative lens unit in the first lens unit. 6. One surface of a negative lens in the first lens group,
The two-unit zoom lens according to any one of claims 1 to 5, further comprising an aspherical layer formed by applying and curing a transparent resin layer. 7. The two-unit zoom lens according to claim 6, further satisfying the following conditional expression (5). 2.0 <| f _H | / D (5) where f _{H is} the paraxial focal length of the hybrid lens resin layer, and D is the diagonal length of the photographing screen. 8. A first lens having a positive refractive power in order from the object side.
Each lens is composed of a lens group and a second lens group having a negative refractive power, such that the distance between the first lens group and the second lens group is reduced during zooming from the wide-angle end to the telephoto end. In the two-unit zoom lens for moving the group to the object side, the first group
The lens group includes, in order from the object side, a negative lens group and a positive lens group. The negative lens group in the first lens group includes, in order from the object side, a negative lens having a stronger curvature on the object side and a lens on the object side. The positive lens group of the first lens group is composed of at least one negative lens and a positive lens, and the second lens group is composed of at least one positive lens and a negative lens. A two-unit zoom lens comprising a lens and satisfying the following conditional expressions. 0.2 <| f _1F /D|<2.1 (4) 5 <ν _d R−ν _d F <20 (2) where f _{1F is} the focal length of the negative lens group in the first lens group,
D: diagonal length of the photographing screen, ν _d R: Abbe number of the negative lens closest to the image, ν _d F: Abbe number of the negative lens closest to the object. 9. The two-unit zoom lens according to claim 1, wherein an aspheric surface is used for at least one surface in said second lens unit. 10. The second lens group according to claim 1, wherein at least one surface of the second lens group has an aspherical layer formed by applying and curing a transparent resin layer. Group zoom lens. 11. A first lens unit having a positive refractive power and a second lens unit having a negative refractive power are arranged in order from the object side. In a two-unit zoom lens that moves each lens unit toward the object side such that a distance between the first lens unit and the second lens unit decreases, the first lens unit includes at least one negative lens and one positive lens. The second lens group has at least one negative lens and a positive lens, and one of the negative lenses in the first lens group.
A two-unit zoom lens having an aspherical layer on a surface of which a transparent resin layer is applied and cured. 12. The two-unit zoom lens according to claim 11, wherein an aspheric surface is used for at least one surface in said second lens unit. 13. The two-unit zoom lens according to claim 12, wherein said aspherical surface is formed by an aspherical layer formed by applying and curing a transparent resin layer. 14. The two-unit zoom lens according to claim 13, further satisfying the following conditional expression (5). 2.0 <| f _H | / D (5) where f _{H is} the paraxial focal length of the hybrid lens resin layer, and D is the diagonal length of the photographing screen.