JP2003005070A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens suitable for a lens shutter camera or the like whose variable power ratio is high, whose compactness is enhanced and whose image formation performance is excellent because the various kinds of aberration are excellently corrected. SOLUTION: The expression of 0.16<DT/fT<0.235 is satisfied as a condition to attain the miniaturization of the zoom lens while securing excellent performance, where DT means the distance from the surface of the lens of the entire system closest to the object to the surface of the lens closest to the image at the telephoto end and fT means the focal distance of the entire system at the telephoto end.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a compact, high zoom ratio two-group zoom lens suitable for lens shutter cameras and the like.

[0002]

2. Description of the Related Art As a zoom lens type for a lens shutter camera, there is a two-group zoom lens type including a first lens group having a positive refractive power and a second lens group having a negative refractive power, which are arranged in order from the object side. Well known. This two-group zoom lens type is a lens type that has a simple structure and is advantageous for compactness.
-48523 is proposed.

[0003]

However, although the above-mentioned conventional example can secure a high zoom ratio, the lens barrel is housed in the camera body because the axial thickness of the first lens group is slightly large. At this time, even if the first lens group and the second lens group are brought as close to each other as possible, the distance from the lens surface closest to the object side to the lens surface closest to the image side of the entire system becomes large. There is a problem that the thickness in the optical axis direction increases.

The present invention has been made in view of the above-mentioned problems of the prior art, and is suitable for a lens shutter camera or the like having a high zoom ratio, excellent compactness, and good correction of various aberrations and good imaging performance. To provide a simple zoom lens.

[0005]

A zoom lens according to a first aspect of the present invention comprises a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side. In the zoom lens that performs zooming by changing, the first lens group includes, in order from the object side, a 1a lens group having negative refractive power, a 1b lens group having positive refractive power, and an aperture.
The first-a lens group is composed of a positive lens and a negative lens in order from the object side, the first-b lens group has a negative lens arranged closest to the object side, at least one positive lens, and at least one aspherical surface. And satisfy the following conditional expression. 0.16 <D _T / f _T <0.235 (1) where, D _T : Distance from the most object side lens surface to the most image side lens surface of the entire system at the telephoto end f _T : All at the telephoto end Focal length of system

A second aspect of the zoom lens according to the present invention is characterized in that the second lens group includes two lenses including at least one negative lens and has at least one aspherical surface.

The zoom lens described in claim 3 is characterized in that the following condition is satisfied. 3.0 <f _T / f ₁ <5.0 (2) where f _T : focal length of the entire system at the telephoto end f ₁ : focal length of the first lens group

The zoom lens described in claim 4 is characterized in that the following condition is satisfied. 0.05 <f ₁ / | f _1a | <0.45 (3) where f _{1 is} the focal length of the first lens group f _{1a is} the focal length of the 1a lens group

The zoom lens described in claim 5 is characterized in that the following condition is satisfied. ν _1an <40 (4) where ν _1an : Abbe number of the negative lens of the 1a-th lens group

A zoom lens according to a sixth aspect of the present invention comprises, in order from the object side, a first lens group having a positive refracting power and a second lens group having a negative refracting power, and zooming is performed by changing an interval between both lens groups. In the zoom lens, the first lens group includes, in order from the object side, a 1a lens group having negative refractive power, a 1b lens group having positive refractive power, and a diaphragm, and the 1a lens group is sequentially arranged from the object side. The first-b lens group includes a positive lens and a negative lens, and the negative lens is arranged closest to the object side. The negative lens has at least one positive lens and at least one aspherical surface, and satisfies the following conditional expression. It is characterized by f _T / f _W > 2.5 (5) 0.20 <D ₁ /2Y<0.36 (6) where f _T : focal length of the entire system at the telephoto end f _W : focal point of the entire system at the wide-angle end Distance D ₁ : Distance from the most object side lens surface of the first lens group to the most image side lens surface 2Y: Screen diagonal length

The zoom lens according to claim 7 is characterized in that the following conditional expression is satisfied. 0.023 <D _1-2 /2Y<0.050 (7) However, D _1-2 : from the lens surface closest to the image side of the first lens group to the second lens group of the first lens group at the telephoto end during infinity shooting. Distance to lens surface on object side 2Y: diagonal length of screen

The zoom lens according to claim 8 is characterized in that the second lens group is composed of two lenses including at least one negative lens, and has at least one aspherical surface.

A zoom lens according to a ninth aspect is characterized by satisfying the following conditions. 3.0 <f _T / f ₁ <5.0 (2) where f _T : focal length of the entire system at the telephoto end f ₁ : focal length of the first lens group

A zoom lens according to a tenth aspect of the present invention is characterized by satisfying the following conditions. 0.05 <f ₁ / | f _1a | <0.45 (3) where f _{1 is} the focal length of the first lens group f _{1a is} the focal length of the 1a lens group

The zoom lens described in Item 11 is characterized by satisfying the following conditions. ν _1an <40 (4) where ν _1an : Abbe number of the negative lens of the 1a-th lens group

[0016]

According to the first aspect of the present invention, in the two-group zoom lens including the first lens group having positive refracting power and the second lens group having negative refracting power, the first lens group has negative refracting power. If the first-a lens unit and the first-b lens unit having a positive refractive power are used, the position of the second principal point of the first lens unit can be sufficiently close to the first principal point of the second lens unit at the telephoto end. It is possible to perform zooming from the wide-angle end to the telephoto end without making the refractive power of the lens too strong. Therefore, aberrations in all zoom regions can be corrected well. The 1a lens group includes a positive lens and a negative lens in order from the object side. Such a so-called positive lens preceding type is suitable for a zoom lens having a high variable power ratio in which the focal length at the telephoto end becomes long because the telephoto ratio is easily reduced. Further, it is possible to satisfactorily correct lateral chromatic aberration as compared with a case where only a negative lens is used.

Further, the 1b-th lens group is configured such that a negative lens is arranged closest to the object side and at least one positive lens is included. With such a configuration, the first lens group as a whole has an arrangement close to a triplet type having positive, negative, and positive refractive powers, and it is possible to reduce the size while correcting coma aberration, distortion, and the like. Also,
If an aspherical surface is used for the positive lens of the 1b-th lens group, the surface closer to the diaphragm can be made aspherical than that used for the negative lens, which is advantageous for correction of spherical aberration and coma. Further, it is possible to suppress the performance deterioration when the lens in the first lens group is decentered.

In the present invention, the aperture stop is arranged on the most image side of the first lens group, but this makes it necessary for the first lens group to have a built-in precision as compared with the structure in which the stop is provided between the lenses. The merit that it is easy to suppress the eccentricity of each lens in the lens group is obtained. Further, it is possible to reduce the lens outer diameters of the first lens group and the second lens group in a well-balanced manner.

Further, the conditional expression (1) is a condition for downsizing the zoom lens with good performance. 0.16 <D _T / f _T <0.235 (1) In the formula (1), if D _T / f _T is set to fall below the lower limit,
Although the total thickness of each lens group can be reduced, it leads to downsizing,
Deterioration of the performance of each lens when it is decentered increases, and high-precision lens assembly technology is required. On the other hand, if D _T / f _T exceeds the upper limit, the total thickness of each lens group increases,
It becomes difficult to downsize the zoom lens. Therefore, in the currently mainstream lens shutter camera in which the first lens group and the second lens group are brought close to each other and stored in the camera body, the thickness of the camera body (in the direction of the optical axis of the lens) must be increased. It becomes a factor that hinders the overall miniaturization. Therefore, it is desirable that D _T / f _T be in the range that satisfies the expression (1).

Further, in the zoom lens according to the present invention as defined in claims 2 and 8, the second lens group having a negative refractive power is composed of two lenses including at least one aspherical surface. As the configuration of the third lens group, a configuration including three or more lenses is also known, but by configuring it with two lenses, the axial thickness of the second lens group can be suppressed to be small. Also, in the second lens group, there is a difference in the height of light rays passing through the light flux at the center of the screen and the light flux at the peripheral light of the screen, especially in the zoom area on the wide-angle side. The off-axis aberration can be satisfactorily corrected without affecting the above. Further, when the second lens group is composed of a lens having a weaker refractive power than the object side and a lens having a negative refractive power, a plastic lens can be used for the lens having a weaker refractive power, which is advantageous for cost reduction. is there.

The conditional expression (2) described in claims 3 and 9 is high.
Impairs compactness in zoom ratio zoom lenses
Without compromising the aberration of the first lens group
It defines the folding force.     3.0 <f_T/ F₁<5.0 (2) In equation (2), f_T/ F₁Is below the lower limit
When the refracting power of the lens group becomes weak, the total lens length becomes large.
The downsizing of the zoom lens cannot be realized. On the other hand, f _T/ F
₁Is above the upper limit, the refractive power of the first lens group becomes strong
And the aberration generated in the first lens group becomes too large,
The two lens groups cannot be sufficiently corrected. Therefore, f_T/
f₁Is preferably in a range that satisfies the expression (2).

The conditional expression (3) described in claims 4 and 10 is
It defines the refractive power of the 1a-th group. 0.05 <f ₁ / | f _1a | <0.45 (3) In the formula (3), when f ₁ / | f _1a | is below the lower limit and the negative refractive power of the 1a-th lens unit becomes weak, It becomes difficult to secure the back focus at the edge, and the effect of correcting the lateral chromatic aberration that occurs in the second lens unit having a negative refractive power becomes small. On the other hand, when f ₁ / | f _1a | exceeds the upper limit and the negative refracting power of the 1a lens group becomes strong, the positive refracting power of the 1b lens group also becomes strong, and the decentering error sensitivity between these two groups increases. However, the accuracy required at the time of assembly becomes strict, which causes a cost increase. In the high-zoom zoom lens, the aberration generated by the decentering of the lens in the first lens group is greatly magnified by the second lens group at the telephoto end, so that the decentering of each lens in the first lens group is large. A design that pays close attention to error sensitivity is required. Therefore, it is desirable that f ₁ / | f _1a | be in a range that satisfies the expression (3).

The conditional expression (4) described in claims 5 and 11 is
It defines the Abbe number of the negative lens of the 1a lens group. ν _1an <40 (4) Expression (4) is a condition for correcting lateral chromatic aberration that occurs in the second lens group, and the upper limit is its limit value. To further enhance this effect, the following range is desirable. 20 <ν _1an <35 (4 ′) If ν _1an is _less than the lower limit of the equation (4 ′), it becomes very difficult to manufacture the optical glass.

According to the sixth aspect of the present invention, there is provided a second lens group 2 having a positive refractive power first lens group and a negative refractive power second lens group.
In the group zoom lens, when the first lens group is composed of the 1a lens group having a negative refractive power and the 1b lens group having a positive refractive power, the second principal point position of the first lens group is sufficiently small at the telephoto end. It is possible to approach the first principal point of the two lens groups, and it is possible to perform zooming from the wide-angle end to the telephoto end without making the refracting power of each lens too strong. Therefore, aberrations in all zoom regions can be corrected well. The 1a lens group includes a positive lens and a negative lens in order from the object side. Such a so-called positive lens preceding type is suitable for a zoom lens having a high variable power ratio in which the focal length at the telephoto end becomes long because the telephoto ratio is easily reduced. Further, it is possible to satisfactorily correct lateral chromatic aberration as compared with a case where only a negative lens is used.

The 1b-th lens group has a negative lens arranged closest to the object side and includes at least one positive lens. With such a configuration, the first lens group as a whole has an arrangement close to a triplet type having positive, negative, and positive refractive powers, and it is possible to reduce the size while correcting coma aberration, distortion, and the like. Also,
If an aspherical surface is used for the positive lens of the 1b-th lens group, the surface closer to the diaphragm can be made aspherical than that used for the negative lens, which is advantageous for correction of spherical aberration and coma. Further, it is possible to suppress the performance deterioration when the lens in the first lens group is decentered.

In the present invention, the aperture stop is arranged on the most image side of the first lens group, but as a result, compared with the structure in which the stop is provided between the lenses of the first lens group, the first aperture which requires assembling accuracy is required. The merit that it is easy to suppress the eccentricity of each lens in the lens group is obtained. Further, it is possible to reduce the lens outer diameters of the first lens group and the second lens group in a well-balanced manner.

Conditional expression (5) is a basic condition of a zoom lens having a zoom ratio of 2.5 or more, which is generally called high zoom ratio. f _T / f _W > 2.5 (5) When the zoom ratio is less than 2.5 times, the zoom lens has insufficient performance in terms of zoom ratio, and the commercial value of the camera with a zoom lens decreases.

Conditional expression (6) is the total lens thickness of the first lens group in order to reduce the size of the zoom lens while satisfactorily correcting aberrations in the high zoom ratio zoom lens of conditional expression (5). Is defined. 0.20 <D ₁ /2Y<0.36 (6) In the formula (6), if D ₁ / 2Y is less than the lower limit, the total lens thickness of the first lens group becomes small, which leads to downsizing, but variable power. With a zoom lens having a ratio of more than 2.5 times, the performance deterioration of each lens at the time of decentering becomes large, and a highly accurate lens assembling technology is required. On the other hand, when D ₁ / 2Y exceeds the upper limit, the total lens thickness of the first lens group increases, and it is necessary to increase the diameter of the front lens in order to secure the peripheral light amount at the wide-angle end. Becomes difficult. Therefore, it is preferable that D ₁ / 2Y is in the range that satisfies the expression (6).

The conditional expression (7) recited in claim 7 defines the lens surface interval in which the aperture stop is arranged at the telephoto end. 0.023 <D _1-2 /2Y<0.050 (7) In the formula (7), when D _1-2 / 2Y falls below the lower limit and the interval at which the aperture stop is arranged becomes small, the shutter unit is arranged. It will be difficult. On the other hand, if D _1-2 / 2Y exceeds the upper limit and the interval at which the aperture stop is arranged becomes large, the arrangement of the shutter unit becomes easy, but the total lens thickness of the entire system becomes large, and the overall size of the camera is reduced. It becomes an obstacle.

In the above equation (7), D _1-2 /
If 2Y is below the upper limit, the position of the second principal point of the first lens group can be sufficiently close to the first principal point of the second lens group at the telephoto end, and the refracting power of each lens must be too strong. Instead, it is possible to perform zooming from the wide-angle end to the telephoto end, and at the same time, it is possible to reduce the total lens length (distance from the lens surface closest to the object side of the entire system to the image formation position) at the telephoto end.

[0031]

Embodiments of the zoom lens of the present invention will be described below. The symbols used in each example are as follows. F: F number ω: Half angle of view r: Radius of curvature of lens surface d: Distance between lens surfaces Nd: Refractive index νd of lens material at d-line: Abbe number of lens material f: Focal length fb: Back focus or surface * In No represents an aspherical surface, and the vertex curvature is set in the Cartesian coordinate system with the vertex of the surface as the origin and the optical axis direction as the X axis.
C, the conic constant are K, and the aspherical coefficients are A4, A6, A8, A10, and A12, which are represented by the following mathematical expressions.

[Equation 1]

(Embodiment 1) FIG. 1 is a lens sectional view of a zoom lens of Embodiment 1 at the wide-angle end. FIG. 2 is an aberration diagram of Example 1 at (A) wide-angle end, (B) middle, and (C) telephoto end. The lens data is shown in Table 1. In addition, after this (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰³ ) is changed to E (for example,
2.5 × E-03).

[Table 1]

(Embodiment 2) FIG. 3 is a lens sectional view of a zoom lens of Embodiment 2 at the wide-angle end. 4A to 4C are aberration diagrams of Example 2 at the wide-angle end, at the middle of FIG. 4B, and at the telephoto end of FIG. The lens data is shown in Table 2.

[Table 2]

(Embodiment 3) FIG. 5 is a lens sectional view of a zoom lens of Embodiment 3 at the wide-angle end. FIG. 6 is an aberration diagram of Example 3 at the wide-angle end (A), the intermediate portion (B), and the telephoto end (C). Table 3 shows the lens data.

[Table 3]

(Embodiment 4) FIG. 7 is a lens sectional view of a zoom lens of Embodiment 4 at the wide-angle end. FIG. 8 is an aberration diagram of Example 4 at the wide-angle end (A), the intermediate portion (B), and the telephoto end (C). Table 4 shows the lens data.

[Table 4]

Numerical values corresponding to the conditional expressions (1) to (7) in each example are as shown in Table 5.

[Table 5]

In the above embodiments, an aspherical shape is added to the glass lens closest to the image in the first lens group. However, the method of forming the aspherical surface is not limited to molding, but may be, for example, an aspherical surface. It may be a composite aspherical surface in which a thin resin layer having a shape is formed on the surface of the glass lens. Also,
The most object-side lens of the second lens group is made of a polycarbonate plastic material, but an acrylic or polyolefin plastic material may be used.

[0038]

According to the present invention, it is possible to provide a zoom lens suitable for a lens shutter camera or the like, which has a high zoom ratio and is excellent in compactness, and in which various aberrations are well corrected and which has good image forming performance.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view at a wide-angle end of a zoom lens according to a first exemplary embodiment.

FIG. 2A is a wide-angle end, FIG. 2B is a middle portion, and FIG.
It is an aberration diagram at the telephoto end.

FIG. 3 is a lens cross-sectional view of a zoom lens according to a second exemplary embodiment at a wide-angle end.

4 (A) wide-angle end, (B) middle, and (C) of Example 2. FIG.
It is an aberration diagram at the telephoto end.

FIG. 5 is a lens cross-sectional view at a wide-angle end of a zoom lens according to a third exemplary embodiment.

FIG. 6A is a wide-angle end, FIG. 6B is a middle portion, and FIG.
It is an aberration diagram at the telephoto end.

FIG. 7 is a lens cross-sectional view at a wide-angle end of a zoom lens according to a fourth exemplary embodiment.

8 (A) wide-angle end, (B) middle, (C) of Example 4. FIG.
It is an aberration diagram at the telephoto end.

[Explanation of symbols]

LG1 first lens group LG2 second lens group 1a 1a lens group 1b 1b lens group

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H087 KA02 LA01 PA05 PA06 PA17                       PA18 PB06 PB07 QA02 QA07                       QA12 QA22 QA26 QA37 QA41                       QA45 RA05 RA12 RA13 RA36                       SA06 SA10 SA62 SA63 SB15                       SB16 SB23

Claims (11)

[Claims] 1. A zoom lens comprising, 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, wherein the distance between both lens groups is changed to perform zooming. The group comprises, in order from the object side, a 1a lens group having negative refractive power, a 1b lens group having positive refractive power, and a diaphragm, and the 1a lens group is composed of a positive lens and a negative lens in order from the object side. A zoom lens characterized in that the negative lens is arranged closest to the object side in the 1b-th lens group, has at least one positive lens, and has at least one aspherical surface, and satisfies the following conditional expression. 0.16 <D _T / f _T <0.235 (1) where, D _T : Distance from the most object side lens surface to the most image side lens surface of the entire system at the telephoto end f _T : All at the telephoto end Focal length of system 2. The zoom lens according to claim 1, wherein the second lens group includes two lenses including at least one negative lens and has at least one aspherical surface. 3. The zoom lens according to claim 1, which satisfies the following condition. 3.0 <f _T / f ₁ <5.0 (2) where f _T : focal length of the entire system at the telephoto end f ₁ : focal length of the first lens group 4. The zoom lens according to claim 1, which satisfies the following condition. 0.05 <f ₁ / | f _1a | <0.45 (3) where f _{1 is} the focal length of the first lens group f _{1a is} the focal length of the 1a lens group 5. The zoom lens according to claim 1, wherein the zoom lens satisfies the following conditions. ν _1an <40 (4) where ν _1an : Abbe number of the negative lens of the 1a-th lens group 6. A zoom lens comprising, 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, wherein zooming is performed by changing the distance between both lens groups. The group comprises, in order from the object side, a 1a lens group having negative refractive power, a 1b lens group having positive refractive power, and a diaphragm, and the 1a lens group is composed of a positive lens and a negative lens in order from the object side. A zoom lens characterized in that the negative lens is arranged closest to the object side in the 1b-th lens group, has at least one positive lens, and has at least one aspherical surface, and satisfies the following conditional expression. f _T / f _W > 2.5 (5) 0.20 <D ₁ /2Y<0.36 (6) where f _T : focal length of the entire system at the telephoto end f _W : focal point of the entire system at the wide-angle end Distance D ₁ : Distance from the most object side lens surface of the first lens group to the most image side lens surface 2Y: Screen diagonal length 7. The zoom lens according to claim 6, wherein the following conditional expression is satisfied: 0.023 <D _1-2 /2Y<0.050 (7) However, D _1-2 : from the lens surface closest to the image side of the first lens group to the second lens group of the first lens group at the telephoto end during infinity shooting. Distance to lens surface on object side 2Y: diagonal length of screen 8. The zoom lens according to claim 6, wherein the second lens group includes two lenses including at least one negative lens and has at least one aspherical surface. 9. The zoom lens according to claim 6, wherein the following conditions are satisfied. 3.0 <f _T / f ₁ <5.0 (2) where f _T : focal length of the entire system at the telephoto end f ₁ : focal length of the first lens group 10. The zoom lens according to claim 6, wherein the zoom lens satisfies the following conditions. 0.05 <f ₁ / | f _1a | <0.45 (3) where f _{1 is} the focal length of the first lens group f _{1a is} the focal length of the 1a lens group 11. The zoom lens according to claim 6, wherein the zoom lens satisfies the following conditions. ν _1an <40 (4) where ν _1an : Abbe number of the negative lens of the 1a-th lens group