JPH1073763A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens capable of macrophotographing which can be produced at low cost by moving a 2nd group in an optical axis direction in the case of macrofocusing in the zoom lens consisting of four groups having positive, negative, positive and positive refractive power in order from an object side. SOLUTION: This zoom lens is constituted of the 1st group Gr1 having the positive refractive power, the 2nd group Gr2 having the negative refractive power, the 3rd group Gr3 having the positive refractive power and the 4th group Gr4 having the positive refractive power in order from the object side. In the zoom lens, zooming is performed by fixing the 1st group Gr1 and the 3rd group Gr3 and moving the 2nd group Gr2 and the 4th group Gr4 to an image side in the case of zooming. Meanwhile, macrofocusing is performed by moving only the 2nd group Gr2 to the object side in the optical axis direction from lens arrangement at a wide angle end in the case of macrofocusing. Then, the moving direction of the 2nd group Gr2 at the time of variable power is linear, so that lens barrel constitution with respect to movement for macrofocusing is simplified.

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 zoom lens suitable for a digital camera or a lens shutter camera capable of macro photography.

[0002]

2. Description of the Related Art Conventionally, as a zoom lens used in a digital camera or a lens shutter camera, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, Various types of zoom lenses including a third lens unit having a refractive power and a fourth lens unit having a positive refractive power have been proposed.

[0003] In recent years, there has been an increasing demand for photographing a close subject even in a zoom lens of a digital camera or a lens shutter camera, and a zoom lens capable of macro photography has been proposed even in a zoom lens having the above-described refractive power arrangement. (Japanese Patent Publication No. 5-76009).

[0004]

However, the zoom lenses described in the above publications have a configuration in which the lens group moves in the optical axis direction in a complicated manner for macro focusing and zooming. Therefore, it was necessary to manufacture the lens barrel with high precision. If the lens barrel is not manufactured with high precision, the lens group moves eccentrically during macro focusing and zooming, so that the image is significantly degraded.

In view of the above problems, an object of the present invention is to provide a zoom lens that can be manufactured at a low cost with a simple configuration and that can perform macro photography.

[0006]

To achieve the above object, a zoom lens according to the present invention comprises, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power,
A third group having a positive refractive power and a fourth group having a positive refractive power
A first lens unit and a third lens unit are fixed during zooming, and the second lens unit and the fourth lens unit are moved in the optical axis direction. It is characterized by being moved in the axial direction.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a zoom lens embodying the present invention will be described with reference to the drawings. 1 to 3 correspond to the lens configuration diagrams of the zoom lens according to the embodiment. The upper figures show the in-focus state with respect to the macro shooting distance of 0.065 m at the wide-angle end focal length, and the lower figures show the focusing state with respect to the shooting distance of 3 m at the wide-angle end focal length. Each shows a lens arrangement in a focused state.

The zoom lens according to the embodiment has, in order from the object side, a first lens unit (Gr1) having a positive refractive power, a second lens unit (Gr2) having a negative refractive power, and a positive lens unit having a positive refractive power. The zoom lens includes a third lens unit (Gr3) including the stop (S) and a fourth lens unit (Gr4) having a positive refractive power. In the zoom lens according to each of the embodiments, during zooming from the wide-angle end to the telephoto end, the first unit (Gr1) and the third unit (Gr3) are fixed, and the second unit (Gr2) and the fourth unit (Gr4)
Are zoom lenses that move to the image side to perform zooming. Arrows m1 to m4 in FIGS.
The movement from the wide-angle end (W) to the telephoto end (T) of (Gr1) to the fourth lens unit (Gr4) is schematically shown. An arrow m5 indicates the movement of the second lens unit (Gr2) from the infinity in-focus condition at the wide-angle end to the closest cemented condition during macro focusing.

A zoom lens according to an embodiment (see FIGS. 1 to 3)
Are, in order from the object side, a negative meniscus first lens (L1) convex to the object side, a biconvex second lens (L2), and a positive meniscus third lens (L3) convex to the object side. The first consisting of
Group (Gr1), a negative meniscus fourth lens (L4) convex to the object side, a biconcave fifth lens (L5) and a biconvex sixth lens
A second group (Gr2) including a first cemented lens (DL1) formed by cementing a lens (L6), an aperture (S), and a biconvex seventh lens (L
7), a second cemented lens (Jr) formed by joining an eighth lens (L8) having a negative meniscus shape convex on the object side and a ninth lens (L9) having a biconvex shape on the object side. DL2) (Gr.
4) and a filter (F).

As described above, the zoom lens according to the embodiment has a configuration in which only the second lens unit (Gr2) is moved to the object side in the optical axis direction from the lens arrangement at the wide-angle end shown in each drawing during macro focusing. Has adopted.

In general, when performing macro-focusing, it is necessary to move any lens group or a part of the lens group constituting the zoom lens in the optical axis direction. However, in the zoom lens of the embodiment, the first
When moving the group (Gr1), the third group (Gr3), or a part of any lens group, it is necessary to provide a moving mechanism in the lens barrel to newly move a lens group that has nothing to do with zooming. Occurs, and the lens barrel configuration becomes complicated, resulting in an increase in cost. In particular, in the arrangement of the zoom lens according to the embodiment, when the first unit (Gr1) is moved for focusing,
In order to secure the peripheral illuminance, it is necessary to increase the effective diameter of the lens constituting the first group (Gr1), and the lens becomes large.

On the other hand, in the zoom lens of the embodiment, of the second lens unit (Gr2) and the fourth lens unit (Gr4) that move in the optical axis direction during zooming, the second lens unit (Gr2) mainly performs zooming. The contributing variator, fourth group (Gr4), corresponds to a compensator that corrects the position of the image subjected to the magnification change. For this reason, the movement in the optical axis direction during zooming is linear in the second lens unit (Gr2), while the fourth lens unit (Gr4) is very complicated.

Therefore, when the fourth unit is moved in the optical axis direction in macro focusing, a lens barrel structure for performing macro focusing is required in addition to a lens barrel structure used for movement for zooming. This results in a very complicated lens barrel configuration. If the lens barrel is made to have a complicated configuration in this way, extremely high precision is required for processing and assembling the lens barrel.
This leads to higher costs.

On the other hand, since the movement of the second lens unit (Gr2) at the time of zooming is linear, the fourth lens unit (Gr2) can be added even if a lens barrel configuration for movement for macro focusing is newly added.
The lens barrel configuration is not as complicated as when 4) is moved. Therefore, in this case, even if a lens barrel configuration for performing macro focusing is provided in addition to the lens barrel configuration used for moving for zooming, the fourth lens unit is a moving lens group for macro focusing. A simple lens barrel configuration can be achieved as compared with the conventional case.

For the above reasons, in the zoom lens according to the embodiment, only the second lens unit (Gr2) is moved toward the object side in the optical axis direction during macro focusing from the lens arrangement at the wide-angle end shown in each drawing. It adopts a configuration.

The zoom lens of the embodiment performs macro focusing with the lens arrangement at the wide-angle end as a start. By performing macro focusing in this manner, the close-up shooting distance can be further reduced.

Further, in the zoom lens of the embodiment, the focusing is not performed by moving the lens group even when the photographing distance changes during the normal focusing, and the zoom lens is used fixed at a predetermined finite photographing distance. A pan-focus configuration is adopted. The zoom lens according to the embodiment has two fixed photographing distances on the telephoto side and the wide-angle side, respectively. In this way, by adopting the pan-focus configuration, when configuring the lens barrel of the zoom lens, it is not necessary to dispose a moving mechanism such as a cam or a helicoid for focusing movement. Easy to do.

Next, the conditional expression ranges (1) to (3) that the zoom lens of the embodiment should satisfy will be described. In addition,
In the zoom lens having the above configuration, it is preferable that all of the conditional expression ranges (1) to (3) described below are satisfied. However, it is not always necessary to satisfy all of the conditional expression ranges at the same time. By satisfying the conditional expression range, a corresponding effect can be obtained.

In order from the object side, a first lens having a positive refractive power
Group, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, wherein the first group is fixed upon zooming, It is preferable that the second group satisfies the following conditional expression range (1) in a zoom lens moving in the optical axis direction. 1.5 <| f1,2 / fw | <1.85 (1) where f1,2 is the combined focal length of the first and second lens groups at the wide-angle end, and fw is the wide-angle end. The focal length of the whole system at. Conditional expression range (1) defines the combined focal length of the first and second units at the wide-angle end in the zoom lens having the above configuration, and makes the focal length on the wide-angle side smaller while maintaining compactness. This is the condition for If the lower limit of the conditional expression range (1) is exceeded, the combined focal length of the first and second units becomes too small, so that the refractive power of the third and fourth units becomes relatively large. As a result, the back focus of the zoom lens becomes longer, and the overall length of the zoom lens becomes too long, resulting in an increase in the size of the zoom lens. Conversely, if the value exceeds the upper limit of the conditional expression range (1), the combined focal length of the first and second lens units becomes too large, and the peripheral illuminance decreases particularly on the wide-angle side, which is not preferable. Attempting to correct this decrease in the peripheral illuminance would result in an increase in the lens diameter of the lens constituting the first group, which is also undesirable.

In order from the object side, a first lens having a positive refractive power
Group, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, wherein the first group is fixed upon zooming, It is preferable that the second group satisfies the following conditional expression range (2) in a zoom lens moving in the optical axis direction. 0.65 <| f1,2 / f3,4 | <0.95 (2) where f3,4 is the combined focal length of the third and fourth units at the wide-angle end. . Conditional expression range (2) defines the ratio between the combined focal length of the first and second units and the combined focal length of the third and fourth units at the wide-angle end in the zoom lens having the above configuration,
This is a condition for maintaining good aberration performance with a small number of lenses. If the lower limit value of the conditional expression range (2) is exceeded, the field curvature particularly at the telephoto side becomes too large toward the underside, which is not preferable. Conversely, if the value exceeds the upper limit of the conditional expression range (2), the field curvature on the telephoto side becomes large on the over side, and the peripheral illuminance on the wide angle side is undesirably reduced. Attempting to correct this decrease in the peripheral illuminance would result in an increase in the lens diameter of the lens constituting the first group, which is also undesirable.

In order from the object side, a first lens having a positive refractive power
A first lens unit, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. In a zoom lens in which the second lens unit and the fourth lens unit move in the optical axis direction, it is preferable that the following conditional expression range (3) is satisfied. 3.0 <| f3 / fw | <5.0 (3) where f3 is the focal length of the third lens unit. The conditional expression range (3) is a condition for defining the focal length of the third lens unit and maintaining good aberration performance with a small number of lenses in the zoom lens having the above configuration. If the lower limit value of the conditional expression range (3) is exceeded, the focal length of the third lens unit becomes too small, so that the spherical aberration becomes undesirably large, particularly on the wide-angle side. Conversely, when the value exceeds the upper limit of the conditional expression range (3), the focal length of the third lens unit becomes too large, so that the burden of refractive power and the burden of aberration correction in the fourth lens unit become too large. . For this reason, it is necessary to increase the number of lenses in the fourth group, and the lenses constituting the fourth group are undesirably increased in size.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The zoom lens according to the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. Examples 1 to 3 described below correspond to the above-described embodiment, and FIGS. 1 to 3 are lens configuration diagrams of Examples 1 to 3.

In each embodiment, ri (i = 1, 2, 3,...) Is the radius of curvature of the i-th surface counted from the object side, and di (i = 1, 2, 3,...)
Indicates the i-th axial top surface distance counted from the object side, and Ni (i = 1,
2,3 ...) and νi (i = 1,2,3 ...) indicate the refractive index and Abbe number of the i-th lens from the object side with respect to the d-line.

Further, the focal length f of the entire system, the first unit (Gr1) and the second unit (Gr2), the second unit (Gr2) and the third unit (Gr3), and the third unit (Gr3)
And the distance between the fourth group (Gr4) and the fourth group (Gr4) and the filter (F)
(Axis top surface intervals d6, d11, d14, d17) are, in order from the left, a focusing state for a shooting distance of 3 m at a wide-angle end focal length (W), a focusing state for a shooting distance of 3 m in an intermediate focal length state (M), This corresponds to each value at a shooting distance of 7 m at the telephoto end focal length (T). The value at the time of macro shooting is a shooting distance of 0.06.
This corresponds to a state of 5 m.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

FIGS. 4 to 9 show the first to third embodiments, respectively.
FIG. 9 is an aberration diagram corresponding to FIG. 4, 6 and 8 show Examples 1 to
3 is an aberration diagram at a normal focus, where (W) is a focused state at a shooting distance of 3 m at a wide-angle end focal length, (M) is a focused state at a shooting distance of 3 m at an intermediate focal length state, and (T) is a focal point at a telephoto end. 9 shows respective aberrations in a focused state with respect to a shooting distance of 7 m. 5, 7, and 9 show Examples 1 to 3.
FIG. 10 is an aberration diagram in a macro focus condition with a focusing distance of 0.065 m. Each aberration diagram corresponds to spherical aberration, astigmatism, and distortion in order from the left.

In the spherical aberration diagram, the solid line (d) shows the spherical aberration with respect to the d line, the broken line (c) shows the c line, and the one-dot chain line (g) shows the spherical aberration with respect to the g line. In the astigmatism diagram, a solid line (Y) and a solid line (X) represent astigmatism on a meridional surface and a sagittal surface, respectively.

In the first to third embodiments, the conditional expression (1) is satisfied.
To (3) are satisfied. The following table shows values corresponding to the conditional expressions (1) to (3) in Examples 1 to 3.

[0031]

[Table 4]

[0032]

As described above, according to the present invention,
It is possible to provide a zoom lens capable of macro photography that can be manufactured at a low cost with a simple configuration. Therefore, when the zoom lens of the present invention is used as a photographing optical system of a digital camera or a lens shutter camera, it is possible to contribute to the performance enhancement and cost reduction of these cameras.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram according to a first embodiment of the present invention.

FIG. 2 is a lens configuration diagram according to a second embodiment of the present invention.

FIG. 3 is a lens configuration diagram according to a third embodiment of the present invention.

FIG. 4 is an aberration diagram in a normal focusing area according to the first embodiment of the present invention.

FIG. 5 is an aberration diagram in a normal focusing area according to the second embodiment of the present invention.

FIG. 6 is an aberration diagram in a normal focusing area according to the third embodiment of the present invention.

FIG. 7 is an aberration diagram of a macro focusing region according to the first embodiment of the present invention.

FIG. 8 is an aberration diagram of a macro focusing region according to the second embodiment of the present invention.

FIG. 9 is an aberration diagram of a macro focusing region according to the third embodiment of the present invention.

[Explanation of symbols]

 Gr1 ... first group Gr2 ... second group Gr3 ... third group Gr4 ... fourth group

Claims (6)

[Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a third lens unit having a positive refractive power. Consists of 4 groups,
In zooming, the first and third units are fixed, and the second and fourth units are zoom lenses that move in the optical axis direction. In macro focusing, the second unit is moved in the optical axis direction. A zoom lens characterized in that: 2. The zoom lens according to claim 1, wherein at the time of macro focusing, the second lens unit is moved in the optical axis direction from the lens arrangement at the wide-angle end of the zoom lens. 3. The zoom lens according to claim 1, wherein a pan focus in which normal focusing is not performed in all magnification ranges. 4. The zoom lens according to claim 1, further satisfying the following conditional expression: 1.5 <| f1,2 / fw | <1.85, where f1,2: wide-angle end Where fw is the focal length of the entire system at the wide-angle end. 5. The zoom lens according to claim 1, further satisfying the following conditional expression: 0.65 <| f1,2 / f3,4 | <0.95, where f3,4: The composite focal length of the third unit and the fourth unit at the wide-angle end. 6. The zoom lens according to claim 1, further satisfying the following conditional expression: 3.0 <f3 / fw <5.0, where f3 is a focal length of the third lens unit. is there.