JPH1073764A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens whose focal distance on a wide angle side is short and where aberration is excellently compensated by fixing a 1st group and moving a 2nd group in an optical axis direction in the case of variable power in the zoom lens constituted of specified 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 including a diaphragm (s), and the 4th group Gr4 having the positive refractive power in order from the object side. In the zoom lens, the variable power 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. In such a case, 1.5<|f1, 2/fw|<1.85 is satisfied. Provided that f1, 2 is the composite focal distance of the 1st and the 2nd groups at a wide angle end, and (fw) is the focal distance of an entire system at the wide angle end.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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.

[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 comprising a third lens unit having a refractive power and a fourth lens unit having a positive refractive power have been proposed (JP-A-3-33710).

[0003]

However, each of the zoom lenses described in the above publications has a focal length at the wide angle end of 40 in terms of a camera used for 135 film.
mm. SUMMARY OF THE INVENTION It is an object of the present invention to provide a zoom lens which has a shorter focal length on the wide-angle side than a zoom lens used in a conventionally known digital camera or lens shutter camera, and in which aberration is well corrected.

[0004]

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
The first group is fixed during zooming,
The second group is a zoom lens that moves in the optical axis direction, and satisfies the following conditional expression.

1.5 <| f1,2 / fw | <1.85 where f1,2 is the combined focal length of the first lens unit and the second lens unit at the wide-angle end, and fw is the focal point of the entire system at the wide-angle end. The distance,.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a zoom lens embodying the present invention will be described with reference to the drawings. 1 to 3 show the first
FIG. 4 corresponds to the lens configuration of the zoom lens according to the second embodiment, and
The lens arrangement at (W) is shown.

Each of the zoom lenses of the first and second embodiments includes, in order from the object side, a first group (Gr1) having a positive refractive power and a second group (Gr2) having a negative refractive power. A third lens unit (Gr3) having a positive refractive power and including a stop (S), and a fourth lens unit (Gr4) having a positive refractive power. In the zoom lens of each embodiment, during zooming from the wide-angle end to the telephoto end, the first unit (Gr1) and the third unit (Gr3) are fixed,
The second lens unit (Gr2) and the fourth lens unit (Gr4) are both zoom lenses that move toward the image side to perform zooming. Arrow m1 in FIGS.
To m4 schematically show the movement of the first group (Gr1) to the fourth group (Gr4) from the wide-angle end (W) to the telephoto end (T).

The zoom lens according to the first embodiment (see FIGS. 1 to 3) includes a negative meniscus first lens (L1) convex to the object side and a biconvex second lens in order from the object side. (L
2) a first group (Gr1) including a positive meniscus third lens (L3) convex on the object side, a negative meniscus fourth lens (L4) convex on the object side, and a biconcave fourth lens (L4). A first cemented lens obtained by cementing a fifth lens (L5) and a biconvex sixth lens (L6)
A second group (Gr2) composed of (DL1), a third group (Gr3) composed of a stop (S) and a biconvex seventh lens (L7), and an eighth meniscus having a negative meniscus shape convex on the object side. The fourth lens unit (Gr4) includes a second cemented lens (DL2) formed by cementing a lens (L8) and a bi-convex ninth lens (L9), and a filter (F).

The zoom lens according to the second embodiment (see FIG. 4) includes, in order from the object side, a negative meniscus first lens (L1) convex to the object side and a positive meniscus first lens (L1) convex to the object side. A first group (Gr1) composed of two lenses (L2), a positive meniscus third lens (L3) convex to the object side, and a negative meniscus shape convex to the object side, and the object side surface having a shape described later. A second lens unit (DL1) comprising a first cemented lens (DL1) formed by joining a spherical fourth lens (L4), a biconcave fifth lens (L5) and a biconvex sixth lens (L6). Gr2), a stop (S), a third lens unit (Gr3) including a biconvex seventh lens (L7), a negative meniscus eighth lens (L8) convex to the object side, and a biconvex lens. Ninth
A fourth unit (Gr4) including a second cemented lens (DL2) formed by cementing the lens (L9) and a filter (F).

Next, the conditional expression range (1) that must be satisfied by the zoom lens of each embodiment will be described. In order from the object side, there are 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. In zooming, the first unit is fixed, and the second unit preferably satisfies the following conditional expression range (1) in a zoom lens that moves in the optical axis direction. 1.5 <| f1,2 / fw | <1.85 (1) where f2 is the composite focal length of the first and second lens units at the wide-angle end, and fw is the composite focal length at the wide-angle end. The focal length of the whole system. 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.

Further, the range of conditional expressions (2) to (5) which should be satisfied by the zoom lens of each embodiment will be described. In a zoom lens that satisfies the conditional expression range (1), it is preferable that all of the conditional expression ranges (2) to (5) described below be satisfied. It is not necessary to satisfy the condition, and a corresponding effect can be obtained by satisfying the range of a single conditional expression.

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 composite 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.

By limiting the numerical value range defined by the conditional expression range (2) to the range of the following conditional expression range (3), the above-mentioned effect becomes more remarkable, and further excellent. Thus, it is possible to obtain a zoom lens whose aberration has been corrected. 0.70 <| f1,2 / f3,4 | <0.85 (3) In order from the object side, a first group having a positive refractive power and a second group having a negative refractive power And a third group having a positive refractive power;
Consisting of a fourth unit having a positive refractive power, upon zooming,
In a zoom lens in which the first and third units are fixed and the second and fourth units move in the optical axis direction, it is preferable that the following conditional expression range (4) is satisfied. 3.0 <| f3 / fw | <5.0 (4) where f3 is the focal length of the third lens unit. Conditional expression range (4) 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-described configuration. If the lower limit value of the conditional expression range (4) is exceeded, the focal length of the third lens unit becomes too small, so that the spherical aberration becomes large toward the under side, especially on the wide angle side, which is not preferable. Conversely, when the value exceeds the upper limit of the conditional expression range (4), the focal length of the third lens unit becomes 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.

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, When the second group is a zoom lens moving in the optical axis direction and the third group is made up of one positive lens, it is preferable that the following conditional expression range (5) is satisfied. −2.0 <rb / ra <−0.5 (5) where, ra: radius of curvature of the object side surface of the positive lens, rb: radius of curvature of the image side surface of the positive lens. Conditional expression range (5) is a condition for defining the shape of the positive lens that forms the third unit in the zoom lens having the above configuration. If the lower limit value of the conditional expression range (5) is exceeded, the coma on the wide-angle side becomes particularly large, which is not preferable. Conversely, when the value exceeds the upper limit of conditional expression range (5),
In particular, the spherical aberration on the wide-angle side becomes undesirably large.

When the third unit is composed of one positive lens as in the above configuration, the third unit has a shape in which the positive refractive power is reduced as the distance from the vicinity of the optical axis to the periphery increases. It is desirable to arrange an aspheric surface having the same. F of zoom lens
In order to obtain a bright lens by reducing the number, on-axis and off-axis light fluxes incident on the positive lens of the third group pass through a higher incident height. It is greatly affected by the surface shape. At this time, if both surfaces of the positive lens are spherical, it is not possible to sufficiently correct aberrations, especially for a light beam passing through a peripheral portion where the incident height is high, and the F-number of the lens is reduced. It is difficult. On the other hand, if an aspherical surface having a shape in which the positive refractive power is reduced as the distance from the vicinity of the optical axis to the peripheral portion increases is arranged in the positive lens of the third group, the aberration correction of the light beam passing through the peripheral portion can be sufficiently corrected. It can be carried out. Therefore, by arranging an aspherical surface having such a shape in the third lens unit, it is possible to provide a bright lens whose aberration has been well corrected.

[0016]

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 first embodiment, and Example 4 corresponds to the above-described second embodiment, respectively. FIGS. , And corresponding lens configurations of Examples 1 to 4 are shown.

In each embodiment, ri (1, 2, 3,...) Is the radius of curvature of the eye surface counted from the object side, and di (i = 1, 2, 3,...) Is counted from the object side. Denotes the i-th axis upper surface interval, and Ni (i = 1,2,
3 ...) and νi (i = 1, 2, 3 ...) indicate the refractive index and the 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)
(Shaft upper surface distances d6, d11, d14, d17) are from the left
(W), the intermediate focal length (M), and the values at the telephoto end (T).

The object side surface (the surface marked with *) of the seventh lens (L7) of the third group (Gr3) of the fourth embodiment is formed as an aspheric surface. The aspherical surface shape is defined by the following equation.

[0020]

(Equation 1)

Here, X: height in the direction perpendicular to the optical axis, Y: displacement from the reference plane in the optical axis direction, C: paraxial curvature, ε: quadratic surface parameter, Ai: ith non-order surface parameter The spherical coefficient,

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

In the zoom lenses of the first to third embodiments, the focal length at the wide-angle end is 4.8 mm. In the zoom lens according to the fourth embodiment, the focal length at the wide-angle end is 4.4 m.
m. These correspond to a focal length of 32 mm and a focal length of 34 mm in terms of 135 film, respectively.
It can be seen that sufficient widening of the angle has been achieved.

The object side surface (r13, the surface of the seventh lens (L7) of the third lens unit (Gr3) of the fourth embodiment (Gr3) defined by the equation representing the aspherical surface, where the radius of curvature is marked with an asterisk) is The aspheric surface has a shape in which positive refractive power is reduced as the distance from the axis to the periphery increases.

FIGS. 5 to 8 show the first to fourth embodiments, respectively.
FIG. 9 is an aberration diagram corresponding to FIG. In each figure, (W) is the focal length at the wide-angle end, (M) is the intermediate focal length state, (T) is the aberration at infinity focus state at the telephoto end focal length, each aberration diagram, in order from the left , Spherical aberration, astigmatism, and distortion.

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 fourth embodiments, the conditional expression (1) is satisfied.
To (5) are satisfied. The following table shows values corresponding to the conditional expressions (1) to (5) in Examples 1 to 4.

[0031]

[Table 5]

[0032]

As described above, according to the present invention, it is possible to provide a zoom lens which has a short focal length on the wide-angle side and is well corrected for aberrations. Therefore, when the zoom lens of the present invention is applied as a photographing optical system of a digital camera or a lens shutter camera, it is possible to contribute to the performance enhancement 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 a lens configuration diagram according to a fourth embodiment of the present invention.

FIG. 5 is an aberration diagram of the first embodiment of the present invention.

FIG. 6 is an aberration diagram of the second embodiment of the present invention.

FIG. 7 is an aberration diagram of the third embodiment of the present invention.

FIG. 8 is an aberration diagram of the fourth 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 unit is fixed, and the second unit is a zoom lens that moves in the direction of the optical axis, and satisfies the following conditional expression: 1.5 <| f1 Where f1,2 is the combined focal length of the first and second lens groups at the wide-angle end, and fw is the focal length of the entire system at the wide-angle end. 2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied: 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. 3. The zoom lens according to claim 2, further satisfying the following conditional expression: 0.70 <| f1,2 / f3,4 | <0.85. 4. The zoom lens according to claim 1, wherein said first and third units are fixed during zooming, and said second and fourth units move in the optical axis direction and satisfy the following conditional expression. Claim 2
3.0 <| f3 / fw | <5.0 where f3 is the focal length of the third lens unit. 5. The zoom lens according to claim 1, wherein said third lens unit includes one positive lens and satisfies the following conditional expression: -2.0 <rb / ra <- 0.5 where, ra: radius of curvature of the object side surface of the positive lens, rb: radius of curvature of the image side surface of the positive lens. 6. The zoom lens according to claim 5, wherein the third lens group includes an aspheric surface having a shape in which positive refractive power is reduced as the distance from the vicinity of the optical axis to the periphery increases.