JP2006053437A - Zoom lens - Google Patents

Abstract

A zoom lens that is as small as a single focus standard lens, has a small number of lenses, has a zoom ratio of about 2.9 times, is easy to manufacture, and has a high performance.
A zoom lens has a first negative lens group G1 and a second positive lens group G2 from the object side, and varies the air distance Ds between the first lens group G1 and the second lens group G2. in the zoom lens to perform, from the first lens group G1 is the object side, a negative lens L _1, and a positive lens L _1p least, the second lens group G2 from the object side, a positive lens L _a, the positive lens having a front lens group G _2-1 having a positive refractive power and a cemented lens composed of a L _ap and a negative lens L _an,, the positive refractive power has a cemented lens of a negative lens L _bn and the positive lens L _bp and a rear lens group _{G 2-2,} further the second lens group G2 have the aperture stop S for determining the F value to the object side near the front lens group _{G 2-1} during or front lens group _{G 2-1} And a predetermined conditional expression is satisfied.
[Selection] Figure 1

Description

  The present invention relates to a zoom lens.

Among the so-called negative and positive two-group zoom lenses covering the standard and wide-angle regions, there is a zoom lens using a lens group obtained by developing a Gauss type lens group as the second lens group having a positive refractive power. (For example, refer to Patent Document 1). Such a zoom lens has also been proposed by the applicant of the present application (see, for example, Patent Documents 2, 3, 4, and 5).
Japanese Patent Laid-Open No. 55-60911 JP-A-8-334694 JP-A-9-171140 JP 2000-2837 A JP 2002-6214 A

However, the zoom lens disclosed in Patent Document 1 is large and the aberration correction state is not satisfactory. In addition, the zoom lenses disclosed in Patent Documents 2 and 5 have a large number of lenses and are difficult to manufacture. Further, the zoom lenses disclosed in Patent Documents 3 and 4 have a large number of lenses and are large.
Therefore, even if the techniques disclosed in the above patent documents are extended, a small zoom lens with a small number of lenses, easy manufacture, and high performance cannot be achieved.

  Accordingly, the present invention has been made in view of the above problems, and a zoom lens that is as small as a single focus standard lens, has a small number of lenses, has a zoom ratio of about 2.9 times, and is easy to manufacture and has a high performance. The purpose is to provide.

In order to solve the above problems, the present invention
In order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power,
In the zoom lens that performs zooming by changing an air interval between the first lens group and the second lens group,
The first lens group includes at least a negative lens and a positive lens L _{1p in} order from the object side.
The second lens group is in order from the object side.
And a positive lens, the front lens group G _2-1 having a positive (convex) lens L _ap and a negative (concave) lens L _an, and positive refractive power and a cemented lens consisting of a bond,
A rear lens group _G2-2 having a cemented lens formed by cementing a negative (concave) lens _Lbn and a positive (convex) lens _Lbp and having a positive refractive power;
Further, the second lens group on the object side near the front lens group G _2-1 or in the front lens group G _2-1, having an aperture stop for determining the F value,
Provided is a zoom lens characterized by satisfying the following conditional expression (1).
(1) 0.27 ≦ Ds / D ≦ 0.8
However,
Ds: air space on the optical axis from the front lens group G the most image side lens surface of _2-1 to the lens surface on the most object side in the rear lens group G _2-2,
D: Distance on the optical axis from the most object side lens surface to the most image side lens surface in the second lens group.

According to a preferred embodiment of the present invention,
It is desirable to satisfy the following conditional expression (2).
(2) 0.5 ≦ f _b / f _a ≦ 15
However,
f _a : the focal length of the front lens group G _2-1 ,
f _b : focal length of the rear lens group _G2-2 .

According to a preferred embodiment of the present invention,
It is desirable to satisfy the following conditional expression (3).
(3) 0 <n _an −n _ap <0.45
However,
n _ap : refractive index of the medium with respect to d-line (λ = 587.56 nm) of the positive lens L _{ap in} the cemented lens in the front lens group G _2-1 .
n _an,: the negative lens _{L an,} the d-line (lambda = 587.56 nm) refractive index of the medium with respect to in the cemented lens in the front lens group _{G 2-1.}

According to a preferred embodiment of the present invention,
It is desirable to satisfy the following conditional expression (4).
(4) 0 <n _bn −n _bp <0.45
However,
n _bn: the negative lens _{L bn} of the d-line (lambda = 587.56 nm) medium refractive index of the relative in the cemented lens in the rear lens group _{G 2-2,}
n _bp: the positive lens _{L bp} of the d-line (lambda = 587.56 nm) refractive index of the medium with respect to in the cemented lens in the rear lens group _{G 2-2.}

According to a preferred embodiment of the present invention,
It is desirable to satisfy the following conditional expression (5).
(5) ν _1p <23.2
However,
ν _1p : Abbe number of the medium of the positive lens L _1p in the first lens group.

According to a preferred embodiment of the present invention,
It is desirable to satisfy the following conditional expression (6).
(6) 1.790 <n _1p
n _1p : refractive index of the medium with respect to the d-line (λ = 587.56 nm) of the positive lens L _1p in the first lens group.

According to a preferred embodiment of the present invention,
The first lens group includes, in order from the object side, the negative lens and the positive lens L _1p .
The positive lens L _1p is preferably a positive lens having a convex surface facing the object side.

The present invention also provides:
In order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power,
In the zoom lens that performs zooming by changing an air interval between the first lens group and the second lens group,
The first lens group includes, in order from the object side, a negative lens and a positive lens _L1p having a convex surface facing the object side.
The second lens group includes, in order from the object side, a positive lens, a first cemented lens formed by cementing a positive (convex) lens and a negative (concave) lens, a negative (concave) lens, and a positive (convex) lens. A second cemented lens made of
A zoom lens having an aperture stop in the second lens group on the object side of the second cemented lens or near the object side of the second lens group is provided.

  According to the present invention, it is possible to provide a high-performance zoom lens that is as small as a single focus standard lens, has a small number of lenses, has a zoom ratio of about 2.9 times, and is easy to manufacture.

First, the basic structure of the zoom lens according to the present invention will be described.
In general, in a zoom lens having a negative / positive two-group configuration, the second lens group having a positive refractive power serves as a master lens for the entire zoom lens system. Normally, this second lens group must ensure the back focus while ensuring the air gap between the first lens group and the second lens group for zooming (the minimum air gap necessary for the variable). I must. In view of the compactness and cost reduction of the zoom lens, it is necessary to further reduce the size of the second lens group and reduce the number of lenses as much as possible.
As lens types that satisfy these requirements, there are an Ernostar type, a modified triplet type, or a Zoner type having basic configurations of positive, positive, negative, and positive. However, these types of lenses have a drawback that the sensitivity of decentering is high because each beam has a large declination angle when it is refracted by each lens surface. In other words, these types of lenses have the drawback of increasing the accuracy of components during the manufacture of components and improving the accuracy of adjustment during assembly, resulting in increased costs.

Therefore, the present invention has created a new lens type for the second lens group in the zoom lens having a negative / positive two-group configuration. The second lens group in the zoom lens of the present invention basically starts with a Gaussian structure, and in the order from the object side, a positive lens, a positive lens L _ap, and a negative lens L, as in the following embodiments. a front lens group _{G 2-1} composed of a cemented lens of a _an, and a composed rear lens group _{G 2-2} Prefecture in the negative lens _{L bn} and the positive lens _{L bp} and the cemented lens . Alternatively, the second lens group includes, in order from the object side, a positive lens, the front lens group _{G 2-1} composed of a positive lens _{L ap} and a negative lens _{L an,} the cemented lens, a negative lens _{L bn} and positive a cemented lens of a lens L _bp, and a composed rear lens group G _2-2 Metropolitan a positive lens.

The second lens group having such a configuration has a Gaussian type feature in which the center negative lens in the triplet type is replaced with an air lens. Further, by sufficiently widening the air space between the two cemented lenses, that is, the space between the front lens group _G2-1 and the rear lens group _G2-2 , the front lens group _{G2-1 in} the second lens group. And the refractive power of the rear lens group _G2-2 can be reduced. Accordingly, it is possible to keep the aberration generated on each lens surface small, so that not only the design performance can be improved, but also the performance after manufacture can be stabilized. With the configuration of the second lens group, the zoom lens of the present invention can be improved in performance, improved in productivity, reduced in cost, and reduced in size.

An aperture stop in the present invention is disposed on the object side near the front lens group G _2-1 during or front lens group G _2-1. Thus, by arranging the aperture stop closer to the object side than the rear lens group _G2-2 , the exit pupil position can be located closer to the object side with respect to the image plane. This effect is effective for reducing peripheral dimming due to shading or the like in a so-called digital camera optical system. Usually, in a very small zoom lens as in the present invention, the back focus and the total length are shortened, so that the exit pupil approaches the image plane side. However, due to the above-described effects, the present invention can sufficiently secure the distance of the exit pupil position with respect to the image plane.
Note that shading means that an off-axis light beam incident on the image sensor has an increased angle with respect to the optical axis, and the off-axis light beam is vignetted by a microlens disposed immediately in front of the image sensor.

Next, conditional expressions of the zoom lens according to the present invention will be described.
Condition (1) has two air interval between the cemented lens in the second lens group, i.e. to maximize the effect of the above by the interval between the front lens group G _2-1 and the rear lens group G _2-2 It is a conditional expression for exhibiting.
If the upper limit value of conditional expression (1) is exceeded, the ratio of the distance between the front lens group _G2-1 and the rear lens group _G2-2 to the total thickness of the second lens group will be significantly increased. For this reason, the front lens group _G2-1 and the rear lens group _G2-2 are remarkably thinned. Therefore, it becomes difficult to correct aberrations, and it becomes difficult to improve performance, improve productivity, reduce costs, and reduce size. If the upper limit value of conditional expression (1) is set to 0.7 or less, more preferably 0.6 or less, further performance enhancement, productivity improvement, significant weight reduction, and cost reduction are achieved. be able to.

On the other hand, if the lower limit value of conditional expression (1) is not reached, the refraction action of the air lens formed between the front lens group _G2-1 and the rear lens group _G2-2 cannot be optimized. For this reason, in order to maintain a state in which the aberration is favorably corrected, the refractive power of each lens surface in the front lens group _G2-1 and the rear lens group _G2-2 increases, and the amount of aberration generated also increases. Therefore, it becomes difficult to achieve high performance, productivity improvement, cost reduction, and miniaturization. Moreover, as a method of correcting aberrations favorably, there is a method of increasing the thickness of each lens in the front lens group _G2-1 and the rear lens group _G2-2 . However, this method is not preferable because it goes against cost reduction and miniaturization. If the lower limit value of conditional expression (1) is set to 0.33 or more, more preferably 0.35 or more, the effect of the present invention can be exhibited to the maximum.

The conditional expression (2) is a conditional expression for setting an appropriate refractive power ratio between the front lens group _G2-1 and the rear lens group _G2-2 in the second lens group. In the second lens group in the zoom lens according to the present invention, the difference between the refractive power of the front lens group _{G2-1 and} the refractive power of the rear lens group _G2-2 does not become remarkably large as in the case of a Gaussian refractive power arrangement. It is desirable. That is, securing the symmetry of refractive power arrangement within the range of conditional expression (2) leads to higher performance and improved productivity.
Above the upper limit of the condition (2), significantly stronger refractive power of the front lens group G _2-1 are compared with the refractive power of the rear lens group G _2-2. For this reason, the second lens group approaches a lens type such as an asymmetrical Elnostar type having a refractive power arrangement. Thus, resulting in particular increases the sensitivity of the eccentricity of the lens in the front lens group G _2-1, increase productivity, it is difficult to reduce the cost, and miniaturization. If the upper limit value of conditional expression (2) is set to 10.0 or less, further improvement in productivity, cost reduction, and size reduction can be achieved. Moreover, if the upper limit of conditional expression (2) is set to 7.0 or less, the effect of the present invention can be exhibited to the maximum.

On the other hand, if the lower limit value of conditional expression (2) is not reached, the refractive power of the rear lens group _G2-2 is significantly higher than the refractive power of the front lens group _G2-1 , contrary to the case where the upper limit value is exceeded. Become stronger. For this reason, the second lens group approaches an asymmetric lens type with refractive power arrangement. Therefore, in particular, the sensitivity of _decentering of each lens of the rear lens group G2-2 is increased. In addition, spherical aberration and upper coma are deteriorated, and it is difficult to correct the aberration satisfactorily. Further, there is a high possibility that the second lens group will be enlarged. Therefore, it becomes difficult to achieve high performance, productivity improvement, cost reduction, and miniaturization. If the lower limit value of conditional expression (2) is set to 1.0 or more, further improvement in performance, improvement in productivity, and reduction in size can be achieved. Moreover, if the lower limit of conditional expression (2) is set to 1.2 or more, the effects of the present invention can be exhibited to the maximum.

The conditional expression (3) is a conditional expression regarding the refractive index difference between the two lenses L _an and L _ap with respect to the cemented lens formed by cementing the negative lens L _an and the positive lens L _ap in the front lens group G _2-1 . .
If the upper limit of conditional expression (3) is exceeded, the refractive index of the positive lens _Lap will be too small. For this reason, it is necessary to increase the thickness in order to ensure the thickness of the edge of the lens edge. Further, it is not preferable because it becomes difficult to correct spherical aberration. If the upper limit value of conditional expression (3) is set to 0.4 or less, it is advantageous for achieving high performance, miniaturization, and small diameter. Moreover, if the upper limit of conditional expression (3) is set to 0.35 or less, the effects of the present invention can be exhibited to the maximum.

If the lower limit value of conditional expression (3), the magnitude relation of the refractive index is reversed negative lens L _an, refractive index and a positive lens L _ap, refractive index of refraction of the negative lens L _an, is a positive lens L _ap Smaller than the rate. For this reason, it is difficult for the zoom lens of the present invention to set the Petzval sum to an optimum value. Therefore, it becomes difficult to correct astigmatism and curvature of field, and as a result, it becomes difficult to widen the angle. If the lower limit value of conditional expression (3) is set to 0.1 or more, it is advantageous for achieving high performance, miniaturization, and small diameter. If the lower limit value of conditional expression (3) is set to 0.25 or more, the effects of the present invention can be exhibited to the maximum.

The conditional expression (4), for a cemented lens consisting of a cemented negative lens _{L bn} and the positive lens _{L bp} at the rear lens group _{G 2-2,} 2 two lenses _{L bn,} is condition concerning the refractive index difference between the _{L bp} .
If the upper limit of conditional expression (4) is exceeded, the refractive index of the positive lens _Lbp will be too small. For this reason, it is necessary to increase the thickness in order to ensure the thickness of the edge of the lens edge. Further, it is not preferable because it becomes difficult to correct spherical aberration. If the upper limit value of conditional expression (4) is set to 0.4 or less, it is advantageous for achieving high performance, miniaturization, and small diameter. Moreover, if the upper limit of conditional expression (4) is set to 0.35 or less, the effects of the present invention can be exhibited to the maximum.

If the lower limit value of conditional expression (4), a negative lens L and the magnitude relationship is reversed in the refractive index and the positive lens L _bp refractive index of _bn, the refractive index of refraction of the negative lens L _bn is a positive lens L _bp Smaller than the rate. For this reason, it is difficult for the zoom lens of the present invention to set the Petzval sum to an optimum value. Therefore, it becomes difficult to correct astigmatism and curvature of field, and as a result, it becomes difficult to widen the angle. If the lower limit value of conditional expression (4) is set to 0.1 or more, it is advantageous for achieving high performance, miniaturization, and small diameter. Moreover, if the lower limit of conditional expression (4) is set to 0.25 or more, the effects of the present invention can be exhibited to the maximum.

The conditional expression (5) is a conditional expression that defines the Abbe number of the positive lens L _1p in the first lens group. When reducing the number of lenses to the limit as in the zoom lens of the present invention, it is effective to configure the positive lens L _1p using a special glass material that has not been used so far. In particular, in order to correct magnification chromatic aberration and axial chromatic aberration well in a balanced manner up to a high angle of view, it is necessary to use a remarkably high dispersion glass. Therefore, when the conditional expression (5) is not satisfied, it becomes impossible to realize a compact zoom lens with excellent productivity by reducing the number of lenses in the first lens group to the limit while covering a wide angle range. .

The conditional expression (6) is a conditional expression that defines the refractive index of the positive lens L _1p in the first lens group. When the number of lenses is reduced to the limit as in the zoom lens of the present invention, it is necessary to form the positive lens L _1p using a high refractive index glass material. In particular, it is necessary to use a remarkably high refractive index glass material in order to satisfactorily correct the lower coma aberration and the spherical aberration on the telephoto side. Therefore, when the conditional expression (6) is not satisfied, it becomes impossible to realize a compact zoom lens with excellent productivity by reducing the number of lenses in the first lens group to the limit while covering a wide angle range. .

Hereinafter, zoom lenses according to embodiments of the present invention will be described with reference to the accompanying drawings.
Example 1
FIG. 1 is a diagram illustrating the configuration of the zoom lens according to Example 1 and the movement locus of each lens group.
The zoom lens according to Example 1 is a zoom lens having a negative / positive two-group configuration, and in order from the object side, a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power. It is composed of G2 and a flare stopper F.
The first lens group G1 includes, in order from the object side, a negative meniscus lens L ₁ having a convex surface facing the object side, a positive meniscus lens L _1p having a convex surface directed toward the object side. The negative meniscus lens L ₁ is a composite lens comprising a composite of resin and glass, are arranged resin lens surface on the image side, the image side surface of the resin is an aspherical surface.

The second lens group G2 includes a front lens group _G2-1 and a rear lens group _{G2-2 in} order from the object side.
Front lens group G _2-1 includes, in order from the object side, a cemented between the positive lens L _a double convex, an aperture stop S, a positive lens L _ap with a double concave negative lens L _an, biconvex And a cemented negative lens.
Rear lens group G _2-2 includes, in order from the object side, has a cemented positive lens consisting of the junction between the positive lens L _bp of the negative meniscus lens L _bn and bi-convex shape with its convex surface facing the object side.

In the zoom lens according to the present embodiment, zooming is performed when the lens position changes from the wide-angle end state (W) to the telephoto end state (T), and the air gap between the first lens group G1 and the second lens group G2. This is performed by moving the first lens group G1 and the second lens group G2 so that Ds is reduced. The flare stopper F described above has a fixed diameter, and moves independently along a movement locus different from that of the second lens group G2 at the time of zooming.
In the zoom lens according to the present embodiment, the short distance focusing is performed by moving the first lens group G1 to the object side.

Table 1 below lists values of specifications of the zoom lens according to Example 1 of the present invention.
In (overall specifications), f represents a focal length, A represents a half angle of view, and FNO represents an F number.
In (lens data), the surface number is the order of the lens surfaces counted from the object side, ri is the radius of curvature of the i-th lens surface Ri from the object side, and di is on the optical axis between the lens surface Ri and the lens surface Ri + 1. Νi is the Abbe number of the medium between the lens surface Ri and the lens surface Ri + 1, ni is the d line of the medium between the lens surface Ri and the lens surface Ri + 1 (λ = 587.56 nm) Refractive index for each is shown.

  Here, the aspherical surface in the zoom lens according to the present embodiment has a distance (sag amount) along the optical axis direction from the tangential plane of the apex of each aspherical surface at a height y in the vertical direction from the optical axis. ), Where R is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conical coefficient, and Cn is the nth-order aspherical coefficient, the following aspherical expression is used.

(Equation 1)
S (y) = (y ² / R) / [1+ (1-κ · y ² / R ² ) ^1/2 ]
+ C3 · | y | ³ + C4 · y ⁴ + C6 · y ⁶ + C8 · y ⁸ + C10 · y ¹⁰

The aspherical surface represented as described above has an asterisk (*) attached to the surface number in (lens data) and the paraxial radius of curvature in the column of the radius of curvature r. Each aspheric coefficient is listed.
In (aspherical surface data), “En” represents “× 10 ⁻ⁿ ”.
In (lens interval data), β indicates the imaging magnification between the object and the image, 1-POS is at the infinite focus at the wide angle end, 2-POS is at the infinite focus in the intermediate focal length state, 3-POS indicates focusing at infinity at the telephoto end, 4-POS indicates focusing at β = -0.02500 at the wide angle end, and 5-POS indicates focusing at β = -0.02500 in the intermediate focal length state. 6-POS indicates telephoto end and in focus at β = -0.02500, 7-POS indicates wide-angle end and close-up focus, 8-POS indicates intermediate focal length and close-up focus 9-POS indicates the close-up focus at the telephoto end.

Here, the unit of the focal length f, the radius of curvature r, and other lengths listed in all the following specification values is generally “mm”. However, the optical system is not limited to this because an equivalent optical performance can be obtained even when proportionally enlarged or proportionally reduced.
In addition, the same code | symbol as a present Example is used also in the specification value of all the following Examples.

[Table 1]
(Overall specifications)
f = 18.5 to 53.5
A = 38.9 to 14.93 ° FNO = 3.56 to 5.9

(Lens data)
Surface number r d v n
1) 181.0591 2.0000 49.61 1.772500
2) 17.2000 0.2000 38.09 1.553890
★ 3) 12.7630 12.2500
4) 33.8814 2.8000 23.06 1.860740
5) 65.8125 D5

6) 42.5378 2.6000 81.61 1.497000
7) -94.5446 1.8000
8> 2.0000 Aperture stop S
9) 24.2385 4.0000 64.10 1.516800
10) -35.8523 0.8000 49.61 1.772500
11) 67.2430 11.2000
12) 54.1555 0.8000 37.17 1.834000
13) 15.5723 4.5000 64.10 1.516800
14) -35.4635 D14

15) D15 Flare stopper F

(Aspheric data (κ and each aspheric coefficient))
Surface number κ C3 C4 C6 C8 C10
3 0.0375 0.79879E-05 3.03680E-06 -2.15160E-08 5.25940E-11 -2.58910E-13

(Lens spacing data)
1-POS 2-POS 3-POS 4-POS 5-POS
f or β 18.50000 35.00000 53.50000 -0.02500 -0.02500
D5 44.09357 13.18951 1.20774 45.43445 13.89826
D14 0.00000 11.09166 23.52778 0.00000 11.09166
D15 41.84285 50.91785 61.09285 41.84285 50.91785

6-POS 7-POS 8-POS 9-POS
β -0.02500 -0.13159 -0.23049 -0.38023
D5 1.67141 51.15122 19.72380 8.25968
D14 23.52778 0.00000 11.09166 23.52778
D15 61.09285 41.84285 50.91785 61.09285

  2, 3 and 4 are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state of the zoom lens according to the present embodiment.

In each aberration diagram, FNO represents an F number, and A represents a half angle of view (unit: degree). In the spherical aberration diagram, the F number value corresponding to the maximum aperture is shown, and in the astigmatism diagram and the distortion diagram, the maximum half field angle A is shown. D and g indicate aberration curves of the d-line (λ = 587.56 nm) and the g-line (λ = 435.84 nm), respectively. Further, in the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane.
In addition, in the various aberration diagrams of all the examples shown below, the same symbols as in this example are used.

  2, 3, and 4, it can be seen that the zoom lens according to the present example corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state.

(Example 2)
FIG. 5 is a diagram illustrating the configuration of the zoom lens according to Example 2 and the movement locus of each lens group.
The zoom lens according to Example 2 is a zoom lens having a negative / positive two-group configuration, and in order from the object side, a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power. And G2.
The first lens group G1 includes, in order from the object side, a negative meniscus lens L ₁ having a convex surface facing the object side, a positive meniscus lens L _1p having a convex surface directed toward the object side. The negative meniscus lens L ₁ is a composite lens comprising a composite of resin and glass, are arranged resin lens surface on the image side, the image side surface of the resin is an aspherical surface.

The second lens group G2 includes, in order from the object side, an aperture stop S, a front lens group _G2-1 , a rear lens group _G2-2, and a fixed stop FS. The aperture stop S is disposed in the vicinity of the object side of the front lens group _G2-1 .
Front lens group G _2-1, in order from the object side, a positive lens L _a double convex, a cemented negative lens consisting of the junction between the positive lens L _ap with a double concave negative lens L _an, biconvex Have
Rear lens group G _2-2 includes, in order from the object side, has a cemented positive lens consisting of the junction between the positive lens L _bp of the negative meniscus lens L _bn and bi-convex shape with its convex surface facing the object side.

In the zoom lens according to the present embodiment, zooming is performed when the lens position changes from the wide-angle end state (W) to the telephoto end state (T), and the air gap between the first lens group G1 and the second lens group G2. This is performed by moving the first lens group G1 and the second lens group G2 so that Ds is reduced. The aperture stop S moves integrally with the front lens group _G2-1 and the rear lens group _G2-2 at the time of zooming.
In the zoom lens according to the present embodiment, the short distance focusing is performed by moving the first lens group G1 to the object side.
Table 2 below lists values of specifications of the zoom lens according to Example 2 of the present invention.

[Table 2]
(Overall specifications)
f = 18.5 to 53.4
A = 38.3 to 14.92 ° FNO = 3.6 to 5.9

(Lens data)
Surface number r d v n
1) 86.5539 1.8000 49.61 1.772500
2) 16.0000 0.2000 38.70 1.552230
★ 3) 12.1665 10.7995
4) 26.9923 2.5000 22.76 1.808090
5) 44.6158 D5

6> 0.1000 Aperture stop S
7) 38.5505 2.5000 55.38 1.638540
8) -55.9183 0.1000
9) 18.6738 3.5000 64.10 1.516800
10) -32.6160 0.8000 46.58 1.804000
11) 26.8523 10.7839
12) 85.5647 0.8000 37.17 1.834000
13) 16.4881 4.0000 64.10 1.516800
14) -23.7659 0.0000
15) D15 Fixed aperture FS

(Aspheric data (κ and each aspheric coefficient))
Surface number κ C3 C4 C6 C8 C10
3 -0.5076 0.00000E-00 5.17550E-05 -5.62150E-08 5.34710E-11 -2.24340E-13

(Lens spacing data)
1-POS 2-POS 3-POS 4-POS 5-POS
f or β 18.50000 31.50000 53.40000 -0.02500 -0.02500
D0 ∞ ∞ ∞ 710.5943 1230.5943
D5 40.13414 15.53955 1.18562 41.47502 16.32705
D15 38.95217 53.39662 77.72995 38.95217 53.39662

6-POS 7-POS 8-POS 9-POS
β -0.02500 -0.07154 -0.11715 -0.20636
D0 2106.5943 229.1933 239.4904 229.3666
D5 1.65016 43.97117 19.22964 5.02007
D15 77.72995 38.95217 53.39662 77.72995

  FIGS. 6, 7 and 8 are graphs showing various aberrations when the zoom lens according to the present embodiment is in focus at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state.

  6, 7, and 8, it can be seen that the zoom lens according to the present example corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state.

(Example 3)
FIG. 9 is a diagram illustrating the configuration of the zoom lens according to Example 3 and the movement locus of each lens group.
The zoom lens according to Example 3 is a zoom lens having a negative / positive two-group configuration, and in order from the object side, a first lens group G1 having a negative refractive power and a second lens group having a positive refractive power. It is composed of G2 and a flare stopper F.
The first lens group G1 includes, in order from the object side, a negative meniscus lens L ₁ having a convex surface facing the object side, a positive meniscus lens L _1p having a convex surface directed toward the object side. The negative meniscus lens L ₁ is a composite lens comprising a composite of resin and glass, are arranged resin lens surface on the image side, the image side surface of the resin is an aspherical surface.

The second lens group G2 includes a front lens group _G2-1 and a rear lens group _{G2-2 in} order from the object side.
Front lens group G _2-1 includes, in order from the object side, a cemented between the positive lens L _a double convex, an aperture stop S, a positive lens L _ap with a double concave negative lens L _an, biconvex And a cemented negative lens.
Rear lens group G _2-2, in order from the object side, a cemented negative lens consisting of the junction between the positive lens L _bp double concave negative lens L _bn and biconvex, and a positive lens L _b biconvex Have

In the zoom lens according to the present embodiment, zooming is performed when the lens position changes from the wide-angle end state (W) to the telephoto end state (T), and the air gap between the first lens group G1 and the second lens group G2. This is performed by moving the first lens group G1 and the second lens group G2 so that Ds is reduced. The flare stopper F described above has a fixed diameter, and moves independently along a movement locus different from that of the second lens group G2 at the time of zooming.
In the zoom lens according to the present embodiment, the short distance focusing is performed by moving the first lens group G1 to the object side.
Table 3 below lists values of specifications of the zoom lens according to Example 3 of the present invention.

[Table 3]
(Overall specifications)
f = 18.5 to 53.4
A = 38.2 to 14.93 ° FNO = 3.6 to 5.9

(Lens data)
Surface number r d v n
1) 83.0076 1.8000 49.61 1.772500
2) 16.5000 0.2000 38.70 1.552230
★ 3) 12.6003 13.3087
4) 28.5874 2.8000 22.76 1.808090
5) 43.4120 D5

6) 28.4446 3.0000 55.38 1.638540
7) -79.3719 0.1000
8> 0.0000 Aperture stop S
9) 33.4115 3.5000 64.10 1.516800
10) -31.0350 1.0000 46.58 1.804000
11) 65.3951 10.0718
12) -28.2267 1.0000 46.58 1.804000
13) 21.7458 4.2000 82.52 1.497820
14) -17.9528 0.1000
15) 91.5812 2.3000 70.41 1.487490
16) -47.8355 D16

17) D17 Flare stopper F

(Aspheric data (κ and each aspheric coefficient))
Surface number κ C3 C4 C6 C8 C10
3 -0.9766 0.00000E-00 7.59690E-05 -1.78000E-07 4.03250E-10 -5.80270E-13

(Lens spacing data)
1-POS 2-POS 3-POS 4-POS 5-POS
f or β 18.50000 31.43000 53.40000 -0.02500 -0.02500
D0 ∞ ∞ ∞ 710.5710 1227.7709
D5 43.62877 17.01071 1.34180 44.96965 17.79996
D16 0.00000 6.23924 16.84063 0.00000 6.23924
D17 41.78742 51.14628 67.04837 41.78742 51.14628

6-POS 7-POS 8-POS 9-POS
β -0.02500 -0.07502 -0.12191 -0.21637
D0 2106.5709 217.1797 228.3744 217.3682
D5 1.80634 47.65235 20.85957 5.36231
D16 16.84063 0.00000 6.23924 16.84063
D17 67.04837 41.78742 51.14628 67.04837

[Table 4]
(Values for conditional expressions)
Example 1 Example 2 Example 3
(1) Ds / D 0.404 0.480 0.399
(2) f _b / f _a 2.16 1.76 4.17
(3) n _an -n _ap 0.256 0.287 0.287
(4) n _bn −n _bp 0.317 0.317 0.306
(5) ν _1p 23.1 22.8 22.8
(6) n _1p 1.861 1.808 1.808

  FIGS. 10, 11 and 12 are graphs showing various aberrations at the time of focusing at infinity in the wide-angle end state, the intermediate focal length state, and the telephoto end state of the zoom lens according to the present embodiment.

  10, 11, and 12, it can be seen that the zoom lens according to the present example corrects various aberrations well in each of the wide-angle end state, the intermediate focal length state, and the telephoto end state.

As described above, according to the present invention, as shown in the respective embodiments, the angle of view 2A is about 76.4 ° to 29.9 °, the zoom ratio is about 2.9 times, the cost performance is excellent, and the productivity is high. It is possible to realize a standard, wide-angle zoom lens with good performance, small size and light weight.
In the zoom lens according to the present invention, the front lens group G _2-1 and the rear lens group G _2-2 can be individually removed from the optical axis, thereby providing a sufficient effect as a so-called vibration-proof lens. The zoom lens of the present invention can also provide a sufficient effect as a so-called vibration-proof lens by removing the entire second lens group from the optical axis.

Although a two-group lens system has been shown as an example of the present invention, a lens system having a three-group structure including the two groups and a group system of two or more groups is also a lens system having the effects of the present invention. Needless to say.
In addition, in the configuration in each lens group, it goes without saying that a lens group in which an additional lens is added to the configuration in the embodiment is an equivalent lens group in which the effects of the present invention are inherent.

  According to the present invention, it is possible to provide a zoom lens that is as small as a single focus standard lens, has a small number of lenses, has a zoom ratio of about 2.9 times, and is easy to manufacture and has a high performance.

FIG. 2 is a diagram illustrating a configuration of a zoom lens according to Example 1 of the present invention and a movement locus of each lens group. FIG. 6 is a diagram illustrating various aberrations when the zoom lens according to Example 1 of the present invention is focused at infinity in the wide-angle end state. FIG. 6 is a diagram illustrating various aberrations when the zoom lens according to Example 1 of the present invention is focused at infinity in the intermediate focal length state. FIG. 3 is a diagram illustrating various aberrations when the zoom lens according to Example 1 of the present invention is focused at infinity in the telephoto end state. It is a figure which shows the structure of the zoom lens which concerns on Example 2 of this invention, and the movement locus | trajectory of each lens group. FIG. 9 is a diagram illustrating various aberrations when the zoom lens according to Example 2 of the present invention is focused at infinity in the wide-angle end state. FIG. 10 is a diagram illustrating various aberrations when the zoom lens according to Example 2 of the present invention is focused at infinity in the intermediate focal length state. FIG. 6 is a diagram illustrating various aberrations when the zoom lens according to Example 2 of the present invention is focused at infinity in the telephoto end state. It is a figure which shows the structure of the zoom lens which concerns on Example 3 of this invention, and the movement locus | trajectory of each lens group. FIG. 10 is a diagram illustrating various aberrations when the zoom lens according to Example 3 of the present invention is focused at infinity in the wide-angle end state. FIG. 10 is a diagram illustrating various aberrations when the zoom lens according to Example 3 of the present invention is focused at infinity in the intermediate focal length state. FIG. 10 is a diagram illustrating all aberrations when the zoom lens according to Example 3 of the present invention is focused on infinity in the telephoto end state.

Explanation of symbols

G1 First lens group G2 Second lens group _G2-1 Front lens group _{G2-2 in} the second lens group Rear lens group _{L1-2 in} the second lens group _L1p Positive lens _Lap front lens group in the first lens group positive lens S aperture stop FS fixed diaphragm F in the cemented lens of the negative lens L _bp rear lens group in the cemented lens of the negative lens L _bn rear lens group in the cemented lens in the positive lens L _an, front lens group in the cemented lens in Flare stopper I Image plane

Claims (8)

In order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power,
In the zoom lens that performs zooming by changing an air interval between the first lens group and the second lens group,
The first lens group includes at least a negative lens and a positive lens L _{1p in} order from the object side.
The second lens group is in order from the object side.
And a positive lens, the front lens group G _2-1 having a positive refractive power and a cemented lens consisting of a junction between the positive lens L _ap and a negative lens L _an,,
And a rear lens group G _2-2 having a positive refractive power has a cemented lens consisting of a junction between the negative lens L _bn and the positive lens L _bp,
Further, the second lens group on the object side near the front lens group G _2-1 or in the front lens group G _2-1, having an aperture stop for determining the F value,
A zoom lens satisfying the following conditional expression:
(1) 0.27 ≦ Ds / D ≦ 0.8
However,
Ds: air space D along the optical axis from the lens surface on the most image side in the front lens group G _2-1 to the most object side lens surface of the rear lens group G _2-2: the second lens group Distance on the optical axis from the most object-side lens surface to the most image-side lens surface The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
(2) 0.5 ≦ f _b / f _a ≦ 15
However,
f _a : focal length of the front lens group G _2-1 f _b : focal length of the rear lens group G _2-2 The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
(3) 0 <n _an −n _ap <0.45
However,
n _ap: wherein in the cemented lens in the front lens group _{G 2-1} positive lens _L refractive index of the medium with respect to the d-line _{ap n an,:} the negative lens in the cemented lens in the front lens group _{G 2-1} the refractive index of the medium at the d-line of the L _an, The zoom lens according to any one of claims 1 to 3, wherein the following conditional expression is satisfied.
(4) 0 <n _bn −n _bp <0.45
However,
n _bn: said negative lens _{L bn} refractive index of the medium _{n bp} with respect to the d-line of in the cemented lens at the rear lens group _{G 2-2:} the positive lens in the cemented lens in the rear lens group _{G 2-2} Refractive index of medium for d line of L _bp The zoom lens according to any one of claims 1 to 4, wherein the following conditional expression is satisfied.
(5) ν _1p <23.2
However,
ν _1p : Abbe number of the medium of the positive lens L _1p in the first lens group The zoom lens according to claim 1, wherein the following conditional expression is satisfied.
(6) 1.790 <n _1p
n _1p : Refractive index of the medium for the d-line of the positive lens L _1p in the first lens group. The first lens group includes, in order from the object side, the negative lens and the positive lens L _1p .
The zoom lens according to any one of claims 1 to 6, wherein the positive lens _L1p is a positive lens having a convex surface directed toward the object side. In order from the object side, a first lens group having a negative refractive power and a second lens group having a positive refractive power,
In the zoom lens that performs zooming by changing an air interval between the first lens group and the second lens group,
The first lens group includes, in order from the object side, a negative lens and a positive lens _L1p having a convex surface facing the object side.
The second lens group includes, in order from the object side, a positive lens, a first cemented lens composed of a positive lens and a negative lens, and a second cemented lens composed of a negative lens and a positive lens. ,
A zoom lens having an aperture stop in the second lens group and closer to the object side than the second cemented lens or near the object side of the second lens group.

Images