JP2005227569A - Two-group zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight and compact two-group zoom lens having a high performance adaptable to high pixels of mega-order, long in exit pupil position, and having a zoom ratio of aboout three times. <P>SOLUTION: The zoom lens 100 has a negative power first lens group A and a positive power second lens group B. The first lens group A includes a negative power first lens whose image side lens face is slightly concave, and a positive power second lens 2 whose object side lens face is convex. The second lens group B includes a front group lens I and a rear group lens II. The front group lens I has a positive power third lens 3 whose object side lens face is slightly convex. The rear lens group II has a compound lens composed of a positive power fourth lens 4 whose object side lens face is convex and a negative power fifth lens 5 whose image side lens face is slightly concave, and a sixth lens 6 whose image side face is convex. The lens faces of both sides of each of the first, second, third, sixth lenses are made aspheric. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a small and lightweight two-group zoom lens compatible with high-order megapixels used in small video cameras, surveillance cameras, digital cameras, mobile phone cameras and the like using light receiving elements such as CCD and CMOS. It is.

  Light receiving elements such as CCDs and CMOSs have been reduced in size from 1/3 inch to 1/4 inch at any time, and the camera itself has been reduced in size accordingly. There is a growing demand for downsizing and light weight in the zoom lens as well as in the taking lens incorporated therein. Furthermore, light receiving elements such as CCDs have become higher in the order of mega pixels, contrary to the miniaturization of CCDs. A zoom lens used in a camera using such a high-pixel light-receiving element must inevitably exhibit high optical performance. Conventionally, in order to exhibit such high optical performance, aberration correction has been performed using a large number of lenses.

  In addition, as a feature of a light receiving element such as a CCD or CMOS, there is a restriction on the angle of the light beam taken into each pixel. If this is ignored, the amount of peripheral light is reduced, resulting in a dark image in the peripheral part. Conventionally, in order to cope with this, measures have been taken to increase the amount of light on the element surface by providing an electrical correction circuit or arranging a microlens so as to be paired with a pixel of the light receiving element. .

  However, both of these measures are factors that increase costs. Therefore, it is necessary to lengthen the exit pupil position to prevent shading, and at the same time, it is necessary to increase the rear focal length because of the necessity of interposing an IR / UV cut filter between the optical system and the light receiving element. A focus type zoom lens is required.

Conventionally, as a zoom lens having a similar two-group configuration, for example, a zoom lens having a zoom ratio of 2.1 times or more and a lens for 35 mm having a good imaging performance aimed at thinning is used as a basis. It is disclosed in the following Patent Document 1.
Japanese Patent Laid-Open No. 5-88084

  Here, in the zoom lens of the two-group configuration disclosed in the above publication, the zoom ratio is 2.1 times or more, but on the wide side, the distortion is as large as (−) 5%, and in addition, the peripheral light amount is abrupt. Has decreased. On the tele side, the air gap on the optical axis between the first lens group G1 and the second lens group G2 is already small, so the zoom ratio is limited to about 2.5 times considering the air gap necessary for the mechanism. it is conceivable that.

  The subject of the present invention is a compact and light-weight compact with a zoom ratio of about three times the exit pupil position, which is small enough to match a digital camera or a camera equipped with a mobile phone, has high performance corresponding to high-order megapixels Another object of the present invention is to provide a zoom lens having a two-group configuration.

The two-group zoom lens of the present invention is
A first lens group having negative power arranged on the object side, and a second lens group having positive power arranged on the image plane side,
The first lens group includes a first lens having negative power arranged on the object side and a second lens having positive power arranged on the image plane side,
A concave surface is formed on the image surface side lens surface of the first lens, and a convex surface is formed on the object side lens surface of the second lens;
The second lens group includes a front group lens arranged on the object side and a rear group lens arranged on the image plane side,
The front group lens includes a third lens, and the third lens is a convex lens in which a convex surface is formed on the object side lens surface;
The rear lens group includes a negative lens composite lens having a configuration in which a fourth lens located on the object side and a fifth lens located on the image side are bonded together, and a sixth lens having negative power. ,
The fourth lens is a lens having a positive power in which a convex surface is formed on the object side lens surface,
The fifth lens is a lens having negative power in which a concave surface is formed on the image side lens surface,
Of the lens surfaces of the first lens group, at least two surfaces are aspherical, and among the lens surfaces of the second lens group, at least two surfaces are aspherical,
The zooming is performed by changing the distance between the first lens group and the second lens group along the optical axis.

  In particular, when the object side lens surface of the first lens is an aspherical surface, it is desirable that the aspherical surface has an inflection point. In this way, it is possible to effectively function aberration correction at the periphery of the screen such as distortion, coma and astigmatism on the wide side.

  Further, the refractive index Nd1 and Abbe number νd1 of the first lens are set to Nd1 <1.6 and νd1> 50, respectively, and the refractive index Nd2 and Abbe number νd2 of the second lens are set to Nd2 <1.6, respectively. , Νd2 <35 is desirable. As a result, axial chromatic aberration and lateral chromatic aberration can be corrected well, and the first and second lenses can be plastic lenses. As a result, the weight of the entire optical system as well as the first lens group can be reduced. In addition, since the sliding resistance during the zoom operation can be reduced, zooming can be facilitated.

  In the two-group zoom lens of the present invention, when zooming, the second lens group is moved closer to the first lens group along the optical axis to switch from the wide end to the tele end, and conversely, the second lens By moving the group away from the first lens group, the tele end is switched to the wide end. Correction of the image plane movement caused by the zooming operation can be performed by keeping the image plane position constant by moving the first lens group in accordance with the movement of the second lens group. When zooming from the wide end to the tele end, the first lens group is moved closer to the second lens group and then moved away from the second lens group to ensure a zoom ratio of 3 times. Is possible.

Next, it is desirable that the second group zoom lens of the present invention satisfies the following conditional expression.
0.65 <| fB / fA | <0.75 (1)
0.05 <| f1 / f2 | <0.2 (2)
10 <tanθw · ΣdW <15 (3)
However,
fA: focal length of the first lens group fB: focal length of the second lens group f1: focal length of the first lens of the first lens group f2: focal length of the second lens of the first lens group ΣdW: of all optical systems From the first lens surface on the object side of the first lens at the wide end to the imaging surface
Distance on the optical axis at θw: Half field angle at the wide end (1/2 of field angle)

  Conditional expression (1) regulates the total length of the zoom lens. In general, it is desirable that this type of lens is set so that the total length is minimized at either the tele end or the wide end. Sets the power of fA and fB so that the tele end is minimized relative to the wide end. In the present invention, when the distance on the optical axis from the object side lens surface of the first lens to the imaging surface at the wide end is ΣdW and the total optical total length at the telephoto end is ΣdT, 0.9 <ΣdW / ΣdT <1. .2 or so, preferably 1.0 <ΣdW / ΣdT <1.2.

  If the upper limit of 0.75 of the conditional expression (1) is exceeded, the total length on the tele side becomes long and the original size reduction cannot be satisfied. If the lower limit of 0.65 is exceeded, the total length of the tele end can be shortened, but the total length of the wide end becomes long, which is not suitable for the purpose of downsizing. In addition, the power of the second lens group becomes too strong and cannot be kept safe against each aberration.

  Conditional expression (2) relates to axial chromatic aberration and chromatic aberration of magnification in the entire zoom range. When the upper limit of 0.2 is exceeded, axial chromatic aberration on the wide side increases, and the performance at the center of the screen deteriorates. On the other hand, if the lower limit of 0.05 is not reached, chromatic aberration of magnification on the wide side cannot be corrected.

  Conditional expression (3) defines the total length and angle of view of the entire optical system at the wide end. If the upper limit of 15 is exceeded, the total length becomes too long to satisfy the desired miniaturization. In addition, the widening of the zoom system cannot be achieved. If the lower limit of 10 is exceeded, the overall length can be shortened, but the power of each lens group becomes stronger and the power of each lens also becomes stronger. This makes lens processing disadvantageous and makes it impossible to stably correct aberrations throughout the entire zoom range. .

  In the two-group zoom lens of the present invention, the rear lens group of the second lens group is composed of a synthetic lens having negative power and a sixth lens having negative power, so that the main point of the second lens group can be reduced. Since the position can be moved to the object side, the entire length of the entire optical system can be shortened. Further, since the first lens group can be a plastic lens, the weight can be reduced and the zoom operation can be performed smoothly. Furthermore, by making the object side lens surface of the first lens an aspherical surface with an inflection point, it is possible to satisfactorily correct off-axis aberrations such as wide-side distortion and coma, A spherical surface can be used to achieve mega-order high resolution. Therefore, according to the present invention, it is possible to realize a small, compact, and lightweight two-group zoom lens having optical performance corresponding to mega-order high pixels.

  Embodiments of a two-group zoom lens to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1A is a configuration diagram illustrating a state at the wide end of the zoom lens 100 according to the first embodiment. The zoom lens 100 includes a first lens group A having negative power and a second lens group B having positive power, which are arranged from the object side toward the image plane 9. A diaphragm 7 is disposed on the object side of the third lens 3, and a cover glass 8 is disposed between the second lens group B and the image plane 9.

  The first lens group A includes a first lens 1 having a negative power in which a concave surface is formed on the image side lens surface, and a second meniscus lens 2 having a positive power having a convex object side lens surface. It is composed of The second lens group B includes a front group lens I and a rear group lens II.

  The front lens group I located on the object side in the second lens group B includes a third lens 3 having a positive power and having a convex surface formed on the object side lens surface. The rear lens group II includes a synthetic lens (junction lens) having a negative power having a configuration in which the fourth lens 4 and the fifth lens 5 are bonded together, and a sixth lens 6 having the same negative power.

  The 4th lens 4 located in the object side of a synthetic lens is a lens which has the positive power in which the object side lens surface is a convex surface. The fifth lens 5 positioned on the image plane side of the synthetic lens is a lens having negative power in which a concave surface is formed on the image plane side lens surface. On the other hand, the sixth lens is a meniscus lens having negative power whose object side lens surface is concave. Note that the synthetic lens of this example is a synthetic lens made of optical glass.

  Here, each of the first lens 1, the second lens 2, the third lens 3, and the sixth lens 6 has an aspheric lens surface on both sides, and the object side lens surface of the first lens 1 is changed. It is an aspherical surface with curved points.

  In the zoom system of the zoom lens 100, zooming is performed by moving the second lens group B along the optical axis 100a, and the image plane position is corrected by the first lens group A. As shown in FIG. 1B, when zooming from the wide end W toward the tele end T, the second lens group B gradually moves toward the object side as indicated by a straight line b. On the other hand, the first lens group A adopts a moving form in which it gradually moves toward the object side and then gradually returns toward the object side as indicated by a curve a.

The lens data of the entire optical system of the zoom lens 100 is as follows.
F number: 3.0 4.26 5.65
Focal length: 3.70 7.13 11.03 mm
fA: −7.355 mm
fB: 4.987 mm
f1: -5.909 mm
f2: 30.732 mm
f45: -14.9777 mm
ΣdW: 19.057mm
tan θw: 0.6216
(Note) f45 is a combined focal length of the fourth lens and the fifth lens of the rear lens.

  The meaning of these symbols is the same in Examples 2 and 3 described later.

  Table 1A shows lens data of the zoom lens 100, and Table 1B shows aspheric coefficients for defining the aspherical shape of the aspherical lens surface. In Table 1A, i represents the order of the lens surfaces counted from the object side, R represents the radius of curvature of the lens surfaces, d represents the distance between the lens surfaces, Nd represents the refractive index of each lens, and νd represents Represents the Abbe number of each lens. The lens surface with a star on the number i is aspheric. Note that W, S, and T in the rightmost column in Table 1A represent distances d between lens surfaces at the wide end, standard, and tell end, respectively.

  The aspherical shape adopted for the lens surface is as follows, assuming that the axis in the optical axis direction is X, the height in the direction orthogonal to the optical axis is H, the conical coefficient is k, and the aspherical coefficients are A, B, C, and D. It can be expressed by a formula.

  The meaning of each symbol and the expression representing the aspherical shape are the same in Examples 2 and 3 described later.

  FIG. 4 is an aberration diagram illustrating various aberrations in the zoom lens 100 according to the first example. (W) is wide, (S) is standard, (T) is tele position, SA is spherical aberration, AS is astigmatism, and DIST is distortion. The meanings of these symbols are the same in Examples 2 and 3 described later.

  In the zoom lens 100 according to Example 1, the refractive index and Abbe number of the first lens 1 are Nd1 = 1.5247 and νd1 = 56.2, respectively, and the refractive index and Abbe number of the second lens are Nd2 = 1.585 and νd2 = 29.9. Therefore, the following conditions are satisfied: Nd1 <1.6, νd1> 50, Nd2 <1.6, νd2 <35.

The zoom lens 100 satisfies the following conditional expressions (1) to (3).
0.65 <| fB / fA | <0.75 (1)
0.05 <| f1 / f2 | <0.2 (2)
10 <tan θw · ΣdW <15 (3)
However,
fA: focal length of the first lens group fB: focal length of the second lens group f1: focal length of the first lens of the first lens group f2: focal length of the second lens of the first lens group θw: half at the wide end Angle of View ΣdW: Distance on the optical axis from the first lens surface on the object side of the first lens to the imaging surface at the wide end

  That is, | fB / fA | = 0.678, | f1 / f2 | = 0.192, and tan θw · ΣdW = 11.85, which satisfies the conditional expressions (1) to (3).

  FIG. 2 is a configuration diagram illustrating the wide end state of the zoom lens 200 according to the second embodiment. The configuration of the optical system of the zoom lens 200 is basically the same as that of the first embodiment, and the first lens group A having a negative power and the second lens group having a positive power from the object side toward the imaging surface. B. The first lens group A includes a first lens 11 having a negative power with a small concave surface facing the image surface side and a second lens 12 having a positive power with a convex surface facing the object side. The second lens group B includes a front group lens I and a rear group lens II. The front group lens I is a third lens 13 having a positive power with a small convex surface facing the object side. The rear lens group II includes a cemented lens of a fourth lens 14 having a positive power with a convex surface facing the object side, a fifth lens 15 having a negative power with a concave surface facing the image surface side, and a concave surface on the object side. And a sixth lens 16 having a negative power directed thereto. The cemented lens is a synthetic lens made of optical glass having negative power. Both surfaces of the lens surfaces of the first lens 11, the second lens 12, the third lens 13, and the sixth lens 16 are aspheric surfaces, and the object side lens surface of the first lens 11 is an aspheric surface having an inflection point. It has become. A diaphragm 17 is disposed on the object side of the third lens 13, and a cover glass 8 is disposed between the sixth lens 16 and the imaging plane 9. The zoom method of the zoom lens 200 is the same as that of the zoom lens 100 of the first embodiment.

The lens data of the entire optical system of the zoom lens 200 is as follows.
F number: 3.0 4.23 5.63
Focal length: 3.70 7.13 11.04 mm
fA: −7.36 mm
fB: 4.98 mm
f1: −6.15 mm
f2: 38.14 mm
f45: -19.204 mm
ΣdW: 19.055mm
tan θw: 0.6216

  Table 2A shows lens data of each lens surface of the zoom lens 200, and Table 2B shows aspheric coefficients for defining the aspheric shape of the aspheric lens surface.

  FIG. 5 is an aberration diagram showing various aberrations of the zoom lens 200.

  In the zoom lens 200, the refractive index and Abbe number of the first lens 11 are Nd1 = 1.5247 and νd1 = 56.2, respectively, and the refractive index and Abbe number of the second lens 12 are Nd2 = 1.585 and νd2, respectively. = 29.9. Therefore, the following conditions are satisfied: Nd1 <1.6, νd1> 50, Nd2 <1.6, νd2 <35.

  The zoom lens 200 satisfies the conditional expressions (1) to (3). That is, | fB / fA | = 0.679, | f1 / f2 | = 0.16, and tan θw · ΣdW = 11.84.

  FIG. 3 is a configuration diagram illustrating the wide end state of the zoom lens 300 according to the third embodiment. The zoom lens 300 is basically the same as the zoom lens 100 of the first embodiment, and the first lens group A having negative power and the second lens group having positive power are sequentially directed from the object side toward the imaging surface. B. The first lens group A includes a first lens 21 having a negative power with a small concave surface facing the image surface side and a second lens 22 having a positive power with a convex surface facing the object side. The second lens group B includes a front group lens I and a rear group lens II. The front lens group I is a third lens 23 having a positive power with a small convex surface facing the object side. The rear lens group II includes a cemented lens of a fourth lens 24 having a positive power with a convex surface facing the object side and a fifth lens 25 having a negative power with a small concave surface facing the image surface, and an image surface side. And a sixth lens 26 having a negative power with a convex surface facing the surface. The cemented lens is a synthetic lens having a negative power made of optical glass. Both the lens surfaces of the first lens 21, the second lens 22, the third lens 23, and the sixth lens 26 are aspheric surfaces, and the object-side lens surface of the first lens 21 is an aspheric surface having an inflection point. ing. A diaphragm 27 is disposed on the object side of the third lens 27, and a cover glass 8 is disposed between the sixth lens 26 and the imaging plane 9. The zoom method of the zoom lens 300 is the same as that of the zoom lens 100 of the first embodiment.

The lens data of the entire optical system of the zoom lens 300 is as follows.
F-number: 2.86 4.01 5.37
Focal length: 3.70 7.15 11.08 mm
fA: −7.38 mm
fB: 4.96 mm
f1: -5.88mm
f2: 31.61 mm
f45: -13.534 mm
ΣdW: 18.968mm
tan θw: 0.6216

  Table 3A shows lens data of each lens surface of the zoom lens 300, and Table 3B shows aspheric coefficients for defining the aspheric shape of the aspheric lens surface.

  FIG. 6 is an aberration diagram showing various aberrations in the zoom lens 300.

  In the zoom lens 300, the refractive index and Abbe number of the first lens 21 are Nd1 = 1.5247 and νd1 = 56.2, respectively, and the refractive index and Abbe number of the second lens 22 are Nd2 = 1.585 and νd2, respectively. = 29.9. Therefore, the following conditions are satisfied: Nd1 <1.6, νd1> 50, Nd2 <1.6, νd2 <35.

  The zoom lens 300 satisfies the conditional expressions (1) to (3). That is, | fB / fA | = 0.67, | f1 / f2 | = 0.186, and tan θw · ΣdW = 11.79.

1 is a schematic configuration diagram of an optical system of a zoom lens 100 according to Embodiment 1. FIG. 5 is a schematic configuration diagram of an optical system of a zoom lens 200 according to Embodiment 2. FIG. 6 is a schematic configuration diagram of an optical system of a zoom lens 300 according to Embodiment 3. FIG. FIG. 6 is an aberration diagram of the zoom lens 100 according to Example 1. FIG. 6 is an aberration diagram of the zoom lens 200 according to Example 2. FIG. 6 is an aberration diagram of the zoom lens 300 according to Example 3.

Explanation of symbols

1, 11, 21 First lens 2, 12, 22 Second lens 3, 13, 23 Third lens 4, 14, 24 Fourth lens 5, 15, 25 Fifth lens 6, 16, 26 Sixth lens 7 Aperture 8 Cover glass 9 Imaging surface I Front lens group
II Rear lens group A First lens group B Second lens group 100, 200, 300 Zoom lens

Claims (4)

A first lens group having negative power arranged on the object side, and a second lens group having positive power arranged on the image plane side,
The first lens group includes a first lens having negative power arranged on the object side and a second lens having positive power arranged on the image plane side,
A concave surface is formed on the image surface side lens surface of the first lens, and a convex surface is formed on the object side lens surface of the second lens;
The second lens group includes a front group lens arranged on the object side and a rear group lens arranged on the image plane side,
The front group lens includes a third lens, and the third lens is a convex lens in which a convex surface is formed on the object side lens surface;
The rear lens group includes a negative lens composite lens having a configuration in which a fourth lens located on the object side and a fifth lens located on the image side are bonded together, and a sixth lens having negative power. ,
The fourth lens is a lens having a positive power in which a convex surface is formed on the object side lens surface,
The fifth lens is a lens having negative power in which a concave surface is formed on the image side lens surface,
Of the lens surfaces of the first lens group, at least two surfaces are aspheric, and among the lens surfaces of the second lens group, at least two surfaces are aspheric,
A two-group zoom lens that performs zooming by changing an interval between the first lens group and the second lens group along the optical axis. In claim 1,
A two-group zoom lens satisfying the following conditions, where the refractive index of the first lens is Nd1, the Abbe number is νd1, the refractive index of the second lens is Nd2, and the Abbe number is νd2.
Nd1 <1.6
νd1> 50
Nd2 <1.6
νd2 <35 In claim 2,
At the wide end in the entire optical system, the half field angle is θw, the distance on the optical axis from the object side lens surface of the first lens to the imaging surface is ΣdW, and the focal length of the first lens group is fA, A two-group zoom lens that satisfies the following conditional expression, where fB is the focal length of the second lens group, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.
0.65 <| fB / fA | <0.75
0.05 <| f1 / f2 | <0.2
10 <tanθw · ΣdW <15 In claim 3,
When the total optical total length at the tele end is ΣdT,
0.9 <ΣdW / ΣdT <1.2
2 group zoom lens that satisfies

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