JP2006201492A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens reduced in length, thickness, size and cost, wherein emission angle of the outermost angle light beams at a wide angle end is made small and it is made suitable for a solid state imaging device. <P>SOLUTION: The zoom lens is provided with: a first lens group I having negative refractive power; a second lens group II having positive refractive power; and a third lens group III having positive refractive power. The first lens group I has a first lens 1 having negative refractive power and a second lens 2 which has positive refractive power and has a meniscus shape whose convex surface is facing toward an object side. The second lens group II has a third lens 3 which has positive refractive power and has a curvature of the object side surface to be greater than the curvature of the image surface side surface and a fourth lens 4 which has negative refractive power and has a curvature of the surface of the image surface side to be greater than the curvature of the object side surface. The third lens group III has a fifth lens 5 having positive refractive power. All of the first lens 1 to the fifth lens 5 are formed by a plastic material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a small zoom lens applied to a digital still camera, a video camera or the like equipped with a solid-state image sensor such as a CCD, and more particularly to a mobile phone, a personal digital assistant (PDA), a PC camera (attached to a personal computer). In addition, the present invention relates to a small zoom lens suitable for a mobile camera used in a connected manner.

  In recent years, solid-state imaging devices such as CCDs used in digital still cameras, video cameras, and the like have been downsized due to the increase in the number of pixels and the increase in density. Is required. In particular, optical systems used for cellular phones, portable information terminals, etc. have a limited allowable mounting space, and therefore are mainly composed of about 1 to 3 fixed focus lenses. At present, there are still few lenses.

On the other hand, as a three-group zoom lens having a zoom ratio of about 2 to 3 times, the first lens group has a positive or negative refractive power, the second lens group has a positive refractive power, and the third lens group has a negative refractive power. (See, for example, Patent Document 1 and Patent Document 2), or negative refractive power in the first lens group, positive refractive power in the second lens group, and positive power in the third lens group. Are known, and the first lens group and the second lens group are each composed of about 3 to 4 glass spherical lenses and glass aspherical lenses (for example, Patent Document 3 and Patent Document 4). , See Patent Document 5).
JP-A-5-173069 JP 2003-315679 A JP 2001-290075 A JP 2004-13169 A JP 2003-307777 A

Incidentally, in a solid-state imaging device such as a CCD, a microlens is provided on the imaging surface in order to efficiently use light. For this reason, if the angle of light incident on the solid-state imaging device, that is, the emission angle is too large, a vignetting phenomenon (shading phenomenon) occurs. Accordingly, it is desirable that the lens system used for the solid-state imaging device is a telecentric optical system in which the exit pupil position is sufficiently away from the image plane and the exit angle is small (about 15 ° at the maximum).
However, in the conventional three-unit zoom lens in which the third lens unit as described above has a negative refractive power, since the emission angle of the outermost angle light beam is too large at the wide-angle end, it is applied to a solid-state imaging device such as a CCD. It was difficult.
Further, in the conventional three-group zoom lens in which the first lens group and the second lens group are formed by about 3 to 4 glass spherical lenses and glass aspherical lenses, respectively, and the third lens group has a positive refractive power. Although it is possible to reduce the exit angle of the outermost light beam at the wide-angle end, the use of a glass aspheric lens increases the cost and the total length of the lens system during shooting and storage. was there.

The present invention has been made in view of the above circumstances, and its object is to reduce the size, weight, thickness, and cost of an outermost light beam at the wide-angle end while keeping the emission angle of the outermost light beam small. It is an object of the present invention to provide a zoom lens with high optical performance suitable for being mounted on a mobile phone, a portable information terminal, a PC camera or the like.
Specifically, a magnification ratio (zoom magnification) of about 2.5 times can be secured, the lens brightness (F number) at the wide-angle end is as bright as about 2.8, and the total length of the lens system at the time of shooting (maximum) A zoom lens satisfying the condition that the distance from the front lens tip to the image plane is 23 mm or less and the total thickness on the optical axis of each lens group is 12 mm or less in order to reduce the thickness when retracted. Is to provide.

The zoom lens according to the present invention includes, in order from the object side to the image plane side, a first lens group having a negative refractive power as a whole, a second lens group having a positive refractive power as a whole, and a positive lens as a whole. A first lens group having a negative refractive power and a positive refractive power arranged in order from the object side to the image plane side. A second meniscus lens having a convex surface facing the object side, and the second lens group has a positive refractive power and an object side surface arranged in order from the object side to the image surface side A third lens having a larger curvature than the curvature of the image side surface, and a meniscus fourth lens having negative refractive power and a curvature of the image side surface larger than the curvature of the object side surface. The third lens group includes a fifth lens having a positive refractive power, and the first lens and the second lens. A third lens, the fourth lens and the fifth lens are all formed of a plastic material, is characterized in that.
According to this configuration, the three-group zoom lens can be constituted by five lenses, so that the total length of the lens system during photographing and storage (collapse) can be shortened, thinned, and miniaturized. In addition, by configuring the third lens group with a lens having a positive refractive power, the exit angle of the outermost angle light beam at the wide-angle end can be suppressed small, and the zoom lens is suitable for a solid-state imaging device. Furthermore, by forming all the lenses constituting the first to third lens groups from a plastic material, the cost can be reduced and the entire weight can be reduced.

In the above configuration, the second lens unit is moved from the image plane side to the object side to perform zooming from the wide-angle end to the telephoto end, and the first lens unit is moved to adjust the image plane variation accompanying zooming. A configuration in which the first lens group or the third lens group is moved to adjust the image plane variation accompanying the variation of the object can be adopted.
According to this configuration, by moving the first lens unit and adjusting the image plane variation accompanying the variation of the object (focus adjustment in the variation of the object distance), the variation of various aberrations particularly at a finite distance is reduced. By moving the third lens group and adjusting the image plane variation accompanying the object variation (focus adjustment when the object distance changes), the total lens length can be reduced. Since the zoom lens does not change and the diameter of the first lens group can be reduced, the size and thickness can be reduced.

In the above configuration, the focal length of the first lens unit is f1, the focal length of the second lens unit is f2, the focal length of the third lens unit is f3, and the lens system from the front surface of the first lens to the image plane at the wide angle end. When the focal length is fw, the following conditional expressions (1), (2),
(1) 0.5 <f2 / | f1 | <1.3
(2) 1.25 <f3 / fw <4.5
A configuration that satisfies the above can be adopted.
According to this configuration, by satisfying conditional expression (1), it is possible to obtain good optical performance by particularly correcting distortion aberration and lateral chromatic aberration while securing a zoom ratio of about 2.5 times. In addition, by satisfying conditional expression (2), it is possible to set the appropriate exit pupil position and achieve telecentricity suitable for the solid-state imaging device by satisfying conditional expression (2). it can.

In the above configuration, when the curvature radius of the object side surface of the fourth lens is R8 and the curvature radius of the image side surface of the fourth lens is R9, the following conditional expression (3):
(3) 1.0 <R8 / R9 <3.0
A configuration that satisfies the above can be adopted.
According to this configuration, in the fourth meniscus lens having a large curvature (small curvature radius) on the image side surface, the condition is that the curvature radius R8 of the object side surface and the curvature radius R9 of the image side surface are the conditions. In particular, astigmatism and coma can be corrected satisfactorily by setting so as to satisfy Expression (3).

In the above configuration, when the distance on the optical axis between the first lens and the second lens is D2, and the focal length of the lens system from the front surface of the first lens to the image plane at the wide angle end is fw, the following conditional expression ( 4),
(4) D2 / fw> 0.2
A configuration that satisfies the above can be adopted.
According to this configuration, various aberrations, particularly spherical aberration, can be improved by setting the distance on the optical axis between the first lens and the second lens constituting the first lens group so as to satisfy the conditional expression (4). It is possible to achieve a reduction in size and thickness while correcting.

In the above configuration, at least one surface of the first lens on the object side and the image surface side, a surface of the second lens group having a convex surface facing the object side, and at least one surface of the fifth lens on the object side and image surface side Can adopt a configuration in which each is formed on an aspherical surface.
According to this configuration, distortion and astigmatism can be corrected particularly well by the aspherical surface provided on the first lens, and the spherical surface provided on the convex surface on the object side of the second lens group is particularly spherical. Aberration can be corrected well, and astigmatism and coma can be corrected particularly well by the aspherical surface provided in the fifth lens. Thereby, various aberrations can be favorably corrected as a whole, and a zoom lens with high optical performance can be obtained.

In the above-described configuration, the aspherical surface of the first lens may be configured to have an aspherical surface on the surface with the smaller radius of curvature.
According to this configuration, particularly, distortion and astigmatism can be favorably corrected, and a zoom lens with high optical performance can be obtained.

In the above configuration, it is possible to adopt a configuration in which the aspherical surface of the first lens is formed such that the negative refractive power becomes weaker toward the peripheral portion.
According to this configuration, particularly, distortion and astigmatism can be favorably corrected, and a zoom lens with high optical performance can be obtained.

In the above configuration, the first lens and the second lens may be formed of the same material.
According to this configuration, by making the plastic material of the first lens and the second lens the same, it is possible to manufacture with one injection molding machine equipment, and the material can be used efficiently, Simplification, simplification, and cost reduction can be achieved.

In the above configuration, a configuration in which the third lens and the fourth lens are formed of the same material can be employed.
According to this configuration, by making the plastic material of the third lens and the fourth lens the same, it is possible to manufacture with one injection molding machine equipment, and the material can be used efficiently, Simplification, simplification, and cost reduction can be achieved.

In the above configuration, a configuration in which the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all formed of the same material can be employed.
According to this configuration, by making all the plastic materials of the first lens to the fifth lens the same, it becomes possible to manufacture with one injection molding machine equipment, and the material can be used more efficiently. Procurement of materials can be further facilitated and simplified, and costs can be further reduced.

According to the present invention, it is possible to reduce the outermost light beam angle at the wide-angle end while reducing the size, weight, thickness, cost, etc., and to be mounted on mobile phones, portable information terminals, PC cameras, etc. Therefore, it is possible to obtain a zoom lens with high optical performance that is suitable for the operation.
In particular, it has a zoom ratio of about 2.5 times, and the brightness (F number) of the lens at the wide angle end is as bright as about 2.8, and the entire length of the lens system at the time of photographing (from the front end of the front lens to the image plane) The distance between the lens and the optical axis is 23 mm or less, and the total thickness of all lens groups on the optical axis is 12 mm or less. Thus, a zoom lens with high optical performance in which various aberrations are corrected is obtained. be able to.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 to 3 show an embodiment of a zoom lens according to the present invention. FIG. 1 is a basic configuration diagram, FIG. 2 is an optical path diagram of the zoom lens shown in FIG. 1, and FIGS. ), (C) are states showing the positional relationship at the wide-angle end, the intermediate position and the telephoto end.

  In this zoom lens, as shown in FIG. 1, a first lens group (I) having a negative refractive power as a whole and a second lens having a positive refractive power as a whole from the object side to the image plane side. The lens group (II) and the third lens group (III) having a positive refractive power as a whole are sequentially arranged.

The first lens group (I) is formed by the first lens 1 and the second lens 2, and the second lens group (II) is formed by the third lens 3 and the fourth lens 4, and the third lens group (III ) Is formed by the fifth lens 5. In the second lens group (II), an aperture stop SD that defines a predetermined aperture is disposed in the vicinity of the front surface of the third lens 3.
In the third lens group (III), a glass filter 6 such as an infrared cut filter, a low-pass filter, and a CCD cover glass is disposed closer to the image plane side than the fifth lens 5, and a CCD or the like is connected behind the filter. An image plane P is disposed.

Here, the focal length of the first lens group (I) is f1, the focal length of the second lens group (II) is f2, the focal length of the third lens group (III) is f3, and the lens system at the wide angle end (first The focal length from the front surface of the lens 1 to the image plane P) is represented by fw.
Further, in the first lens 1 to the fifth lens and the glass filter 6, as shown in FIG. 1, each surface is Si (i = 1 to 13), and the curvature radius of each surface Si is Ri (i = 1-13), the refractive index with respect to d-line is represented by Ni and the Abbe number is represented by νi (i = 1-6).
Further, the distance (thickness, air distance) on each optical axis L from the first lens 1 to the glass filter 6 is represented by Di (i = 1 to 12), and from the rear surface of the glass filter 6 to the image plane P. The interval (back focus) is represented by BF.

In the above configuration, the second lens group (II) moves from the image plane side to the object side, that is, from the wide-angle end shown in FIG. 3A to the intermediate position shown in FIG. The zooming operation is performed by moving to the telephoto end shown in FIG. At this time, the first lens group (I) moves so as to adjust (correct) the image plane fluctuation accompanying the zooming operation. For this reason, the entire length of the lens system (the distance from the front surface S1 of the first lens 1 to the image plane P) changes according to the movement of the first lens group (I).
Further, the first lens group (I) or the third lens group (II) moves so as to adjust the image plane variation accompanying the variation of the object (adjust the focus when the object distance changes). That is, by moving the first lens group (I) and adjusting the image plane variation accompanying the variation of the object (focusing adjustment in the variation of the object distance), the variation of various aberrations especially at a finite distance is reduced. Good optical characteristics can be obtained, and the third lens group (III) is moved to adjust the image plane variation accompanying the variation of the object (focus adjustment in the variation of the object distance). However, the zoom lens does not change the overall lens length, and the lens diameter of the first lens group (I) can be reduced, so that a reduction in size and thickness can be achieved.

  In the zoom lens configured as described above, as shown in FIG. 2, the light beam L1 (subject light) passes through the first lens 1 having a negative refractive power, due to its front surface S1 (concave surface) and rear surface S2 (concave surface). The first lens group (I) is refracted in a diverging direction and refracted in a direction converged by its front surface S3 (convex surface) and rear surface S4 (concave surface) when passing through the second lens 2 having a positive refractive power. As a whole, the light is refracted in a diverging direction, and when passing through the third lens 3 having a positive refractive power, it is refracted in a direction converged by its front surface S6 (convex surface) and rear surface S7 (convex surface), and has a negative refractive power. When passing through the fourth lens 4, it is refracted in a diverging direction by its front surface S8 (convex surface) and rear surface S9 (concave surface), and the second lens group (II) is refracted in a converging direction and has a positive refractive power. When passing through the fifth lens 5 having After refracted in a direction to converge the front S10 (convex) and a rear surface S11 (convex), and reaches the image plane P of the CCD through the glass filter 6.

The first lens 1 is a biconcave lens having negative refractive power with concave surfaces S1 and S2 facing the object side and the image surface side.
The second lens 2 is a meniscus lens having a positive refractive power with the convex surface S3 facing the object side and the concave surface S4 facing the image surface side.
The third lens 3 is a biconvex lens having positive refracting power with the convex surfaces S6 and S7 facing the object side and the image plane side, and the curvature 1 / R6 of the convex surface S6 on the object side is a convex surface on the image plane side. It is formed to be larger than the curvature 1 / R7 of S7.
The fourth lens 4 is a meniscus lens having negative refractive power with the convex surface S8 facing the object side and the concave surface S9 facing the image side, and the curvature 1 / R9 of the concave surface S9 on the image side is the object side. It is formed to be larger than the curvature 1 / R8 of the convex surface S8.
The fifth lens 5 is a biconvex lens having positive refractive power with the convex surfaces S10 and S11 facing the object side and the image surface side.

The first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5 are all made of a plastic material. In this way, by configuring all the lenses constituting the zoom lens with plastic lenses instead of glass lenses, it is possible to reduce the cost and weight.
Here, the first lens 1 and the second lens 2 may be formed of the same plastic material, the third lens 3 and the fourth lens 4 may be formed of the same plastic material, All of the first lens 5 to the fifth lens 5 may be formed of the same plastic material. Thus, the first lens 1 and the second lens 2 are formed of the same material, the third lens 3 and the fourth lens 4 are formed of the same material, or all of the first lens 1 to the fifth lens 5 are formed of the same material. By forming, the first lens group (I), the second lens group (II), or all the lens groups (I), (II), (III) can be manufactured with one injection molding machine equipment. Thus, the material can be used efficiently, facilitating and simplifying material procurement, and reducing costs.

The most representative plastic materials for forming the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5 are acrylic resin (methacrylic resin, PMMA), polycarbonate resin. In recent years, various plastic materials with improved impact resistance, heat resistance, hygroscopicity, birefringence and the like have been developed, and these materials can be appropriately selected.
As materials represented by acrylic resin, for example, “ACRYPET” manufactured by Mitsubishi Rayon Co., Ltd. can be cited. In addition, “ZEONEX 330R” manufactured by Nippon Zeon Co., Ltd., a cycloolefin polymer, JSR of norbornene resin Various plastic materials including “ARTON” manufactured by the company can be selected.
In addition, examples of polycarbonate resin materials include “Panlite” manufactured by Teijin Kasei Co., Ltd. and “Iupilon” manufactured by Mitsubishi Engineering Plastics Co., Ltd. In addition to these, Osaka Gas Chemical Co., Ltd., a fluorene-based polyester. Various plastic lens materials can be selected, including “OKP4” and the like.

In the above configuration, the surface S2 having the smaller radius of curvature among the object-side surface S1 and the image-side surface S2 of the first lens 1 is formed as an aspherical surface. And this aspherical surface S2 is formed so that negative refractive power becomes weak as it goes to a peripheral part. As described above, the first lens 1 is provided with the aspherical surface S2, and the aspherical surface S2 is formed so that the negative refractive power becomes weaker toward the peripheral portion, so that particularly distortion and astigmatism are excellent. Can be corrected.
Further, among the third lens 3 and the fourth lens 4 constituting the second lens group (II), the convex surface on the object side, for example, the convex surface S6 of the third lens 3 is formed as an aspherical surface. Thus, by providing the aspherical surface on the convex surface S6 on the object side, it is possible to particularly correct spherical aberration.
Further, among the convex surface S10 on the object side and the convex surface S11 on the image surface side of the fifth lens 5, for example, the convex surface S11 on the image surface side is formed as an aspherical surface. As described above, by providing the fifth lens 5 with the aspherical surface S11, it is possible to particularly favorably correct astigmatism and coma.
As described above, since the first lens group (I), the second lens group (II), and the third lens group (III) are each provided with an aspheric surface, various aberrations can be satisfactorily corrected as a whole, and optical performance is improved. High zoom lens can be obtained.

Here, the surface having an aspheric surface is defined by the following equation.
Z = Cy ² / [1+ (1-εC ² y ² ) ^1/2 ] + Dy ⁴ + Ey ⁶ + Fy ⁸ + Gy ¹⁰ + Hy ¹²
However, Z: distance from the tangent plane at the vertex of the aspheric surface to a point on the aspheric surface whose height from the optical axis L is y, y: height from the optical axis L, C: at the vertex of the aspheric surface Curvature (1 / R), ε: conic constant, D, E, F, G, H: aspheric coefficient.

In the above configuration, the focal length f1 of the first lens group (I), the focal length f2 of the second lens group (II), the focal length f3 of the third lens group (III), and the first lens 1 at the wide angle end. The focal length fw of the lens system from the front surface S1 to the image plane P is preferably conditional expressions (1), (2),
(1) 0.5 <f2 / | f1 | <1.3,
(2) 1.25 <f3 / fw <4.5,
It is formed so as to satisfy.

Conditional expression (1) defines an appropriate focal length ratio between the first lens group (I) and the second lens group (II). When the lower limit is exceeded, the magnification is about 2.5 times. It becomes difficult to obtain the ratio, and when the value exceeds the upper limit, distortion and lateral chromatic aberration are particularly increased, making correction difficult. That is, by satisfying conditional expression (1), it is possible to achieve good optical performance and downsizing while securing a zoom ratio of about 2.5 times.
Conditional expression (2) defines an appropriate focal length range of the third lens group (III). When the lower limit value is exceeded, it becomes difficult to reduce the size of the entire lens system. As the pupil position approaches the image plane P, it becomes difficult to obtain telecentricity. That is, by satisfying conditional expression (2), it is possible to achieve downsizing and optimize the exit pupil position to obtain telecentricity, thereby obtaining a zoom lens suitable for a solid-state imaging device.

In the above configuration, the curvature radius R8 of the object-side surface S8 and the curvature radius R9 of the image-side surface S9 of the fourth lens 4 included in the second lens group (II) are preferably conditional expressions (3 ),
(3) 1.0 <R8 / R9 <3.0,
It is formed so as to satisfy.
Conditional expression (3) defines the ratio of the curvature radii of the object-side surface and the image-side surface of the fourth lens 4 having a meniscus shape. By satisfying conditional expression (4), various aberrations, in particular, Astigmatism and coma can be satisfactorily corrected.

Furthermore, in the above configuration, the distance D2 on the optical axis L between the first lens 1 and the second lens 2 of the first lens group (I) and the lens system at the wide angle end (the front surface S1 to the image plane P of the first lens 1). The focal length fw is preferably conditional expression (4),
(4) D2 / fw> 0.2,
It is formed so as to satisfy.
Conditional expression (4) defines the surface interval on the optical axis L of the negative lens component (first lens 1) and the positive lens component (second lens 2) in the first lens group (I). Outside the range, the distance between the first lens 1 and the second lens 2 on the optical axis is shortened, which is advantageous from the viewpoint of miniaturization, but it is difficult to correct various aberrations, particularly spherical aberration. That is, by satisfying conditional expression (4), it is possible to correct spherical aberration well while achieving miniaturization and thinning.

  Next, specific numerical examples of the zoom lens having the configuration shown in FIGS. 1 to 3 will be described below as Examples 1 to 4.

Main specifications in the first embodiment are shown in Table 1, various numerical data (setting values) are shown in Table 2, numerical data relating to the aspherical surface are shown in Table 3, and each lens system at the wide-angle end, intermediate position, and telephoto end. Table 4 shows numerical data regarding the focal length f (fw, fm, ft) and the distances D4, D9, D11 on the optical axis.
In this embodiment, the numerical data of the conditional expressions (1) to (4) are
(1) f2 / | f1 | = 5.652 / | -7.350 | = 0.769
(2) f3 / fw = 8.814 / 2.820 = 3.13
(3) R8 / R9 = 3.677 / 2.149 = 1.711
(4) D2 / fw = 1.20 / 2.820 = 0.426
It becomes. In Table 1, the air-converted back focus is the distance from the rear surface S11 of the fifth lens 5 to the image plane P at an infinite object distance. In Table 4, fm is the focal length of the lens system from the front surface S1 of the first lens 1 to the image plane P at the intermediate position, and ft is the lens system from the front surface S1 of the first lens 1 to the image plane P at the telephoto end. Indicates the focal length.

  In addition, aberration diagrams regarding spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end, the intermediate position, and the telephoto end are as shown in FIG. 4, FIG. 5, and FIG. 4 to 6, F represents aberration due to the F line, d represents aberration due to the d line, C represents aberration due to the C line, S represents aberration on the sagittal plane, and M represents aberration on the meridional plane. .

  In Example 1 described above, the zoom ratio is about 2.45, the exit angle of the outermost light beam at the wide-angle end is -11.52 °, and the total length of the lens system at the time of photographing (the front surface S1 to the image plane of the first lens 1). P) is 20.90 mm (wide-angle end) to 18.59 mm (intermediate position) to 18.95 mm (telephoto end), and the total thickness on the optical axis of the first lens group (I) to the third lens group (III) The value is 8.67 mm, the F-number at the wide-angle end is 2.80, and the field angle (2ω) is 62.1 ° (wide-angle end) to 36.3 ° (intermediate position) to 25.9 ° (telephoto end). It is possible to obtain a zoom lens with high optical performance in which the exit angle of the outermost light beam at the wide-angle end is kept small, is small and thin when stored, and various aberrations are well corrected.

Main specifications in the second embodiment are shown in Table 5, various numerical data (setting values) are shown in Table 6, numerical data relating to aspheric surfaces are shown in Table 7, and each lens system at the wide angle end, intermediate position, and telephoto end. Table 8 shows numerical data on the focal length f (fw, fm, ft) and the distances D4, D9, D11 on the optical axis.
In this embodiment, the numerical data of the conditional expressions (1) to (4) are
(1) f2 / | f1 | = 5.652 / | -7.607 | = 0.743
(2) f3 / fw = 7.921 / 2.820 = 2.809
(3) R8 / R9 = 3.706 / 2.133 = 1.737
(4) D2 / fw = 1.20 / 2.820 = 0.426
It becomes. In Table 5, the air-converted back focus is the distance from the rear surface S11 of the fifth lens 5 to the image plane P at an infinite object distance. In Table 8, fm is the focal length of the lens system from the front surface S1 of the first lens 1 to the image plane P at the intermediate position, and ft is the lens system from the front surface S1 of the first lens 1 to the image plane P at the telephoto end. Indicates the focal length.

  In addition, aberration diagrams regarding spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end, the intermediate position, and the telephoto end are as shown in FIG. 7, FIG. 8, and FIG. 7 to 9, F represents the aberration due to the F line, d represents the aberration due to the d line, C represents the aberration due to the C line, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane. .

  In Example 2 described above, the zoom ratio is about 2.45, the exit angle of the outermost angle light beam at the wide-angle end is −10.73 °, and the entire length of the lens system at the time of photographing (the front surface S1 to the image plane of the first lens 1). P) is 20.81 mm (wide angle end) to 18.45 mm (intermediate position) to 18.76 mm (telephoto end), and the total thickness on the optical axis of the first lens group (I) to the third lens group (III) The value is 8.67 mm, the F-number at the wide-angle end is 2.82, and the field angle (2ω) is 61.4 ° (wide-angle end) to 36.0 ° (intermediate position) to 25.7 ° (telephoto end). It is possible to obtain a zoom lens with high optical performance in which the exit angle of the outermost light beam at the wide-angle end is kept small, is small and thin when stored, and various aberrations are well corrected.

Main specifications in the third embodiment are shown in Table 9, various numerical data (setting values) are shown in Table 10, numerical data relating to the aspherical surface are shown in Table 11, and each lens system at the wide-angle end, intermediate position, and telephoto end. Table 12 shows numerical data regarding the focal length f (fw, fm, ft) and the distances D4, D9, D11 on the optical axis.
In this embodiment, the numerical data of the conditional expressions (1) to (4) are
(1) f2 / | f1 | = 5.719 / | -7.127 | = 0.802
(2) f3 / fw = 9.464 / 2.820 = 3.356
(3) R8 / R9 = 3.606 / 2.167 = 1.664
(4) D2 / fw = 1.20 / 2.820 = 0.426
It becomes. In Table 9, the air-converted back focus is the distance from the rear surface S11 of the fifth lens 5 to the image plane P at an infinite object distance. In Table 12, fm is the focal length of the lens system from the front surface S1 of the first lens 1 to the image plane P at the intermediate position, and ft is the lens system from the front surface S1 of the first lens 1 to the image plane P at the telephoto end. Indicates the focal length.

  In addition, aberration diagrams relating to spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end, the intermediate position, and the telephoto end are as shown in FIG. 10, FIG. 11, and FIG. 10 to 12, F represents the aberration due to the F line, d represents the aberration due to the d line, C represents the aberration due to the C line, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane. .

  In Example 3 described above, the zoom ratio is about 2.45, the exit angle of the outermost angle light beam at the wide-angle end is -10.82 °, and the entire length of the lens system at the time of photographing (the front surface S1 to the image plane of the first lens 1). P) is 21.05 mm (wide-angle end) to 18.92 mm (intermediate position) to 19.39 mm (telephoto end), and the total thickness on the optical axis of the first lens group (I) to the third lens group (III) The value is 8.67 mm, the F number at the wide angle end is 2.84, and the field angle (2ω) is 62.3 ° (wide angle end) to 36.4 ° (intermediate position) to 26.0 ° (telephoto end). It is possible to obtain a zoom lens with high optical performance in which the exit angle of the outermost light beam at the wide-angle end is kept small, is small and thin when stored, and various aberrations are well corrected.

Main specifications in the fourth embodiment are shown in Table 13, various numerical data (setting values) are shown in Table 14, numerical data relating to aspheric surfaces are shown in Table 15, and each lens system at the wide-angle end, intermediate position, and telephoto end. Table 16 shows numerical data regarding the focal length f (fw, fm, ft) and the distances D4, D9, D11 on the optical axis.
In this embodiment, the numerical data of the conditional expressions (1) to (4) are
(1) f2 / | f1 | = 5.626 / | −7.455 | = 0.755
(2) f3 / fw = 8.674 / 2.820 = 3.076
(3) R8 / R9 = 3.720 / 2.122 = 1.753
(4) D2 / fw = 1.20 / 2.820 = 0.426
It becomes. In Table 13, the air-converted back focus is a distance from the rear surface S11 of the fifth lens 5 to the image plane P at an infinite object distance. In Table 16, fm is the focal length of the lens system from the front surface S1 of the first lens 1 to the image plane P at the intermediate position, and ft is the lens system from the front surface S1 of the first lens 1 to the image plane P at the telephoto end. Indicates the focal length.

  In addition, aberration diagrams regarding spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end, the intermediate position, and the telephoto end are as shown in FIG. 13, FIG. 14, and FIG. In FIG. 13 to FIG. 15, F represents the aberration due to the F line, d represents the aberration due to the d line, C represents the aberration due to the C line, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane. .

  In Example 4 described above, the zoom ratio is about 2.45, the exit angle of the outermost angle light beam at the wide-angle end is -11.16 °, and the entire length of the lens system at the time of photographing (the front surface S1 to the image plane of the first lens 1). P) is 20.84 mm (wide angle end) to 18.43 mm (intermediate position) to 18.72 mm (telephoto end), and the total thickness on the optical axis of the first lens group (I) to the third lens group (III) The value is 8.67 mm, the F number at the wide angle end is 2.83, and the field angle (2ω) is 62.1 ° (wide angle end) to 36.2 ° (intermediate position) to 25.9 ° (telephoto end). It is possible to obtain a zoom lens with high optical performance in which the exit angle of the outermost light beam at the wide-angle end is kept small, is small and thin when stored, and various aberrations are well corrected.

  As described above, the zoom lens of the present invention can be applied not only to a digital still camera and a video camera using a solid-state image sensor such as a CCD, but also to a silver salt film camera.

It is a block diagram which shows one Embodiment of the zoom lens which concerns on this invention. FIG. 2 is an optical path diagram of the zoom lens in FIG. 1. (A), (b), (c) is a state diagram which shows the wide-angle end, intermediate position, and telephoto end of the zoom lens shown in FIG. FIG. 4 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide angle end of the zoom lens according to Example 1; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position of the zoom lens according to Example 1; FIG. 4 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end of the zoom lens according to Example 1; FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide angle end of the zoom lens according to Example 2; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position of the zoom lens according to Example 2; FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end of the zoom lens according to Example 2; FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of the zoom lens according to Example 3; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position of the zoom lens according to Example 3; FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end of the zoom lens according to Example 3; FIG. 9 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the wide-angle end of the zoom lens according to Example 4; FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at an intermediate position of the zoom lens according to Example 4; FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, distortion, and lateral chromatic aberration at the telephoto end of the zoom lens according to Example 4;

Explanation of symbols

I First lens group II Second lens group III Third lens group 1 First lens (first lens group)
2 Second lens (first lens group)
SD Aperture stop 3 Third lens (second lens group)
4 Fourth lens (second lens group)
5 Fifth lens (third lens group)
6 Glass filter L Optical axis D1 to D12 Distance on optical axis BF Back focus R1 to R13 Curvature radius S1 to S13 Surface N1 to N6 Refractive index ν1 to ν6 Abbe number

Claims (11)

In order from the object side to the image surface side, a first lens group having a negative refractive power as a whole, a second lens group having a positive refractive power as a whole, and a third lens having a positive refractive power as a whole A group,
The first lens group includes a first lens having negative refractive power arranged in order from the object side to the image plane side, and a second meniscus shape having positive refractive power and a convex surface facing the object side. A lens, and
The second lens group includes a third lens that is arranged in order from the object side to the image plane side, has a positive refractive power, and has a curvature of the object side surface larger than that of the image side surface, and a negative lens A meniscus fourth lens having a refractive power of 5 and a curvature of the image side surface larger than that of the object side surface,
The third lens group includes a fifth lens having a positive refractive power,
The first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all made of a plastic material.
A zoom lens characterized by that. The second lens group is moved from the image plane side to the object side to perform zooming from the wide-angle end to the telephoto end, and the first lens group is moved to adjust image plane variation accompanying the zooming, Moving the first lens group or the third lens group to adjust the image plane variation accompanying the variation of the object;
The zoom lens according to claim 1. The focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, and the lens system from the front surface of the first lens to the image plane at the wide angle end. The zoom lens according to claim 1 or 2, wherein the following conditional expressions (1) and (2) are satisfied when the focal length is fw.
(1) 0.5 <f2 / | f1 | <1.3
(2) 1.25 <f3 / fw <4.5 When the radius of curvature of the object side surface of the fourth lens is R8 and the radius of curvature of the image side surface of the fourth lens is R9, the following conditional expression (3) is satisfied. Item 4. The zoom lens according to any one of Items 1 to 3.
(3) 1.0 <R8 / R9 <3.0 When the distance on the optical axis between the first lens and the second lens is D2, and the focal length of the lens system from the front surface of the first lens to the image plane at the wide angle end is fw, the following conditional expression (4) 5. The zoom lens according to claim 1, wherein the zoom lens satisfies the following.
(4) D2 / fw> 0.2 At least one surface of the first lens on the object side and the image surface side, a surface of the second lens group with a convex surface facing the object side, and at least one surface of the fifth lens on the object side and image surface side are , Each aspherical,
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The aspherical surface of the first lens has an aspherical surface on the surface with the smaller radius of curvature.
The zoom lens according to claim 6. The aspherical surface of the first lens is formed such that the negative refractive power becomes weaker toward the periphery.
The zoom lens according to claim 7. The first lens and the second lens are formed of the same material,
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. The third lens and the fourth lens are made of the same material,
The zoom lens according to claim 1, wherein: The first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all formed of the same material.
The zoom lens according to claim 1, wherein the zoom lens is a zoom lens.

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