JP2006039174A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost, compact zoom lens which is particularly suitable to be loaded to a small-sized information terminal apparatus while corresponding to the accomplishment of a pixel of high quality. <P>SOLUTION: The zoom lens is provided with a 1st negative meniscus lens G1 having a convex face on the object side near a para-axis, a 2nd lens G2, both faces of which are convex near the para-axis, and a 3rd lens G3, both faces of which are concave near the para-axis in this order from the object side. Regarding the 1st lens G1 to the 3rd lens G3, both faces of each lens are aspherical, and the 2nd lens G2 and the 3rd lens G3 are moved on an optical axis Z1 at zooming. Besides, the zoom lens satisfies prescribed conditional expressions (1) to (5). Consequently, the whole length of the zoom lens is shortened and the zoom lens is made compact, and also, various kinds of aberration are satisfactorily corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zoom lens suitable for mounting on a small information terminal device such as a mobile phone with a camera or a PDA (Personal Digital Assistant).

  In recent years, with the spread of personal computers to ordinary homes and the like, digital still cameras (hereinafter simply referred to as digital cameras) capable of inputting image information such as photographed landscapes and human images to personal computers have rapidly spread. It's getting on. As mobile phones become more sophisticated, camera-equipped mobile phones equipped with a small imaging module are also rapidly spreading. In addition, small information terminal devices such as PDAs that are equipped with an imaging module have become widespread.

  In devices equipped with these imaging functions, imaging devices such as a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) are used. In recent years, these image sensors have been extremely reduced in size and increased in pixels, and accordingly, the main body of the image pickup apparatus and the lens mounted thereon are also required to have a compact configuration with high resolution performance. Yes. For example, camera-equipped mobile phones and the like that are compatible with megapixels of 1 million pixels or more have been put into practical use, and the demand for performance has been increasing.

  By the way, there are an optical zoom method and an electronic zoom method as a method for realizing a zoom function in an imaging device using an image sensor. In the optical zoom system, a zoom lens is mounted as a photographing lens, and the photographing magnification is optically changed. The electronic zoom method electronically changes the size of a subject image by trimming an image by signal processing. In general, the optical zoom method can obtain higher resolution performance than the electronic zoom method. Therefore, when zooming with high resolution performance, the optical zoom method is preferable.

Conventionally, as a relatively small zoom lens used for a digital camera or the like, for example, there is a lens described in Patent Document 1 below. Patent Document 1 describes a zoom lens of a two-group zoom system that is composed of five or six lenses as a whole.
JP 2003-270533 A

  In small information terminal devices such as camera-equipped mobile phones, conventionally, fixed-focus lenses are generally used in terms of cost and miniaturization, but with the recent increase in functionality and multifunction, There is a demand for a zoom function. Therefore, recently, some mobile phones with cameras using fixed focus lenses have realized a zoom function by adopting an electronic zoom method. However, in the case of the electronic zoom method, the resolution deteriorates as the image enlargement ratio increases, and it has become difficult to cope with the recent increase in the number of pixels of the image sensor.

  Therefore, it is conceivable that a camera-equipped mobile phone or the like is equipped with a zoom lens and adopts an optical zoom system. In this case, it is not practical to use a high-performance zoom lens developed for a conventional digital camera as it is in terms of cost and compactness. Although the zoom lens described in Patent Document 1 is also reduced in size with a relatively small number of lenses for a digital camera, it is further reduced in size when used in a small information terminal device. It is preferable that On the other hand, a low-cost and compact zoom lens composed of about three lenses has been developed in the past, but it is insufficient in terms of aberration performance, and further improved in compactness such as further reduction in the overall length. It has been demanded.

  SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a zoom that can realize a low-cost and compact optical system that is suitable for mounting on a small information terminal device, while corresponding to an increase in the number of pixels. To provide a lens.

  A zoom lens according to the present invention includes, in order from the object side, a first lens having a negative meniscus shape with a convex surface facing the object side in the vicinity of the paraxial axis, a second lens having a biconvex shape in the vicinity of the paraxial axis, And a third lens having a biconcave shape in the vicinity. Both the first lens to the third lens are aspherical on both surfaces, and the second lens and the third lens move on the optical axis during zooming. This zoom lens further satisfies the following conditional expressions (1) to (5).

2.0 <ft / fw <3.5 (1)
2.5 <TCLw / fw <5.0 (2)
−1.2 <f2 / f3 <−0.4 (3)
Nd (G1)> 1.65 (4)
νd (G2)> 45 (5)
Where ft is the focal length of the entire system at the telephoto end, fw is the focal length of the entire system at the wide angle end, TCLw is the total length at the wide angle end, f2 is the focal length of the second lens, and f3 is the focal length of the third lens. Distance, Nd (G1) represents the refractive index of the first lens, and νd (G2) represents the Abbe number of the second lens.

  In the zoom lens according to the present invention, zooming is performed by moving the second lens and the third lens on the optical axis. Accordingly, the first lens closest to the object remains fixed during zooming.

  Although this zoom lens has a simple configuration of 3 elements in 3 groups, aspherical lenses are often used, and the overall length is shorter and more compact than the conventional 3 zoom lenses. It has been corrected. In addition to these, conditional distributions (1) to (3) are satisfied, and power distribution and the like are made appropriate, so that a good balance between the length of the entire length and the aberration performance is maintained. In particular, in order to shorten the overall length, the refractive index of the first lens is defined by conditional expression (4). In order to reduce axial chromatic aberration, the Abbe number of the second lens is defined by conditional expression (5).

  According to the zoom lens of the present invention, in order from the object side, a first lens having a negative meniscus shape having a convex surface facing the object side in the vicinity of the paraxial axis, and a second lens having a biconvex shape in the vicinity of the paraxial direction; And a third lens having a biconcave shape in the vicinity of the paraxial axis. Both the first lens to the third lens are aspherical on both sides, and the second lens and the third lens are on the optical axis during zooming. Since it is configured to move and further satisfies predetermined conditional expressions (1) to (5), various aberrations can be corrected well while shortening the overall length and reducing the size. . Therefore, it is possible to realize a low-cost and compact optical system that is suitable for mounting on a small information terminal device, while accommodating high pixels.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration example of a zoom lens according to an embodiment of the present invention. This configuration example corresponds to the lens configuration of a first numerical example (FIGS. 4A to 4C) described later. 2 and 3 show other configuration examples of the zoom lens according to the present embodiment. 2 and 3 correspond to the lens configurations of second and third numerical examples (FIGS. 5A to 5C and FIGS. 6A to 6C) described later. . 1 to 3 show the lens arrangement at the wide-angle end.

  In FIG. 1 to FIG. 3, the reference symbol Ri is attached so as to increase sequentially toward the image side (imaging side) with the surface of the component closest to the object side including the stop St as the first. The radius of curvature of the i-th (i = 1 to 14) plane Si is shown. A symbol Di indicates a surface interval on the optical axis Z1 between the i-th surface Si and the i + 1-th surface Si + 1. Since the basic configuration is the same in each configuration example, the following description is based on the configuration of the zoom lens shown in FIG.

  This zoom lens is particularly suitable for mounting on an imaging device using a small imaging device, for example, a small information terminal device such as a mobile phone with a camera. This zoom lens has, in order from the object side along the optical axis Z1, a first lens G1 having a negative refractive power, a stop St, a second lens G2 having a positive refractive power, and a negative refractive power. And a third lens G3. The stop St is provided on the object side of the second lens G2.

  An imaging element such as a CCD (not shown) is disposed on the image plane (imaging plane) Simg of the zoom lens. Various optical members may be disposed between the third lens G3, which is the final lens, and the imaging surface Simg, depending on the configuration of the camera on which the lens is mounted. In the configuration example of FIG. 1, a cover glass GC for protecting the imaging surface Simg is disposed. In addition, optical members such as an infrared cut filter and a low-pass filter may be disposed.

  This zoom lens is a two-group zoom system, and zooming is performed by moving the second lens G2 and the third lens G3 on the optical axis. The first lens G1 is always fixed. Here, as the second lens G2 and the third lens G3 are zoomed from the wide-angle end to the telephoto end, the second lens G2 and the third lens G3 move so as to draw a locus indicated by a solid line in FIG. The focus adjustment is performed at least one of the second lens and the third lens.

  Further, both the first to third lenses G1 to G3 are aspherical on both surfaces. The first lens G1 has a negative meniscus shape with a convex surface facing the object side in the vicinity of the paraxial axis. The second lens G2 has a biconvex shape in the vicinity of the paraxial region. Furthermore, the third lens G3 has a biconcave shape in the vicinity of the paraxial region. The first lens G1 is made of a glass material having a high refractive index. The second and third lenses G2 and G3 are preferably formed of plastic lenses from the viewpoints of ease of processing, light weight, low cost, and the like.

This zoom lens is configured to satisfy the following conditional expressions (1) to (5). Where ft is the focal length of the entire system at the telephoto end, fw is the focal length of the entire system at the wide-angle end, TCLw is the total length at the wide-angle end), f2 is the focal length of the second lens G2, and f3 is the third lens. The focal length of G3, Nd (G1) represents the refractive index of the first lens G1, and νd (G2) represents the Abbe number of the second lens G2.
2.0 <ft / fw <3.5 (1)
2.5 <TCLw / fw <5.0 (2)
−1.2 <f2 / f3 <−0.4 (3)
Nd (G1)> 1.65 (4)
νd (G2)> 45 (5)

  Next, operations and effects of the zoom lens configured as described above will be described.

  In this zoom lens, zooming is performed by moving the second lens G2 and the third lens G3 on the optical axis. At this time, the first lens G1 is kept fixed. Focus adjustment can be performed by the first lens G1, but fixing the first lens G1 during zoom and focus adjustment is advantageous in terms of reducing the number of moving groups. In particular, in the case of a camera-equipped mobile phone or the like, it is preferable that the number of movable parts is small because it is advantageous in terms of mechanical strength and robustness. Further, it is preferable to always fix the first lens G1, which is the most object side lens, because it is easy to reduce the size when modularized.

  This zoom lens has a simple configuration of 3 elements in 3 groups, but aspherical lenses are frequently used. Therefore, the overall length is shorter than that of the conventional 3 zoom lenses, while ensuring a more compact configuration. Various aberrations are corrected well. Furthermore, by satisfying the conditional expressions and making power distribution appropriate, the overall length is short and compact, and it has higher performance than the conventional three-lens zoom lens that supports higher pixels. A lens is obtained.

  In this zoom lens, the first lens G1 is a glass lens having a high refractive index, so that the total length is shortened. Further, by applying plastic lenses as the second and third lenses G2 and G3, cost and weight can be reduced. A plastic lens has a greater change in optical characteristics due to temperature than glass. On the other hand, in the case of a small photographic lens, recently, a plurality of moving groups can be independently and freely controlled by a small actuator using a piezo element as a moving mechanism. Therefore, even if there is a change in the optical characteristics due to temperature, for example, it is relatively easy to control the movement of the second lens G2 and the third lens G3 so as to correct it, and it is assumed that a lot of plastic lenses are used. Is not so much of a problem.

  Conditional expression (1) defines the zoom ratio. If this zoom lens has a zoom ratio of about 3 times, it can maintain high performance corresponding to the increase in the number of pixels. Conditional expression (2) relates to the total length of the lens system. If the lower limit of conditional expression (2) is exceeded and the total length is made too short, it will be difficult to maintain the performance at the telephoto end. If the upper limit of conditional expression (2) is exceeded, the performance will be improved, but the overall length will be too long, and the market competitiveness when actually commercialized will be lost.

  Conditional expression (3) defines the power ratio between the second lens G2 and the third lens G3. If the lower limit of conditional expression (3) is not reached, it is advantageous in reducing the total length, but the difference in aberration between the center and the periphery becomes too large, and a well-balanced lens system cannot be obtained. Exceeding the upper limit is not preferable because the total length becomes too large. Conditional expression (4) defines the refractive index of the first lens G1. Exceeding the upper limit is not preferable because the total length becomes too large. Conditional expression (5) defines the Abbe number of the second lens G2. If the conditional expression (5) is not satisfied, it is not preferable because chromatic aberration (particularly axial chromatic aberration) cannot be suppressed appropriately.

  As described above, according to the present embodiment, while having a simple configuration of three sheets, it is possible to cope with a certain degree of increase in pixels, and is particularly suitable for mounting on a small information terminal device. A compact optical system can be realized at low cost.

  Next, specific numerical examples of the zoom lens according to the present embodiment will be described. Below, the 1st-3rd numerical example (Examples 1-3) is demonstrated collectively. 4A to 4C show specific lens data corresponding to the configuration of the zoom lens shown in FIG. FIGS. 5A to 5C and FIGS. 6A to 6C show specific lens data corresponding to the configuration of the zoom lens shown in FIGS. 2 and 3, respectively. 4A, 5A, and 6A (hereinafter collectively referred to as FIG. 4A, etc.), the basic data portion of the lens data of the embodiment is shown. 4B, FIG. 5B, and FIG. 6B (hereinafter collectively referred to as FIG. 4B, etc.), the data portion relating to the aspherical shape of the lens data of the embodiment is shown. Indicates. 4C, FIG. 5C, and FIG. 6C (hereinafter collectively referred to as FIG. 4C, etc.) show other data.

  In the field of the surface number Si in each lens data in FIG. 4A and the like, the image of the zoom lens of each embodiment is designated with the surface of the component closest to the object side including the stop St and the cover glass GC as the first. The numbers of the i-th (i = 1 to 9) planes that are sequentially added to the side are indicated. In the column of the curvature radius Ri, the value of the curvature radius of the i-th surface Si from the object side is shown in correspondence with the symbol Ri given in FIG. The column of the surface interval Di also indicates the interval on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the object side, corresponding to the reference numerals in FIG. The unit of the value of the curvature radius Ri and the surface interval Di is millimeter (mm). In the columns of Ndj and νdj, the refractive index for the d-line (587.6 nm) and the Abbe number of the j-th (j = 1 to 4) optical element from the object side including the cover glass GC are shown.

  In each lens data such as FIG. 4A, the symbol “*” attached to the left side of the surface number indicates that the lens surface is aspherical. In the zoom lenses of Examples 1 to 3, all the surfaces of the first to third lenses G1 to G3, that is, the surfaces S1, S2 and S4 to S7 are aspherical. Here, the first lens G1 is a glass lens, and the second and third lenses are plastic lenses. In addition, in the basic lens data such as FIG. 4A, the numerical value of the radius of curvature near the optical axis (near the paraxial axis) is shown as the radius of curvature of these aspheric surfaces.

In the numerical values of each aspherical data such as FIG. 4B, the symbol “E” indicates that the subsequent numerical value is a “power exponent” with 10 as the base, and an exponent function with 10 as the base. The numerical value represented by “E” is multiplied by the numerical value before “E”. For example, “1.0E-02” indicates “1.0 × 10 ⁻² ”.

In each aspheric surface data, the values of the coefficients A _i and KA in the aspheric surface expression represented by the following expression (A) are described. More specifically, Z is the length (mm) of a perpendicular line drawn from a point on the aspheric surface at a height h from the optical axis to the tangential plane (plane perpendicular to the optical axis) of the apex of the aspheric surface. Show.

Z = C · h ² / {1+ (1−KA · C ² · h ² ) ^1/2 } + ΣA _i · h ⁱ (A)
However,
Z: Depth of aspheric surface (mm)
h: Distance from the optical axis to the lens surface (height) (mm)
KA: eccentricity C: paraxial curvature = 1 / R
(R: paraxial radius of curvature)
A _i : i-th order (i = 3,4,5,6,7,8) aspheric coefficient

  However, in Examples 1 to 3, since the eccentricity KA is 0 (zero), the equation (A) can be rewritten as the following equation (B).

^{Z = C · h 2/2} + ΣA i · h i ...... (B)

  As shown in FIG. 4B and the like, in any of the embodiments, the aspherical surface of the second lens G2 uses only even-order terms. In contrast, the aspheric surfaces of the first and third lenses G1 and G3 effectively use odd-order terms in addition to even-order terms.

  In each of the zoom lenses of each of the embodiments, the second lens G2 and the third lens G3 move on the optical axis with zooming. Therefore, the front and rear surface distances D2 and D5 of these groups are variable. ing. As data at the time of zooming of these surface distances D2 and D5, values of each embodiment at the wide-angle end and the telephoto end are shown in FIG.

  FIG. 7 collectively shows the values related to the conditional expressions (1) to (5) described above for each example. As shown in FIG. 7, the values of the respective examples are within the numerical ranges of the conditional expressions (1) to (5).

  8A to 8C show spherical aberration, astigmatism, and distortion (distortion aberration) at the wide-angle end in the zoom lens of Example 1. FIG. 9A to 9C show similar aberrations at the telephoto end. Each aberration diagram shows an aberration with the d-line as a reference wavelength. In the astigmatism diagram, the solid line indicates the sagittal direction and the broken line indicates the tangential direction. FNO. Indicates an F value, and ω indicates a half angle of view.

  Similarly, various aberrations relating to Example 2 are shown in FIGS. 10A to 10C (wide-angle end) and FIGS. 11A to 11C (telephoto end). Further, various aberrations for Example 3 are shown in FIGS. 12A to 12C (wide-angle end) and FIGS. 13A to 13C (telephoto end).

  As can be seen from the numerical data and aberration diagrams, a compact and high-performance optical system suitable for mounting on a small information terminal device can be realized in each embodiment.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible. For example, the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the above numerical examples, and may take other values.

1 is a lens cross-sectional view illustrating a configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 1. FIG. FIG. 9 is a lens cross-sectional view illustrating another configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 2; FIG. 6 is a lens cross-sectional view illustrating another configuration example of a zoom lens according to an embodiment of the present invention and corresponding to Example 3; 6 is a diagram illustrating lens data of a zoom lens according to Example 1. FIG. 7 is a diagram illustrating lens data of a zoom lens according to Example 2. FIG. 7 is a diagram illustrating lens data of a zoom lens according to Example 3. FIG. It is a figure which shows the value regarding the conditional expression which the zoom lens which concerns on each Example satisfy | fills. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide angle end of the zoom lens according to Example 1; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 1; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide angle end of the zoom lens according to Example 2; FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 2; FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 3; FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 3;

Explanation of symbols

G1 to G3: 1st lens to 3rd lens, GC: cover glass, Si: i-th lens surface from the object side, Ri: radius of curvature of the i-th lens surface from the object side, Di: 1st lens surface from the object side The distance between the i-th lens surface and the (i + 1) -th lens surface, Simg: imaging surface (imaging surface), Z1: optical axis.

Claims (1)

In order from the object side, a first lens having a negative meniscus shape with a convex surface facing the object side near the paraxial axis, a second lens having a biconvex shape near the paraxial axis, and a biconcave shape near the paraxial axis A third lens,
The first lens to the third lens are both aspherical on both sides,
The second lens and the third lens are configured to move on the optical axis during zooming,
Further, the zoom lens is configured to satisfy the following conditional expressions (1) to (5).
2.0 <ft / fw <3.5 (1)
2.5 <TCLw / fw <5.0 (2)
−1.2 <f2 / f3 <−0.4 (3)
Nd (G1)> 1.65 (4)
νd (G2)> 45 (5)
However,
ft: focal length of the entire system at the telephoto end fw: focal length of the entire system at the wide angle end TCLw: full length at the wide angle end f2: focal length of the second lens f3: focal length of the third lens Nd (G1): Refractive index of the first lens νd (G2): Abbe number of the second lens

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