JP5299985B2 - Zoom lens and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens constituted of three lens groups as a whole and constituted by arranging them so that the power of each group may be negative, positive and negative in order from an object side, thereby shortening the entire length of an optical system as a zoom lens which includes a wide angle area at a wide angle end and whose variable power ratio is about 3 to 4; and to provide a camera using the same. <P>SOLUTION: The zoom lens is constituted of a first lens group, a second lens group and a third lens group (constituted of seven lenses in total) in order from the object side. The first lens group has negative refractive power as a whole, the second lens group has positive refractive power as a whole, and the third lens group has negative refractive power as a whole. Power is varied by moving the positions of the first lens group and the second lens group in an optical axis direction or moving the position of the third lens group in addition to the first lens group and the second lens group. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention is about 3 to 4 times including a wide-angle region at a high-performance wide-angle end, which is used in a small-sized image pickup device using an image sensor such as a CCD (charged coupled device) to be mounted on a digital still camera or the like. This relates to a standard zoom lens.

  The so-called pixel number competition of image sensors used in digital still cameras, which has been unfolding at an unusual speed in recent years, has come to an end, and in the past few years digital still cameras have differentiated and personalized other than the number of pixels. There is a flow. The biggest trend among them is the downsizing of cameras, and many of the popular types of so-called compact camera-type compact cameras have been marketed with "card size". In the camera with the card size as a specification, it is natural that the size when viewed from the front is almost the size of a credit card etc. Naturally, the thickness (thinness) of the camera body is also thin with impact. This is an important factor that determines whether the product itself is accepted by the market. In many cases, the size of the photographing lens in the optical axis direction is the biggest obstacle to designing a thin camera body. In other words, as long as general camera components are arranged, the front of the product and the optical axis of the photographic lens are perpendicular to each other, so the dimension in the direction of the optical axis is an element that determines the thickness of the camera body. Reducing the product thickness directly means reducing the dimension of the photographic lens in the optical axis direction, which is difficult. For this reason, at the initial stage of a card-size digital still camera, a single-focus lens that can reduce the dimension in the optical axis direction as much as possible is employed. As described in Japanese Patent Laid-Open No. 228922 (Patent Document 1), a product such as creation of a unique lens type including a review of telecentricity unique to an image sensor such as a CCD was commercialized. However, there is a strong demand for mounting a zoom lens on a camera, and as a result, at present, even in card-sized digital still cameras, the mainstream product is a camera with a zoom lens.

    This flow is the same for mobile phones with camera functions. In many cases, the dimensions of the photographic lens determine the thickness of the product, and a single-focus lens is used, and mobile phones using an optical zoom lens. However, the current situation is that the zoom is limited to double zoom for compact products. However, although the imaging lens mounted on the mobile phone uses the same image sensor, there is no demand for image quality as high as that of a digital still camera, so it is predicted that a solution will be devised that includes a divisor in terms of performance. Has been.

  In a card-sized digital still camera, the entire length of the optical system is structurally or structurally long compared to a single-focus lens. Currently, it can be classified into two technologies. The first technique is represented by, for example, what is disclosed in Japanese Patent Application Laid-Open No. 2004-056362 (Patent Document 2), and is a technique called a so-called bending type. In the bending type, a reflecting element such as a mirror or a prism is provided in the vicinity of the front and rear of the front lens of the optical system, and the lens portion is prevented from becoming large (thick) by bending the optical axis by 90 degrees. Flex-type reflective elements are often placed before and after the front lens as mentioned above due to the contribution to the thinness of the camera, the loss of space as an optical system, and the problem of sensitivity. While this is not suitable for wide-angle systems, there is no complicated structure such as a retracting operation, and there is no lens barrel to which external force is directly applied. In addition, there is a feature that the restriction on the total length in the optical axis direction is relaxed. It can also be said that the larger the zoom ratio, the more effective means. However, the bending type technically has excellent features as described above. However, when evaluated as a camera product, there is no lens barrel in the appearance, and only the lens near the front lens can be seen. It has been pointed out that there is a problem in product planning that it is difficult to express values as a camera lens.

  The second technique is represented by, for example, what is disclosed in Japanese Patent Application Laid-Open No. 2004-004765 (Patent Document 3), and is a so-called sliding type technique. The sliding type can be said to be an advanced technology of the retractable storage system for zoom lenses, which has been adopted in conventional compact cameras using film. In this method, a part of the lens group constituting the zoom lens is slid (shifted) away from the optical axis when the lens is stored, and moved to a position where it does not interfere with other optical elements and stored to move from the optical axis. The total length of the lens group is shortened by the thickness of the lens group. Usually, a lens group that is advantageous in terms of mechanism or a lens group having a large size in the optical axis direction is often retracted in the middle lens group instead of the front group or the rear group. The problem with this method is that it is based on a complicated retractable structure. In addition to inheriting the problems of conventional retractable methods such as ensuring the required accuracy and adapting to external forces, the sensitivity of the retracting lens group is particularly high. It is necessary to set a low value, which is an important factor for stable production. Also, in principle, it is easy to think that the product thickness can be reduced by performing a plurality of sliding operations. However, it turns out that it does not make much sense for the following reasons.

  In zoom lens optical systems based on the assumption that the retracted state is retracted, the total sum of the thicknesses of each lens group is reduced to shorten the total length during storage, while the air between the lens group and the lens group is reduced. A design method is used in which a wide interval is taken into consideration so-called sensitivity. Therefore, the sliding zoom lens is designed to reduce the total thickness of the lens group excluding the sliding group. It will not be established. Therefore, although it is related to the specifications of the optical system, the optical system designed in this way is compact when stored, but it is many times larger than the stored size during actual use. The result will be a size. Normally, in order to realize such an optical system, a structure in which a plurality of collapsible lens barrels are stacked is adopted. However, as the number of steps is increased, a lens disposed in front of the zoom lens. It becomes difficult to secure the arrangement accuracy on the mechanism structure with respect to the group, which is a big problem in terms of strength. Currently, the number of collapsible stages that is practically established is approximately three, and those with more than that are not practically established for the reasons described above, even though they can be designed. Therefore, there is actually a close relationship between the total length of the optical system during storage and the total length during actual use, and can only be used within the range where the retracting mechanism is established. Therefore, it can be understood that it is not meaningful to reduce the total length during storage with a plurality of sliding objects. In other words, in order to achieve a thin product thickness, the dimension in the optical axis direction during storage is important, but this can be dealt with by sliding a group of zoom lens groups. However, it can be said that the obstacle in optical design is the size in the optical axis direction during actual use.

  On the other hand, the latest digital still camera products give priority to size and thinness, and in order to express the commercial value of the lens, the retractable method can reduce the length of storage and especially the length of use. In addition to the above specifications, there is a strong demand for an optical design solution that can realize high specifications that add to the demand for differentiation from other companies such as higher magnification and wider angle.

At present, when designing a lens based on a conventional lens configuration, the one disclosed in, for example, the above-mentioned Japanese Patent Application Laid-Open No. 2004-004765 (Patent Document 3) and the like will be representative. Is generally arranged in three lens groups having negative, positive, and positive powers in order from the object side. This is the most suitable lens type for securing back focus for arranging optical elements such as quartz optical filters and CCD cover glass, and for ensuring sufficient telecentricity required from the characteristics of the CCD. When the specification of high magnification and wide angle is requested in consideration of differentiation, these characteristics are adversely affected, and it is impossible to reduce the size with future impact.
JP 2002-228922 A JP 2004-056362 A JP 2004-004765 A

  In view of the circumstances described above, the present invention is a zoom lens that includes a wide-angle region at the wide-angle end and has a zoom ratio of about 3 to 4 times. The entire optical system is composed of three lens groups. By applying negative, positive, and negative powers in order from the object side, it is possible to shorten the total length in the optical axis direction during use, and it is likely to occur due to a wide angle by adopting a symmetric configuration as a group configuration. An object of the present invention is to fundamentally reduce the occurrence of off-axis aberrations such as distortion and astigmatism, to realize a high-performance and compact zoom lens system, and to provide a camera using the zoom lens system.

The zoom lens of the present invention includes, in order from the object 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 group having a negative refractive power as a whole. The first lens group is a lens having negative refractive power (hereinafter referred to as negative lens), a first lens having a meniscus shape convex toward the object side, and a lens having positive refractive power (hereinafter referred to as positive lens). A second lens having a non-meniscus shape and a third lens being a negative lens are arranged, and the second lens group has a fourth lens that is a positive lens and a meniscus shape that is negative and convex toward the object side. The zoom lens includes a fifth lens and a sixth lens that is a positive lens, and the third lens group includes a seventh lens that is a negative lens. 1 lens group and the second lens The first lens group is formed by moving the position of the group in the optical axis direction, or by moving the position of the third lens group in addition to the first lens group and the second lens group. The following conditional expression (1) is satisfied with respect to the power of the third lens group, the following conditional expression (2) is satisfied with respect to the size of the entire lens system, and the following conditional expression (3 with respect to the power of the third lens group) is satisfied. ) Is satisfied. (Claim 1)
(1) −0.8 ≦ f _w / f _I ≦ −0.4
(2) 5.5 ≦ TL _w / f _w ≦ 7.5
(3) −0.4 ≦ f _w / f _III ≦ 0
However,
f _w : Composite focal length of the entire lens system at the wide angle end f _I : Composite focal length of the first lens group f _III : Composite focal length of the third lens group TL _w : First lens constituting the first lens group at the wide angle end Distance from the object side of the lens to the image plane (however, the air equivalent distance for the parallel plane glass part)

Another zoom lens according to the present invention includes, in order from the object 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 negative refractive power as a whole. The first lens group is a lens having negative refractive power (hereinafter referred to as negative lens), a first lens having a meniscus shape convex toward the object side, and a lens having positive refractive power (hereinafter referred to as positive lens). ), A second lens having a non-meniscus shape and a third lens being a negative lens are arranged, and the second lens group includes a fourth lens that is a positive lens and a meniscus shape that is convex on the object side with a negative lens. A fifth lens and a sixth lens that is a positive lens, and the third lens group is a zoom lens that is configured by arranging a seventh lens that is a negative lens. The first lens group and the second lens group By moving the position of the lens group in the optical axis direction, or by moving the position of the third lens group in addition to the first lens group and the second lens group, and the second lens The following conditional expression (4) is satisfied with respect to the power possessed by: (Claim 2 )
(4) 0.22 ≦ f _w / f ₂ ≦ 0.45
However,
f _w : Combined focal length of the entire lens system at the wide-angle end f ₂ : Focal length of the second lens constituting the first lens group It is preferable to mount the zoom lens as described above as a photographing lens of the camera. (Claim 3 )

  According to the present invention, while maintaining the same size and cost as those of a standard zoom lens optical system having a conventional zoom ratio of about 3 times, the whole is constituted by three lens groups, and each lens group is negatively charged in order from the object side. By adopting a lens type that features positive and negative power, the zoom ratio is maintained or expanded to 3 to 4 times, and the wide angle end angle of view is extended to a wide angle range. We can provide a camera that realizes a zoom lens and can be differentiated from other companies.

  Hereinafter, specific numerical examples relating to the present invention will be described as Examples 1 to 5. In the following first to fifth embodiments, the first lens group LG1, the second lens group LG2, and the third lens group LG3 are sequentially arranged from the object side, and the first lens group LG1 has a negative refractive power as a whole. A first lens L1 having a negative refractive power (hereinafter, negative lens) and having a meniscus shape convex toward the object side (the object side surface of the first lens L1 is one surface and the image side surface is two surfaces). , A second lens L2 that is a lens having positive refractive power (hereinafter, positive lens) (the second lens L2 has three object side surfaces and four image side surfaces) and a negative lens third lens L3 (first lens). The third lens L3 has five object side surfaces and six image side surfaces, and the second lens group LG2 has a positive refractive power as a whole, and is a fourth lens L4 that is a positive lens. (The fourth lens L4 has 7 object side surfaces and 8 image side surfaces), negative A fifth lens L5 having a meniscus shape that is convex toward the object side at the lens (the object side surface of the fifth lens L5 is nine and the image side surface is ten) and a sixth lens L6 that is a positive lens (of the sixth lens L6) The third lens group LG3 has a negative refracting power as a whole and has a seventh lens L7 (seventh lens) which is a negative lens. The object side surface of L7 is 13 surfaces, and the image side surface is 14 surfaces). In addition, an air gap is provided between the image side surface 14 and the image surface of the seventh lens L7, and a quartz optical filter LPF (15 object side surfaces and 16 image side surfaces of the crystal optical filter LPF) and a CCD are provided. Cover glass CG for protecting the imaging portion (17 on the object side of the cover glass CG and 18 on the image side) is disposed. Infrared light cut, which is usually required when handling an image sensor such as a CCD, is not shown as being dealt with by applying an infrared reflection coating to one surface of the refractive surface of the quartz optical filter LPF. Regarding zooming, the third lens is moved by moving the positions of the first lens group LG1 and the second lens group LG2 in the optical axis direction or in addition to the first lens group LG1 and the second lens group LG2. This is done by moving the position of the group LG3. In each embodiment, the focus adjustment for an object of a finite distance can be achieved by moving the position of the first lens group LG1 or the third lens group LG3 in the optical axis direction. It is not limited to.

Furthermore, as is well known, the aspherical surface used in each embodiment has an aspherical formula when taking the Z axis in the optical axis direction and the Y axis in the direction orthogonal to the optical axis:
Z = (Y ² / R) / [1 + √ {1- (1 + K) (Y / R) ² }]
+ A ・ Y ⁴ + B ・ Y ⁶ + C ・ Y ⁸ + D ・ Y ¹⁰ +
Is a curved surface obtained by rotating the curve given by around the optical axis, and the shape is defined by giving paraxial radius of curvature: R, conic constant: K, and higher order aspherical coefficients: A, B, C, D To do. In the notation of the conic constant and the higher-order aspheric coefficient in the table, “E and the number following it” represent “power of 10”. For example, “E-04” means 10 ⁻⁴ , and this numerical value is multiplied by the immediately preceding numerical value.

[Example 1]
Table 1 shows numerical examples of the first embodiment of the zoom lens according to the present invention. FIG. 1 is a diagram showing the lens configuration, and FIG. 2 is a diagram showing various aberrations thereof. In the tables and drawings, f represents the focal length of the entire lens system (hereinafter, the values are shown at the wide-angle end, intermediate range, and telephoto end from the left side), F _no represents the F number, and 2ω represents the total angle of view of the lens. Further, r is a radius of curvature, d is a lens thickness or a lens interval, n _d is a refractive index of the d line, and ν _d is an Abbe number of the d line. In the spherical aberration diagrams in the various aberration diagrams, d, g, and C are aberration curves at the respective wavelengths. S. C. Indicates a sine condition. In the astigmatism diagram, S indicates sagittal and M indicates meridional.

[Example 2]
Table 2 shows numerical examples of the second embodiment of the zoom lens according to the present invention. FIG. 3 is a diagram showing the lens configuration, and FIG. 4 is a diagram showing various aberrations thereof.

[Example 3]
Table 3 shows numerical examples of the third embodiment of the zoom lens according to the present invention. FIG. 5 is a diagram showing the lens configuration, and FIG. 6 is a diagram showing various aberrations.

[Example 4]
Table 4 shows numerical examples of the fourth embodiment of the zoom lens according to the present invention. FIG. 7 is a diagram showing the lens configuration, and FIG. 8 is a diagram showing various aberrations.

[Example 5]
Table 5 shows numerical examples of the fifth embodiment of the zoom lens according to the present invention. FIG. 9 is a lens configuration diagram, and FIG. 10 is a diagram showing various aberrations.

  Next, Table 6 collectively shows values corresponding to the conditional expressions (1) to (15) with respect to the first to fifth embodiments.

  As is clear from Table 6, the numerical values related to the examples of Examples 1 to 5 satisfy the conditional expressions (1) to (15) and are also apparent from the aberration diagrams in the examples. Each aberration is corrected well.

1 is a lens configuration diagram of a first embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the first example The lens block diagram of 2nd Example of the zoom lens by this invention. Various aberration diagrams of the lens of the second example 3 is a lens configuration diagram of a third embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of the third example 4 is a lens configuration diagram of a fourth embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of the fourth example 5 is a lens configuration diagram of a fifth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the fifth example

Claims (3)

In order from the object side, the 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 group having a negative refractive power as a whole, The lens group includes a first lens having a negative meniscus shape having a negative refractive power (hereinafter, negative lens) and a convex meniscus shape on the object side, and a second lens having a positive refractive power (hereinafter, positive lens) having a non-meniscus shape. The second lens group includes a fourth lens that is a positive lens, a fifth lens that is a negative lens and has a meniscus shape that is convex on the object side, and a positive lens. The zoom lens is configured by disposing a sixth lens, and the third lens group is configured by disposing a seventh lens that is a negative lens, and the first lens group and the second lens with respect to zooming. Move the position of the lens group in the optical axis direction. Or by moving the position of the third lens group in addition to the first lens group and the second lens group, and the following conditional expression (1) regarding the power of the first lens group: ), The following conditional expression (2) is satisfied regarding the size of the entire lens system, and the following conditional expression (3) is satisfied regarding the power of the third lens group: Zoom lens.
(1) −0.8 ≦ f _w / f _I ≦ −0.4
(2) 5.5 ≦ TL _w / f _w ≦ 7.5
(3) −0.4 ≦ f _w / f _III ≦ 0
However,
f _w : Composite focal length of the entire lens system at the wide angle end f _I : Composite focal length of the first lens group f _III : Composite focal length of the third lens group TL _w : First lens constituting the first lens group at the wide angle end Distance from the object side of the lens to the image plane (however, the air equivalent distance for the parallel plane glass part) In order from the object side, the 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 group having a negative refractive power as a whole, The lens group includes a first lens having a negative meniscus shape having a negative refractive power (hereinafter, negative lens) and a convex meniscus shape on the object side, and a second lens having a positive refractive power (hereinafter, positive lens) having a non-meniscus shape. The second lens group includes a fourth lens that is a positive lens, a fifth lens that is a negative lens and has a meniscus shape that is convex on the object side, and a positive lens. The zoom lens is configured by disposing a sixth lens, and the third lens group is configured by disposing a seventh lens that is a negative lens, and the first lens group and the second lens with respect to zooming. Move the position of the lens group in the optical axis direction. Or by moving the position of the third lens group in addition to the first lens group and the second lens group, the following conditional expression (4) regarding the power of the second lens: A zoom lens characterized by satisfying
(4) 0.22 ≦ f _w / f ₂ ≦ 0.45
However,
f _w : Total focal length of the entire lens system at the wide angle end f ₂ : Focal length of the second lens constituting the first lens group A camera equipped with the zoom lens according to any one of claims 1 to 2 .

Images