JP2007212937A - Zoom lens and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large-aperture zoom lens whose power variation ratio is about 3, which is constituted of three lens groups as a whole, and which is constituted by arranging the lens groups so that their powers are to be negative, positive and negative in order from an object side, thereby achieving the shortening of the entire length of an optical system, and to provide a camera using the zoom lens. <P>SOLUTION: The zoom lens has a first lens group having negative refractive power as a whole, a second lens group having positive refractive power as a whole, a third lens group having negative refractive power as a whole in order from the object side. Variable magnification is performed by positionally moving the first lens group and the second lens group in an optical axis direction, or positionally moving the third lens group in addition to the first lens group and the second lens group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a high-performance bright (small F-number) zoom of about 3 times used in a small-sized image pickup device using an image sensor such as a CCD (charged coupled device) for mounting mainly on a digital still camera or the like. It relates to lenses.

  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 trend 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. The current situation is that telephones have not become widespread, and compact zoom products only stop at 2x zoom. 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. On the other hand, there is no complicated structure such as a retracting operation or a lens barrel to which external force is applied, so there is no need for mechanical consideration of external strength, and the optical design limits the total length in the optical axis direction. Has a feature such as relaxation. 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 ensure the arrangement accuracy on the mechanism structure with respect to the group. 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. Furthermore, when the sliding method is adopted, it is easy to think of the lens storage state as determining the product thickness in order to reduce the thickness, but it is necessary to design an optical system that will be thinned in the storage state. Even if it is possible, depending on the size in use, it is essential to have a structure in which a plurality of barrels that perform the retracting operation are stacked, and it becomes impossible to ensure the placement accuracy of the optical system. . 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.

  Therefore, in the case of a digital still camera product with a card size with a zoom ratio of about 3 times, the retractable method is used to express the commercial value of the lens while giving priority to thinness. There is a demand for an optical design solution that can reduce the time length.

  On the other hand, as a recent trend, there are many products that have succeeded in promoting the use of the camera shake correction function. In order to prevent camera shake to some extent, the principle is to move a part of the lens or the image sensor itself in the direction to cancel the camera shake. In addition to blurring, there is subject blurring that causes the subject to move during exposure, and the camera shake correction function is not useful for subject blurring. Therefore, there is nothing other than shutter release as fast as possible to be effective for both camera shake and subject blur. For this reason, a zoom lens that is brighter, that is, has a smaller F number is currently required. It can be said that there is a situation, but this is nothing but an increase in the factors that prevent the above-mentioned miniaturization.

Under such circumstances, if the lens is designed based on the conventional lens configuration, the lens disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-004765 (Patent Document 3) is representative. Thus, the entire zoom lens 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 considering a decrease in F-number and further miniaturization, these characteristics are adversely affected, and miniaturization with a future impact becomes impossible.
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 having an F number of about 2 brightness and a zoom ratio of about 3, and the entire optical system is composed of three lens groups, and each lens group is arranged in order from the object side. By applying negative, positive and negative power, it is possible to shorten the total length in the optical axis direction during use, and not only the configuration of the lens group but also the object direction from the object direction of each lens constituting the whole By symmetrically arranging the positive and negative power arrangements and the general shape, the occurrence of off-axis aberrations such as distortion and astigmatism is fundamentally reduced. It is possible to realize a zoom lens that is bright and compact and maintains high performance, and is a compact zoom lens that is less susceptible to camera shake and subject blur. And to provide a camera using.

The zoom lens of the present invention, in order from the object side, includes a first lens group having an overall negative refractive power, a second lens group having an overall positive refractive power, and a third lens group having an overall negative refractive power. A zoom lens configured, wherein the first lens group has a negative refractive power as a whole and moves the positions of the first lens group and the second lens group in the optical axis direction with respect to zooming; Alternatively, the third lens group is moved in addition to the first lens group and the second lens group, and the following conditional expression (1) is satisfied with respect to the power of the first 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) is satisfied with respect to the power of the third lens group. (Claim 1)
(1) −0.8 ≦ f _w / f _I ≦ −0.45
(2) 4.5 ≦ TL _w / f _w ≦ 7.5
(3) −0.55 ≦ 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 : Synthetic 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)

  Conditional expression (1) relates to appropriate distribution of power to the first lens group having negative power. This is a balance of conditions for appropriately correcting the size of the entire optical system and various aberrations. When the lower limit is exceeded, the negative power of the first lens group becomes large, and accordingly, the positive power of the second lens group must be strengthened, and it becomes difficult to balance various aberrations and the performance deteriorates. . On the other hand, if the upper limit is exceeded, the air gap from the positive power second lens group must be increased, resulting in an increase in the size of the entire optical system, resulting in a loss of compactness. Conditional expression (2) defines the total lens length at the wide-angle end. That is, it is a condition that serves as a measure for downsizing the lens of the present invention. If the upper limit is exceeded, it is advantageous in terms of aberration correction, but it becomes impossible to provide a compact zoom lens that is an object of the present invention. On the other hand, if the lower limit is exceeded, the power of each lens must be increased, which leads to deterioration of various aberrations and deterioration of sensitivity, making it practically difficult to manufacture. Conditional expression (3) is a conditional expression regarding the power of the third lens group. The greatest feature is that it is in the negative range, which has the effect of bringing the exit pupil of the optical system closer to the image plane side. In general, the position of the exit pupil close to the image plane is effective for downsizing the overall length, but the telecentricity around the screen is destroyed. This is because the light beam has an angle, which is not preferable in an optical system using an image sensor such as a CCD. Usually, in the case of a zoom lens of about 3 times, the chief ray angle of the peripheral image point of the screen changes due to the zooming operation. The amount of change naturally varies depending on the design, but is generally about 10 ° or more at the maximum image height (for example, 10 ° at the wide-angle end and 0 ° at the telephoto end). However, in the case of a single focus lens in which the angle of the chief ray does not change, it is possible to exceed 20 ° by adapting the structure of the CCD microlens. In the zoom lens of the present invention, the negative power is applied to the third lens group, so that the change of the chief ray angle at the time of zooming is about 1.9 ° to 4.9 °, which is a normal zoom lens type. Since the amount of change is extremely small compared to the amount of change, it is possible to increase the angle of the principal ray. In the examples described later, the principal ray at the maximum image point on the screen (when the bisector of the angle formed by the upper ray and the lower ray is defined as the principal ray) is limited so that the angle is 20 ° at the maximum. The lower limit value defined by the conditional expression of conditional expression (3) is the range in which the negative power of the third lens group in that state can be taken. If the lower limit is exceeded, it is effective for downsizing. However, since the angle of the principal ray exceeds 20 °, problems such as shading and insufficient amount of peripheral light occur, and it becomes impossible to maintain high image quality required for a digital still camera or the like. On the other hand, if the upper limit is exceeded, the optical system has a size that does not require compacting according to the present invention.

In addition, the first lens group, in order from the object side, is a first lens that is a lens having a negative refractive power (hereinafter, negative lens), and a second lens that is a lens having a positive refractive power (hereinafter, positive lens). And a third lens which is a negative lens, which satisfies the following conditional expression (4) with respect to the power of the second lens, and is distributed to each lens of the first lens group It is preferable that the following conditional expression (5) is satisfied, and that the following conditional expression (6) is satisfied regarding the refractive index of the second lens. (Claim 2)
(4) 0.22 ≦ f _w / f ₂ ≦ 0.55
(5) 15 ≦ (ν ₁ + ν ₃ ) / 2−ν ₂
(6) 1.65 ≦ n ₂
However,
f ₂ : focal length ν ₁ of the second lens constituting the first lens group ν ₁ : Abbe number of the first lens constituting the first lens group ν ₂ : Abbe number ν _{3 of} the second lens constituting the first lens group : Abbe number n ₂ of the third lens constituting the first lens group: Refractive index with respect to d-line of the second lens constituting the first lens group

  Conditional expression (4) is a requirement for satisfactorily correcting the basic aberration of the entire first lens group. That is, the first lens group has negative, positive, and negative power configurations as described above. However, the first lens group appropriately applies positive power to the second lens within the range indicated by the conditional expression (4), and the conditional expression ( By combining the selection of the glass material according to 5) and conditional expression (6), chromatic aberration and curvature of field can be basically corrected. If the upper limit is exceeded, the power of the positive lens will become excessive, but the power of the negative lens will inevitably become excessive, and high-order aberrations will occur. If the lower limit is exceeded, small combinations of power are possible, but chromatic aberration and field curvature correction effects are small, and in this case as well, various aberrations cannot be corrected satisfactorily. Conditional expression (5) relates to the distribution of the Abbe numbers of the negative lens and the positive lens constituting the first lens group. This is a conditional expression for maintaining good correction of chromatic aberration of the first lens group. By selecting the glass material of the negative lens and the positive lens constituting the first lens group under the condition of the conditional expression (5), Appropriate power distribution can be realized, and chromatic aberration can be corrected well. If the lower limit is exceeded, the power of each lens becomes excessive for correcting chromatic aberration, and various aberrations deteriorate. The following conditional expression (6) is a condition for field curvature correction. In order to reduce the Petzval sum, the second lens, which is the only positive lens in the first lens group, corresponds to a larger refractive index. Therefore, if the lower limit is exceeded, the field curvature increases.

Further, the first lens constituting the first lens group is an aspherical lens, satisfies the following conditional expression (7) with respect to the shape of the surface on the image plane side, and the first lens group constituting the first lens group. It is preferable that the following conditional expression (8) is satisfied with respect to the relative characteristics of the shape of the two lenses with the object side surface. (Claim 3)
(7) 0.4 ≦ f _w / r ₂ ≦ 1.4
(8) 0 ≦ r ₂ / r ₃ ≦ 1.5
However,
r ₂ : radius of curvature of the image side surface of the first lens constituting the first lens group r ₃ : radius of curvature of the object side surface of the second lens constituting the first lens group

  Conditional expression (7) is basically a concentric shape with respect to the entrance pupil under the condition of strong negative power applied to the first lens, so that basically off-axis aberrations such as coma aberration and distortion aberration can be obtained. It is a shape for suppressing the occurrence and is a condition for realizing the shape. That is, the first lens has a meniscus shape with strong negative power. (However, when the object side surface of the first lens is aspherical, and when the total length is strongly shortened, the approximate shape is a meniscus shape, but when looking at the paraxial radius of curvature, it becomes a biconcave lens. If the lower limit of conditional expression (7) is exceeded, the occurrence of coma and distortion cannot be sufficiently suppressed. Conversely, when the upper limit is exceeded, it is effective to suppress the occurrence of aberrations, but the curved shape of the meniscus negative lens becomes too strong, making it difficult to manufacture. In order to effectively correct off-axis aberrations such as distortion and astigmatism, the shape of the image side surface of the first lens is preferably an aspherical shape. An aspherical surface, a composite aspherical surface with a resin material, and the like are favorable, but are not particularly limited. The following conditional expression (8) is a conditional expression for satisfactorily correcting the positive spherical aberration due to the strong diverging action generated on the image side surface of the first lens having the negative power. If the upper limit is exceeded, the negative spherical aberration due to the second lens will be excessive, and if the lower limit is exceeded, the positive spherical aberration due to the first lens will be excessive, and it will not be possible to correct the spherical aberration satisfactorily.

The second lens group includes a fourth lens that is a positive lens, a fifth lens that is a positive lens, a sixth lens that is a negative lens, and a seventh lens that is a positive lens in order from the object side. The following conditional expression (9) is satisfied for the positive combined power of the fourth lens and the fifth lens, and the following conditional expression (10) is satisfied for the negative power of the sixth lens: In the second lens group, the following conditional expression (11) is satisfied with respect to the dispersion characteristic distributed to the fourth lens, the fifth lens, and the sixth lens that are disposed closer to the object than the object. It is preferable that the following conditional expression (12) is satisfied in relation to the refractive index of the lens. (Claim 4)
(9) 0.5 ≦ f _w / f _4,5 ≦ 1.5
(10) −1.5 ≦ f _w / f ₆ ≦ −0.25
(11) 28 ≦ (ν ₄ + ν ₅ ) / 2−ν ₆
(12) (n ₄ + n ₅ ) / 2−n ₆ ≦ −0.24
However,
f _4,5 : Composite focal length of the fourth lens and the fifth lens constituting the second lens group f ₆ : Focal length of the sixth lens constituting the second lens group (however, the sixth lens is a compound aspherical lens) Is the combined focal length of the base spherical lens and the resin part)
ν ₄ : Abbe number of the fourth lens constituting the second lens group ν ₅ : Abbe number of the fifth lens constituting the second lens group ν ₆ : Abbe number of the sixth lens constituting the second lens group (however, When the sixth lens constitutes a composite aspheric lens, the Abbe number of the glass material of the base spherical lens)
n ₄ : refractive index with respect to d-line of the fourth lens constituting the second lens group n ₅ : refractive index with respect to d-line of the fifth lens constituting the second lens group n ₆ : sixth constituting the second lens group Refractive index for d-line of lens

  Conditional expression (9) relates to the fourth lens and the fifth lens which are arranged on the most object side of the second lens group and have strong positive power. This is a condition for imparting a large positive power for converging the divergent light beam from the first lens group and appropriately correcting various aberrations. If the upper limit is exceeded, the positive power will be excessive and at the same time the spherical aberration will be undercorrected.If the upper limit is exceeded, the positive power for converging will be insufficient, and the spherical aberration will be overcorrected. In addition to aberrations, off-axis aberrations such as coma and chromatic aberrations are also adversely affected. Conditional expression (10) relates to the power of the negative lens constituting the second lens group, and is an important requirement for correcting basic chromatic aberration and field curvature as the second lens group. That is, if the upper limit is exceeded, a lens configuration with a small combination of the power of each lens in the second lens group is obtained, but chromatic aberration correction and field curvature correction are insufficient, and if the lower limit is exceeded, each lens power is excessively large. Therefore, high-order spherical aberration and coma are generated, and good performance cannot be obtained. Conditional expression (11) is used for a portion that maintains a balance of aberrations while having a strong positive power for focusing a divergent light beam from the first lens unit disposed on the object side in the second lens unit. This is related to the distribution of the Abbe number of the positive lens and the negative lens. In this case, the seventh lens constituting the second lens group also has a relatively large positive power. However, since there are many factors that are determined by the balance with the negative power of the third lens group that follows, Expression is omitted in Equation (11). Therefore, it is expressed using the fourth lens of the positive lens, the fifth lens, and the sixth lens of the negative lens, and conditions for maintaining a balance with each aberration while satisfactorily correcting the chromatic aberration of the entire lens system. It becomes. If the lower limit is exceeded, the power of each lens must be increased to correct chromatic aberration, which is a disadvantageous condition for correcting spherical aberration and coma. Conditional expression (12) relates to field curvature correction in the second lens group. In order to balance the negative Petzval sum generated from the first lens group, it is necessary to be within the range of this condition. If the upper limit is exceeded, the Petzval sum becomes too small, and the correction of field curvature becomes excessive.

Further, among the refracting surfaces of the lenses constituting the second lens group, at least one refracting surface has an aspherical shape, and the following conditional expression (13) is satisfied with respect to the shape of the object side surface of the fourth lens. In addition, it is preferable that the following conditional expression (14) is satisfied with respect to the shape of the image-side surface of the sixth lens. (Claim 5)
(13) 0.2 ≦ f _w / r ₇ ≦ 1.0
(14) 0.4 ≦ f _w / r ₁₂ ≦ 1.6
However,
r ₇ : radius of curvature of the object side surface of the fourth lens constituting the second lens group r ₁₂ : radius of curvature of the image side surface of the sixth lens constituting the second lens group (however, the image of the sixth lens (If the side surface is a resin lens surface of a compound lens, the radius of curvature of the interface between the resin and air)

  Conditional expression (13) is a conditional expression related to the shape of the fourth lens object side surface. Since the fourth lens object side surface is arranged immediately after the aperture stop, it plays an important role in correcting spherical aberration. In connection with the negative power of the first lens group, this is a condition for satisfactorily correcting spherical aberration. When the upper limit of conditional expression (13) is exceeded, off-axis aberrations such as coma and astigmatism are easily corrected, but spherical aberration is insufficiently corrected. On the contrary, if the lower limit is exceeded, the spherical aberration is overcorrected, and at the same time, it is difficult to satisfactorily correct off-axis aberrations. The following conditional expression (14) is a conditional expression related to the shape of the image side surface of the sixth lens. The object side surface of the fourth lens expressed by the conditional expression (13) is a surface disposed on the most incident side of the second lens group, and appropriate negative spherical aberration and coma aberration generated on the surface. Correction is performed by generating positive aberration on the image side surface of the sixth lens. Therefore, if the upper limit is exceeded, the positive spherical aberration becomes excessive, and conversely if the lower limit is exceeded, the negative spherical aberration becomes excessive. In any case, spherical aberration and coma cannot be corrected well.

Furthermore, it is preferable that the third lens group includes only an eighth lens that is a negative lens, and satisfies the following conditional expression (15) with respect to the shape of the object-side surface of the eighth lens. (Claim 6)
(15) −2.0 ≦ f _w / r ₁₅ ≦ 0.2
However,
r ₁₅ : radius of curvature of the object side surface of the eighth lens constituting the third lens group

  As shown by the conditional expression (15), the object side surface of the eighth lens is basically shaped as the second lens in order to focus the light beam collected from the second lens group on the image plane with less aberration. A concentric shape for the group is preferred. Therefore, the value of conditional expression (15) is basically good as a negative value. However, depending on design specifications such as the total length, when this surface is aspherical, it is shown as the upper limit of conditional expression (15). In some cases, it may take a slightly positive value. However, if the upper limit is exceeded and the positive value becomes too large, the peripheral shape and the concentric shape change, and aberrations such as coma and distortion occur. If the lower limit is exceeded, the Petzval sum due to the object side surface of the eighth lens becomes negative and too large, and the exit ray angle becomes excessive.

  The 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 zoom lens includes a first lens group, and the first lens group includes a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a negative lens. The second lens group includes a fourth lens that is a positive lens, a fifth lens that is a positive lens, a sixth lens that is a negative lens, and a seventh lens that is a positive lens. The third lens group includes an eighth lens that is a negative lens, and the zoom lens moves the positions of the first lens group and the second lens group in the optical axis direction with respect to zooming, or the first lens group In addition to the lens group and the second lens group The fourth lens is configured by moving the position of the third lens group, and the positive / negative configuration of the power of each lens in the entire lens system is negative, positive, negative, positive, positive, negative, positive, negative. And the fifth lens as a boundary. Similarly, the amount of power is approximately symmetrically distributed. (Claim 7)

  This is achieved only by making the power of the third lens group negative in a zoom lens optical system having a zoom ratio of about 3 in which a meniscus lens having the strongest negative power is arranged on the most object side. With regard to off-axis aberrations such as distortion and coma, symmetric monofocal lenses often choose their lens type because of the superiority that basically these aberrations are not generated. Since the air spacing between groups changes greatly, the effect of a single focus lens cannot be expected, but the advantage of the advantage that off-axis aberrations are basically reduced by adopting the lens configuration described above is used. It shows that it is possible to do.

  Thus, by mounting the zoom lens according to the present invention as a photographing lens of a camera, it is thin or small that does not bother carrying even though it has an optical zoom function, and there is little camera shake or subject blurring. It is possible to provide a so-called card-sized camera. (Claim 8)

  According to the present invention, a zoom lens optical system having a zoom ratio of about 3 is composed of three lens groups, and negative, positive, and negative powers are given to each lens group in order from the object side, so that light in use can be obtained. The overall length in the axial direction can be shortened, and the positive and negative power arrangement from the object direction to the image side direction and the general shape of each lens constituting the whole as well as the configuration of the lens group are symmetrically arranged. Therefore, the occurrence of off-axis aberrations such as distortion and astigmatism is fundamentally reduced, and thus, the degree of freedom of the correction environment for each aberration is improved as a whole. However, it is possible to realize a compact zoom lens that maintains high performance, and to provide a compact zoom lens that does not cause camera shake and subject blurring, and a camera that uses the zoom lens.

  Hereinafter, specific numerical examples relating to the present invention will be described as Examples 1 to 16. In Examples 1 to 16, 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 that is a lens having negative refractive power (hereinafter referred to as a negative lens) (the first lens L1 has one object side surface and two image side surfaces), and a lens having positive refractive power A second lens L2 (hereinafter referred to as a positive lens) (three object side surfaces of the second lens L2 and four image side surfaces) and a third lens L3 (a third lens L3 having 5 object side surfaces). The second lens group LG2 has a positive refracting power as a whole, and is a fourth lens L4 that is a positive lens (the object side surface of the fourth lens L4). The fifth lens L5 which is a positive lens) The fifth lens L5 has nine object side surfaces and ten image side surfaces, and a negative lens sixth lens L6 (the sixth lens L6 has eleven object side surfaces and twelve image side surfaces. When the fifth lens L5 and the sixth lens L6 are joined, only the surface number of the eleventh surface is displayed in parentheses, and when the eleventh surface or the twelve surface is a resin surface of a composite aspheric lens, And a seventh lens L7 that is a positive lens (the object side surface of the seventh lens L7 is 13 surfaces and the image side surface is 14 surfaces), and the third lens group LG3. Has a negative refracting power as a whole, and is configured by arranging an eighth lens L8 which is a negative lens (the object side surface of the eighth lens L8 is 15 surfaces and the image side surface is 16 surfaces). Further, an air gap is provided between the image side surface 16 of the eighth lens L8 and the image surface, and a quartz optical filter LPF (17 object side surfaces of the quartz optical filter LPF and 18 image side surfaces) and a CCD are provided. Cover glass CG for protecting the image pickup portion (the object side surface of the cover glass CG is 19 surfaces and the image side surface is 20 surfaces) 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 performed 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 may multiply the previous 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. R is a radius of curvature, D is a lens thickness or a lens interval, N _d is a refractive index of d-line, and ν _d is an Abbe number of 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 lens configuration diagram, and FIG.

[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.

[Example 6]
Table 6 shows numerical examples of the sixth embodiment of the zoom lens according to the present invention. FIG. 11 is a diagram showing the lens configuration, and FIG. 12 is a diagram showing various aberrations.

[Example 7]
Table 7 shows numerical examples of the seventh embodiment of the zoom lens according to the present invention. FIG. 13 is a lens configuration diagram thereof, and FIG. 14 is a diagram showing various aberrations thereof.

[Example 8]
Table 8 shows numerical examples of the eighth embodiment of the zoom lens according to the present invention. FIG. 15 is a lens configuration diagram, and FIG. 16 is a diagram showing various aberrations.

[Example 9]
Table 9 shows numerical examples of the ninth embodiment of the zoom lens according to the present invention. FIG. 17 is a lens configuration diagram, and FIG.

[Example 10]
Table 10 shows numerical examples of the tenth embodiment of the zoom lens according to the present invention. FIG. 19 is a lens configuration diagram, and FIG. 20 is a diagram showing various aberrations.

[Example 11]
Table 11 shows numerical examples of the eleventh embodiment of the zoom lens according to the present invention. FIG. 21 is a lens configuration diagram, and FIG. 22 is a diagram showing various aberrations.

[Example 12]
Table 12 shows numerical examples of the twelfth embodiment of the zoom lens according to the present invention. FIG. 23 is a lens configuration diagram, and FIG.

[Example 13]
Table 13 shows numerical examples of the thirteenth embodiment of the zoom lens according to the present invention. FIG. 25 is a diagram showing the lens configuration, and FIG. 26 is a diagram showing various aberrations thereof.

[Example 14]
Table 14 shows numerical examples of the fourteenth embodiment of the zoom lens according to the present invention. FIG. 27 is a lens configuration diagram, and FIG. 28 is a diagram showing various aberrations.

[Example 15]
Table 15 shows numerical examples of the fifteenth embodiment of the zoom lens according to the present invention. FIG. 29 is a diagram showing the lens configuration, and FIG. 30 is a diagram showing various aberrations thereof.

[Example 16]
Table 16 shows numerical examples of the sixteenth embodiment of the zoom lens according to the present invention. FIG. 31 is a diagram showing the lens configuration, and FIG. 32 is a diagram showing various aberrations thereof.

  Next, Table 17 collectively shows values corresponding to the conditional expressions (1) to (15) regarding the first to the sixteenth embodiments.

  As is clear from Table 17, the numerical values related to the examples of Examples 1 to 16 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 6 is a lens configuration diagram of a sixth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the sixth example 7 is a lens configuration diagram of a seventh embodiment of the zoom lens according to the present invention. Various aberration diagrams of the lens of the seventh example The lens block diagram of 8th Example of the zoom lens by this invention. Various aberration diagrams of the lens of the eighth example 9 is a lens configuration diagram of a ninth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of Example 9 10 is a lens configuration diagram of a tenth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the tenth example 11 is a lens configuration diagram of an eleventh embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the eleventh example 12 is a lens configuration diagram of a twelfth embodiment of a zoom lens according to the present invention. FIG. Various aberration diagrams of the lens of Example 12 Lens configuration diagram of a thirteenth embodiment of a zoom lens according to the present invention Various aberration diagrams of the lens of the 13th example 14 is a lens configuration diagram of a fourteenth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the fourteenth example 15 is a lens configuration diagram of a fifteenth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of Example 15 16 is a lens configuration diagram of a sixteenth embodiment of a zoom lens according to the present invention. Various aberration diagrams of the lens of the 16th example

Claims (8)

In order from the object side, a zoom lens including 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 third lens group is moved by moving the positions of the first lens group and the second lens group in the optical axis direction with respect to zooming or in addition to the first lens group and the second lens group. This is achieved by moving the position, and the following conditional expression (1) is satisfied with respect to the power of the first lens group, and the following conditional expression (2) is satisfied with respect to the size of the entire lens system. And a zoom lens that satisfies the following conditional expression (3) regarding the power of the third lens group:
(1) −0.8 ≦ f _w / f _I ≦ −0.45
(2) 4.5 ≦ TL _w / f _w ≦ 7.5
(3) −0.55 ≦ 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 : Synthetic 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 is a first lens that is a lens having a negative refractive power (hereinafter, negative lens), a second lens that is a lens having a positive refractive power (hereinafter, positive lens), and a negative lens. A third lens as a lens is arranged, the following conditional expression (4) is satisfied with respect to the power of the second lens, and the following condition is satisfied with respect to the dispersion characteristic distributed to each lens of the first lens group. 2. The zoom lens according to claim 1, wherein the zoom lens satisfies the formula (5) and satisfies the following conditional formula (6) with respect to the refractive index of the second lens.
(4) 0.22 ≦ f _w / f ₂ ≦ 0.55
(5) 15 ≦ (ν ₁ + ν ₃ ) / 2−ν ₂
(6) 1.65 ≦ n ₂
However,
f ₂ : focal length ν ₁ of the second lens constituting the first lens group ν ₁ : Abbe number of the first lens constituting the first lens group ν ₂ : Abbe number ν _{3 of} the second lens constituting the first lens group : Abbe number n ₂ of the third lens constituting the first lens group: Refractive index with respect to d-line of the second lens constituting the first lens group The first lens constituting the first lens group is an aspherical lens, satisfies the following conditional expression (7) with respect to the shape of the surface on the image plane side, and the second lens constituting the first lens group 3. The zoom lens according to claim 1, wherein the following conditional expression (8) is satisfied with respect to a relative characteristic of the shape of the object side surface:
(7) 0.4 ≦ f _w / r ₂ ≦ 1.4
(8) 0 ≦ r ₂ / r ₃ ≦ 1.5
However,
r ₂ : radius of curvature of the image side surface of the first lens constituting the first lens group r ₃ : radius of curvature of the object side surface of the second lens constituting the first lens group The second lens group includes, in order from the object side, a fourth lens that is a positive lens, a fifth lens that is a positive lens, a sixth lens that is a negative lens, and a seventh lens that is a positive lens. The following conditional expression (9) is satisfied with respect to the positive combined power of the fourth lens and the fifth lens, and the following conditional expression (10) is satisfied with respect to the negative power of the sixth lens. The following conditional expression (11) is satisfied with respect to the dispersion characteristic distributed to the fourth lens, the fifth lens, and the sixth lens arranged on the object side in the two-lens group, and each of the lenses similarly. The zoom lens according to claim 1, wherein the following conditional expression (12) is satisfied in relation to the refractive index of the zoom lens.
(9) 0.5 ≦ f _w / f _4,5 ≦ 1.5
(10) −1.5 ≦ f _w / f ₆ ≦ −0.25
(11) 28 ≦ (ν ₄ + ν ₅ ) / 2−ν ₆
(12) (n ₄ + n ₅ ) / 2−n ₆ ≦ −0.24
However,
f _4,5 : Composite focal length of the fourth lens and the fifth lens constituting the second lens group f ₆ : Focal length of the sixth lens constituting the second lens group (however, the sixth lens is a compound aspherical lens) Is the combined focal length of the base spherical lens and the resin part)
ν ₄ : Abbe number of the fourth lens constituting the second lens group ν ₅ : Abbe number of the fifth lens constituting the second lens group ν ₆ : Abbe number of the sixth lens constituting the second lens group (however, When the sixth lens constitutes a composite aspheric lens, the Abbe number of the glass material of the base spherical lens)
n ₄ : refractive index with respect to d-line of the fourth lens constituting the second lens group n ₅ : refractive index with respect to d-line of the fifth lens constituting the second lens group n ₆ : sixth constituting the second lens group Refractive index for d-line of lens Of the refracting surfaces of the lenses constituting the second lens group, at least one refracting surface is aspherical and satisfies the following conditional expression (13) with respect to the shape of the object side surface of the fourth lens: 5. The zoom lens according to claim 1, wherein the following conditional expression (14) is satisfied with respect to a shape of an image side surface of the sixth lens.
(13) 0.2 ≦ f _w / r ₇ ≦ 1.0
(14) 0.4 ≦ f _w / r ₁₂ ≦ 1.6
However,
r ₇ : radius of curvature of the object side surface of the fourth lens constituting the second lens group r ₁₂ : radius of curvature of the image side surface of the sixth lens constituting the second lens group (however, the image of the sixth lens (If the side surface is a resin lens surface of a compound lens, the radius of curvature of the interface between the resin and air) The third lens group includes only an eighth lens that is a negative lens, and satisfies the following conditional expression (15) with respect to the shape of the object-side surface of the eighth lens. Zoom lens.
(15) −2.0 ≦ f _w / r ₁₅ ≦ 0.2
However,
r ₁₅ : radius of curvature of the object side surface of the eighth lens constituting the third lens group   In order from the object side, a zoom lens including 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 includes a first lens that is a negative lens, a second lens that is a positive lens, and a third lens that is a negative lens, and the second lens group includes: The fourth lens is a positive lens, the fifth lens is a positive lens, the sixth lens is a negative lens, and the seventh lens is a positive lens. The third lens group is a negative lens. An eighth lens as a lens is arranged, and the first lens group and the second lens group are moved in the optical axis direction with respect to zooming, or the first lens group and the second lens are moved. Position of the third lens group in addition to the group The positive / negative configuration of the power of each lens in the entire lens system is negative, positive, negative, positive, positive, negative, positive, negative, and between the fourth lens and the fifth lens. The zoom lens is characterized in that it has a symmetrical configuration with respect to the boundary, and the amount of power is also approximately symmetrically distributed.   A camera comprising the zoom lens according to any one of claims 1 to 7.

Images