JP4552872B2 - Zoom lens and camera - Google Patents

Description

  The present invention relates to a high-performance zoom lens of about 3 times that is used in a small-sized imaging device using an image sensor such as a CCD (charged coupled device) to be mounted mainly in a digital still camera or the like.

  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 orthogonal, so the dimensions of this optical axis will determine the thickness of the camera body. Reducing the 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, as a technology to make the entire camera thinner even if a zoom lens is installed, which tends to be longer than the single focal length lens, either structurally or structurally. Can be classified into two technologies at present. 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 related to the specifications of the optical system, the optical system designed according to such a policy is compact when stored, it is several 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 is difficult to ensure the placement accuracy for 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.

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 an excellent lens type selection for securing the back focus for arranging optical elements such as a quartz optical filter and a CCD cover glass, and sufficiently ensuring the telecentricity required from the characteristics of the CCD. When further downsizing is considered, these characteristics are adversely affected, and it is impossible to downsize with future impact.
JP 2002-228922 A JP 2004-056362 A JP 2004-004765 A

  In the present invention, in view of the circumstances described above, a zoom lens optical system having a zoom ratio of about 3 is configured by three lens groups, and each lens group is given negative, positive, and negative power in order from the object side, It is possible to shorten the total length in the optical axis direction during use, and since the power distribution of each lens group is nearly symmetrical, the occurrence of off-axis aberrations such as distortion and astigmatism is fundamentally reduced. In other words, the objective is to provide a zoom lens that is compact and maintains high performance, and a camera that uses the zoom lens.

ただし、

The zoom lens of the present invention includes, in order from the object side, a first lens group, a second lens group, and a third lens group, and the first lens group has a negative refractive power as a whole, and has a negative refractive power. A first lens that is a lens having a positive refractive power (hereinafter, positive lens), and a second lens that is a meniscus lens that is convex on the object side. The lens group has a positive refractive power as a whole, and includes a third lens that is a positive lens, a fourth lens that is a negative lens, and a fifth lens that is a positive lens, and the third lens group as a whole. And having a negative refracting power and disposing a sixth lens as a negative lens, and 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, the third lens The power of the first lens group satisfies the following conditional expression (1), and the power of the third lens group satisfies the following conditional expression (2). Further, it satisfies the following conditional expression (3) with respect to the size of the entire lens system. (Claim 1)

However,

  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. If 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 overall size of the optical system, resulting in a loss of compactness.

  Conditional expression (2) 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 example described later, the chief ray angle change at the time of zooming is small, and the chief ray at the maximum image point of the screen (when the bisector of the angle formed by the upper ray and the lower ray is defined as the chief ray) angle Is about 18 ° at the maximum, and can be handled by adapting the structure of the CCD microlens. The lower limit value defined by the conditional expression (2) is the range that can be taken by the negative power of the third lens group in that state. If the lower limit value is exceeded, it is effective for downsizing, but the chief ray The angle exceeds 20 °, causing problems such as shading and insufficient amount of peripheral light, 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.

  Conditional expression (3) 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, leading to deterioration of various aberrations and deterioration of sensitivity, making it practically difficult to manufacture.

ただし、

Further, at least one of the object-side and image-side surfaces of the first lens constituting the first lens group is aspheric, and the following conditional expression (4) is satisfied with respect to the power of the lens: The following conditional expression (5) is satisfied with respect to the chromatic dispersion characteristic distributed to each lens of the first lens group, and the following conditional expression (6) is satisfied with respect to the shape of the object side surface of the first lens. It is preferable to be satisfied. (Claim 2)

However,

  Conditional expression (4) favorably corrects the aberration of the first lens group as a whole by defining the focal length of the first lens constituting the first lens group. If the upper limit is exceeded, the power of the first lens will be too low, and correction of chromatic aberration and curvature of field will be insufficient. When the lower limit is exceeded, the power of the first lens becomes excessive, and accordingly, the power of the second lens also becomes excessive. As a result, the curvature radius of each surface becomes small, high-order aberrations such as spherical aberration and coma occur, and good performance cannot be obtained.

  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.

  Conditional expression (6) basically forms off-axis aberrations such as coma and distortion by forming a concentric shape with respect to the entrance pupil under the condition of strong negative power applied to the first lens. 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 overall length is strongly reduced, 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 (6) is exceeded, the occurrence of coma and distortion cannot be sufficiently suppressed. On the contrary, if the upper limit is exceeded, it is effective to suppress the occurrence of aberration, but the curved shape of the meniscus negative lens becomes too strong, which makes 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 may be an aspherical shape. An aspheric surface, a composite aspheric surface with a resin material, and the like are preferable, but are not particularly limited.

ただし、

Further, the following conditional expression (7) is satisfied regarding the power of the third lens constituting the second lens group, and the following conditional expression (7) regarding the chromatic dispersion characteristic distributed to each lens of the second lens group: 8) is satisfied, the following conditional expression (9) is satisfied in relation to the refractive index of the third lens, and the following conditional expression (10) is satisfied with respect to the shape of the object side surface of the third lens. It is preferable that the following conditional expression (11) is satisfied in relation to the shape of the image side surface of the third lens and the shape of the image side surface of the fifth lens. (Claim 3)

However,

  Conditional expression (7) relates to the third lens which is disposed closest to the object side of the second lens group and has a 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 (8) is used for a portion that maintains a balance of aberrations while having a strong positive power for focusing a divergent 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 fifth 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 (8). Therefore, the expression uses the third lens of the positive lens and the fourth lens of the negative lens, and is a condition for maintaining the balance with each aberration while satisfactorily correcting the chromatic aberration of the entire lens system. 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 (9) 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.

  Conditional expression (10) is a conditional expression related to the shape of the third lens object side surface. Since the third lens object side surface is disposed 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. If the upper limit of conditional expression (10) is exceeded, off-axis aberrations such as coma and astigmatism will be easily corrected, but spherical aberration will be undercorrected. 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 (11) is a condition for correcting spherical aberration and other various aberrations in a well-balanced manner together with conditional expression (10). If the upper limit is exceeded, it becomes difficult to correct various aberrations. Conversely, if the lower limit is exceeded, spherical aberration cannot be corrected satisfactorily.

ただし、

Moreover, it is preferable that the following conditional expression (12) is satisfied with respect to the shape of the object-side surface of the sixth lens constituting the third lens group. (Claim 4)

However,

  As described above, by mounting the zoom lens according to the present invention as a photographing lens of a camera, it is possible to provide a thin or small so-called card-sized camera that has an optical zoom function but does not suffer even if it is always carried. It becomes possible. (Claim 5)

  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 since the power distribution of the lens group is close to symmetry, the occurrence of off-axis aberrations such as distortion and astigmatism is fundamentally reduced. The degree of freedom of the correction environment for each aberration will be improved, a compact zoom lens that maintains high performance can be realized, and a compact zoom lens and a camera using the zoom lens can be provided.

  Hereinafter, specific numerical examples relating to the present invention will be described as Examples 1 to 10. In the following first to tenth 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 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 has a positive refractive power A second lens L2 (hereinafter referred to as a positive lens) is a second lens L2 (three object side surfaces and four image side surfaces of the second lens L2), and the second lens group LG2 is positive as a whole. A third lens L3 that has a refractive power and is a positive lens (the object side surface of the third lens L3 is 5 surfaces and the image side surface is 6 surfaces), and a fourth lens L4 that is a negative lens (the object of the fourth lens L4) 7 side surfaces and 8 image side surfaces) and a fifth lens L that is a positive lens (The fifth lens L5 has nine object side surfaces and ten image side surfaces), and the third lens group LG3 has a negative refractive power as a whole and is a negative lens. A lens L6 (11 object side surfaces and 12 image side surfaces of the sixth lens L6) are arranged. The sixth lens L6 has a quartz optical filter LPF (13 side surfaces of the quartz optical filter LPF and 14 side surfaces of the image side) with an air space between the image side surface 12 and the image surface of the sixth lens L6, and a CCD. Cover glass CG (15 for the object side of the cover glass CG and 16 for the image side) is provided. 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. For zooming, the positions of the first lens group LG1 and the second lens group LG2 are moved in the optical axis direction, or the third lens group in addition to the first lens group LG1 and the second lens group LG2. This is done by moving the position of LG3. In each embodiment, the focus adjustment for an object of a finite distance is performed by moving the position of the first lens group LG1 or the third lens group LG3 in the optical axis direction. However, the present invention is not limited to these methods. Absent.

Furthermore, for the aspheric surface used in each embodiment, when the intersection of the optical axis and the surface is the origin, the optical axis direction is the Z axis, and the direction orthogonal to the optical axis is the Y axis, the aspherical formula:

[Example 1]

[Example 2]
Table 2 shows numerical examples of the second embodiment of the zoom lens according to the present invention. FIG. 2 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. 3 is a diagram showing the lens configuration, and FIG. 13 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. 4 is a lens configuration diagram, and FIG. 14 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. 5 is a lens configuration diagram thereof, and FIG. 15 is a diagram showing various aberrations thereof.

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

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

[Example 8]
Table 8 shows numerical examples of the eighth embodiment of the zoom lens according to the present invention. FIG. 8 is a lens configuration diagram, and FIG. 18 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. 9 is a diagram showing the lens configuration, and FIG. 19 is a diagram showing various aberrations.

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

  Next, Table 11 collectively shows values corresponding to the conditional expressions (1) to (12) regarding the first to tenth embodiments.

  As is clear from Table 11, the numerical values related to the examples of Examples 1 to 10 satisfy the conditional expressions (1) to (12) 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. The lens block diagram of 2nd Example of the zoom lens by this invention. 3 is a lens configuration diagram of a third embodiment of a zoom lens according to the present invention. FIG. 4 is a lens configuration diagram of a fourth embodiment of a zoom lens according to the present invention. FIG. 5 is a lens configuration diagram of a fifth embodiment of a zoom lens according to the present invention. 6 is a lens configuration diagram of a sixth embodiment of a zoom lens according to the present invention. 7 is a lens configuration diagram of a seventh embodiment of the zoom lens according to the present invention. The lens block diagram of 8th Example of the zoom lens by this invention. 9 is a lens configuration diagram of a ninth embodiment of a zoom lens according to the present invention. 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 first example Various aberration diagrams of the lens of the second example Various aberration diagrams of the lens of the third example Various aberration diagrams of the lens of the fourth example Various aberration diagrams of the lens of the fifth example Various aberration diagrams of the lens of the sixth example Various aberration diagrams of the lens of the seventh example Various aberration diagrams of the lens of the eighth example Various aberration diagrams of the lens of Example 9 Various aberration diagrams of the lens of the tenth example

Claims (5)

In order from the object side, a first lens group, a second lens group, and a third lens group are configured. The first lens group has a negative refractive power as a whole, and a lens having a negative refractive power (hereinafter, a negative lens). ) And a lens having a positive refractive power (hereinafter referred to as a positive lens) and a second lens that is a convex meniscus lens on the object side, and the second lens group is positive as a whole. A third lens that is a positive lens, a fourth lens that is a negative lens, and a fifth lens that is a positive lens, and the third lens group has a negative refractive power as a whole. And a sixth lens which is a negative lens, and is configured to move 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 and the In addition to the second lens group, the position of the third lens group is moved. 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 power of the third lens group. A zoom lens characterized by satisfying the following conditional expression (3) with respect to the size of the entire system.

However,

At least one of the object-side and image-side surfaces of the first lens constituting the first lens group is aspheric, and the following conditional expression (4) is satisfied with respect to the power of the lens: The following conditional expression (5) is satisfied with respect to the chromatic dispersion characteristic distributed to each lens of the first lens group, and the following conditional expression (6) is satisfied with respect to the shape of the object side surface of the first lens. The zoom lens according to claim 1, wherein:

However,

The following conditional expression (7) is satisfied with respect to the power of the third lens constituting the second lens group, and the following conditional expression (8) is satisfied with respect to the chromatic dispersion characteristic distributed to each lens of the second lens group. The following conditional expression (9) is satisfied with respect to the refractive index of the third lens, and the following conditional expression (10) is satisfied with respect to the shape of the object side surface of the third lens. 2. The relationship between the shape of the image side surface of the third lens and the shape of the image side surface of the fifth lens satisfies the following conditional expression (11): Zoom lens.

However,

2. The zoom lens according to claim 1, wherein the following conditional expression (12) is satisfied with respect to a shape of an object side surface of the sixth lens constituting the third lens group.

However,

  A camera equipped with the zoom lens according to any one of claims 1 to 4.

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