KR100711116B1 - Zoom lens - Google Patents

Abstract

An object of the present invention is to realize a low-cost and compact zoom lens suitable for mounting on a small information terminal device while responding to high pixel size.

To this end, the first group 11, the second group 12 positive, and the third group 13 positive are provided in order from the object side, and the first group at the time of zooming is provided. The group 11 and the second group 12 move. The first group 11 includes a sub-lens (first lens Gl) consisting of a spherical or aspherical lens and a positive meniscus spherical lens (second lens G2 facing the convex surface toward the object side). ), And the second group 12 includes both convex plastic aspherical lenses (third lens G3) and both convex spherical lenses [fourth lens G4] near the paraxial axis. And both concave spherical lenses (fifth lens G5) bonded to the fourth lens G4, and the third group 13 is spherical or aspheric facing the convex surface toward the image side. It consists of only one positive lens (sixth lens G6) At least one of the 1st lens G1 or the 6th lens G6 is comprised by a plastic lens.

zoom lens

Description

Zoom Lens {ZOOM LENS}

1 shows an example of a configuration of a zoom lens according to an embodiment of the present invention, the lens sectional view corresponding to Example 1,

2 shows another example of the configuration of a zoom lens according to an embodiment of the present invention.

3 shows another example of the configuration of a zoom lens according to an embodiment of the present invention.

4 shows another example of the configuration of a zoom lens according to an embodiment of the present invention.

5 is a view showing lens data of a zoom lens according to the first embodiment of the present invention;

6 is a view showing lens data of a zoom lens according to the second embodiment of the present invention;

7 is a view showing lens data of a zoom lens according to the third embodiment of the present invention;

8 is a view showing lens data of a zoom lens according to the fourth embodiment of the present invention;

9 is a view showing a value regarding a conditional expression satisfied by a zoom lens according to each embodiment of the present invention;

10 is aberration diagrams showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to the first embodiment of the present invention;

Fig. 11 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the telephoto end of the zoom lens according to the first embodiment of the present invention;

12 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to the second embodiment of the present invention;

Fig. 13 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the telephoto end of the zoom lens according to the second embodiment of the present invention;

14 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to the third embodiment of the present invention;

15 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the telephoto end of the zoom lens according to the third embodiment of the present invention;

16 is aberration diagrams showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to the fourth embodiment of the present invention;

Fig. 17 is an aberration diagram showing spherical aberration, astigmatism, and distortion in the telephoto end of the zoom lens according to the fourth embodiment of the present invention.

[Description of the code]

11: first group 12: second group

13: 3rd group GC: cover glass

G1 to G6: first to sixth lenses

Ri: radius of curvature of the i-th lens surface from the object side

Di: Surface spacing between the i th and i + 1 th lens surfaces from the object side

Simg: imaging plane (imaging plane) Z1: optical axis

The present invention relates to a zoom lens suitable for mounting on a small information terminal device such as a cellular phone with a camera or a personal digital assistant (PDA).

Background Art In recent years, digital still cameras (hereinafter, simply referred to as digital cameras) capable of inputting image information such as landscapes and portraits photographed in a personal computer in accordance with the widespread use of personal computers and the like are rapidly spreading. In addition, with the high functionality of mobile phones, mobile phones with cameras equipped with small imaging modules are also rapidly spreading. In addition, small-capacity information terminal devices such as PDAs are also widely used with mounting imaging modules.

In devices with these imaging functions, imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal 0xide Semiconductor) are used. In recent years, these image pickup devices have been greatly downsized and have a high pixel size. Accordingly, the image pickup device body and the lens mounted thereon are also required to have high resolution and compact structure. For example, in the case of a mobile phone with a camera or the like, megapixels or more corresponding to 1 million pixels or more are put to practical use, and the demand for performance is also increasing.

By the way, the optical zoom method and the electronic zoom method are two methods for realizing a zoom function in an imaging device using an imaging device. The optical zoom system is equipped with a zoom lens as a photographing lens and optically changes the photographing magnification. The electronic zoom method is to electronically change the size of a subject image by trimming an image by signal processing or the like. In general, the optical zoom method can obtain a higher resolution than the electronic zoom method. For this reason, when zooming with high resolution, the optical zoom method is preferable.

Conventionally, as a comparatively small zoom lens used for a digital camera etc., there exist some which were described in following patent document 1, for example. Patent Document 1 describes a zoom lens of a two-group zoom system composed of five or six lenses as a whole.

[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-270533

BACKGROUND ART In a small information terminal device such as a cellular phone with a camera, a fixed focus lens is generally used in terms of price and size, but there is a demand for a zoom function in recent years due to high performance and multifunction. Therefore, in recent years, the zoom function has been realized by adopting the electronic zoom method even in a mobile phone with a camera using a fixed focus lens. However, in the case of the electronic zoom system, the resolution deteriorates as the magnification of the image increases, so that it is difficult to cope with the recent high pixel resolution.

Therefore, it is conceivable to mount a zoom lens and adopt an optical zoom method also in a cellular phone with a camera. In this case, using the high-performance zoom lens developed for a conventional digital camera as it is is not practical in terms of cost and compactness. The zoom lens described in Patent Document 1 is also designed to be downsized with a relatively small number of lenses for digital cameras. However, when the zoom lens is used in a small information terminal device, it is preferable that the zoom lens is further downsized. On the other hand, although a low-cost and compact zoom lens composed of three sheets has been conventionally developed, it becomes difficult to cope with high pixels with it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a zoom lens capable of realizing a low cost and compact optical system suitable for mounting on a small information terminal device, while responding to high pixel size.

The zoom lens according to the present invention includes a first group having negative refractive power and a second group having positive refractive power and a third group having positive refractive power in order from the object side. In this case, the first group and the second group are configured to move on the optical axis. The first group is composed of a first lens of negative refractive power composed of a spherical lens or an aspherical lens, and a second lens composed of a positive meniscus spherical lens facing the convex surface toward the object side. The second group consists of a third lens composed of both convex plastic aspherical lenses in the vicinity of the paraxial axis, a fourth lens composed of both convex spherical lenses, and a concave spherical lens of both concave shapes. And a fifth lens joined together. The third group is composed of only one sixth lens having positive refractive power composed of a spherical lens or an aspherical lens facing the convex surface toward the image side. In addition, at least one sheet of the first lens or the sixth lens is composed of a plastic lens. Moreover, it is comprised so that the following conditional expressions (1)-(4) may be satisfied.

2.0 <ft / fw <4.0 (1)

4.0 <TCLw / fw <5.0 (2)

-2.0 <φ1 / φ3 <-0.5 (3)

νd (G3)> 45 (4)

Where ft is the focal length of the electric field at the telephoto end, fw is the focal length of the electric field at the wide-angle end, TCLw is the full length at the wide-angle end, and φ1 is zero. The refractive power of group 1, φ3 represents the refractive power of the third group, and νd (G3) represents the number of Abbe of the third lens.

In the zoom lens according to the present invention, zooming is performed by moving the first group and the second group on the optical axis. The focus adjustment may be performed in the third group, but it is advantageous in that the one fixed by the third group when zooming and focus adjustment reduces the moving group. In the case where the third group is a fixed group, the focus adjustment is performed by continuously outputting the first group group, or the first group and the second group to the front during close-up photography.

In this zoom lens, the aberration is well corrected by increasing the number of lenses as compared with the conventional simple zoom lens of about three elements in a three-group six-element configuration. In particular, in order to reduce chromatic aberration on the axis, a bonding lens is used in the second group. In addition, aspherical lenses are frequently used to shorten the overall length. In addition to this, by satisfying each conditional expression and appropriately distributing power and the like, a shorter electric field is obtained, and a high-performance lens corresponding to high pixel is obtained. In addition, the cost reduction is achieved by using a large number of plastic lenses.

In this zoom lens, it is preferable that the surface of the image side of the third lens has a shape having a curvature of a sign different from the vicinity of the paraxial axis as it goes to the periphery. It is further advantageous to correct aberration by appropriately employing these preferable conditions as necessary.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings.

1 shows an example of the configuration of a zoom lens according to an embodiment of the present invention. This configuration example corresponds to the lens configuration of the first numerical embodiment (Figs. 5A to 5C) described later. 2 to 4 show another example of the configuration of the zoom lens according to the present embodiment. 2 to 4 are examples of second to fourth numerical examples described later (Figs. 6A to 6C, 7A to 7C, and 8A to 8C). ] Lens configuration. 1 to 4 show the lens arrangement at the wide-angle end.

1 to 4, the symbol Ri denotes the i-th symbol (i), which is sequentially increased as the surface of the component on the object side toward the upper side (image forming side) as the first as well as the aperture St. = 1 to 14) the curvature radius of the surface. The symbol Di represents the surface spacing on the optical axis Z1 of the i-th surface and the i + 1th surface. In addition, since each structure example is the same in basic structure, it demonstrates based on the structure of the zoom lens shown in FIG. 1 below.

This zoom lens is particularly suitable for mounting on an imaging device using a small imaging device, for example, a small information terminal such as a mobile phone with a camera. This zoom lens comprises a first group 11 having negative refractive power along the optical axis Z1, a second group l2 having positive refractive power, and a third group 13 having positive refractive power. The stop St is provided on the object side of the second group 12.

An imaging device such as a CCD (not shown) is disposed on an imaging surface (imaging surface) (Simg) of the zoom lens. Various optical members may be arrange | positioned between the 3rd group 13 which is a final lens group, and the imaging surface Simg according to the structure of the camera side which mounts a lens. In the structural example of FIG. 1, cover glass GC for protecting the imaging surface Simg is arrange | positioned. In addition, an optical member such as an infrared cut-off filter or a low-pass filter may be disposed.

This zoom lens is a two-group zoom system, and zooming is performed by moving the first group 11 and the second group 12 on the optical axis. As the first group 11 and the second group 12 zoom in from the wide-angle end to the telephoto end, the first group 11 and the second group 12 roughly move to draw the trajectory indicated by the solid line in FIG. 1. Focus adjustment is performed in the 3rd group 13, for example. However, by using the third group 13 as a fixed group, for example, the first group 11 or the first group 11 and both of the first group 11 and the second group 12 are continuously output to the front side at the time of close-up photography. The focus may be adjusted.

The first group 11 is composed of a first lens G1 and a second lens G2. The first lens G1 is made of a spherical lens or an aspherical lens and has negative refractive power. In the case where the first lens G1 is an aspherical lens, it is preferable to constitute a plastic lens. In addition to the meniscus shape, the first lens G1 may have both concave shapes as in the configuration examples of FIGS. 2 to 4. The second lens G2 is a spherical lens of positive meniscus facing the convex surface toward the object side.

The second group 12 is composed of a third lens G3, a fourth lens G4, and a fifth lens G5. The fourth lens G4 and the fifth lens G5 are combined lenses. The third lens G3 is a plastic aspherical lens, and has both convex shapes in the vicinity of the paraxial axis. It is preferable that the image side surface of the third lens G3 has a curvature with a sign different from the vicinity of the paraxial axis as it goes to the periphery, that is, it is convex toward the image side and concave as the periphery goes to the periphery. . The fourth lens G4 is a convex spherical lens. The fifth lens G5 is a spherical lens of both concave shapes.

The third group 13 is composed of only one sixth lens G3. The sixth lens G6 is composed of a spherical lens or an aspherical lens facing the convex surface toward the image side and has positive refractive power. In the case where the sixth lens G6 is an aspherical lens, it is preferable to constitute a plastic lens.

This zoom lens is configured to satisfy the following conditional expressions (1) to (4). Where ft is the focal length of the electric field at the telephoto end, fw is the focal length of the electric field at the wide-angle end, TCLw is the electric field at the wide-angle end, φ1 is the refractive power of the first group, φ3 is the refractive power of the third group 13 and v d (G3) represent the Abbe's number of the third lens G3.

2.0 <ft / fw <4.0 (1)

4.0 <TCLw / fw <5.0 (2)

-2.0 <φ1 / φ3 <-0.5 (3)

νd (G3)> 45 (4)

Next, the operation and effects of the zoom lens constructed as described above will be described.

In this zoom lens, zooming is performed by moving the first group 11 and the second group 12 on the optical axis. The focus adjustment may be performed by the third group 13, but it is advantageous in that the one fixed by the third group 13 when zooming and focus adjustment reduces the moving group. In particular, in the case of a cellular phone with a camera or the like, it is preferable that the less movable part is advantageous in terms of mechanical strength and fastness.

In this zoom lens, the aberration is well corrected by increasing the number of lenses as compared with the conventional simple zoom lens of about three elements in a three-group six-element configuration. In particular, when the bonding lens is used in the second group 12, chromatic aberration on the axis can be reduced. In addition, since the aspherical lens is used abundantly, the overall length can be shortened while correcting the aberration well. In addition to this, by satisfying each conditional expression and appropriately distributing power and the like, the electric field is short, compact, and a high-performance lens corresponding to high pixel is obtained.

In this zoom lens, the third lens G3 is used as a plastic lens, and at least one of the first lens G1 or the sixth lens G6 is used as a plastic lens and the plastic lens is used abundantly. Plastic lenses have a larger change in optical characteristics due to temperature than glass. On the other hand, in the case of a small photographic lens, in recent years, a small actuator using a piezo element as a moving mechanism has made it possible to independently and freely control a plurality of moving groups. Therefore, even if there is a change in the optical characteristics due to temperature, it is relatively easy to control the movement of the first group 11 and the second group 12 so as to correct it, for example. Do not.

Conditional expression (1) is to define the zoom ratio. If the zoom lens has a zoom ratio of about 2 to 4 times, it is possible to maintain high performance corresponding to high pixels. Conditional Expression (2) relates to the overall length of the lens system. If it is less than the lower limit of the conditional formula (2) and the electric field is made too short, it becomes difficult to maintain the performance especially in a telephoto. In addition, when the upper limit of the conditional expression (2) is exceeded, the performance is improved, but the overall length becomes too long, and the market competitiveness when the product is actually produced is lost.

Conditional Expression (3) defines the power ratio of the first group 11 and the third group 13. If the lower limit of the conditional expression (3) is less than the lower limit of the electric field, it is advantageous in terms of making the electric field small, but the difference between the center and the aberration of the surroundings becomes too large, and a well-balanced lens system cannot be obtained. Beyond the upper limit, the battlefield becomes too large, which is undesirable. Conditional Expression (4) defines the Abbe's number of the third lens G3. If the conditional expression (4) is not satisfied, chromatic aberration cannot be appropriately suppressed, which is not preferable.

As described above, according to the present embodiment, a low-cost and compact optical system suitable for mounting on a small information terminal device can be realized while corresponding to high pixel size.

EXAMPLE

Next, a specific numerical example of the zoom lens according to the present embodiment will be described. In the following, the first to fourth numerical examples (Examples 1 to 4) are collectively described. 5A to 5C show specific lens data corresponding to the configuration of the zoom lens shown in FIG. 6 (A)-(C), 7 (A)-(C), and 8 (A)-(C) correspond to the configuration of the zoom lens shown in Figs. 2, 3 and 4, respectively. Specific lens data is shown. 5 (A), 6 (A), 7 (A) and 8 (A) show basic data parts of the lens data of the embodiment, and FIGS. 5 (B) and 6 (B). 7B and 8B show data portions relating to the aspherical shape among the lens data of the embodiment. 5 (C), 6 (C), 7 (C), and 8 (C) show other data.

In the column number Si in the lens data of Fig. 5A and the like, the surface of the component on the most object side, including the iris St and the cover glass GC, is included for the zoom lens of each embodiment. The numbers of the i-th (i = 1 to 14) planes, which are designated as the first and are sequentially increased upward, are indicated. In the column of curvature radius Ri, the value of the curvature radius of the i-th surface from an object side is shown corresponding to code | symbol Ri shown in FIG. The space | interval of surface space Di also respond | corresponds to the code | symbol attached in FIG. 1 etc., and shows the space | interval on the optical axis of the i-th surface Si and the i + 1th surface Si + 1 from the object side. The unit of the value of the curvature radius Ri and the surface spacing Di is millimeter (mm). In the columns of Ndj and vdj, the refractive index and Abbe's number of the j-th (j = 1 to 7) optical element from the object side including the cover glass GC are also shown.

In each lens data of Fig. 5 (A) or the like, the symbol &quot; * &quot; attached to the left side of the surface number indicates that the lens surface is aspheric. In the zoom lenses of the first and second embodiments, both surfaces S6 and S7 of the third lens G3 and both surfaces S11 and S12 of the sixth lens G6 are aspheric. In the zoom lens of Example 3, both surfaces S1 and S2 of the first lens G1 and both surfaces S6 and S7 of the third lens G3 are aspheric. In the zoom lens of Example 4, both surfaces S1 and S2 of the first lens G1 and both surfaces S6 and S7 of the third lens G3 and both surfaces S11 and S12 of the sixth lens G6 are aspherical. It is shaped. These aspherical lenses are all made of plastic lenses. In the basic lens data of Fig. 5A and the like, numerical values of the radius of curvature near the optical axis (near the paraxial axis) are shown as the radius of curvature of these aspherical surfaces.

In the numerical values of the aspheric data in Fig. 5B and the like, the symbol "E" indicates that the subsequent numerical value is the "square power index" with 10 as the base, and is represented by the exponential function with 10 as the base. Indicates that the value to be multiplied by the value before "E". For example, "1.0E-02" shows that "1.0x10 <^-2>".

In each aspherical surface data, the value of each coefficient Ai and KA in the aspherical surface formula shown by following formula (A) is written. In more detail, Z represents the length (mm) of the perpendicular | vertical line which fell from the point on the aspherical surface at the position of height h from an optical axis to the tangent plane (plane perpendicular | vertical to an optical axis) of the aspherical vertex.

Z = C · h ² / {1+ (1-KA, C ² h ² ) ^1/2 } + _{Σ A i} h ^{i ...}

Z is the depth of aspherical surface (mm)

    h: Distance (height) from the optical axis to the lens surface (mm)

    KA: eccentricity

    C: paraxial curvature = 1 / R (R: paraxial curvature radius)

A _i : i-th (i = 4,6,8,10) aspherical surface coefficient

Since the first group 11 and the second group 12 move on the optical axis in accordance with the change in both zoom lenses of the embodiments, the values of the surface spacings D4 and D10 before and after these groups are variable. The values of the embodiments in the wide-angle end and the telephoto end as data at the time of variation of these plane intervals D4 and D10 are shown in FIGS. 5 (C), 6 (C), 7 (C), and 8 (C). ).

The values concerning the conditional formulas (1) to (4) described above in FIG. 9 are collectively shown for each example. As shown in FIG. 9, the value of each Example is in the numerical range of each conditional formula (1)-(4).

10A to 10C show spherical aberration, astigmatism, and distortion (distortion aberration) at the wide-angle end in the zoom lens of the first embodiment. 11A to 11C show the same aberration as in the telephoto end. The aberration diagrams show aberrations based on the d-line, but the spherical aberration diagrams also show aberrations for the g line (wavelength 435.8 nm) and the C line (wavelength 656.3 nm). In the astigmatism diagram, the solid line indicates aberration in the sagittal direction and the dashed line indicates aberration in the tangential direction. FNO. Is an F value, and ω represents a half angle of view.

Similarly, various aberrations for the second embodiment are shown in Figs. 12A to 12C (wide-angle end), and Figs. 13A to 13C (telephoto end). Various aberrations for Example 3 are shown in Figs. 14A to 14C (wide end) and 15A to 15C (telephoto end). Various aberrations for Example 4 are shown in Figs. 16A to 16C (wide end) and 17A to 17C (telephoto end).

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

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

According to the zoom lens according to the present invention, aspherical lenses and plastic lenses are suitably used in the configuration of six elements in three groups, and the power distribution and the like are satisfied by satisfying each conditional expression. A low cost and compact optical system suitable for mounting on an information terminal device can be realized.

Claims (3)

A first group having negative refractive power, a second group having positive refractive power, and a third group having positive refractive power in order from the object side, wherein the first group and the second group move on the optical axis during zooming; Configured to The first group is composed of a first lens of negative refractive power made of a spherical lens or an aspherical lens, and a second lens made of a spherical lens of positive meniscus facing the convex surface toward the object side, The second group is composed of a third lens composed of both convex plastic aspherical lenses in the vicinity of the paraxial axis, a fourth lens composed of both convex spherical lenses, and a concave spherical lens formed in both concave shapes and joined to the fourth lens. Consisting of a fifth lens, The third group is composed of only one sixth lens of positive refractive power composed of a spherical lens or an aspherical lens facing the convex surface toward the image side, At least one of the first lens or the sixth lens is a plastic lens, A zoom lens configured to satisfy the following conditional expressions (1) to (4). 2.0 <ft / fw <4.0 (1) 4.0 <TCLw / fw <5.0 (2) -2.0 <φ1 / φ3 <-0.5 (3) νd (G3)> 45 (4) However, ft: focal length of the electric field in the telephoto end     fw: focal length of electric field in wide-angle end     TCLw: Overall length at wide angle     φ1: refractive power of the first group     φ3: refractive power of the third group     νd (G3): Abbe's number of the third lens The method of claim 1, A zoom lens, characterized in that it has a shape with a curvature of a sign different from the vicinity of the paraxial axis as the image surface of the third lens moves toward the periphery. The method according to claim 1 or 2, And the third group is fixed at the time of zooming and focus adjustment.

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