JP2009031697A - Photographic lens unit, photographing device and personal digital assistant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographic lens unit which is reduced in height while suppressing deterioration of optical performance within the range of thickness which does not exceed the limit of manufacture of respective lenses constituting the photographic lens unit. <P>SOLUTION: The photographic lens unit is constituted of a first lens L1, a diaphragm, a second lens L2, a third lens L3 and a cover glass CG or the like in order from an object side to an image side as shown in Fig.5(a). The object-side surface of the first lens L1 is convex to the object side and the image-side surface thereof is concave to the image side near an optical axis and also convex to the image side toward a periphery part as shown in Fig.5(b). The second lens L2 is a meniscus lens with its convex surface facing the image side. The third lens L3 is an aspherical lens whose object-side surface is convex to the object side near the optical axis and concave to the object side toward a periphery part and whose image-side surface is concave to the image side near the optical axis and convex to the object side toward the periphery part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photographing lens unit, and more particularly to a photographing lens unit suitable for mounting on a small photographing device. The present invention also relates to an imaging device and a portable terminal.

With the downsizing of the photographing apparatus, there is a growing demand for downsizing of the photographing lens unit. In particular, an imaging device is generally mounted on a portable terminal, and in order to match the thickness of the portable terminal, it is required to be extremely miniaturized in the optical axis direction, that is, to greatly reduce the height. To reduce the height, it is effective to reduce the number of lenses that make up the photographic lens unit. However, with one or two lens configurations, the aberrations cannot be corrected sufficiently, so the optical characteristics tend to be insufficient. . Therefore, as a technique that enables a reduction in height while suppressing a decrease in optical characteristics, there is a three-lens photographing lens unit that uses meniscus-shaped lenses as the first and second lenses as viewed from the object side. It has been proposed (for example, Patent Document 1 or Patent Document 2).
JP 2006-154767 A JP 2006-301403 A

  By the way, in order to correct the aberration with a limited number of lenses, it is preferable to use an aspherical lens in which each lens constituting the photographing lens unit hardly generates aberration. Since it is difficult to manufacture such an aspheric lens using glass, it is usually manufactured by injection molding plastic. In order to maintain strength in injection molding, there is a limit to the thickness of the lens, and an extremely thin plastic lens cannot be manufactured.

  On the other hand, as the mobile terminal becomes thinner, there is an increasing demand for lowering the height of the photographing device provided in the mobile terminal. In order to meet such demands, it is necessary to further reduce the size of each lens constituting the photographic lens unit in order to achieve a further reduction in height using the technology of Patent Document 1 or Patent Document 2. However, as described above, there is a limit in the manufacturing process to thin the plastic lens.

  The present invention has been made in view of such a situation, and without reducing the thickness of each lens constituting the photographing lens unit below the limit of the plastic lens production, while suppressing the deterioration of the optical performance, further lowering the optical performance. An object is to supply a photographing lens unit that can achieve a height reduction.

  The photographing lens unit according to the present invention is arranged in order from the object side to the image side, the object side surface is convex toward the object side, and the image side surface is concave toward the image side near the optical axis. A first lens that is convex toward the image side toward the periphery, an aperture stop, a meniscus second lens that has a convex surface toward the image side, and an object side surface near the optical axis. And convex toward the object side as it goes toward the periphery, and the image side surface is concave toward the image side near the optical axis and convex toward the object side as it goes toward the periphery It is characterized by arranging a third lens.

  According to the above configuration, the first lens has a concave surface on the image side in the vicinity of the optical axis and a convex shape on the image side toward the peripheral portion. Even with the same lens thickness, the position of the aperture stop can be moved closer to the object side. As a result, the distance from the aperture stop to the imaging surface can be increased, and the optical performance can be improved as compared with a conventional lens unit of the same back position.

  In the photographing lens unit according to the present invention, the first lens is preferably formed of a resin material. Since the first lens is formed of a resin material, the first lens shape can be created easily and inexpensively by injection molding. In addition, even if the outer thickness of the optical effective diameter is ensured for injection molding, the first lens has the specific shape described above, so that it is possible to reduce the height while suppressing a decrease in optical performance.

  In the photographing lens unit according to the present invention, it is preferable that the object-side surface and the image-side surface of the first lens are aspherical. By making the object side surface and the image side surface of the first lens aspherical, aberration can be suppressed by a limited number of lenses.

  An imaging apparatus according to the present invention includes the above-described imaging lens unit and an image element that converts an optical image formed by the imaging lens unit into an electrical signal.

  The portable terminal concerning this invention is provided with the above-mentioned imaging device.

  According to the present invention, by changing the shape of the first lens, it is possible to supply a photographing lens unit that can achieve a further reduction in height while suppressing a decrease in optical performance.

  Hereinafter, an embodiment of a portable terminal embodying the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the portable terminal according to the present embodiment is a telephone configured to be folded around a hinge H. FIG. 1 is a diagram showing a folded state, and a photographing device 50 is provided on the front surface. FIG. 2A is a diagram in which the portable terminal is opened and the display unit 23 and the operation unit 24 are faced to the front. FIG. 2B is a view of the opened portable terminal viewed from the back. In this state, the subject can be photographed by operating the shutter button toward the subject to be photographed.

  The configuration of the mobile terminal is shown in the block diagram of FIG. The portable terminal includes a call unit 11, a function control unit 21, and a photographing device 50. The call unit 11 includes a microphone 12, a speaker 13, and a radio unit 14. The radio unit 14 includes an antenna, a transmission / reception circuit, a modulation / demodulation circuit, a compression / decompression circuit, an audio codec, and the like. The voice input from the microphone 12 is transmitted as a voice signal, and the voice signal of the other party of the call is received and output to the speaker 13.

  The display unit 23 and the operation unit 24 are used for operation and display for data communication via the Internet network in addition to display and operation for a call on the mobile terminal. The operation unit 24 is used for inputting a desired character string in order to input a telephone number during a call and to use various data communication services via an Internet network such as an electronic mail. The display unit 23 includes a liquid crystal display unit (LCD unit), and is also used to display an image captured by the image capturing device 50 and an image acquired through communication.

  The operation unit 24 is provided with a call key 241, a shutter key 242, a function selection key 243, and a numeric keypad 245. When a call is made, the numeric keypad 245 is operated to input a telephone number and the call key 241 is operated to make a call. Further, alphanumeric characters, katakana and hiragana characters are assigned to the numeric keypad 245, and character code conversion is performed by an alphanumeric kana conversion control unit (not shown). The character code conversion is converted into an input character code corresponding to each operated key depending on whether the input mode is alphanumeric kana or kana-kanji conversion mode. The function selection key 243 is a key for enabling a predetermined function of the mobile terminal, and the function assigned to this key differs depending on the manufacturer and model.

  When the shutter key 242 is operated, an image is photographed by the photographing device 50 via the main control unit 22 and the photographing device control unit 29. The captured image is stored in the temporary storage device 25 as image data via the imaging device control unit 29 and the main control unit 22, and then displayed again on the display unit 23 via the main control unit 22 as necessary. Or stored in an external storage device (not shown), and further communicated to the outside via the wireless unit 14.

  As shown in FIG. 4, the imaging device provided in the portable terminal has an imaging device 53 such as a CCD (charged coupled device) sensor or a CMOS (complementary metal-oxide-semiconductor) sensor fixed on a substrate and a substantially cylindrical shape. The cover glass CG is fixed via the base 2 (56). The base 2 (56) is provided with a base 1 (55) having a substantially cylindrical shape and having an internal thread on the inner peripheral surface so as to protrude to the object side. Further, a lens barrel 51 having a substantially bottomed cylindrical shape and having a male screw corresponding to the female screw of the base 2 (56) on the outer peripheral surface is screwed and fixed to the base 2 (56) with the bottom portion facing the object side. Yes. A circular through hole is formed in the center of the bottom of the lens barrel 51.

  The first lens L <b> 1 is fixed to the inner plane of the bottom portion of the lens barrel 51 in such a manner that the optically effective diameter portion is fitted in the through hole. That is, the outer side (hereinafter referred to as the peripheral portion) of the optical effective diameter of the first lens L1 is fixed to the inner surface of the bottom of the lens barrel 51 with UV curable resin or the like. A diaphragm S is fixed to the image side of the first lens L1 with UV curable resin or the like, and a third lens L3 is similarly fixed to the image side via a second lens L2 and a spacer 52. In this imaging apparatus, since the lens barrel 51 is screwed and fixed to the base 1 (55), the distance between the lens barrel 51 and the imaging element 53 can be adjusted by adjusting the screwing amount, and the inside of the lens barrel 51 can be adjusted. It is possible to adjust the distance between the photographing lens unit including the first lens L1 to the third lens L3 and the photographing element 53, that is, to focus.

  The image formed on the imaging surface 54, which is the surface of the imaging element 53 by the imaging lens unit, is converted into digital data by the imaging element 53, and then the main control is performed via the imaging device control unit 29 as described above. The image data is processed in the unit 22 as image data.

  Further, the photographing lens unit will be described in detail with reference to FIGS. In FIGS. 5A and 5B, only the portion of the optical effective diameter of the lens is shown for simplification of description. The same applies to the subsequent drawings. As described above, the photographing lens unit includes the first lens L1, the diaphragm S, the second lens L2, the third lens L3, the cover glass CG, and the like in order from the object side to the image side. The first lens L1, the second lens L2, and the third lens L3 are all plastic lenses formed by injection molding of a resin material and are aspherical lenses. As shown in FIG. 5B, in the first lens L1, the object side surface is convex toward the object side, the image side surface is concave toward the image side near the optical axis, and as it goes toward the periphery. Is convex on the image side.

  Here, the width of the lens is indicated by the difference between the point closest to the object side and the point closest to the image side. Conventionally, since the first lens has a meniscus shape that is convex toward the object side, the position of the convex vertex on the object side surface, which is the point closest to the object side, and the point closest to the image side, The difference from the position of the end on the image side was the width d1 of the first lens. In this embodiment, the image side surface is concave on the image side in the vicinity of the optical axis and convex toward the image side toward the periphery, so the position of the end of the lens on the image side is conventional. The convex vertex on the image side is the closest point to the image side. As a result, the width d2 of the first lens in the present embodiment can be made smaller than the width d1 of the conventional first lens. Therefore, it is possible to provide the diaphragm S closer to the object side.

  The second lens L2 is a meniscus lens having a convex surface facing the image side. The third lens L3 has an object-side surface convex toward the object side near the optical axis and concave toward the object side toward the periphery, and an image-side surface near the optical axis. The aspherical lens is concave on the side and convex toward the object side toward the periphery. The light transmitted through the first lens is corrected for aberrations by transmitting through the second lens L2 and the third lens L3, and after passing through the cover glass CG, is condensed on the imaging surface 54 to form an image.

  According to the above embodiment, the following effects can be obtained.

  (1) In the above embodiment, the first lens L1 has an object-side surface convex toward the object side, the image-side surface is concave toward the image side in the vicinity of the optical axis, and is imaged toward the periphery. It is convex on the side. Therefore, the width d2 of the first lens in this embodiment is smaller than the width d1 of the conventional first lens. Therefore, it is possible to provide the diaphragm S closer to the object side. Therefore, if the distance from the position closest to the image side of the first lens to the imaging plane 54 (hereinafter referred to as the full length) is the same, the distance from the stop S to the imaging plane 54 can be made longer than before. Therefore, aberration correction becomes easy and optical performance is improved. Therefore, it is possible to provide a photographing lens unit that is further reduced in height while suppressing a decrease in optical performance.

  (2) In the above embodiment, since the first lens L1, the second lens L2, and the third lens L3 are all plastic lenses formed by injection molding of a resin material, they can be easily and inexpensively manufactured by injection molding. In addition, it is easy to reduce the weight of the entire lens unit.

  (3) In the above embodiment, since the first lens L1, the second lens L2, and the third lens L3 are all aspherical lenses, even with three lenses, it is easier to correct aberrations and optical performance. This is a photographic lens unit that has been further reduced in height while suppressing the decrease in image quality.

  (4) In the above-described embodiment, an imaging apparatus that is further reduced in height can be supplied by using a photographing lens unit that is further reduced in height while suppressing a decrease in optical performance.

  (5) In the above-described embodiment, by using an imaging device that is further reduced in height, it is possible to supply a portable terminal that is further reduced in height.

  In addition, you may change this embodiment as follows.

  In the above embodiment, the first lens L1, the second lens L2, and the third lens L3 are all aspherical lenses. However, as long as equivalent optical characteristics can be maintained, all of them need to be aspherical lenses. Absent. Using part of a spherical lens that is easy to manufacture contributes to cost reduction.

  In the above embodiment, the first lens L1, the second lens L2, and the third lens L3 are all plastic lenses formed of a resin material, but are not essential. A glass molded aspherical lens may be used as long as the same optical characteristics are maintained.

  In the above embodiment, the cover glass CG is provided between the third lens L3 and the imaging plane 54, but it is not essential. In addition to the cover glass CG or in addition to the cover glass CG, a filter or the like for cutting infrared rays may be provided.

  In the above embodiment, the photographing device 50 is a digital system by using the photographing element 53 constituted by a CCD sensor or a CMOS sensor. However, by using an optical film as the photographing element 53, a silver salt photograph It is good also as an imaging device.

  In the above embodiment, the photographing device 50 is used for a portable terminal, but may be used for a normal camera or a personal computer. Further, it may be used not only for still images but also for shooting moving images.

FIG. 6A is a cross-sectional view of a surface including the optical axis of the photographic lens unit according to the above embodiment. Numerical data of optical members constituting the photographing lens unit are shown below.
Angle of view Diagonal: 63.8 ° Horizontal: 53.0 ° Vertical: 41.0 °
Total focal length: 2.90 mm Back focus: 1.08
Total lens length: 3.30mm Effective image height: Φ3.6mm

  Table 1 shows the lens data. However, in Table 1, the number i of each surface is set so that the object-side surface of the first lens is the first surface and is swung toward the image side in order. Ri is a radius of curvature in each surface, Di is a surface interval between the i-th surface and the (i + 1) -th surface, nd is a refractive index, and νd is an Abbe number. In addition, the aspherical surface is indicated by * to the right of the surface number.

The aspherical shape is represented by the following formula.

  In Equation (1), the optical axis direction is the z-axis, R is the radius of curvature, the height in the direction orthogonal to the H optical axis, K is the conic constant, and A4, A6, A8, A10, A12, and A14 are 4 respectively. The aspherical coefficients are the sixth, eighth, tenth, twelfth, and fourteenth.

  The aspheric coefficients on each surface are as shown in Table 2 below.

  [Comparative Example 1]

FIG. 6B is a cross-sectional view of a surface including the optical axis of the photographic lens unit according to the above embodiment. Numerical data of optical members constituting the photographing lens unit are shown below.
Angle of view Diagonal: 60.4 ° Horizontal: 50.0 ° Vertical: 38.4 °
Total focal length: 3.08 mm Back focus: 1.01
Total lens length: 3.30mm Effective image height: Φ3.6mm

Table 1 shows the lens data. However, in Table 1, the number i of each surface is set so that the object-side surface of the first lens is the first surface and is swung toward the image side in order. Ri is a radius of curvature in each surface, Di is a surface interval between the i-th surface and the (i + 1) -th surface, nd is a refractive index, and νd is an Abbe number.

The aspherical shape is represented by the following formula.

  In Equation (1), the optical axis direction is the z-axis, R is the radius of curvature, the height in the direction orthogonal to the H optical axis, K is the conic constant, and A4, A6, A8, A10, A12, and A14 are 4 respectively. The aspherical coefficients are the sixth, eighth, tenth, twelfth, and fourteenth.

The aspheric coefficients on each surface are as follows.

  [Comparison between Example 1 and Comparative Example 1]

  As shown in FIGS. 6A and 6B, the photographic lens unit of Example 1 and the photographic lens unit of Comparative Example 1 have the same overall length of 3.30 mm. The position of the aperture S of the photographic lens unit approaches the object side. As a result, the distance from the stop S to the imaging plane 54 is long.

  7A and 7B, the aberrations of the photographing lens unit of Example 1 and the photographing lens unit of Comparative Example 1 are compared. It can be seen that, at any imaging position, the variation in points is smaller in the example, and various aberrations are further suppressed. In addition, it can be seen that the variation due to the wavelength of light is small, and the axial chromatic aberration and lateral chromatic aberration are also suppressed in Example 1.

  8A and 8B, the field curvature and distortion of the photographic lens unit of Example 1 and the photographic lens unit of Comparative Example 1 are compared. Although it is difficult to determine the curvature of field because the shape of the graph is different, it can be seen that the distortion in the first embodiment is less distorted even when it is away from the optical axis, and the distortion is suppressed.

  9A and 9B, spherical aberrations of the photographing lens unit of Example 1 and the photographing lens unit of Comparative Example 1 are compared. It can be seen that, at any wavelength, the aberration blur is smaller in Example 1 and the spherical aberration is suppressed.

  FIGS. 10A and 10B show the transfer function (MTF) between the photographic lens unit of Example 1 and the photographic lens unit of Comparative Example 1, and FIGS. It is the graph which compared and described the transfer function (MTF) of Example 1 and Comparative Example 1 in each position. The graph of Example 1 exceeds the transfer function value of Comparative Example 1 in almost all regions of the spatial frequency at any position on the image plane and in any of the tangential and sagittal directions. It can be seen that the imaging performance of the photographic lens unit of 1 exceeds the imaging performance of the photographic lens unit of Comparative Example 1.

  Since the photographic lens unit according to the present invention is a photographic lens unit suitable for mounting on a small photographic device, it can be used in a wide range including a photographic device used for a portable terminal.

It is an external view at the time of non-use of the portable terminal concerning an embodiment. It is an external view at the time of use of the portable terminal concerning an embodiment, (a) is a front perspective view, and (b) is a back perspective view. It is a block diagram which shows the structure of the portable terminal concerning embodiment. It is a figure explaining the structure of the imaging device concerning embodiment, and is a cross-sectional schematic diagram by the surface containing an optical axis. It is a figure explaining the lens composition of the photographic lens unit concerning an embodiment, and is a section schematic diagram by the field containing an optical axis, (a) is a sectional view by the plane containing an optical axis, and (b) is the 1st. It is an expansion schematic cross section of 1 lens. It is a figure explaining the effect of the photographic lens unit concerning an Example, (a) is a sectional view containing the optical axis of the photographic lens unit concerning an example, and (b) is the photographic lens unit concerning a comparative example. It is sectional drawing containing an optical axis. It is a figure explaining the effect of the photographic lens unit concerning an Example, (a) is a spot diagram of a photographic lens unit concerning an example, and (b) is a spot diagram of a photographic lens unit concerning a comparative example. . It is a figure explaining the effect of the photographic lens unit concerning an Example, (a) is field curvature and distortion of a photographic lens unit concerning an example, and (b) is a photographic lens unit concerning a comparative example. Curvature of field and distortion. It is a figure explaining the effect of the photographic lens unit concerning an Example, (a) is the spherical aberration of the photographic lens unit concerning an example, (b) is the spherical aberration of the photographic lens unit concerning a comparative example. . It is a figure explaining the effect of the photographic lens unit concerning an Example, (a) is a graph of a transfer function of a photographic lens unit concerning an example, and (b) is a transfer function of a photographic lens unit concerning a comparative example. It is a graph of. It is a figure explaining the effect of the photographic lens unit concerning an Example, Comprising: It is a graph of the transfer function in the image height 0.000mm position of Example 1 and Comparative Example 1. FIG. It is a figure explaining the effect of the photographic lens unit concerning an Example, Comprising: It is a graph of the transfer function in the image height 0.900mm position of Example 1 and Comparative Example 1. FIG. It is a figure explaining the effect of the photographic lens unit concerning an Example, Comprising: It is a graph of the transfer function in the image height 1.000mm position of Example 1 and Comparative Example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Call part, 12 ... Microphone, 12 ... Holding part, 13 ... Speaker, 14 ... Wireless part, 21 ... Function control part, 22 ... Main control part, 23 ... Display unit, 24 ... Operating unit, 25 ... Temporary storage device, 29 ... Shooting device controller, 50 ... Shooting device, 51 ... Tube, 52 ... Spacer, 53 ... Imaging element, 54 ... Imaging plane, 55 ... Base 1, 56 ... Base 2, 241 ... Call key, 242 ... Shutter key, 243 ... Function selection key 245, numeric keypad, CG, cover glass, d1, width, d2, width, H, hinge, L1, first lens, L2, second lens, L3. .. Third lens, S ... Aperture.

Claims (5)

Arranged in order from the object side to the image side,
A first lens in which the object side surface is convex toward the object side, the image side surface is concave toward the image side in the vicinity of the optical axis, and convex toward the image side toward the periphery;
An aperture stop,
A second meniscus lens with a convex surface facing the image side;
The object side surface is convex toward the object side near the optical axis and concave toward the object side toward the periphery, and the image side surface is concave toward the image side near the optical axis and the periphery A photographic lens unit in which a third lens that is convex toward the object side is arranged as it goes to the part.   The photographing lens unit according to claim 1, wherein the first lens is formed of a resin material.   3. The photographic lens unit according to claim 1, wherein an object side surface and an image side surface of the first lens are aspherical. The taking lens unit according to any one of claims 1 to 3,
An imaging device comprising: an image element that converts an optical image formed by the imaging lens unit into an electrical signal.   The portable terminal provided with the imaging device of any one of Claims 1-4.

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