JP4935235B2 - Compact imaging system and imaging apparatus - Google Patents

Description

  The present invention relates to a novel compact imaging system and imaging apparatus. Specifically, the present invention relates to a small imaging system that has a small optical size but good optical performance, and an imaging apparatus that uses the small imaging system.

  In general, an imaging system for a portable imaging device is desired to be small and have a wide imaging range at a short distance. In order to satisfy such a requirement, for example, as shown in Patent Document 1, Patent Document 2, etc., it has a brightness of about F4 composed of a single plastic lens and has a horizontal field angle of about 50 °. It has been known.

JP 2003-131124 A JP 2000-24991 A

  However, in recent portable imaging devices, since there is a strong demand for downsizing, the downsizing of the imaging device further proceeds, and it is desired to improve the imaging performance while shortening the optical total length. The imaging system shown in No. 1 and Patent Document 2 cannot satisfy these requirements.

  The present invention has been made in view of the above problems, and has a small F-number, a wide shooting angle of view, a well-corrected aberration, and a compact imaging system composed of a low-cost single lens. It is another object of the present invention to provide an image pickup apparatus using the small image pickup system.

A compact imaging system according to an embodiment of the present invention includes a single lens having a biconvex shape and both surfaces being aspherical, and an aperture stop positioned close to the object side surface of the single lens. The spherical surface is an aspherical surface that increases the positive refractive power as it goes from the optical axis to the periphery, and the aspherical surface on the image plane side is an aspherical surface that decreases the positive refractive power as it goes from the optical axis to the periphery, and the following conditional expression (1) , (2), (3), (4) are satisfied.
(1) 1.10 ≦ r1 / f <1.43
(2) 0.63 <| r2 | / f <1.19
(3) 0.15 <d / D <0.7
(4) 50 <νd
However,
r1: paraxial radius of curvature of object side surface r2: paraxial radius of curvature of image side surface f: focal length of single lens d: distance from r1 surface to aperture stop D: thickness of single lens νd: single lens The Abbe number for the d-line (λ = 587.6 nm).

An image pickup apparatus according to an embodiment of the present invention includes a small image pickup system and an image pickup element that converts an optical image formed by the small image pickup system into an electric signal. Is composed of a single lens composed of an aspherical surface and an aperture stop located close to the object side surface of the single lens, and the aspherical surface increases the positive refractive power as the aspherical surface on the object side moves from the optical axis to the periphery And the aspherical surface on the image plane side is an aspherical surface whose positive refractive power is weakened from the optical axis toward the periphery, and conditional expressions (1) 1.10 ≦ r1 / f <1.43, (2) 0.63 < | R2 | / f <1.19, (3) 0.15 <d / D <0.7, and (4) 50 <νd are satisfied.

  According to the present invention, it has a small F number and a wide shooting angle of view while being compact, and aberrations are corrected well.

  The best mode for carrying out the small imaging system and imaging apparatus of the present invention will be described below with reference to the drawings and tables.

The small imaging system of the present invention is composed of a single lens having a biconvex shape and both surfaces being aspherical, and an aperture stop positioned close to the object side surface of the single lens, and the object-side aspherical surface from the optical axis. An aspheric surface that increases the positive refractive power toward the periphery, and an aspheric surface that decreases the positive refractive power toward the periphery from the optical axis to the aspheric surface on the image plane side. The following conditional expressions (1), (2), Satisfy (3) and (4).
(1) 1.10 ≦ r1 / f <1.43
(2) 0.63 <| r2 | / f <1.19
(3) 0.15 <d / D <0.7
(4) 50 <νd
However,
r1: paraxial radius of curvature of object side surface r2: paraxial radius of curvature of image side surface f: focal length of single lens d: distance from r1 surface to aperture stop D: thickness of single lens νd: single lens The Abbe number for the d-line (λ = 587.6 nm).

  When trying to obtain a short-length imaging system consisting of a single lens suitable for using a small image sensor, the object-side surface of the lens is convex instead of concave with respect to the aperture stop placed in front of it. It is desirable to employ a biconvex lens. Accordingly, the focal length of the lens can be shortened as compared with the case where the object side surface is a concave surface, so that the total length of the imaging system can be shortened.

  However, if the first surface following the aperture stop is a convex surface, in addition to the distortion that occurs when the aperture stop and the positive lens are arranged in this order from the object side, further negative distortion is generated on the convex surface of the first surface. It will be.

  Therefore, in the small imaging system of the present invention, the aspherical shape of the image side surface, that is, the second surface, is an aspherical surface having a shape in which the positive refractive power is weakened from the optical axis toward the periphery. The aspherical surface having such a shape acts to add positive distortion to the peripheral rays, and the distortion aberration can be satisfactorily corrected as a whole system.

  In addition, since the object side surface is not concentric with the aperture stop, it is difficult to correct astigmatism. Therefore, in the small imaging system of the present invention, the aspherical surface on the object side is an aspherical surface that increases the positive refractive power as it goes from the optical axis to the periphery, so that the sagittal of the peripheral luminous flux, the radius of curvature of the meridional ray Astigmatism is corrected by reducing the difference between the two.

  Furthermore, by making the first surface, that is, the object side surface of the single lens convex, it is advantageous in the case of a configuration of a front diaphragm, that is, a configuration in which the aperture diaphragm is disposed in the forefront of the optical system. For example, when an opening is formed on the front surface of the resin housing of the image pickup device and this opening is used as an aperture stop, the extended portion (the portion that becomes the lens flange) of the object side surface from the optically effective surface is the image surface side. Therefore, a space is secured between the lens flange and the portion adjacent to the aperture stop of the housing, and the thickness of the housing can be increased by the amount of the space. Since the strength against deformation of the portion increases and the aperture stop has good moldability, the dimensional accuracy of the aperture stop is improved.

  Conditional expression (1) defines the paraxial radius of curvature of the first surface, that is, the object side surface of the single lens.

  When the upper limit value of conditional expression (1) is exceeded, the radius of curvature at the center of the object side surface becomes too large, and the difference in position in the optical axis direction between the lens flange and the first surface becomes small. In order to reduce the distance between the front surface of the case and the single lens when trying to shorten the overall length of the lens barrel when the aperture stop is made of resin, A sufficient thickness cannot be ensured, the risk of deformation after molding increases, and it becomes difficult to ensure the dimensional accuracy of the aperture stop.

  If the lower limit of conditional expression (1) is not reached, the radius of curvature of the object side surface becomes small, which is desirable for shortening the total length, but the field curvature becomes under and the flat image surface cannot be secured.

  Conditional expression (2) defines the paraxial radius of curvature of the second surface, that is, the image side surface of the single lens.

  If the upper limit of conditional expression (2) is exceeded, the radius of curvature at the center of the image side surface becomes large, the field curvature becomes excessive, and flat imaging performance cannot be ensured.

  If the lower limit of conditional expression (2) is not reached, the radius of curvature of the image side surface becomes small, and it becomes difficult to correct negative distortion even with an aspherical surface.

  Conditional expression (3) defines the center thickness of a single lens.

  If the lower limit of conditional expression (3) is not reached, the center thickness of the single lens becomes small, and when molding the lens by an injection molding machine, it becomes extremely difficult to control the molding conditions, and it becomes difficult to ensure mass productivity.

  If the upper limit value of conditional expression (3) is exceeded, the center thickness of the single lens becomes large, and as a result, the total length becomes long, which is not preferable.

  Conditional expression (4) defines a condition for maintaining good chromatic aberration.

  Since the image pickup system of the present invention is composed of a single lens, it has no means for correcting chromatic aberration. Therefore, when the chromatic aberration with respect to the d-line of the single lens is 50 or less, both axial chromatic aberration and lateral chromatic aberration are deteriorated.

  With the configuration as described above, in the small imaging system of the present invention, the F number is reduced and the horizontal angle of view is 55 in spite of a very simple configuration in which the lens is only a single lens having both aspheric surfaces. Each aberration can be satisfactorily corrected up to about 0 °, and the total length can be shortened.

  Hereinafter, specific embodiments of the small imaging system of the present invention and numerical examples in which specific numerical values are applied to these embodiments will be described.

  An aspherical surface is employed in the small imaging system of the present invention. Therefore, in the orthogonal coordinate system in which the aspherical surface deformation amount ΔH (h) is an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is the X axis, the direction perpendicular to the optical axis is h, the vertex curvature radius is r, and the conic constant is K. It is assumed that the fourth, sixth, eighth, tenth, twelfth, and fourteenth aspherical coefficients are defined by Equation 1 as A, B, C, D, E, and F.

FIG. 1 shows the lens configuration of the first embodiment of the small imaging system of the present invention. The small imaging system 1 is configured by arranging, in order from the object side, an aperture stop S and a positive lens L1 having a biconvex shape and both surfaces being aspherical. In FIG. 1, IMG is an imaging surface, and G is a cover glass located on the object side of the imaging surface and also serving as a low-pass filter.

  Table 1 shows lens data of Numerical Example 1 in which specific numerical values are applied to the compact imaging system 1 according to the first embodiment. In Table 1 and other lens data tables, Si is the i-th surface from the object side, R is the paraxial radius of curvature of the i-th surface, D is the i-th surface and i + 1-th surface from the object side. Nd is the refractive index for the d-line of the medium having the i-th surface on the object side, νd is the Abbe number for the d-line of the medium having the i-th surface on the object side, f Indicates the focal length of the positive lens L1, respectively, and regarding the radius of curvature R, inf indicates that the surface is a plane.

The second surface (S2) and the third surface (S3) are aspherical. Table 2 shows the fourth, sixth, eighth, tenth, twelfth, and fourteenth aspherical coefficients of A, B, C, D, E, and F together with the conic constant κ in Numerical Example 1. Show. In Table 2 and the following table showing aspherical coefficients, “E-i” represents an exponential expression with a base of 10, that is, “10- ⁱ ”. For example, “0.12345E-05” represents “ 0.12345 × 10 ^-5 ".

  FIG. 2 shows longitudinal aberrations (spherical aberration, astigmatism, distortion) of Numerical Example 1. The diagram shows spherical aberration, where the solid line is for the d line and the broken line is the g line (λ = 435.84 nm). ), The solid line indicates the sagittal image plane, and the broken line indicates the meridian image plane.

  FIG. 2 shows the lens configuration of the second embodiment of the small imaging system of the present invention. The small imaging system 2 is configured by arranging, in order from the object side, an aperture stop S and a positive lens L1 having a biconvex shape and both surfaces being aspherical. In FIG. 2, IMG is an imaging surface, and G is a cover glass that is located on the object side of the imaging surface and also serves as a low-pass filter.

  Table 3 shows lens data of Numerical Example 1 in which specific numerical values are applied to the compact imaging system 2 according to the second embodiment.

  The second surface (S2) and the third surface (S3) are aspherical. The fourth-order, sixth-order, eighth-order, tenth-order, twelfth-order, and fourteenth-order aspherical coefficients of the respective surfaces in Numerical Example 2 are shown in Table 4 together with A, B, C, D, E, and F with the conic constant κ. Show.

  FIG. 4 shows longitudinal aberrations (spherical aberration, astigmatism, distortion) of Numerical Example 2. In the graph showing spherical aberration, the solid line is for d line, the broken line is for g line, In the diagram showing the point aberration, the solid line shows the sagittal image plane, and the broken line shows the meridional image plane.

  Table 5 shows values corresponding to the conditional expressions (1) to (4) in Numerical Example 1 and Numerical Example 2.

  As can be seen from the above tables and aberration diagrams, in both numerical example 1 and numerical example 2, the conditional expressions (1) to ( 4) was satisfied, the F-number was as bright as about 3, and each aberration was corrected satisfactorily until the horizontal angle of view reached about 55 °, and the total length could be shortened. Further, by forming the lens L1 from plastic, it can be configured at a lower cost and lighter, and an aspherical surface can be easily formed.

  Next, the imaging apparatus of the present invention will be described.

The image pickup apparatus of the present invention includes a small image pickup system and an image pickup element that converts an optical image formed by the small image pickup system into an electric signal, and the small image pickup system is configured to be biconvex and have both aspheric surfaces. It consists of a single lens and an aperture stop located close to the object side surface of the single lens. The aspherical surface on the object side is an aspherical surface that increases its positive refractive power as it goes from the optical axis to the periphery. The spherical surface is an aspheric surface that weakens the positive refractive power from the optical axis toward the periphery, and the following conditional expressions (1) 1.10 ≦ r1 / f <1.43, (2) 0.63 <| r2 | / f <1.19, (3) 0.15 <d / D <0.7, (4) 50 <νd is satisfied.

  5 to 7 show an embodiment in which the imaging apparatus of the present invention is applied to a camera unit of a mobile phone.

  5 and 6 show the appearance of the mobile phone 10.

  The mobile phone 10 is configured such that the display unit 20 and the main body unit 30 are foldably connected to each other at the center hinge portion. The mobile phone 10 is folded as shown in FIG. As shown, the display unit 20 and the main body unit 30 are opened.

  An antenna 21 for transmitting / receiving radio waves to / from a base station is provided at a position close to one side on the back side of the display unit 20, and the inner surface of the display unit 20 includes the antenna 21. A liquid crystal display panel 22 having a size that occupies substantially the entire side surface is disposed, and a speaker 23 is disposed above the liquid crystal display panel 22. Further, the display unit 20 is provided with an imaging unit 1A of a digital camera unit, and an imaging system 1 (or imaging system 2) of the imaging unit 1A has a facing hole 24 formed on the back surface of the display unit 20. Through the outside. Here, the term “imaging unit” is used as a configuration including the imaging lens 1 and the imaging element 4. That is, the imaging lens 1 and the imaging device 4 need to be provided in the display unit 20 at the same time, but other parts constituting the digital camera unit, such as a camera control unit and a recording medium, are arranged in the main body unit 30. The concept of the imaging unit was used to clarify that it may be acceptable. For example, a device using a photoelectric conversion device such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) can be used as the imaging device 4. Further, the opening peripheral edge 24a of the facing hole 24 becomes the aperture stop S of the imaging system 1 (or imaging system 2).

  Furthermore, an infrared communication unit 25 is disposed at the distal end of the display unit 20, and the infrared communication unit includes an infrared light emitting element and an infrared light receiving element (not shown).

  On the inner surface of the main body 30, there are provided operation keys 31, 31,... Such as numeric keys "0" to "9", a calling key, a power key, etc., and the operation keys 31, 31,. A microphone 32 is disposed below the portion where the symbol is disposed. In addition, a memory card slot 33 is provided on the side surface of the main body 30, and the memory card 40 can be inserted into and removed from the main body 30 via the memory card slot 33.

  FIG. 7 is a block diagram showing the configuration of the mobile phone 10.

  The mobile phone 10 includes a CPU (Central Processing Unit) 50, and the CPU 50 controls the overall operation of the mobile phone 10. That is, the CPU 50 develops a control program stored in a ROM (Read Only Memory) 51 in a RAM 52 (Random Access Memory), and controls the operation of the mobile phone 10 via the bus 53.

  The camera control unit 60 controls the image pickup unit 1A including the image pickup system 1 and the image pickup device 4 to shoot images such as still images and moving images. The obtained image information is compressed into JPEG, MPEG, etc. And then on the bus 53. The image information placed on the bus 53 is temporarily stored in the RAM 52, and is output to the memory card interface 41 as necessary, and stored in the memory card 40 by the memory card interface 41, or the display control unit 54. Is displayed on the liquid crystal display panel 22. In addition, audio information recorded through the microphone 32 at the same time as shooting is also temporarily stored in the RAM 52 together with image information via the audio codec 70, stored in the memory card 40, and displayed on the liquid crystal display panel 22. At the same time, it is output from the speaker 23 via the audio codec 70. Furthermore, the image information and the sound information are output to the infrared interface 55 as necessary, and output to the outside via the infrared communication unit 25 by the infrared interface 55, and a device including a similar infrared communication unit, For example, it is transmitted to an external information device such as a mobile phone, a personal computer, or a PDA (Personal Digital Assistance). When displaying a moving image or a still image on the liquid crystal display panel 22 based on the image information stored in the RAM 52 or the memory card 40, the camera control unit 60 decodes the file stored in the RAM 52 or the memory card 40. The image data after decompression is sent to the display control unit 54 via the bus 53.

  The communication control unit 80 transmits and receives radio waves to and from the base station via the antenna 21. In the voice call mode, the received voice information is processed and then output to the speaker 23 via the voice codec 70. The voice collected by the microphone 32 is received via the voice codec 70, subjected to predetermined processing, and transmitted.

  Since the imaging system 1 (or imaging system 2) described above can be configured to have a short depth, it can be easily mounted on a device with a limited thickness such as the mobile phone 10. In addition, since it has a wide horizontal angle of view, a large amount of information can be captured on one screen, which is suitable as an imaging system for a mobile phone that is a portable information device.

  In the above embodiment, an example in which the imaging device of the present invention is applied to a mobile phone has been shown. However, the imaging device of the present invention can also be applied to other information devices such as personal computers and PDAs. Of course, it has a great advantage when applied to these information devices.

  It should be noted that the specific structures, shapes, and numerical values shown in the embodiments and numerical examples described above are only examples of the implementations that are carried out in carrying out the present invention, and thus the technology of the present invention. The scope should not be interpreted in a limited way.

It is a figure which shows the lens structure of 1st Embodiment of this invention small imaging system. It is a figure which shows the longitudinal aberration (spherical aberration, astigmatism, distortion aberration) of the numerical example 1 which applied the specific numerical value to 1st Embodiment. It is a figure which shows the lens structure of 2nd Embodiment of this invention small imaging system. It is a figure which shows the longitudinal aberration (spherical aberration, astigmatism, distortion aberration) of Numerical Example 2 which applied the specific numerical value to 2nd Embodiment. 6 and 7 show an embodiment in which the imaging apparatus of the present invention is applied to a camera unit of a mobile phone, and this figure is a perspective view showing a non-use state or a standby state. It is a perspective view which shows a use condition. It is a block diagram which shows an internal structure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Small imaging system, 2 ... Small imaging system, L1 ... Lens, S ... Aperture stop, 4 ... Imaging element, 10 ... Mobile phone (imaging device)

Claims (2)

Consists of a single lens having a biconvex shape and both surfaces being aspherical, and an aperture stop located close to the object side surface of the single lens,
The aspherical surface on the object side is an aspherical surface that increases its positive refractive power as it goes from the optical axis to the periphery.
The aspherical surface on the image side is an aspherical surface that weakens the positive refractive power from the optical axis toward the periphery,
A compact imaging system characterized by satisfying the following conditional expressions (1), (2), (3), and (4).
(1) 1.10 ≦ r1 / f <1.43
(2) 0.63 <| r2 | / f <1.19
(3) 0.15 <d / D <0.7
(4) 50 <νd
However,
r1: paraxial radius of curvature of object side surface r2: paraxial radius of curvature of image side surface f: focal length of single lens d: distance from r1 surface to aperture stop D: thickness of single lens νd: single lens The Abbe number for the d-line (λ = 587.6 nm). An image pickup apparatus including a small image pickup system and an image pickup element that converts an optical image formed by the small image pickup system into an electric signal,
The small imaging system is composed of a single lens having a biconvex shape and two aspheric surfaces, and an aperture stop located close to the object side surface of the single lens. The aspherical surface that increases the positive refractive power as it goes to the surface and the aspherical surface on the image plane side as the aspherical surface that weakens the positive refractive power as it goes from the optical axis to the periphery, and the following conditional expressions (1), (2), ( 3) An image pickup apparatus satisfying (4).
(1) 1.10 ≦ r1 / f <1.43
(2) 0.63 <| r2 | / f <1.19
(3) 0.15 <d / D <0.7
(4) 50 <νd

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