JP2007086818A - Photographic lens for digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small, low-cost photographic lens for a digital camera capable of high-quality imaging. <P>SOLUTION: The photographic lens 100 for a digital camera comprises, arranged sequentially from an object side to an imaging surface 6, a positive-meniscus first lens 1 with its convex plane facing the object side, an aperture diaphragm 4, a meniscus second lens 2 with its concave plane facing the object side and a third aspherical lens 3 having an inflection point on the object side. Regarding the photographic lens 100, the first lens 1 has power stronger than that of the second lens 2. When the synthetic focal distance of the photographic lens is f, the focal distance of the first lens f1, the distance from the incident surface on the object side to the imaging surface 6 of the first lens Σd, and the Abbe number of the second lens νd2, the following conditional expressions are separately satisfied; 0.50<Σd/f<1.5 (1), 50>νd2 (2) and 0.50<f1/f<1.5 (3). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a small and lightweight photographic lens for a digital camera used for a vehicle-mounted camera, a monitoring camera, a digital camera, a mobile phone camera, and the like using a light receiving element such as a CCD or a CMOS.

  It is desirable that a photographing lens for a digital camera incorporated in a monitoring camera or a digital camera using a light receiving element such as a CCD or a CMOS has faithful subject reproducibility. Recently, the CCD itself and the CCD camera have been downsized, and along with this, the demand for downsizing and downsizing of the photographic lens for the digital camera incorporated therein has inevitably increased. Furthermore, light receiving elements such as CCDs have become higher in the order of mega pixels, contrary to the miniaturization of CCDs. A photographic lens for a digital camera used in a camera using this must inevitably have a high optical performance. Conventionally, aberrations are corrected using a large number of lenses in order to exhibit high optical performance.

Further, as a feature of a light receiving element such as a CCD or a CMOS, there is a restriction on a light ray angle taken into each pixel. In a camera in which an optical system that ignores this is incorporated, the amount of peripheral light is reduced, so that the camera becomes a so-called dark peripheral camera. Conventionally, in order to cope with these, a method of providing an electrical correction circuit as shown in Patent Document 1 or a microlens that forms a pair with a light receiving element as shown in Patent Document 2 are arranged on the element surface. A method such as enlarging the light receiving angle was taken.
Japanese Patent Laid-Open No. 5-137062 JP-A-5-110047

  The object of the present invention is to prevent shading by making the maximum emission angle with respect to the element surface of the light receiving element smaller than the angle of view, and to perform aberration correction so as to correspond to high-order pixels in mega order, An object of the present invention is to provide a photographing lens for a digital camera that is light and compact.

  In order to solve the above-mentioned problem, in the photographing lens for a digital camera according to claim 1, a first lens arranged in order from the object side to the imaging surface side with the imaging surface as a light receiving element, The first lens is a meniscus lens having a positive power with a convex surface facing the object side, and the second lens is a meniscus with a concave surface facing the object side. The third lens is an aspherical lens having a positive power having an inflection point on the object side, and a stop is disposed between the first lens and the second lens.

  The imaging lens for a digital camera according to claim 2, wherein the imaging surface is a light receiving element, and the first lens, the second lens, and the third lens are arranged in order from the object side toward the imaging surface side. The first lens is a meniscus lens having a positive power with a convex surface facing the object side, and the second lens is a meniscus lens having a negative power with a concave surface facing the object side, The third lens is an aspherical lens having an inflection point on the object side, and a stop is disposed between the first lens and the second lens.

  The imaging lens for a digital camera according to claim 3, wherein the imaging surface is a light receiving element, and the first lens, the second lens, and the third lens are arranged in order from the object side toward the imaging surface side. The first lens is a meniscus lens having a positive power with a convex surface facing the object side, the second lens is a meniscus lens with a concave surface facing the object side, and the third lens is An aspheric lens having an inflection point on the object side, and a stop is disposed between the first lens and the second lens, and the first lens has a stronger power than the second lens. It was configured as follows.

The imaging lens for a digital camera according to claim 4, wherein the imaging surface is a light receiving element, and the first lens, the second lens, and the third lens are sequentially arranged from the object side toward the imaging surface side. The first lens is a meniscus lens having a positive power with a convex surface facing the object side, the second lens is a meniscus lens with a concave surface facing the object side, and the third lens is An aspherical lens having an inflection point on the object side, a stop is disposed between the first lens and the second lens, and the combined focal length of the digital camera photographing lens is f, the first lens When the distance from the incident surface on the object side to the imaging surface is Σd,
0.50 <Σd / f <1.5 (1)
The following conditional expression is satisfied.

Furthermore, in the photographing lens for a digital camera according to claim 5, a first lens, a second lens, and a third lens, which are arranged in order from the object side to the imaging surface side with the imaging surface as a light receiving element. The first lens is a meniscus lens having a positive power with a convex surface facing the object side, the second lens is a meniscus lens with a concave surface facing the object side, and the third lens When the lens is an aspherical lens having an inflection point on the object side, a diaphragm is disposed between the first lens and the second lens, and the Abbe number of the second lens is νd2,
50> νd2 (2)
The following conditional expression is satisfied.

Further, in the digital camera photographing lens according to any one of claims 1 to 5, in the invention according to claim 6, at least one of the two lens surfaces of the first lens is aspheric. And when the combined focal length of the digital camera photographing lens is f and the focal length of the first lens is f1,
0.50 <f1 / f <1.5 (3)
The following conditional expression is satisfied.

  By forming the lens surfaces of the first to third lenses in this way, coma and astigmatism can be corrected well, and distortion can be corrected well.

  Here, the conditional expression (1) is a condition for keeping the entire lens system more compact. In particular, for a taking lens used in a camera mounted on a mobile phone, it is necessary to make the entire lens system small and at the same time make the total length of the lens system shorter. In order to satisfy such a requirement, it is desirable to set the optical system so as to satisfy the conditional expression (1). If the lower limit of conditional expression (1) is not reached, the lens system can be made compact, but various aberration corrections become difficult. If the upper limit is exceeded, the lens system becomes large, which is not preferable.

  Conditional expression (2) is a condition for keeping on-axis chromatic aberration and off-axis chromatic aberration stable by setting the Abbe number of the second lens to 50 or less.

  Conditional expression (3) is a condition for keeping the spherical aberration stable and keeping the entire lens system compact. Below the lower limit, the lens system can be made compact, but it becomes difficult to correct the spherical aberration. On the other hand, if the upper limit is exceeded, conversely, correction of spherical aberration becomes easy, but the entire lens system cannot be gathered compactly. By satisfying this conditional expression, the lens system can be made compact while maintaining the spherical aberration in a good state.

  In the present invention, the first lens is a positive meniscus lens having a convex surface directed toward the object side. By satisfying this configuration and conditional expression (3), the total length of the photographing lens can be further shortened.

  In addition, when the imaging plane is a CCD or a CMOS, there is a restriction on the angle of light taken into each pixel, and the light angle increases toward the periphery of the screen. In order to alleviate this phenomenon, as described in the seventh aspect of the invention, the principal ray is formed by using an inflection aspherical surface in which the peripheral portion of the lens surface on the image surface side of the third lens is convex toward the image surface side. It is desirable that the maximum emission angle is 30 degrees or less. In this way, aspheric correction is performed to prevent shading that occurs in the periphery of the screen.

  As described above, according to the photographic lens for a digital camera of the present invention, the total length of the lens system can be shortened. Further, since the lens surface of the third lens is an aspherical surface having an inflection point on the object side, various aberrations can be corrected well, and at the same time, the maximum emission angle of the principal ray can be reduced to prevent shading. it can. Furthermore, satisfactory aberration correction can be performed by the two correction lenses of the second lens and the third lens. Therefore, according to the present invention, it is possible to obtain a compact and compact photographing lens for a digital camera corresponding to mega-order high pixels.

  Embodiments of a photographing lens for a digital camera having a three-group three-element configuration to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 shows a photographic lens for a digital camera according to a first embodiment to which the present invention is applied. The photographing lens 100 for a digital camera of this example includes a first meniscus lens 1 having a positive power with a convex surface facing the object side in order from the object side toward the image plane 6, and an aperture stop following the first lens 1. 4 includes a meniscus second lens 2 having a negative power with a concave surface facing the object side, and a third lens 3 having a positive power. The second and third lenses are correction lenses. Function as. In this example, the lens surfaces on both sides of the lenses 1, 2, and 3 are all aspherical surfaces. In this example, a cover glass 5 is disposed between the second lens surface R6 of the third lens 3 and the imaging surface 6.

  In the third lens 3, an aspherical inflection point is provided at approximately 50% of the aperture on the first lens surface R5, and an aspherical inflection point is provided at approximately 25% of the aperture on the second lens surface R6. Is provided. As a result, the annular zone around the third lens 3 forms a convex surface with respect to the image plane, and the maximum emission angle of the principal ray is adjusted to 22 degrees with respect to the total field angle of 63 degrees. .

The lens data of the entire optical system of the photographic lens 100 for the digital camera of this example is as follows.
F number: 3.5
Focal length: f = 5.7 mm
Total length: Σd = 7.06mm

  Table 1 displays lens data of each lens surface of the photographing lens 100 for the digital camera of this example, and Table 2 displays aspheric coefficients for defining the aspheric shape of each lens surface.

  In Table 1, i indicates the order of the lens surfaces counted from the object side, R indicates the curvature of each lens surface, d indicates the distance between the lens surfaces, Nd indicates the refractive index of each lens, and νd indicates each lens surface. Indicates the Abbe number of the lens. In addition, the lens surface with an asterisk (*) attached to i on the lens surface indicates an aspherical surface.

  The aspherical shape adopted for the lens surface is as follows, assuming that the axis in the optical axis direction is X, the height in the direction orthogonal to the optical axis is H, the conical coefficient is k, and the aspherical coefficients are A, B, C, and D. It is expressed by the formula.

  The meaning of each symbol and the expression representing the aspherical shape are the same in Examples 2, 3, 4, and 5.

  FIG. 3 is an aberration diagram showing various aberrations in the photographing lens 100 for a digital camera of Example 1. In the figure, SA represents spherical aberration, OSC represents sine conditions, AS represents astigmatism, and DIST represents distortion. In the astigmatism AS, T represents a tangential image, and S represents a sagittal image surface. In addition, the aberration diagram shown on the lower side of the drawing represents lateral aberration, in which DX represents lateral X aberration with respect to X pupil coordinates, and DY represents lateral Y aberration with respect to Y pupil coordinates. The meanings of these symbols are the same in the aberration diagrams showing the various aberrations of Examples 2, 3, 4, and 5.

  FIG. 2 is a configuration diagram of a photographic lens for a digital camera according to a second embodiment to which the present invention is applied. In the photographing lens 110 for the digital camera of this example, the first lens 11 which is a positive meniscus lens having a convex surface directed toward the object side in order from the object side toward the imaging surface 16 side, and the aperture stop 14 are used. A second lens 12 that is a negative meniscus lens having a concave surface facing the object side and a third lens 13 that is a biconvex lens are arranged. The first lens surface R5 on the object side of the third lens 13 is provided with an aspherical inflection point at approximately 48% of the lens aperture. The second lens surface R6 on the image surface side is an extension of the convex surface. By forming the lens surface of the third lens 13 in this manner, the maximum emission angle of the chief ray is 23.5 degrees with respect to a total angle of view of 63 degrees. The lens surfaces of the first lens 11, the second lens 12, and the third lens 13 of this example are all aspherical surfaces. Also in this example, the cover glass 15 is disposed between the second lens surface R6 of the third lens 13 and the imaging surface 16.

The lens data of the entire optical system of the photographic lens 110 for the digital camera of this example is as follows.
F number: 3.5
Focal length: f = 5.7 mm
Total length: Σd = 6.985mm

  Table 3 displays lens data of each lens surface of the photographing lens 110 for the digital camera of this example, and Table 4 displays aspheric coefficients for defining the aspheric shape of each lens surface. FIG. 4 is an aberration diagram.

  In the digital camera photographing lenses 100 and 110 according to the first and second embodiments, lenses having both aspherical surfaces are used as the first lenses 1 and 11 on the object side. Also, a lens having both lens surfaces spherical can be used, or a lens having at least one of the two lens surfaces aspherical can be used.

  FIG. 5 shows a photographic lens for a digital camera according to a third embodiment to which the present invention is applied. The photographing lens 120 for a digital camera of this example includes a first meniscus lens 21 having a positive power with a convex surface facing the object side in order from the object side toward the image plane 26, and a diaphragm 24 following the first lens 21. The second meniscus lens 22 having negative power with the concave surface facing the object side, and the third lens 23 having negative power, and the second and third lenses as correction lenses Function. A cover glass 25 is disposed between the third lens 23 and the imaging surface 26. In the third lens 23, the second lens surface R6 on the imaging surface side is formed such that the annular zone around the lens is convex with respect to the imaging surface side, and the maximum emission angle of the principal ray is set to 24 degrees or less.

  In this example, among the lenses 21, 22, and 23, both surfaces of the first lens 21 are spherical. On the other hand, in the second and third lenses 22 and 23, both lens surfaces are aspherical surfaces as in the first and second embodiments.

The lens data of the entire optical system of the photographic lens 120 for the digital camera of this example is as follows.
F number: 3.5
Focal length: f = 5.7 mm
Total length: Σd = 6.46mm

  Table 5 shows lens data of each lens surface of the photographing lens 120 for the digital camera of this example, and Table 6 shows an aspheric coefficient for defining the aspheric shape of each lens surface. FIG. 7 shows aberration diagrams.

  FIG. 6 is a configuration diagram of a photographic lens for a digital camera according to Example 4 to which the present invention is applied. In the photographic lens 130 for the digital camera of this example, the first lens 31 that is a positive meniscus lens having a convex surface facing the object side in order from the object side toward the image plane 36 and the aperture stop 34 are used. A second lens 32 which is a negative meniscus lens having a concave surface facing the object side and a third lens 33 having a positive power are arranged. A cover glass 35 is disposed between the third lens 33 and the image plane 36. In the third lens 33, the second lens surface R6 is formed with the annular portion around the lens as a convex surface with respect to the imaging surface side, and the maximum emission angle of the principal ray is set to 24 degrees or less.

  In the present example, among the lenses 31, 32, 33, the first lens 31 has a spherical surface on both surfaces. On the other hand, as for the second and third lenses 32 and 33, the lens surfaces on both sides are aspherical surfaces as in the first, second and third embodiments.

The lens data of the entire optical system of the photographic lens 130 for the digital camera of this example is as follows.
F number: 3.5
Focal length: f = 5.7 mm
Total length: Σd = 6.66mm

  Table 7 shows lens data of each lens surface of the photographing lens 130 for the digital camera of this example, and Table 8 shows aspheric coefficients for defining the aspheric shape of each lens surface. FIG. 8 shows aberration diagrams.

  Next, referring again to FIG. 5, in the photographic lens 120 for the digital camera of the third embodiment, one lens surface is formed as an aspherical surface instead of the first lens 21 whose both surfaces are formed into spherical surfaces. The digital camera photographing lens 140 using the first lens 41 having the other lens surface formed into a spherical surface will be described. In FIG. 5, the photographing lens 140 for the digital camera 140 and the first lens 41 are shown by enclosing the reference numerals in parentheses, and the configuration of each other part is the same as that of the third embodiment, so that description will be made using the same reference numerals.

  The digital camera photographing lens 140 of this example is a meniscus first lens 41 having a positive power with a convex surface facing the object side in order from the object side toward the image plane 26, and a diaphragm 24 following the first lens 41. The second meniscus lens 22 having negative power with the concave surface facing the object side, and the third lens 23 having positive power, and the second and third lenses as correction lenses Function. A cover glass 25 is disposed between the third lens 23 and the imaging surface 26. In the third lens 23, the second lens surface R6 on the imaging surface side is formed such that the annular zone around the lens is convex with respect to the imaging surface side, and the maximum emission angle of the principal ray is set to 24 degrees or less.

  In this example, among the lenses 41, 22, and 23, the first lens 41 has a first lens surface R1 on the object side out of the lens surfaces on both sides that is aspherical, and a second lens surface on the imaging surface side. R2 is a spherical surface. On the other hand, the second and third lenses 22 and 23 are both aspherical on both lens surfaces.

The lens data of the entire optical system of the photographic lens 140 for the digital camera of this example is as follows.
F number: 3.5
Focal length: f = 5.7 mm
Total length: Σd = 7.07mm

  Table 9 displays lens data of each lens surface of the photographing lens 140 for the digital camera of this example, and Table 10 displays aspheric coefficients for defining the aspheric shape of each lens surface. FIG. 9 shows aberration diagrams.

It is a block diagram of the photographic lens for digital cameras which concerns on Example 1 to which this invention is applied. It is a block diagram of the photographic lens for digital cameras which concerns on Example 2 to which this invention is applied. FIG. 2 is an aberration diagram of the photographic lens for a digital camera of Example 1 illustrated in FIG. 1. FIG. 6 is an aberration diagram of the photographic lens for a digital camera of Example 2 illustrated in FIG. 2. It is a block diagram of the photographic lens for digital cameras which concerns on Example 3 and Example 5 to which this invention is applied. It is a block diagram of the photographic lens for digital cameras which concerns on Example 4 to which this invention is applied. FIG. 6 is an aberration diagram of the photographic lens for a digital camera of Example 3 illustrated in FIG. 5. FIG. 7 is an aberration diagram of the photographic lens for a digital camera of Example 4 illustrated in FIG. 6. FIG. 6 is an aberration diagram of the photographic lens for a digital camera of Example 5 illustrated in FIG. 5.

Explanation of symbols

1, 11, 21, 31, 41 First lens 2, 12, 22, 32 Second lens 3, 13, 23, 33 Third lens 4, 14, 24, 34 Aperture stop 5, 15, 25, 35 Cover glass 6, 16, 26, 36 Imaging surface 100, 110, 120, 130, 140 Photography lens for digital camera R1, R2, R3, R4, R5, R6 Lens surface

Claims (7)

  A first lens, a second lens, and a third lens disposed in order from the object side toward the image plane; the first lens having positive power with a convex surface facing the object side; The second lens is a meniscus lens having a concave surface facing the object side, and the third lens is an aspherical lens having a positive power having an inflection point on the object side, An imaging lens for a digital camera, in which a diaphragm is disposed between the first lens and the second lens, and the imaging surface is a light receiving element.   A first lens, a second lens, and a third lens disposed in order from the object side toward the image plane; the first lens having positive power with a convex surface facing the object side; The second lens is a meniscus lens having negative power with a concave surface facing the object side, and the third lens is an aspheric lens having an inflection point on the object side, An imaging lens for a digital camera, in which a diaphragm is disposed between the first lens and the second lens, and the imaging surface is a light receiving element.   A first lens, a second lens, and a third lens disposed in order from the object side toward the image plane; the first lens having positive power with a convex surface facing the object side; The second lens is a meniscus lens having a concave surface facing the object side, and the third lens is an aspherical lens having an inflection point on the object side, and the first lens and the An imaging lens for a digital camera, in which a diaphragm is disposed between the second lens, the first lens has a stronger power than the second lens, and the imaging surface is a light receiving element. A first lens, a second lens, and a third lens disposed in order from the object side toward the image plane; the first lens having positive power with a convex surface facing the object side; The second lens is a meniscus lens having a concave surface facing the object side, and the third lens is an aspheric lens having an inflection point on the object side, and the first lens and the A diaphragm is arranged between the second lens, the imaging surface is a light receiving element, the combined focal length of the digital camera photographing lens is f, and the imaging surface from the object-side incident surface of the first lens When the distance to is Σd,
0.50 <Σd / f <1.5
Satisfactory lens for digital cameras. A first lens, a second lens, and a third lens disposed in order from the object side toward the image plane; the first lens having positive power with a convex surface facing the object side; The second lens is a meniscus lens having a concave surface facing the object side, and the third lens is an aspheric lens having an inflection point on the object side, and the first lens and the When a diaphragm is disposed between the second lens, the imaging surface is a light receiving element, and the Abbe number of the second lens is νd2,
50> νd2
Satisfactory lens for digital cameras. In any one of Claims 1-5,
The first lens has an aspheric surface at least one of the two lens surfaces, and when the combined focal length of the digital camera photographing lens is f and the focal length of the first lens is f1,
0.50 <f1 / f <1.5
Satisfactory lens for digital cameras. In any one of Claims 1-6,
The third lens is a photographic lens for a digital camera in which a peripheral portion of the lens surface on the image surface side is convex toward the image surface side, and a maximum emission angle of a principal ray of the photographic lens for the digital camera is 30 degrees or less.

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