JP3976714B2 - Shooting lens - Google Patents

Description

  The present invention relates to a small and lightweight photographing lens used for an in-vehicle 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 incorporated in a surveillance camera or a digital camera using a light receiving element such as a CCD or CMOS has faithful subject reproducibility. Recently, the CCD itself and the CCD camera have been miniaturized, and along with this, the photographic lens incorporated in these has inevitably increased the demand for miniaturization and miniaturization. Furthermore, light receiving elements such as CCDs have become higher in the order of mega pixels, contrary to the miniaturization of CCDs. The taking lens used for the camera using this must inevitably have 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, a method of expanding a light receiving angle to the element surface by arranging a pair of microlenses with the light receiving element, and the like have been taken.

  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 a high-order pixel of mega order, The object is to propose a photographic lens that is lightweight and compact.

The photographic lens of the present invention is composed of three elements in three groups, and in order from the object side, a first meniscus lens having a convex surface facing the object side, followed by a second meniscus lens having negative power. A lens and a third lens having positive power are arranged, and the second and third lenses function as correction lenses. The first, second and third lenses have a uniform refractive index. In addition, the first lens has a stronger power than the second and third lenses. Further, among the first lens, the second lens, and the third lens, at least the second lens and the third lens have both aspherical lens surfaces. In addition, at least one aspherical inflection point is formed on the aspherical surface of the third lens.

  Here, instead of using the second lens with negative power and the third lens with positive power, a second lens with negative power and a third lens with negative power may be used.

  Next, regarding the first lens, both surfaces of the lens surface may be formed as an aspherical surface or a spherical surface, and at least one lens surface of the double-sided lens surfaces may be an aspherical surface.

  In the photographic lens of the present invention, the combined focal length of the photographic lens is F, the focal length of the first lens is f1, the distance from the incident surface on the object side of the first lens to the imaging plane is Σd, and the second lens When the Abbe number of νd2 is νd2, it is desirable to satisfy the following conditional expression.

0.50 <f1 / F <1.5 (1)
0.50 <Σd / F <1.5 (2)
50> νd2 (3)

  Conditional expression (1) 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 (1), the total length of the photographing lens can be further shortened.

  Next, conditional expression (2) is also 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 (2). If the lower limit of conditional expression (2) 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 (3) is a condition for keeping the axial chromatic aberration and off-axis chromatic aberration stable by setting the Abbe number of the second lens to 50 or less.

  Next, the third lens in the photographic lens of the present invention is arranged such that the peripheral portion of the lens surface on the image plane side becomes a convex surface on the image plane side, and the lens surface on the object side and the lens surface on the image plane side It is desirable to provide one or more aspherical inflection points. By forming the lens surface in this way, coma and astigmatism can be corrected well, and distortion can be corrected well.

  Here, as a feature when the imaging surface is a CCD or a CMOS, there is a restriction on a light ray angle taken into each pixel, and the light ray angle increases toward the periphery of the screen. In order to alleviate this phenomenon, the peripheral part of the lens surface on the image surface side of the third lens is an inflection aspherical surface with the convex surface facing the image surface side so that the maximum emission angle of the principal ray is 30 degrees or less. It is desirable to make it. In this way, aspheric correction is performed to prevent shading that occurs in the periphery of the screen.

  As described above, the photographic lens of the present invention is a three-group, three-element lens, the second lens and the third lens are correction lenses, and the first lens disposed on the object side is a positive meniscus. The lens has a convex surface facing the object. As a result, the overall length of the lens system can be shortened. The lens surface of the third lens is an aspheric surface provided with one or a plurality of aspherical inflection points, so that various aberrations are corrected well, and at the same time, the maximum emission angle of the principal ray is reduced and shading is performed. Can be prevented. 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 photographic lens corresponding to mega-order high pixels.

  Embodiments of a three-group, three-element photographic lens to which the present invention is applied will be described below with reference to the drawings.

  FIG. 1 shows a photographic lens according to Example 1 to which the present invention is applied. The taking lens 100 of the present example is arranged in order from the object side toward the imaging surface 6 side through a first meniscus lens 1 having a positive power with a convex surface facing the object side, and a diaphragm 4 following the first lens 1. , A second meniscus lens 2 having negative power with the concave surface facing the object side, and a third lens 3 having positive power, and the second and third lenses function as correction lenses. 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 photographing lens 100 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 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 illustrating various aberrations in the photographing lens 100 of the first embodiment. 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 according to Example 2 to which the present invention is applied. In the photographic lens 110 of this example, the first lens 11 that is a positive meniscus lens having a convex surface directed toward the object side in order from the object side toward the image forming surface 16, and the aperture stop 14, the object side A second lens 12 that is a negative meniscus lens having a concave surface facing the lens 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 photographing lens 110 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 photographic lens 110 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 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. It is also possible to use a lens whose both surfaces are spherical or a lens whose at least one lens surface is aspherical.

  FIG. 5 shows a photographic lens according to Example 3 to which the present invention is applied. The taking lens 120 of the present example is arranged in order from the object side toward the imaging surface 26 side through a first meniscus lens 21 having a positive power with the convex surface facing the object side, and a diaphragm 24 following this. , A second meniscus lens 22 having negative power with the concave surface facing the object side, and a third lens 23 having negative power, and the second and third lenses function as correction lenses. 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 photographing lens 120 of this example is as follows.
F number: 3.5
Focal length: f = 5.7 mm
Total length: Σd = 6.46mm

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

  FIG. 6 is a configuration diagram of a photographic lens according to Example 4 to which the present invention is applied. In the photographing lens 130 of the present example, the first lens 31 that is a positive meniscus lens having a convex surface directed toward the object side and the aperture stop 34 in order from the object side toward the image plane 36 and the object side. A second lens 32, which is a negative meniscus lens with a concave surface facing the surface, 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 photographing lens 130 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 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 photographing lens 120 of the third embodiment, instead of the first lens 21 in which both surfaces of the lens surface are formed into spherical surfaces, one lens surface is formed into an aspheric surface, and the other A photographing lens 140 using the first lens 41 having a spherical lens surface will be described. In FIG. 5, the photographing lens 140 and the first lens 41 are denoted by reference numerals in parentheses, and the other components are the same as those in the third embodiment, so that the same reference numerals are used.

  The taking lens 140 of the present example is arranged in order from the object side toward the imaging surface 26 side through a first meniscus lens 41 having a positive power with a convex surface facing the object side, and a diaphragm 24 following the first lens 41. , A second meniscus lens 22 having negative power with the concave surface facing the object side, and a third lens 23 having positive power, and the second and third lenses function as correction lenses. 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 photographing lens 140 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 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 which concerns on Example 1 to which this invention is applied. It is a block diagram of the photographic lens which concerns on Example 2 to which this invention is applied. FIG. 2 is an aberration diagram of the photographing lens of Example 1 illustrated in FIG. 1. FIG. 6 is an aberration diagram of the photographic lens of Example 2 illustrated in FIG. 2. It is a block diagram of the imaging lens which concerns on Example 3 and Example 5 to which this invention is applied. It is a block diagram of the photographic lens which concerns on Example 4 to which this invention is applied. FIG. 6 is an aberration diagram of the photographing lens of Example 3 illustrated in FIG. 5. FIG. 7 is an aberration diagram of the photographing lens of Example 4 illustrated in FIG. 6. FIG. 6 is an aberration diagram of the photographing lens 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 diaphragm 5, 15, 25, 35 Cover glass 6, 16, 26, 36 Imaging surface 100, 110, 120, 130, 140 Shooting lens R1, R2, R3, R4, R5, R6 Lens surface

Claims (7)

A first lens arranged in order from the object side, a diaphragm, a second lens and a third lens functioning as a correction lens;
The first, second and third lenses have a homogeneous refractive index;
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 having negative power with a concave surface facing the object side,
The third lens is a lens having positive power;
The first lens has a stronger power than the second and third lenses,
Among these first, second, and third lenses, at least the lens surfaces of the second and third lenses are both aspheric.
The aspherical surface of the third lens has one or more aspherical inflection points,
A photographic lens satisfying the following conditional expression, where F is the combined focal length and f1 is the focal length of the first lens.
0.50 <f1 / F <1.5 A first lens arranged in order from the object side, a diaphragm, a second lens and a third lens functioning as a correction lens;
The first, second and third lenses have a homogeneous refractive index;
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 having negative power with a concave surface facing the object side,
The third lens is a lens having negative power;
The first lens has a stronger power than the second and third lenses,
Among these first, second, and third lenses, at least the lens surfaces of the second and third lenses are both aspheric.
The aspherical surface of the third lens has one or more aspherical inflection points,
A photographic lens that satisfies the following conditional expression, where F is the combined focal length and f1 is the focal length of the first lens.
0.50 <f1 / F <1.5 In claim 1 or 2,
The first lens is a photographic lens in which at least one of the two lens surfaces is aspheric. In any one of claims 1 to 3,
A photographic lens that satisfies the following conditional expression, where F is the combined focal length of the photographic lens, and Σd is the distance from the object-side incident surface of the first lens to the imaging surface.
0.50 <Σd / F <1.5 In any one of claims 1 to 4,
A photographic lens satisfying the following conditional expression when the Abbe number of the second lens is νd2.
50> νd2 In any one of claims 1 to 5,
A photographic lens in which the maximum emission angle of the principal ray of the photographic lens is 30 degrees or less. In any one of claims 1 to 6,
In the third lens, the periphery of the lens surface on the image plane side is convex on the image plane side,
An imaging lens in which one or a plurality of aspherical inflection points are formed on the first lens surface and the second lens surface.

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