JP2004219982A - Photographic lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and inexpensive photographic lens adaptive to a high pixel. <P>SOLUTION: The photographic lens 1 comprises, arranged sequentially from the object side, a positive-meniscus first lens 1 with its convex plane facing the object side, a negative-power-meniscus second lens 2, and a positive-power third lens 3, and the second and the third lenses 2 and 3 function as a correction lens. The first lens 1 has strong power and both planes of the second and the third lenses are made aspherical. When the synthetic focal distance of the photographic lens is F, the focal distance of the first lens is f1, a distance to the image forming surface from the incident surface on the object side of the first lens is Σd, and the Abbe number of the 2nd lens is νd2, conditional expressions (1): 0.50<f1/F<1.5, (2): 0.50<Σd/F<1.5 and (3): 50>νd2 are satisfied. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a small and lightweight photographing lens used for a vehicle-mounted camera, a monitoring camera, a digital camera, a camera equipped with a mobile phone, 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, digital camera, or the like 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 miniaturized, and accordingly, the demand for miniaturization and compactness of the photographing lens incorporated therein has been inevitably increasing. Furthermore, the number of pixels of light receiving elements such as CCDs has been increased to mega-orders, contrary to the downsizing of CCDs. A photographing lens used for a camera using the same must necessarily be capable of exhibiting high optical performance. Conventionally, in order to exhibit high optical performance, aberration correction has been performed using a large number of lenses.

  Further, as a characteristic of a light receiving element such as a CCD or a CMOS, there is a restriction on an angle of a light beam taken into each pixel. In a camera in which an optical system that disregards this is incorporated, the amount of peripheral light is reduced, resulting in a so-called dark peripheral camera. Conventionally, in order to cope with these, a method of providing an electrical correction circuit, a method of disposing a microlens paired with a light receiving element, and a method of enlarging a light receiving angle to an element surface have been adopted.

  An object of the present invention is to make it possible to prevent shading by making the maximum emission angle of the light receiving element with respect to the element surface smaller than the angle of view, and to perform aberration correction so as to correspond to a megapixel high pixel, Another object of the present invention is to propose a photographic lens that is lightweight and compact.

  The photographic lens of the present invention has a three-group, three-lens configuration, and includes, in order from the object side, a first lens of a positive meniscus having a convex surface facing the object side, and a second lens of a meniscus having a negative power subsequent thereto. It has a configuration in which a lens and a third lens having positive power are arranged, and the second and third lenses function as correction lenses. Further, the first lens has a stronger power than the second and third lenses. Furthermore, among the first lens, the second lens, and the third lens, at least the second lens and the third lens both have aspheric 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 of negative power and the third lens of positive power, a second lens of negative power and a third lens of negative power may be used.

  Next, with respect to the first lens, both surfaces of the lens surface may be formed as an aspheric surface or a spherical surface, and at least one of the two lens surfaces may be formed as an aspheric surface.

  Further, in the taking lens of the present invention, the combined focal length of the taking lens is F, the focal length of the first lens is f1, the distance from the object-side incident surface of the first lens to the imaging surface is Δd, and the second lens is When it is assumed that the Abbe's number 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 for keeping the whole lens system compact. When the value goes below the lower limit, the lens system can be made compact, but it becomes difficult to correct the spherical aberration. On the other hand, when the value exceeds the upper limit, the spherical aberration can be easily corrected, but the entire lens system cannot be compactly assembled. By satisfying this conditional expression, the lens system can be made compact while maintaining the spherical aberration in a favorable state.

  In the present invention, the first lens is a positive meniscus lens having a convex surface facing the object side, and by satisfying this configuration and conditional expression (1), it is possible to further reduce the overall length of the taking lens.

  Next, conditional expression (2) is also a condition for keeping the entire lens system more compact. In particular, with respect to a photographing lens used in a camera mounted on a mobile phone, it is necessary to reduce the overall length of the lens system and at the same time to shorten the overall length of the lens system. In order to satisfy such requirements, it is desirable to set the optical system so as to satisfy the conditional expression (2). When the value goes below the lower limit of conditional expression (2), the lens system can be made compact, but it becomes difficult to correct various aberrations. On the other hand, exceeding the upper limit is not preferable because the lens system becomes large.

  Conditional expression (3) is a condition for keeping the Abbe number of the second lens at 50 or less to stably maintain on-axis chromatic aberration and off-axis chromatic aberration.

  Next, the third lens in the photographing lens of the present invention is configured such that the periphery of the lens surface on the image surface side is convex on the image surface side, and the lens surface on the object side and the lens surface on the image surface side. Preferably, one or more aspherical inflection points are provided. By forming the lens surface in this way, coma and astigmatism can be satisfactorily corrected, and distortion can be corrected satisfactorily.

  Here, as a feature of the case where the imaging surface is a CCD or a CMOS, there is a restriction on the light beam angle taken into each pixel, and the light beam angle increases toward the periphery of the screen. In order to alleviate this phenomenon, the periphery of the lens surface on the image plane side of the third lens is formed as an inflection aspheric surface having a convex surface facing the image plane side, so that the maximum exit angle of the principal ray is 30 degrees or less. Is desirable. In this way, aspheric correction is performed to prevent shading occurring at the periphery of the screen.

  As described above, the taking lens of the present invention is a three-group three-lens structure 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 is a convex surface facing the object side. As a result, the overall length of the lens system can be reduced. Further, since the lens surface of the third lens is formed as an aspheric surface having one or more aspherical inflection points, shading is performed by correcting various aberrations satisfactorily and reducing the maximum exit angle of the principal ray. Can be prevented. Further, excellent 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 small and compact photographing lens corresponding to a high pixel of mega order.

  Hereinafter, with reference to the drawings, each embodiment of a three-group three-lens imaging lens to which the present invention is applied will be described.

  FIG. 1 shows a taking lens according to a first embodiment to which the present invention is applied. The taking lens 100 of the present example is arranged, in order from the object side to the image forming surface 6 side, via a first meniscus lens 1 having a positive power and a convex surface facing the object side, and a stop 4 following the meniscus. , A negative meniscus lens 2 having a concave surface facing the object side, and a third lens 3 having a positive power. The second and third lenses function as correction lenses. In this example, the lens surfaces on both sides of each of the lenses 1, 2, and 3 are all aspherical. In this example, a cover glass 5 is arranged between the second lens surface R6 of the third lens 3 and the image plane 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 orbicular zone around the third lens 3 forms a convex surface on the image forming surface side, and the maximum exit angle of the principal ray is adjusted to 22 degrees with respect to the entire field angle of 63 degrees. .

The lens data of the entire optical system of the taking lens 100 of the present example is as follows.
F-number: 3.5
Focal length: f = 5.7mm
Overall length: Δd = 7.06 mm

  Table 1 shows lens data of each lens surface of the photographic lens 100 of this example, and Table 2 shows 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 the refractive index of each lens. Indicates the Abbe number of the lens. Also, a lens surface with an asterisk (*) attached to i on the lens surface indicates that it is aspheric.

  Assuming that the axis in the optical axis direction is X, the height in the direction orthogonal to the optical axis is H, the cone coefficient is k, and the aspheric coefficients are A, B, C, and D, the aspherical shape adopted for the lens surface is as follows. It is represented by an equation.

  The meanings of the symbols and the expressions representing the aspherical shapes are the same in Examples 2, 3, 4, and 5.

  FIG. 3 is an aberration diagram illustrating various aberrations of the imaging lens 100 according to the first embodiment. In the figure, SA represents spherical aberration, OSC represents a sine condition, AS represents astigmatism, and DIST represents distortion. In the astigmatism AS, T represents a tangential, and S represents a sagittal image plane. Further, the aberration diagram shown in the lower part of the drawing represents the lateral aberration. In the figure, DX represents the lateral X aberration relating to the X pupil coordinate, and DY represents the lateral Y aberration relating to the Y pupil coordinate. The meanings of these symbols are the same in the aberration diagrams showing various aberrations of the second, third, fourth, and fifth embodiments.

  FIG. 2 is a configuration diagram of a photographic lens according to Example 2 to which the present invention is applied. In the taking lens 110 of this example, the first lens 11 is a positive meniscus lens having a convex surface facing the object side in order from the object side to the image forming surface 16 side, and the first lens 11 is connected to the object side via the aperture stop 14. A second lens 12, which is a negative meniscus lens having a concave surface, and a third lens 13, which 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 diameter. 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 exit angle of the principal ray is 23.5 degrees with respect to the total field angle of 63 degrees. Further, each lens surface of the first lens 11, the second lens 12, and the third lens 13 of the present example is also aspherical. Note that, 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 taking lens 110 of this example is as follows.
F-number: 3.5
Focal length: f = 5.7mm
Overall length: Δd = 6.985 mm

  Table 3 shows lens data of each lens surface of the taking lens 110 of this example, and Table 4 shows aspheric coefficients for defining the aspheric shape of each lens surface. FIG. 4 shows the aberration diagram.

  In the photographic lenses 100 and 110 of the first and second embodiments, the first lens 1 and the first lens 11 on the object side use lenses whose both surfaces are aspherical. A lens whose both surfaces are spherical or a lens whose at least one lens surface is aspherical among the two lens surfaces can also be used.

  FIG. 5 shows a photographing lens according to a third embodiment to which the present invention is applied. The taking lens 120 of the present example is arranged such that, in order from the object side to the image forming surface 26 side, a first meniscus lens 21 having a positive power and a convex surface facing the object side, and a stop 24 following the meniscus. , A meniscus second lens 22 having a negative power with the concave surface facing the object side, and a third lens 23 having a negative power, and the second and third lenses function as correction lenses. A cover glass 25 is arranged between the third lens 23 and the image plane 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 exit angle of the principal ray is 24 degrees or less.

  In this example, of the lenses 21, 22, and 23, the first lens 21 has a spherical surface on both surfaces. On the other hand, the second and third lenses 22 and 23 have aspheric surfaces on both lens surfaces as in the first and second embodiments.

The lens data of the entire optical system of the taking lens 120 of the present example is as follows.
F-number: 3.5
Focal length: f = 5.7mm
Overall length: Δd = 6.46 mm

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

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

  In this example, among the lenses 31, 32, and 33, the first lens 31 has a spherical surface on both surfaces. On the other hand, the second and third lenses 32 and 33 have aspherical surfaces on both sides 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 = 5.7mm
Overall length: Σd = 6.66 mm

  Table 7 shows lens data of each lens surface of the taking lens 130 of this example, and Table 8 shows aspheric coefficients for defining the aspheric shape of each lens surface. FIG. 8 shows the aberration diagram.

  Next, referring to FIG. 5 again, in the taking lens 120 of Example 3, one lens surface is formed as an aspheric surface instead of the first lens 21 in which both surfaces of the lens surface are formed as spherical surfaces, and the other is formed. A photographing lens 140 using the first lens 41 having a spherical lens surface will be described. In FIG. 5, the shooting 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.

  The taking lens 140 of the present example is arranged such that, in order from the object side to the image forming surface 26 side, a first meniscus lens 41 having a positive power and a convex surface facing the object side, and a stop 24 following the meniscus. , A meniscus second lens 22 having a negative power with the concave surface facing the object side, and a third lens 23 having a positive power, and the second and third lenses function as correction lenses. A cover glass 25 is arranged between the third lens 23 and the image plane 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 exit angle of the principal ray is 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 among the lens surfaces on both sides, 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 have aspheric surfaces on both lens surfaces.

The lens data of the entire optical system of the taking lens 140 of this example is as follows.
F-number: 3.5
Focal length: f = 5.7mm
Overall length: Σd = 7.07mm

  Table 9 shows lens data of each lens surface of the taking lens 140 of this example, and Table 10 shows aspheric coefficients for defining the aspheric shape of each lens surface. FIG. 9 shows the aberration diagram.

FIG. 1 is a configuration diagram of a photographic lens according to a first embodiment to which the present invention is applied. FIG. 9 is a configuration diagram of a photographic lens according to a second embodiment to which the present invention is applied. FIG. 2 is an aberration diagram of the imaging lens of Example 1 illustrated in FIG. 1. FIG. 3 is an aberration diagram of the imaging lens of Example 2 illustrated in FIG. 2. FIG. 9 is a configuration diagram of a photographic lens according to Example 3 and Example 5 to which the present invention is applied. FIG. 10 is a configuration diagram of a photographic lens according to a fourth embodiment to which the present invention is applied. FIG. 6 is an aberration diagram of the imaging lens of Example 3 illustrated in FIG. 5. FIG. 7 is an aberration diagram of the taking lens of Example 4 shown in FIG. 6. FIG. 6 is an aberration diagram of the imaging lens of Example 5 illustrated in FIG. 5.

Explanation of reference numerals

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 surfaces 100, 110, 120, 130, 140 Photographing lenses R1, R2, R3, R4, R5, R6 Lens surfaces

Claims (8)

A first lens arranged in order from the object side, a second lens and a third lens functioning as a correction lens,
The first lens is a meniscus lens having a positive power with the convex surface facing the object side,
The second lens is a meniscus lens having a negative power with a concave surface facing the object side,
The third lens is a lens having a positive power,
The first lens has a stronger power than the second and third lenses,
Of these first, second and third lenses, at least the lens surfaces of the second and third lenses are both aspherical,
A photographic lens, wherein the aspheric surface of the third lens has one or more aspherical inflection points. A first lens arranged in order from the object side, a second lens and a third lens functioning as a correction lens,
The first lens is a meniscus lens having a positive power with the convex surface facing the object side,
The second lens is a meniscus lens having a negative power with a concave surface facing the object side,
The third lens is a lens having a negative power,
The first lens has a stronger power than the second and third lenses,
Of these first, second and third lenses, at least the lens surfaces of the second and third lenses are both aspherical,
A photographic lens, wherein the aspheric surface of the third lens has one or more aspherical inflection points. In claim 1 or 2,
The first lens is a photographic lens in which at least one of the two lens surfaces is an aspheric surface. In any one of claims 1 to 3,
An imaging lens that satisfies the following conditional expression, where F is a composite focal length of the imaging lens and f1 is a focal length of the first lens.
0.50 <f1 / F <1.5 In any one of claims 1 to 4,
A photographic lens satisfying the following conditional expression, where F is the composite focal length of the photographic lens, and Δd 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 5,
A taking lens satisfying the following conditional expression, where Abbe number of the second lens is νd2.
50> νd2 In any one of claims 1 to 6,
An imaging lens in which the maximum exit angle of the principal ray of the imaging lens is 30 degrees or less. In any one of claims 1 to 7,
In the third lens, a peripheral portion of a lens surface on an image plane side is formed as a convex surface on the image plane side,
A photographic lens in which one or more aspherical inflection points are formed on the first lens surface and the second lens surface.

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