JP2005173319A - Imaging lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a desired optical performance with a configuration of only three lenses and to maintain a resolution corresponding to a megapixel by properly correcting each aberration while ensuring a wide angle of view, and a total lens length of around 6 mm An inexpensive imaging lens that is downsized.
An imaging lens according to the present invention includes, in order from the object side, a biconvex first lens, a meniscus second lens having a concave surface facing the object side, and a meniscus third lens having a convex surface facing the object side. The lens is composed of three lenses, and at least five or more surfaces are aspherical.
[Selection] Figure 1

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens, and in particular, has a small, lightweight, and high-definition performance used for a mobile phone camera, a vehicle-mounted camera, a surveillance camera, etc. using a solid-state imaging device such as a CCD or CMOS in a light receiving part The present invention relates to an imaging lens having a single lens configuration.

  In recent years, the progress of digitalization and multimedia has been remarkable. For example, digital cameras mounted on mobile phones are inexpensive, low-resolution and high-definition imaging with the progress of solid-state imaging devices such as CCD and CMOS. There is a need for lenses.

  Conventionally, as such an imaging lens, a single lens or a dual lens has been adopted according to the number of pixels of the solid-state imaging device (see, for example, Patent Document 1 and Patent Document 2).

  However, when the number of pixels of a solid-state image sensor is highly integrated down to the million pixel class, so-called megapixel class, due to the advancement of technology, such an imaging lens having one or two lenses can cope with the resolution surface. I can't understand.

  In addition, by reducing the effective size of the solid-state imaging device itself, there has been a demand for low cost, small size, and light weight with the overall length of the imaging lens (distance from the first lens surface on the object side lens to the imaging surface) kept to a few millimeters or less. ing.

As a means for solving such a problem, an imaging lens having a three-lens configuration has been considered (see, for example, Patent Document 3 and Patent Document 4).
JP 2001-183578 A JP 2003-215446 A JP 2001-075006 A JP 2001-083409 A

  However, the imaging lenses disclosed in Patent Document 3 and Patent Document 4 still do not satisfy sufficient requirements in terms of the total length and resolution of the lens system, and on the other hand, it is possible to increase the resolution by increasing the number of lenses. However, there is a drawback that the total length of the lens system becomes long, and it is expensive and large.

  The present invention has been made in view of the above, and maintains a desired optical performance with a configuration of only three lenses, and corrects each aberration well while ensuring a wide angle of view, thereby supporting a resolution corresponding to megapixels. It is an object of the present invention to provide an inexpensive imaging lens capable of reducing the total lens length to around 6 mm.

  In order to achieve the above object, an imaging lens according to the first aspect of the present invention includes, in order from the object side, a biconvex first lens, a meniscus second lens having a concave surface facing the object side, and an object side. It is composed of a meniscus third lens having a convex surface and at least five or more surfaces are aspherical.

  In general, the three-lens configuration is known as a triplet type, but in many of them, the second lens has a biconcave shape, and the third lens has a convex surface facing the image surface side.

  However, according to the first aspect of the present invention, the orientation of the second and third lenses and the meniscus shape are not seen in the triplet type, Japanese Patent Laid-Open No. 2001-075006, and Japanese Patent Laid-Open No. 2001-083409. There is a major feature, which makes it possible to correct each aberration satisfactorily, and to shorten the overall length of the lens system and achieve high resolution.

Further, in the invention described in claim 2, in claim 1, the first lens is
The condition of 0.48 <f1 / f <0.63 is satisfied. Here, f1 is the focal length of the first lens, and f is the focal length of the entire lens system.

  The invention according to claim 2 is a condition relating to the power arrangement with respect to the focal length of the entire lens system of the first lens in the imaging lens according to claim 1. This is because it becomes impossible to secure the spherical aberration and it becomes difficult to correct the spherical aberration.

  On the other hand, if the value exceeds 0.63, various aberration corrections cannot be achieved while keeping the entire length of the lens system short.

  Furthermore, the invention according to claim 3 is the imaging lens according to claim 1 or 2, wherein the second lens satisfies 0.52 <| f2 | / <f0.82. To do. Here, f2 is the focal length of the second lens.

  The invention according to claim 3 is a condition relating to the power arrangement with respect to the focal length of the entire lens system of the second lens in the imaging lens according to claim 1, and when the value is less than 0.52, the coma aberration is deteriorated. There is an inconvenience that the resolution is reduced due to overcorrection of the sum of the Wahl.

  On the other hand, if it exceeds 0.82, the necessary back focus cannot be secured, and correction of curvature of field aberration and chromatic aberration due to insufficient correction of Petzval sum becomes difficult.

  Further, according to a fourth aspect of the present invention, in the imaging lens according to the first aspect, the paraxial curvature radius R6 on the object side of the third lens satisfies 0.35 <R6 / f <0.7. It is characterized by this.

  The invention according to claim 4 corrects each aberration that cannot be corrected in claims 1 to 3 in a well-balanced manner. When the value is less than 0.35, there is a disadvantage that distortion is greatly generated. If it exceeds 0.7, the balance of spherical aberration, coma and astigmatism will be lost, and the required resolution will not be obtained.

  As described above, according to the present invention, although it has only three lens configurations, it is inexpensive and has a high resolution capable of supporting the megapixel class, and the total length of the lens is only about 6 mm, and is small and lightweight. An imaging lens can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an optical diagram of the imaging lens of the present invention.

  The imaging lens includes a first first lens, a second second lens, and a third third lens counted from the object side. The first lens is convex on both sides. The second lens has a meniscus shape with a concave surface facing the object side. The third lens has a meniscus shape with a convex surface facing the object side, and the imaging lens has a three-lens configuration.

  The imaging lenses of Examples 1 to 5 commonly include parallel plane glass having a thickness of 0.3 mm on the image plane side, which is an infrared light cut filter. The wavelength range of this imaging lens is 540 nm as the main wavelength, the short wavelength is 440 nm, and the long wavelength is 640 nm.

  In addition, a diaphragm is provided on the object side.

  Further, in Examples 1 to 5 below, Table 1, Table 5, Table 9, Table 13, and Table 17 show the surface number, radius of curvature (R), interval (d), refractive index (nd), and Abbe number. The relationship with (νd) is shown.

  The surface number indicates the number corresponding to the surface of each lens obtained by sequentially counting the imaging lens shown in FIG. 1 from the object surface side. If this surface number is Ri, Ri is the radius of curvature of the i surface, and d is i + 1 from the i surface. The distance to the surface (surface spacing), nd is the refractive index of the medium existing at di (here, the refractive index at the d line (587.56 nm)), νd is the dispersion of the medium existing at di (here, the d line ( Abbe number) at 587.56 nm) is shown respectively. Note that i is an integer from 1 to 9.

  Table 2, Table 6, Table 10, Table 14, and Table 18 show the lens characteristics of the imaging lenses having the configurations shown in Table 1, Table 5, Table 9, Table 13, and Table 17 of Example 1 to Example 5, respectively. Show.

Table 3, Table 7, Table 11, Table 15, and Table 19 show the numerical values of Conditional Expression 1 to Conditional Expression 3 below. In Examples 1 to 5, Conditional Expression 1 to Conditional Expression 3 are also set. Shows satisfaction.
Conditional expression 1
0.48 <f1 / f <0.63
Conditional expression 2
0.52 <| f2 | / f <0.82
Conditional expression 3
0.35 <R6 / f <0.7
Further, Table 4, Table 8, Table 12, Table 16, and Table 20 show the surface numbers of the aspherical surfaces of Examples 1 to 5 and their coefficient values. In the orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is X, the curvature of the surface vertex (reciprocal of the radius of curvature) is C, the conic coefficient is K, and the aspheric coefficient is A _4. , A ₆ , A ₈ , A ₁₀ are represented by the following calculation formulas.

However, h = (Y ² + Z ² ) ^1/2
2 to 6 show a spherical aberration diagram, a field curvature aberration diagram, and a distortion aberration diagram, respectively, of Examples 1 to 5. Reference symbol S represents a sagittal aberration curve, and T represents a tangential aberration curve.
(Example 1)
2 shows an example in which surface number 2 to surface number 7 are aspherical surfaces, and FIG. 2 shows spherical aberration, curvature of field aberration, and distortion aberration of the imaging lens described in Example 1, with six aspherical surfaces. Is.

As is apparent from Tables 2 and 3 and FIG. 2, the imaging lens of Example 1 has a high resolution that is inexpensive and compatible with the megapixel class while having only three lens configurations. It is understood that the total lens length is only about 6 mm and is small and light.
(Example 2)
The imaging lens of Example 2 has six aspheric surfaces, the first first lens counted from the object side, the second second lens counted from the object side, and the object side. The refractive index and dispersion of the third third lens are the same as those of the imaging lens of Example 1, but the main difference from the imaging lens of Example 1 is that the radius of curvature of the second surface of the first lens, The radius of curvature of the seventh surface of the third lens is about twice the radius of curvature of the second surface of the first lens of Example 1 and about half the radius of curvature of the seventh surface of the third lens.

FIG. 3 shows spherical aberration, curvature of field aberration, and distortion of the imaging lens described in Example 2. As is apparent from Tables 6, 7, and FIG. 3, effects similar to those of the imaging lens of Example 1 are shown. Play.
(Example 3)
The imaging lens of Example 3 has six aspheric surfaces, and the refractive index and dispersion of the second lens and the third lens are the same as those of the imaging lens of Example 1, but the main difference is that of the first lens. The refractive index is slightly larger than the refractive index of Example 1.

FIG. 4 shows spherical aberration, curvature of field aberration, and distortion of the imaging lens described in Example 3. As is apparent from Tables 10, 11, and FIG. 4, the imaging lens of Example 3 is also an example. The same effect as that of the first imaging lens can be obtained.
Example 4
The imaging lens of Example 4 has six aspheric surfaces, and the refractive indexes and dispersions of the second lens and the third lens are the same as those of the imaging lens of Example 1, but the main differences are the first lens. The refractive index is made slightly smaller than the refractive index of Example 1, and plastic resin can be used for all three lenses.

FIG. 5 shows spherical aberration, curvature of field aberration, and distortion of the imaging lens described in Example 4. As is apparent from Tables 14, 15 and 5, the imaging lens of Example 4 is also an example. The same effect as that of the first imaging lens can be obtained.
(Example 5)
In the imaging lens of Example 5, the refractive indexes of the first lens, the second lens, and the third lens are set to be the refraction of the first lens, the second lens, and the third lens of the first example of Examples 1 to 4. The surface number 2 and the surface numbers 4 to 7 are aspherical, and the number of aspherical surfaces is five.

  FIG. 6 shows the spherical aberration, curvature of field aberration, and distortion of the imaging lens described in Example 5. The imaging lens of Example 5 is also shown in Table 18, Table 19, and FIG. The imaging lens of Example 4 also has the same effect as the imaging lens of Examples 1 to 4.

It is an optical diagram of the imaging lens concerning this invention. FIG. 3 is an aberration diagram of the imaging lens of Example 1. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. FIG. 6 is an aberration diagram of the imaging lens of Example 4. FIG. 10 is an aberration diagram of the imaging lens of Example 5.

Explanation of symbols

  None

Claims (4)

  In order from the object side, the first lens has a biconvex shape, the second lens has a meniscus shape with a concave surface facing the object side, and the third lens has a meniscus shape with a convex surface facing the object side. An imaging lens, wherein a surface or more has an aspherical surface. The imaging lens according to claim 1, wherein the following condition is satisfied.
0.48 <f1 / f <0.63 ... Conditional expression 1
Where f: focal length of all lens systems
f1: Focal length of the first lens The imaging lens according to claim 1, wherein the following condition is satisfied.
0.52 <| f2 | / f <0.82 ... Conditional expression 2
Where f2: focal length of the second lens The imaging lens according to any one of claims 1 to 3, wherein the following condition is satisfied.
0.35 <R6 / f <0.7 Conditional expression 3
Where R6: paraxial radius of curvature on the object side of the third lens

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