JP2006308847A - Small lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small lens which is small, has high resolution, proper workability, assemblability and proper shading characteristics. <P>SOLUTION: The small lens is constituted of a first lens having positive power, a second lens having negative power and a third lens having positive power from the object side, wherein a diaphragm is arranged between the object side of the first lens and the face of the object side of the second lens and a conditional expression of (1) 15<v2<55 (where v2: Abbe's number of the second lens) is satisfied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a small optical lens used for an electronic camera, a surveillance camera, an in-vehicle camera, a board camera, various sensors, and a video phone, and more particularly to a triplet type small lens.

Currently, with the miniaturization of mobile phone-equipped phones, there is a demand for further miniaturization and higher resolution of the lenses mounted on the phones. As a conventional technique for solving this problem, a lens patent with a high telephoto ratio of a four-lens lens as described in Patent Documents 1 to 4 is known.

The inventions disclosed in these patent documents are roughly composed of a diaphragm and three groups of lenses, and a first group composed of cemented or separated lenses corrects the magnification color and the on-axis color. By making the third lens group close to the image side a negative lens, the telephoto ratio is increased to reduce the size, and an aspheric surface is used around the third lens group to increase the positive power. The exit beam is made telecentric, the shading characteristics are improved, and the second lens unit is composed of a meniscus lens with the concave facing the object side, thereby improving the tilted image plane and astigmatism, and further the second lens unit. By using an aspherical surface, the aberration caused by the extreme third aspherical group is improved.
Japanese Patent No. 3564107 Japanese Patent No. 3424030 JP 2003-365544 A JP-A-8-201686

  However, with the recent increase in pixel pitch of CCD and C moss elements, it is possible to obtain a high pixel with a smaller size, and the size can be reduced without increasing the telephoto ratio as in the invention disclosed in the above-mentioned patent document. It has become possible.

  Therefore, it is conceivable to use a compact triplet type composed of three balls, which is one less than the four balls as disclosed in Patent Document 4. Since this triplet type can correct all Seidel 5 aberrations with a minimum lens configuration, a high-performance lens can be obtained with a small number of lenses.

However, the lens disclosed in Patent Document 4 is a rear diaphragm because it is made for a silver salt compact used shutter, and when used as it is for a CCD or C moss element, the angle incident on the element becomes large. For this reason, there arises a problem that shading characteristics deteriorate.

  Therefore, an object of the present invention is to provide a small lens that is small and has high resolution, good workability and ease of assembly, and good shading characteristics.

  Therefore, according to the present invention, the first lens having a positive power, the second lens having a negative power, and the third lens having a positive power are arranged from the object side. It is disposed between the object side of the lens and the object side surface of the second lens, and satisfies the conditional expression (1) 15 <v2 <55 (where v2 is the Abbe number of the second lens).

  Further, the first lens is a meniscus lens having a convex surface on the object side, the second lens is a biconcave lens, and (2) 0.6 <f1 / f, (3) 0 <( N1 + N3) / 2−N2 <0.4, (4) 0.3 <Σd / f <10 (where f1: focal length of the first lens, f: focal length of the entire lens, N1: refraction of the first lens) It is desirable to satisfy the following conditional expression: refractive index, N2: refractive index of the second lens, N3: refractive index of the third lens, Σd: distance between the optical axes from the first lens object side surface to the third lens image side surface .

  Therefore, according to the present invention, in the triplet type lens, the aperture is provided between the first lens first surface and the second group object side, and by satisfying the various conditional expressions described above, the workability and With a simple structure with good assemblability, the lens can be reduced in size and resolution, and the shading characteristics can be improved, so that good cost performance can be achieved.

  Embodiments of the present invention will be described below.

  As shown in FIGS. 1 and 2, the small lens L according to the embodiment of the present invention includes, from the object side, a first lens L1 having a positive power, a second lens L2 having a negative power, and a positive lens. It is composed of three third lenses L3 having power. The diaphragm St is disposed between the object side surface R1 of the first lens L1 and the object side surface R3 of the second lens L2. FIG. 1 shows Example 1 in which the aperture stop St is disposed at the radial end of the image side surface R2 of the first lens L1, and FIG. 2 shows the diameter of the object side side surface R1 of the first lens L1. The Example 2 arrange | positioned at the direction edge part is shown. G is an IR cut plate for cutting infrared rays.

  As described above, by adopting the triplet type in which the small lens L is composed of three lenses, the aberration can be corrected even with the minimum number of lenses and the number of lenses is small. Can be minimized. Further, by placing the aperture stop St between the object side surface R1 of the first lens L1 and the object side surface R3 of the second lens L2, the emitted light can be made close to telecentric, so that the shading characteristics can be improved.

Conditional expression (1) 15 <v2 <55 (v2: second lens upper number) is an expression that defines the second lens L2 upper number. Deviation from this conditional expression (1) increases chromatic aberration.

  Moreover, various aberrations can be suppressed by making the 1st lens L2 into the meniscus lens by which the object side surface R1 was formed in the convex surface, and comprising the 2nd lens L2 with a biconcave lens.

  Conditional expression (2) 0.6 <f1 / f (f1: focal length of the first lens, f: focal length of the entire lens) is an expression that defines the focal length of the first lens L1. Below the lower limit of this equation, it becomes difficult to balance the curvature of field and the telecentricity of the emitted light and compactness.

    Conditional expression (3) 0 <(N1 + N3) / 2−N2 <0.4 (N1: refractive index of the first lens L1, N2: refractive index of the second lens L2, N3: refractive index of the third lens L3) , Which defines the refractive index (Nd) of the first lens L1, the second lens L2, and the third lens L3. If it is out of the range of this formula, the Petzpearl sum is deteriorated, resulting in a problem that field curvature occurs.

    Conditional expression (4) 0.3 <Σd / f <10 (Σd: distance between the optical axes from the first lens object side surface to the third lens image side surface) is an expression that defines the total thickness of the lens system. If it is less than the lower limit, it is too small to exceed the processing limit, and if it is more than the upper limit, there is a problem in compactness.

  Hereinafter, Example 1 of the present invention is specifically shown in Table 1. Table 1 below shows the object side surface R1 of the first lens L1, the image side surface R2 of the first lens L1, the object side surface R3 of the second lens L2, the image side surface R4 of the second lens L2, and the object of the third lens L3. The side surface R5 and the image side surface R6 of the third lens L3 are shown.

  In Table 1, the surface marked with * represents an aspherical surface and is formed according to the following formula 1.

  In Example 1, the coefficients A, B, C, and D of each surface are shown in Table 2 below.

  3 is a characteristic diagram showing the spherical aberration of the small lens according to Example 1. FIG. 4A is a characteristic diagram of the AS (astigmatism) of the small lens according to Example 1. As shown in FIG. FIG. 4B is a characteristic diagram showing DIST (distortion aberration).

  Hereinafter, Example 1 of the present invention is specifically shown in Table 3. Table 3 below shows the object side surface R1 of the first lens L1, the image side surface R2 of the first lens L1, the object side surface R3 of the second lens L2, the image side surface R4 of the second lens L2, and the object of the third lens L3. The side surface R5 and the image side surface R6 of the third lens L3 are shown.

  In Table 3, the surface marked with * represents an aspherical surface and is formed according to Formula 1 as in the first embodiment.

It is a schematic block diagram of the small lens of Example 1 which concerns on this invention. It is a schematic block diagram of the small lens of Example 2 which concerns on this invention. It is a characteristic diagram which showed the spherical aberration of the small lens which concerns on Example 1 of this invention. (A) is a characteristic diagram of AS (astigmatism) of the small lens according to Example 1 of the present invention, and (b) is a characteristic diagram showing DIST (distortion aberration).

Explanation of symbols

G IR cut plate L Small lens L1 First lens L2 Second lens L3 Third lens St Aperture

Claims (2)

From the object side, in a small lens composed of a first lens having a positive power, a second lens having a negative power, and a third lens having a positive power,
A compact lens, wherein the aperture is disposed between the object side of the first lens and the object side surface of the second lens, and satisfies the following conditional expression:
(1) 15 <v2 <55
Where v2 is the Abbe number of the second lens. 2. The small lens according to claim 1, wherein the first lens is a meniscus lens having a convex surface on the object side, the second lens is a biconcave lens, and satisfies the following conditional expression: .
(2) 0.6 <f1 / f
(3) 0 <(N1 + N3) / 2−N2 <0.4
(4) 0.3 <Σd / f <10
Where f1: focal length of the first lens, f: focal length of the entire lens, N1: refractive index of the first lens, N2: refractive index of the second lens, N3: refractive index of the third lens, Σd: first The distance between the optical axes from the lens object side surface to the third lens image side surface.

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