JP2008180870A - Small-sized lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized lens which is constituted of three lenses, which is small in size and has high resolution, which excels in processibility and assemblability, and all the lenses of which are made of optical plastic. <P>SOLUTION: The small-sized lens is constituted of at least a first lens that is a convex lens having positive power, a second lens that is a lens turning its concave surface to an object side and having negative power paraxially, a third lens that is a lens turning its concave surface to an image side and having negative power paraxially, and a diaphragm arranged between the first surface of the first lens on the object side and the first surface of the second lens on the object side from the object side. The respective lenses have at least one aspherical surface, and the small-sized lens satisfies conditions (1) -0.9<f/f2<-0.3 and (2) -0.5<f/f3<-0.1 (f: focal length of the entire lens, f2: focal length of the second lens and f3: focal length of the third lens). <P>COPYRIGHT: (C)2008,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 small lens having a three-group lens configuration.

  Currently, with the miniaturization of mobile phones, it is necessary to reduce the size of the camera mechanism mounted on the mobile phone. Accordingly, there is a demand for further miniaturization and higher resolution of the lens.

  As conventional techniques for solving this problem, four-lens lenses as described in Patent Documents 1 to 3 are known. These inventions are roughly divided into a stop and three groups, and the first group consisting of a cemented or separated lens corrects the color of magnification and the color on the axis, and the third group close to the image side is negative. By using a lens, the entire optical system can be reduced in size, and by using an aspheric surface around the third lens group, the positive power is increased, the emitted light beam is made telecentric, the shading characteristics are improved, By constructing the second group lens with a meniscus lens with the concave side facing the object side, the tilted image plane and astigmatism are improved, and by using an aspherical surface for the second group, an extremely aspherical shape is achieved. The aberration generated by the third group is improved.

Patent Document 4 discloses an imaging lens having a three-lens configuration. Specifically, the imaging lens includes, in order from the object side, a positive first lens having a convex surface facing the object side, an aperture stop, a negative second lens, and a negative third lens, and the conditional expression: -0.23 <f / f2 <-0.02 (f: focal length of the entire system, f2: focal length of the second lens)
Japanese Patent No. 3564107 Japanese Patent No. 3424030 JP 2003-365544 A JP 2006-98429 A

  The lenses disclosed in Patent Documents 1 to 3 described above are four in number, and there is a problem that further cost reduction and downsizing are difficult as market requirements.

  Further, Patent Document 4 discloses a three-lens configuration, but there is a problem that the F-number is as dark as 4 and cannot respond to a market requiring a bright lens.

  Therefore, an object of the present invention is to provide a small lens having a three-lens configuration, which is small and has high resolution, good workability and ease of assembly, and in which all lenses are made of optical plastics.

  Therefore, the small lens according to the present invention includes a first lens that is a convex lens having a positive power from the object side, and a second lens that is a lens having a concave surface facing the object side and having a paraxial negative power. A concave surface facing the image side and a third lens that is a lens having a paraxial negative power and a first surface on the object side of the first lens and a first surface on the object side of the second lens. Each lens has at least one aspherical surface, and (1) −0.9 <f / f2 <−0.3, (2) −0.5 <f / This satisfies the condition of f3 <−0.1 (f: focal length of the entire lens, f2: focal length of the second lens, f3: focal length of the third lens).

  Further, the stop is disposed between the first surface on the object side and the second surface on the image side of the first lens, the first lens is a biconvex lens or a plano-convex lens, and the second lens is a meniscus lens. 3) It is desirable to satisfy the condition of | r11 | <| r12 | (r11: curvature of the most object side surface of the first lens, r12: curvature of the most image side surface of the first lens).

  Furthermore, the flare cut is disposed on the periphery of the first surface of the first lens and the periphery of the second lens, and the second lens is a biconvex lens or a plano-convex lens, and (4) V1> V2, (5) V3 ≧ V2, (6) r31> r32 (V1: Abbe number of the first lens, V2: Abbe number of the second lens, V3: Abbe number of the third lens, r31: Curvature of the most object side surface of the third lens, r32: It is desirable to satisfy the condition of the curvature of the most image side surface of the third lens.

  According to the present invention, the small lens is a first lens that is a convex lens having a positive power from the object side, and a second lens that is a lens having a concave surface facing the object side and having a paraxial negative power. A concave surface facing the image side and a third lens that is a lens having a paraxial negative power and a first surface on the object side of the first lens and a first surface on the object side of the second lens. Each lens has at least one aspherical surface, and (1) −0.9 <f / f2 <−0.3, (2) −0.5 <f / By satisfying f3 <−0.1 (f: focal length of the entire lens, f2: focal length of the second lens, f3: focal length of the third lens), a low-cost and compact compact lens can be formed. In particular, a bright lens can be realized.

  Embodiments of the present invention will be described below.

  The small lens according to the present invention includes a first lens having a positive power, a second lens having a negative power, and a third lens having a negative power from the object side on the paraxial axis. As a result, the lens type becomes a teletype, which is bright and the optical total length can be shortened. Further, by making the object side surface (second lens first surface) of the second lens concave with respect to the object side, astigmatism, field curvature, and coma aberration can be suppressed.

  Further, by arranging the stop between the object side surface (first lens first surface) of the first lens and the second lens first surface, harmful flare can be cut.

  Furthermore, the shading angle can be relaxed by forming the third lens so as to gradually increase the positive power as the distance from the optical axis increases.

  Conditional expression (1) −0.9 <f / f2 <−0.3 defines the power of the second lens. In this case, if the upper limit is exceeded, it is advantageous in terms of aberration, but the total optical length becomes long. If the lower limit is not reached, aberration correction becomes difficult.

  Conditional expression (2) −0.5 <f / f3 <−0.1 defines the power of the third lens. If the upper limit is exceeded, it is advantageous in terms of aberration, but the optical total length becomes long. If the lower limit is not reached, aberration correction becomes difficult.

  Further, the stop is arranged between the first surface on the object side and the second surface on the image side of the first lens, the second lens is a meniscus lens, and (3) | r11 | <| r12 | ( When r11: curvature of the first object side surface of the first lens is satisfied and r12: curvature of the first image side of the first lens is satisfied, a lens with good workability and performance can be obtained.

  Conditional expression (3) | r11 | <| r12 | defines the shape of the first lens. As a result, the occurrence of spherical aberration and coma can be reduced.

  In particular, by arranging the stop between the first surface of the first lens and the second surface on the image side, the flare component of the off-axis light beam can be cut efficiently. Furthermore, when the first lens is a biconvex lens or a plano-convex lens, the balance between spherical aberration and coma aberration can be improved. In addition, since the second lens is a meniscus lens, the second lens can be made more concentric than the diaphragm, and astigmatism and curvature of field can be corrected.

  Further, the flare cut is arranged on the periphery of the first surface of the first lens and the periphery of the second lens, and the second lens is a biconvex lens or a plano-convex lens, and (4) V1> V2 and (5) V3 ≧ V2. (6) r31> r32 (V1: Abbe number of the first lens, V2: Abbe number of the second lens, V3: Abbe number of the third lens, r31: Curvature of the most object side surface of the third lens, r32: First lens It is desirable to satisfy the condition of the curvature of the most image side surface of the three lenses.

  Since the flare cut is between the first surface and the second surface of the first lens and the second lens, harmful flare can be cut without significantly reducing the peripheral light amount ratio. is there.

  Conditional expression (4) V1> V2 defines the Abbe number of the glass material of the first lens and the second lens. As a result, the occurrence of axial chromatic aberration can be suppressed.

  Conditional expression (5) V3 ≧ V2 defines the Abbe number of the glass material of the third lens and the second lens. As a result, the occurrence of lateral chromatic aberration can be suppressed.

  Conditional expression (6) r31> r32 defines the shape of the third lens. As a result, the occurrence of various aberrations is small, and the shading angle can be relaxed.

  Embodiment 1 of the present invention will be described below. As shown in FIG. 1, a small lens LA according to the present invention includes a first lens L1, a second lens L2, a third lens L3, a protective glass PG, and an image pickup device PC made of a CCD or a CMOS that captures an image as data. It is comprised at least by ST and flare cut FC.

  The aperture stop ST is disposed between the first surface R1 of the first lens L1 and the first surface R3 of the second lens L2, particularly between the first surface R1 and the second surface R2 of the first lens L1. Furthermore, the first flare cut FC1 is disposed on the periphery of the first surface of the first lens, and the second flare cut FC2 is disposed on the periphery of the second lens.

  Further, the object side surface of the first lens L1 is a first surface R1 of the first lens, and the image side surface of the first lens is a second surface R2 of the first lens. The object side surface of the second lens L2 is defined as a first surface R3 of the second lens, and the image side surface of the second lens is defined as a second surface R4 of the second lens. Further, the object side surface of the third lens L3 is a first surface R5 of the third lens, and the image side surface of the third lens is a second surface R6 of the third lens. Furthermore, the object side surface of the protective glass PG is a first surface R7 of the protective glass, and the image side surface of the protective glass PG is a second surface R8 of the protective glass.

  The radius of curvature of each of the surfaces R1 to R8 of the small lens LA according to Example 1 of the present invention, the spacing between the surfaces, the refractive index Nd of the glass material on the surfaces R1, R3, R5, and R7, and the surfaces R1, R3, and R5. , R7, Abbe number Vd, and effective diameters and conic coefficients of surfaces R1 to R7 are shown in Table 1 below.

  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, D, E, F, and G of each surface are shown in Table 2 below.

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

  A second embodiment of the present invention will be described below. As shown in FIG. 4, the small lens LA ′ according to the present invention is similar to the first embodiment in that the first lens L1, the second lens L2, the third lens L3, the protective glass PG, and a CCD that captures an image as data. Alternatively, it is configured at least by an image sensor PC made of CMOS, a diaphragm ST, and a flare cut FC.

  Similarly, the aperture stop ST is also between the first surface R1 of the first lens L1 and the first surface R3 of the second lens L2, particularly between the first surface R1 and the second surface R2 of the first lens L1. In addition, the first flare cut FC1 is disposed on the periphery of the first surface of the first lens, and the second flare cut FC2 is disposed on the periphery of the second lens.

  Further, the object side surface of the first lens L1 is a first surface R1 of the first lens, and the image side surface of the first lens is a second surface R2 of the first lens. The object side surface of the second lens L2 is defined as a first surface R3 of the second lens, and the image side surface of the second lens is defined as a second surface R4 of the second lens. Further, the object side surface of the third lens L3 is a first surface R5 of the third lens, and the image side surface of the third lens is a second surface R6 of the third lens. Furthermore, the object side surface of the protective glass PG is a first surface R7 of the protective glass, and the image side surface of the protective glass PG is a second surface R8 of the protective glass.

  The radius of curvature of each of the surfaces R1 to R8 of the small lens LA according to Example 2 of the present invention, the spacing between the surfaces, the refractive index Nd of the glass material on the surfaces R1, R3, R5, and R7, and the surfaces R1, R3, and R5. , R7, Abbe number Vd, and effective diameters and conic coefficients of surfaces R1 to R7 are shown in Table 3 below.

  In Table 3, the surface marked with * represents an aspherical surface and is formed according to the following mathematical formula 2.

  In Example 2, the coefficients A, B, C, D, E, F, and G of each surface are shown in Table 4 below.

  FIG. 5 is a characteristic diagram showing the spherical aberration of the small lens according to Example 2. FIG. 6A is a characteristic diagram of the AS (astigmatism) of the small lens according to Example 2. FIG. 6B is a characteristic diagram showing Dist (distortion aberration).

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

Explanation of symbols

LA, LA 'Small lens L1 First lens L2 Second lens L3 Third lens PG Protective glass PC Image sensor

Claims (3)

From the object side, a first lens that is a positive lens with positive power, a second lens that has a concave surface facing the object side and having a negative power in a paraxial direction, and a concave surface facing the image side, the paraxial And at least a third lens that is a lens having negative power, and an aperture disposed between the object-side first surface of the first lens and the object-side first surface of the second lens, Each lens has at least one aspheric surface and satisfies the following conditions.
(1) -0.9 <f / f2 <-0.3
(2) -0.5 <f / f3 <-0.1
f: Focal length of the entire lens
f2: focal length of the second lens
f3: focal length of the third lens The diaphragm is disposed between the first surface on the object side and the second surface on the image side of the first lens, the first lens is a biconvex lens or a plano-convex lens, and the second lens is a meniscus lens. The small lens according to claim 1, wherein the condition is satisfied.
(3) | r11 | <| r12 |
r11: curvature of the most object side surface of the first lens
r12: curvature of the most image side surface of the first lens 3. The flare cut is disposed on the periphery of the first surface of the first lens and the periphery of the second lens, and the second lens is a biconvex lens or a plano-convex lens and satisfies the following conditions. Small lens.
(4) V1> V2
(5) V3 ≧ V2
(6) r31> r32
V1: Abbe number of the first lens V2: Abbe number of the second lens V3: Abbe number of the third lens r31: Curvature of the most object side surface of the third lens r32: Curvature of the most image side surface of the third lens

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