JP2015161760A - imaging lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-angle and compact imaging lens that is so fast as Fno≤2.2 and composed of four elements having various aberrations excellently corrected.SOLUTION: The imaging lens is provided which comprises in order from an object side; an aperture diaphragm; a first lens having positive power; a second lens having negative power; a third lens having positive power; and a fourth lens having negative power, and satisfies a following expression. 0.93≤f1/f≤1.30, -3.00≤f2/f≤-1.90, -0.70≤(R1+R2)/(R1-R2)≤-0.10, -2.00≤(R3+R4)/(R3-R4)≤2.00 and 30.00≤f/d6≤65.00 where f, f1 and f2 denote a focal length of an entire lens system, the first lens and the second lens, respectively, R1, R2, R3 and R4 denote a radius of curvature of an object side surface of the first lens, an imaging surface side surface of the first lens, an object side surface of the second lens and an imaging surface side surface of the second lens, respectively, and d6 denotes a distance from an imaging surface side surface of a third lens L3 to an object side surface of a fourth lens L4.

Description

  The present invention relates to an imaging lens. In particular, it has good optical characteristics in which various aberrations are suitably corrected, which is suitable for a small-sized imaging device, an optical sensor, a portable module camera, a WEB camera, and the like using an imaging device such as a high-pixel CCD or CMOS. The present invention relates to an imaging lens that is small and has a wide angle of 75 ° or more and an F value of 2.2 or less (hereinafter referred to as Fno).

In recent years, various imaging devices using an imaging device such as a CCD or a CMOS have been widely used. With the downsizing and high performance of these imaging devices, imaging lenses used in imaging devices are also required to have good optical characteristics with a wide angle, a small size, and a bright Fno.

However, when an imaging element of 1.4 μm or less is used, a lens (miniaturization) that requires a bright Fno representing the brightness of the imaging optical system and a short optical length is required, so that good optical characteristics can be obtained. Technical development relating to an imaging lens composed of four lenses is underway. The four-lens imaging lens includes, in order from the object side, a first lens having positive power, a second lens having negative power, a third lens having positive power, and a fourth lens having negative power. Has been proposed.

The imaging lens disclosed in Patent Document 1 is an imaging lens constituted by the above four lenses, but the power distribution of the first lens and the second lens is insufficient, and thus the disclosed embodiment. Then, the total angle of view 2ω <75 ° and Fno ≧ 2.407, and the wide angle and the brightness of Fno were insufficient.

  The imaging lens disclosed in Patent Document 2 is an imaging lens composed of the above four lenses. The focal length of the entire lens system and the distance from the image surface side surface of the third lens to the object side surface of the fourth lens are as follows. Since the ratio is insufficient, in the disclosed embodiment, the total angle of view 2ω <72 ° and Fno ≧ 2.50, the wide angle and the brightness of Fno were insufficient.

JP 2013-148834 A JP 2013-125073 A

An object of the present invention is to provide an imaging lens composed of four lenses having a wide angle, a small size, bright as Fno ≦ 2.2, and various aberrations corrected satisfactorily.

  In order to achieve the above object, the power distribution of the first lens and the second lens from the entire lens system, the shapes of the first lens and the second lens, the focal length of the entire lens system and the image of the third lens As a result of intensive studies on the ratio of the distance from the surface side surface to the object side surface of the fourth lens, the inventors have found that an imaging lens in which the problems of the prior art are improved is obtained, and the present invention has been achieved.

The imaging lens according to claim 1 includes, in order from the object side, an aperture stop (S1), a positive power first lens (L1), a negative power second lens (L2), a positive power third lens (L3), An imaging lens comprising a fourth lens (L4) having a negative power and satisfying the following conditional expressions (1) to (5).
0.93 ≦ f1 / f ≦ 1.30 (1)
−3.00 ≦ f2 / f ≦ −1.90 (2)
−0.70 ≦ (R1 + R2) / (R1−R2) ≦ −0.10 (3)
−2.00 ≦ (R3 + R4) / (R3−R4) ≦ 2.00 (4)
30.00 ≦ f / d6 ≦ 65.00 (5)
However,
f: focal length of the entire lens system f1: focal length of the first lens L1 f2: focal length of the second lens L2 R1: radius of curvature of the object side surface of the first lens L1 R2: curvature of the image surface side surface of the first lens L1 Radius R3: Radius of curvature of the object side surface of the second lens L2 R4: Radius of curvature of the image surface side surface of the second lens L2 d6: Distance from the image surface side surface of the third lens L3 to the object side surface of the fourth lens L4.

The imaging lens according to claim 2, wherein the following conditional expression (6) is satisfied.
−0.50 ≦ f1 / f2 ≦ −0.40 (6)
However,
f1: focal length of the first lens L1 f2: focal length of the second lens L2.

The imaging lens according to claim 3, wherein the following conditional expressions (7) and (8) are satisfied.
0.60 ≦ f3 / f ≦ 1.00 (7)
0.50 ≦ (R5 + R6) / (R5-R6) ≦ 3.40 (8)
However,
f: focal length of the entire lens system f3: focal length R5 of the third lens L3: radius of curvature of the object side surface of the third lens L3 R6: radius of curvature of the side surface of the image surface of the third lens L3.

The imaging lens according to claim 4, wherein the following conditional expressions (9) and (10) are satisfied.
−2.00 ≦ f4 / f ≦ −0.65 (9)
1.20 ≦ (R7 + R8) / (R7−R8) ≦ 4.00 (10)
However,
f: focal length of the entire lens system f4: focal length R7 of the fourth lens L4: radius of curvature of the object side surface of the fourth lens L4 R8: radius of curvature of the image side surface of the fourth lens L4.

According to the present invention, various aberrations are favorably corrected, particularly suitable for a small-sized image pickup device, an optical sensor, a portable module camera, a WEB camera and the like using an image pickup device such as a high pixel CCD or CMOS. The present invention provides an imaging lens having four optical lenses having optical characteristics, wide angle, small size, and bright Fno ≦ 2.2.

The figure which shows the structure of the imaging lens LA which concerns on one Embodiment of this invention. FIG. 3 is a diagram illustrating a configuration of a specific example 1 of the imaging lens LA. FIG. 3 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 1. FIG. 3 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 1. Field curvature and distortion diagram of imaging lens LA of Example 1 The figure which shows the structure of the specific Example 2 of the said imaging lens LA. FIG. 6 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 2. FIG. 6 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 2. Field curvature and distortion diagram of the imaging lens LA of Example 2 FIG. 6 is a diagram illustrating a configuration of a specific example 3 of the imaging lens LA. FIG. 10 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 3. FIG. 4 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 3. Field curvature and distortion diagram of the imaging lens LA of Example 3 The figure which shows the structure of the specific Example 4 of the said imaging lens LA. FIG. 6 is a spherical aberration (axial chromatic aberration) diagram of the imaging lens LA of Example 4. FIG. 7 is a chromatic aberration diagram of magnification of the imaging lens LA of Example 4. Field curvature and distortion diagram of the imaging lens LA of Example 4

An embodiment of an imaging lens according to the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an imaging lens according to an embodiment of the present invention. The imaging lens LA includes a four-lens lens system in which an aperture stop S1, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 are arranged from the object side to the image plane. ing. A glass flat plate GF is disposed between the fourth lens L4 and the image plane. As this glass flat plate GF, a glass having a function such as a cover glass, an IR cut filter, or a low-pass filter can be used. Further, the glass flat plate GF may not be disposed between the fourth lens L4 and the image plane.

By disposing the aperture stop S1 on the object side of the first lens L1, the entrance pupil position can be located far from the image plane. As a result, high telecentricity can be ensured, and the incident angle with respect to the image plane can be made suitable.

The first lens L1 is a lens having positive power, the second lens L2 is a lens having negative power, the third lens L3 is a lens having positive power, and the fourth lens has negative power. It is a lens that has. In order to reduce the size of the imaging lens LA, the lens power array is a positive, negative, positive, negative, so-called telefort type. Further, it is preferable that the entire surface of the four lenses has an aspherical shape in order to more appropriately correct various aberrations.

This imaging lens LA satisfies the following conditional expressions (1) to (5).
0.93 ≦ f1 / f ≦ 1.30 (1)
−3.00 ≦ f2 / f ≦ −1.90 (2)
−0.70 ≦ (R1 + R2) / (R1−R2) ≦ −0.10 (3)
−2.00 ≦ (R3 + R4) / (R3−R4) ≦ 2.00 (4)
30.00 ≦ f / d6 ≦ 65.00 (5)
However,
f: focal length of the entire lens system f1: focal length of the first lens L1 f2: focal length of the second lens L2 R1: radius of curvature of the object side surface of the first lens L1 R2: curvature of the image surface side surface of the first lens L1 Radius R3: Radius of curvature of the object side surface of the second lens L2 R4: Radius of curvature of the image surface side surface of the second lens L2 d6: Distance from the image surface side surface of the third lens L3 to the object side surface of the fourth lens L4.

Conditional expression (1) defines the positive power of the first lens L1. If the lower limit of conditional expression (1) is exceeded, it is advantageous for miniaturization, but the positive power of the first lens L1 becomes too strong, making it difficult to correct various aberrations. The positive power of the lens becomes too weak, making it difficult to reduce the size.

  Conditional expression (2) defines the negative power of the second lens L2. If the lower limit of conditional expression (2) is exceeded, the negative power of the second lens L2 becomes too weak, making it difficult to correct axial and off-axis chromatic aberrations. Since negative power becomes too strong, it becomes difficult to correct various aberrations, and fluctuation due to on-axis eccentricity of the second lens L2 due to higher-order aberrations becomes large, which is not preferable.

Conditional expression (3) defines the shape of the first lens L1. Outside the range of conditional expression (3), correction of higher-order aberrations such as spherical aberration becomes difficult with widening and miniaturization with Fno ≦ 2.2, which is not preferable.

Conditional expression (4) defines the shape of the second lens L2. Outside the range of conditional expression (4), it is not preferable because correction of on-axis and off-axis chromatic aberrations becomes difficult as the angle of widening with Fno ≦ 2.2 and downsizing are reduced.

Conditional expression (5) defines the ratio between the focal length f of the entire lens system and the distance d6 from the image surface side surface of the third lens L3 to the object side surface of the fourth lens L4. Outside the range of the conditional expression (5), various aberrations are favorably corrected, and wide angle and downsizing with Fno ≦ 2.2 are difficult, which is not preferable.

The first lens L1 is a lens having positive power, and the second lens L2 is a lens having negative power, and satisfies the following conditional expression (6).
−0.50 ≦ f1 / f2 ≦ −0.40 (6)
However,
f1: focal length of the first lens L1 f2: focal length of the second lens L2.

  Conditional expression (6) defines the ratio between the focal length of the first lens L1 and the focal length of the second lens L2. Outside the range of conditional expression (6), various aberrations are corrected favorably, and wide angle and downsizing with Fno ≦ 2.2 are difficult, which is not preferable.

The third lens L3 is a lens having positive power and satisfies the following conditional expressions (7) and (8).
0.60 ≦ f3 / f ≦ 1.00 (7)
0.50 ≦ (R5 + R6) / (R5-R6) ≦ 3.40 (8)
However,
f: focal length of the entire lens system f3: focal length R5 of the third lens L3: radius of curvature of the object side surface of the third lens L3 R6: radius of curvature of the side surface of the image surface of the third lens L3.

  Conditional expression (7) defines the positive power of the third lens L3. When the lower limit is exceeded, the positive power of the third lens L3 becomes too strong, and the fluctuation of the image plane due to axial decentering of the third lens L3 due to higher-order aberrations becomes undesirably large. Since the positive power of the lens L3 becomes too weak, it is difficult to reduce the size, which is not preferable.

  Conditional expression (8) defines the shape of the third lens L3. Outside the range of conditional expression (8), it is difficult to control the positive power of the third lens L3 with Fno ≦ 2.2, which makes it difficult to widen and reduce the size, which is not preferable.

The fourth lens L4 is a lens having negative power and satisfies the following conditional expressions (9) and (10).
−2.00 ≦ f4 / f ≦ −0.65 (9)
1.20 ≦ (R7 + R8) / (R7−R8) ≦ 4.00 (10)
However,
f: focal length of the entire lens system f4: focal length R7 of the fourth lens L4: radius of curvature of the object side surface of the fourth lens L4 R8: radius of curvature of the image side surface of the fourth lens L4.

Conditional expression (9) defines the negative power of the fourth lens L4. If the lower limit is exceeded, the negative power of the fourth lens L4 becomes too weak, making it difficult to correct off-axis chromatic aberration. This is not preferable because of a large fluctuation.

Conditional expression (10) defines the shape of the fourth lens L4. Outside the range of conditional expression (10), it becomes difficult to secure the distance (LB) from the image surface side surface to the image surface of the fourth lens L4, and wide angle and size reduction are satisfied when Fno ≦ 2.2. As a result, it becomes difficult to control the power of the fourth lens L4, and correction of off-axis chromatic aberration may be insufficient, which is not preferable.

When the four lenses constituting the imaging lens LA satisfy the above-described configuration and conditional expressions, respectively, a bright imaging lens having a wide angle, a small size, and Fno ≦ 2.2 can be obtained.

The imaging module using the imaging lens LA of the present invention is used for a portable module camera, a WEB camera, a personal computer, a digital camera, an optical sensor, a monitor, and the like of automobiles and various industrial devices.

Hereinafter, the imaging lens LA of the present invention will be described using examples. The symbols described in each example indicate the following. The unit of distance, radius and center thickness is mm.
f: focal length of imaging lens LA as a whole f1: focal length f2 of first lens L1: focal length f3 of second lens L2: focal length f3 of third lens L3: focal length Fno of fourth lens L4: F value 2ω : Full field angle S1: Aperture stop R: Radius of curvature of optical surface, in case of lens, central radius of curvature R1: Radius of curvature of object side surface of first lens L1 R2: Radius of curvature R3 of image side surface of first lens L1: Radius of curvature R4 of the object side surface of the second lens L2: radius of curvature R5 of the image side surface of the second lens L2: radius of curvature R6 of the object side surface of the third lens L3: radius of curvature R7 of the image side surface of the third lens L3: Curvature radius R8 of the object side surface of the fourth lens L4: Radius of curvature R9 of the image side surface of the fourth lens L4: Radius of curvature R10 of the object side surface of the glass flat plate GF: Radius of curvature d of the image side surface of the glass flat plate GF d: Lens radius During ~ Center thickness or inter-lens distance d0: distance from the aperture stop S1 to the object side surface of the first lens L1 d1: center thickness d2 of the first lens L1: object of the second lens L2 from the image surface side surface of the first lens L1 Distance d3 to the side surface: Center thickness d4 of the second lens L2: Distance from the image surface side surface of the second lens L2 to the object side surface of the third lens L3 d5: Center thickness d6 of the third lens L3: of the third lens L3 Distance d7 from the image side surface to the object side surface of the fourth lens L4: Center thickness d8 of the fourth lens L4: Distance d9 from the image surface side surface of the fourth lens L4 to the object side surface of the glass flat plate GF: Center of the glass flat plate GF Thickness d10: Distance from the image plane side surface of the glass plate GF to the image plane nd: d-line refractive index n1: d-line refractive index n2 of the first lens L1: d-line refractive index n3: second lens L2 3 lens L3 d line Folding index n4: d-line refractive index n5 of the fourth lens L4: d-line refractive index νd of the glass plate GF: d-line Abbe number ν1: Abbe number ν2 of the first lens L1: Abbe number of the second lens L2 ν3: Abbe number of the third lens L3 ν4: Abbe number of the fourth lens L4 ν5: Abbe number TTL of the glass plate GF: Distance from the aperture stop S1 to the image plane (optical length)
LB: Distance from the image surface side surface of the fourth lens L4 to the image surface (including the thickness of the glass flat plate GF)
IH: Image height

The aspherical shape of each lens surface of the first lens L1 to the fourth lens L4 of the imaging lens LA is such that y is an optical axis with the traveling direction of light as positive and x is a direction orthogonal to the optical axis. The following aspheric polynomial is used.

y = (x ² / R) / [1+ {1- (K + 1) (x ² / R ² )} ^1/2 ]
+ A4x ⁴ + A6x ⁶ + A8x ⁸ + A10x ¹⁰ + A12x ¹² + A14x ¹⁴ + A16x ¹⁶ (11)

  However, R is a radius of curvature on the optical axis, k is a conical coefficient, and A4, A6, A8, A10, A12, A14, and A16 are aspherical coefficients.

  As an aspheric surface of each lens surface, an aspheric surface represented by Expression (11) is used for convenience. However, the present invention is not particularly limited to the aspheric polynomial of the formula (11).

Example 1
FIG. 2 shows the configuration of the imaging lens LA of the first embodiment. The curvature radius R on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 1, the lens center thickness or inter-lens distance d, the refractive index nd, and the Abbe number ν are set. Table 1 shows the conic coefficient k and the aspheric coefficient.

Table 9 which will appear later shows values corresponding to the values defined in Examples 1 to 4 and the parameters defined by the conditional expressions (1) to (10). The imaging lens LA of Example 1 satisfies the conditional expressions (1) to (10) as shown in the table.

  The spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 1 is shown in FIG. 3, the lateral chromatic aberration is shown in FIG. 4, and the field curvature and distortion are shown in FIG. Note that S of the field curvature in FIG. 5 is the field curvature with respect to the sagittal image plane, and T is the field curvature with respect to the tangential image plane. The same applies to the second to fourth embodiments. The imaging lens LA of Example 1 is 2ω = 91.7 °, TTL = 2.720 mm, wide-angle, compact, and bright with Fno = 2.00, and has good optical characteristics as shown in FIGS. It can be seen that

(Example 2)
FIG. 6 shows the configuration of the imaging lens LA of the second embodiment. The curvature radius R on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 2, the lens center thickness or the inter-lens distance d, the refractive index nd, and the Abbe number ν are set. Table 3 shows the conic coefficient k and the aspheric coefficient.

  As shown in Table 9, Example 2 satisfies the conditional expressions (1) to (10).

The spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 2 is shown in FIG. 7, the lateral chromatic aberration is shown in FIG. 8, and the field curvature and distortion are shown in FIG. The imaging lens LA of Example 2 is 2ω = 76.0 °, TTL = 2.732 mm, wide-angle, compact, and bright with Fno = 2.06, and has good optical characteristics as shown in FIGS. It can be seen that

(Example 3)
FIG. 10 shows the configuration of the imaging lens LA of Example 3. The curvature radius R on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 3, the lens center thickness or the inter-lens distance d, the refractive index nd, and the Abbe number ν are set. Table 5 shows the cone coefficient k and the aspheric coefficient.

As shown in Table 9, Example 3 satisfies the conditional expressions (1) to (10).

The spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 3 is shown in FIG. 11, the lateral chromatic aberration is shown in FIG. 12, and the field curvature and distortion are shown in FIG. The imaging lens LA of Example 3 is 2ω = 76.2 °, TTL = 2.735 mm, wide-angle, compact, and bright with Fno = 2.20, and has good optical characteristics as shown in FIGS. It can be seen that

Example 4
FIG. 14 illustrates a configuration of the imaging lens LA of the fourth embodiment. The curvature radius R on the object side and the image plane side of each of the first lens L1 to the fourth lens L4 constituting the imaging lens LA of Example 4, the lens center thickness or the inter-lens distance d, the refractive index nd, and the Abbe number ν are set. Table 8 shows the conical coefficient k and the aspheric coefficient.

As shown in Table 9, Example 4 satisfies the conditional expressions (1) to (10).

The spherical aberration (axial chromatic aberration) of the imaging lens LA of Example 4 is shown in FIG. 15, the lateral chromatic aberration is shown in FIG. 16, and the curvature of field and distortion are shown in FIG. The imaging lens LA of Example 4 is 2ω = 90.9 °, TTL = 2.775 mm, wide-angle, compact, and bright with Fno = 2.00, and has good optical characteristics as shown in FIGS. It can be seen that

Table 9 shows values corresponding to various values of the numerical examples and parameters defined by the conditional expressions (1) to (10). The various value units shown in Table 11 are 2ω (°), f (mm), f1 (mm), f2 (mm), f3 (mm), f4 (mm), TTL (mm), LB (mm). , IH (mm).

LA: Imaging lens LA
S1: aperture stop L1: first lens L2: second lens L3: third lens L4: fourth lens GF: glass flat plate R1: radius of curvature R2 of the object side surface of the first lens L1: image surface side surface of the first lens L1 Radius of curvature R3: radius of curvature R4 of the object side surface of the second lens L2: radius of curvature R5 of the side surface of the image surface of the second lens L2: radius of curvature R6 of the object side surface of the third lens L3: side surface of the image surface of the third lens L3 Radius of curvature R7: radius of curvature of the object side surface of the fourth lens L4 R8: radius of curvature of the image side surface of the fourth lens L4 R9: radius of curvature R10 of the object side surface of the glass flat plate GF: curvature of the image side surface of the glass flat plate GF Radius d0: Distance from aperture stop S1 to object side surface of first lens L1: Center thickness d2 of first lens L1: Distance d3 from image surface side surface of first lens L1 to object side surface of second lens L2 Center thickness d4 of the second lens L2: Distance from the image side surface of the second lens L2 to the object side surface of the third lens L3 d5: Center thickness d6 of the third lens L3: Fourth from the image side surface of the third lens L3 Distance d7 to the object side surface of the lens L4: Center thickness d8 of the fourth lens L4: Distance d9 from the image surface side surface of the fourth lens L4 to the object side surface of the glass plate GF d: Center thickness d10 of the glass plate GF: Glass plate GF The distance from the image plane side to the image plane

Claims (4)

In order from the object side, an aperture stop (S1), a positive power first lens (L1), a negative power second lens (L2), a positive power third lens (L3), and a negative power fourth lens (L4) And an imaging lens that satisfies the following conditional expressions (1) to (5):
0.93 ≦ f1 / f ≦ 1.30 (1)
−3.00 ≦ f2 / f ≦ −1.90 (2)
−0.70 ≦ (R1 + R2) / (R1−R2) ≦ −0.10 (3)
−2.00 ≦ (R3 + R4) / (R3−R4) ≦ 2.00 (4)
30.00 ≦ f / d6 ≦ 65.00 (5)
However,
f: focal length of the entire lens system f1: focal length of the first lens L1 f2: focal length of the second lens L2 R1: radius of curvature of the object side surface of the first lens L1 R2: curvature of the image surface side surface of the first lens L1 Radius R3: Radius of curvature of the object side surface of the second lens L2 R4: Radius of curvature of the image surface side surface of the second lens L2 d6: Distance from the image surface side surface of the third lens L3 to the object side surface of the fourth lens L4. The imaging lens according to claim 1, wherein the following conditional expression (6) is satisfied.
−0.50 ≦ f1 / f2 ≦ −0.40 (6)
However,
f1: focal length of the first lens L1 f2: focal length of the second lens L2. The imaging lens according to claim 1, wherein the following conditional expressions (7) and (8) are satisfied.
0.60 ≦ f3 / f ≦ 1.00 (7)
0.50 ≦ (R5 + R6) / (R5-R6) ≦ 3.40 (8)
However,
f: focal length of the entire lens system f3: focal length R5 of the third lens L3: radius of curvature of the object side surface of the third lens L3 R6: radius of curvature of the side surface of the image surface of the third lens L3. The imaging lens according to claim 1, wherein the following conditional expressions (9) and (10) are satisfied.
−2.00 ≦ f4 / f ≦ −0.65 (9)
1.20 ≦ (R7 + R8) / (R7−R8) ≦ 4.00 (10)
However,
f: focal length of the entire lens system f4: focal length R7 of the fourth lens L4: radius of curvature of the object side surface of the fourth lens L4 R8: radius of curvature of the image side surface of the fourth lens L4.

Images