JP2005128273A - Meniscus lens and optical system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a meniscus lens capable of miniaturizing a super wide angle imaging optical system having a field angle of 120° or more, to provide an optical system using the meniscus lens and to provide a composition which does not darken a surrounding part in image-formation in the optical system. <P>SOLUTION: A sagittal depth 1 of a concave 12 of the image side of a meniscus concave lens 10 is made deeper than an opening r of the concave 12. Further, the meniscus concave lens 10 thus formed is arranged on the object side, a biconvex lens 20 is arranged on the image side and, thereby, the super wide angle optical system 1 having a field angle of 120° or more is composed of two sheets of lenses. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wide-angle meniscus lens and an optical system using the meniscus lens.

  As an objective lens for an image sensor such as a CCD or CMOS, there is a high demand for a small and wide-angle imaging lens. However, since the conventional wide-angle imaging lens system is composed of seven or more spherical glass lenses, the size of the optical system in the optical axis direction cannot be shortened due to the large number of lenses, and the size is reduced. It was difficult to meet the demands.

  On the other hand, in recent years, by using an aspherical lens made of glass mold or plastic, the number of lenses constituting the optical system is reduced to two and a diffraction effect is exerted on the surfaces of the lenses constituting the optical system. An optical system capable of correcting chromatic aberration without increasing the number of lenses has been devised (for example, Patent Documents 1 and 2).

Also, as shown in FIG. 8, from the object side toward the CCD image plane 207, the two aspheric lenses 201 and 202 as the front group, the one lens 203 as the rear group, the stop 204, the color By arranging the erasing diffraction grating 205 and the cover glass 206 in this order, an ultra wide-angle imaging optical system 200 having an angle of view of 120 ° or more is devised while reducing the number of lenses to three. ing.
JP-A-10-115777 (FIGS. 9-10) JP 2000-28913 A (FIG. 9)

  However, the angle of view of the imaging lens described in Patent Documents 1 and 2 in which the number of lenses is reduced to two is about 38 ° to 67 °, and an ultra wide-angle imaging lens having an angle of view of 120 ° or more is Not proposed.

  Further, since the imaging optical system 200 shown in FIG. 8 uses two aspheric lenses 201 and 202 in the front group, there is a problem in that it is not necessarily downsized as a whole. Furthermore, since the stop 204 is positioned on the image side of the rear group lens 203, the exit pupil distance is short, and as a result, the incident angle to the sensor peripheral portion including the CCD 207 is large, and therefore the peripheral portion of the imaging is darkened. There is a problem.

  In view of the above problems, an object of the present invention is to provide a meniscus lens capable of reducing the size of an ultra-wide-angle imaging optical system having an angle of view of 120 ° or more, and an optical system using the meniscus lens. It is to propose. Another object of the present invention is to propose a configuration in which the peripheral portion of the image is not darkened in this optical system.

  In order to solve the above problems, the present invention provides a meniscus lens in which a convex surface is formed on one surface and a concave surface is formed on the other surface. It is characterized by being larger.

  When the meniscus lens to which the present invention is applied is used as a meniscus concave lens having a concave power, from the two lenses of the meniscus concave lens and a biconvex lens having a convex power disposed on the image side with respect to the meniscus concave lens, An ultra-wide-angle optical system, for example, an optical system having an angle of view of 120 ° or more can be configured.

  In the present invention, it is preferable to dispose a diaphragm between the meniscus concave lens and the convex lens. With this configuration, since the exit pupil distance can be increased, the light incident angle on the imaging plane can be reduced, and therefore the peripheral portion of the imaging is not darkened.

  In the present invention, it is preferable that a positive diffraction grating is formed on the image side surface of the convex lens. With this configuration, it is not necessary to dispose a lens group for achromaticity in the rear group, so that axial chromatic aberration and lateral chromatic aberration can be corrected without increasing the number of lenses. Both improvements can be achieved. In addition, the diffraction effect reduces the focus shift between visible light and near infrared light, so that image performance can be improved.

  In the present invention, the sagittal depth of the concave surface of the meniscus lens is larger than the radius of the opening of the concave surface, so that the field of view is wide. In addition, the imaging performance is excellent. Accordingly, since the front lens group can be constituted by this single lens, the optical system can be constituted by two lenses by arranging a convex lens on the image side of the meniscus lens. Therefore, the dimension of the optical system in the optical axis direction can be shortened, and the optical system can be downsized. For example, the distance from the lens tip to the imaging plane can be reduced to 10 mm or less. Further, since the sagittal depth of the concave surface of the meniscus lens is considerably deep, it is possible to configure an ultra-wide-angle optical system having an angle of view of 120 ° or more. Furthermore, it is possible to realize an optical system having excellent imaging performance and low distortion. For example, a TV distortion rate of 10% can be realized.

  With reference to the drawings, a meniscus lens of the present invention and an optical system for super wide-angle imaging using the meniscus lens will be described.

[Embodiment 1]
FIG. 1 and FIG. 2 are a configuration diagram of an imaging optical system according to Embodiment 1 of the present invention, and a cross-sectional view showing a specific configuration of this optical system. 3 and 4 are a sectional view of a meniscus concave lens used in the optical system shown in FIGS. 1 and 2 and a sectional view of a biconvex lens. FIG. 5 is a graph showing the spherical aberration, astigmatism, and distortion of the optical system shown in FIGS.

  In FIG. 1, an optical system 1 of this embodiment is an optical system for super wide-angle imaging used for a 1/4 inch CCD, and is composed of two lenses. That is, the meniscus concave lens 10, the stop 30, the biconvex lens 20, and the cover glass 40 as the front group are arranged in this order from the object side toward the image forming surface 50 of the CCD. The positive diffraction grating 25 is formed.

  The optical system 1 of this embodiment has Fno / 2.4, f = 1.14, and the angle of view is 140 °. Therefore, it has a wide field of view sufficient for use in a vehicle-mounted monitoring device.

  In configuring such an optical system 1, for example, as shown in FIG. 2, the meniscus concave lens 10, the diaphragm 30, and the biconvex lens 20 are arranged in this order from the object side to the image side with respect to the lens frame 60. It is installed.

  The lens frame 60 includes a flat small-diameter cylindrical portion 61 and a large-diameter annular flange 62 formed on the object side (opening side) of the cylindrical portion 61. A small-diameter opening 65 is formed in the bottom surface 61 a of the cylindrical portion 61.

  First, the biconvex lens 20 is inserted into the cylindrical portion 61, and is positioned and fixed in a state where the end surface 26a and the bottom surface 61a of the flange 26 formed on the outer peripheral portion are in contact with each other. The small-diameter opening 65 is formed at a position facing the convex surface 22 on which the diffraction grating 25 is formed, and the small-diameter opening 65 has a size that does not interfere with light that has passed through the convex lens 20.

  Next, the diaphragm 30 is inserted into the cylindrical portion 61. A thick portion 32 having a shape that does not interfere with the light incident on the stop 30 is formed on the outer periphery of the aperture 31 of the stop 30, and an end surface 32 a on the image side of the thick portion 32 and the flange 26 of the biconvex lens 20. The diaphragm 30 is positioned and fixed in a state in which the distance from the convex surface 21 is adjusted by contacting the end surface 26b on the object side.

  An annular step portion 63 is formed on the flange surface 62 a of the annular flange 62. Further, an outer peripheral wall 64 that rises toward the object side in the axial direction of the lens frame 60 is formed on the outer peripheral edge of the flange surface 62a. The meniscus concave lens 10 has the edge portion of the annular end surface 13 fitted into the stepped portion 63, and the stepped portion 15 is pressed by an annular lens retainer 70 having an outer peripheral surface fitted to the inner peripheral surface of the outer peripheral wall 64. It is fixed to the annular flange 62.

(Configuration of meniscus concave lens)
The meniscus concave lens 10 used in the optical system 1 of this embodiment is made of a resin molded product. As shown in FIG. 3, an aspherical convex surface 11 is formed on the object side, and an aspherical concave surface 12 is formed on the image side. Is formed.

  In the meniscus concave lens 10, the sagittal depth l of the concave surface 12 is 2.719 mm, which is deeper than 1.6115 mm, which is the radius r of the opening of the concave surface 12.

  A step 15 is formed on the outer peripheral edge of the convex surface 11 to which the lens retainer 70 abuts when the meniscus concave lens 10 is fixed to the lens frame 60 (see FIG. 2). Moreover, the annular surface 13 of the outer part of the opening part of the concave surface 12 is formed flat.

Detailed data of each lens surface of the meniscus concave lens 10 are as follows. Object-side convex surface 11: aspherical surface R = 3.4845
K = −2.087647
Image-side concave surface 12: aspherical surface R = 0.9205
K = -0.6737657
Coeff on r4 -0.0108761
Coeff on r6 0.00257030
Coeff on r8 -1.46910e-4
Coeff on r10 -1.63642e-4
As shown in

(Configuration of biconvex lens)
The biconvex lens 20 used in the first embodiment is also made of a resin molded product. As shown in FIG. 4, a spherical convex surface 21 is formed on the object side, and an aspheric convex surface 22 is formed on the image side. Has been.

  In the biconvex lens 20, a positive diffraction grating 25 composed of a number of concentric steps is formed on the aspherical convex surface 22 located on the image side. A flange 26 is formed on the outer peripheral portions of the convex surfaces 21 and 22 to be used for positioning and fixing when the biconvex lens 20 is mounted on the lens frame 60 (see FIG. 2).

Detailed data of each lens surface of the biconvex lens 20 is as follows. Object-side convex surface 21: spherical surface R = 2.0312
Image-side convex surface 22: aspheric surface R = −2.2157
K = -21.17862
Coeff on r4 -0.11382
Coeff on r6 0.125493
Coeff on r8 -0.0443963
Coeff on r10 9.75092e-3
Diffraction grating φ = −50ρ ²
As shown in

(Details of optical system 1)
Table 1 shows data of each surface in the optical system 1 of the present embodiment. FIG. 5 shows the spherical aberration, astigmatism, and distortion rate of the optical system of this embodiment. In the table, each surface of each optical element is the following convex surface 11 on the object side of the meniscus lens 10 first surface concave surface 12 on the image side of the meniscus lens 10 second surface diaphragm 30 third surface convex surface on the object side of the biconvex lens 20 21 4th surface Image-side convex surface 22 of biconvex lens 20 5th surface Incident surface 41 of cover glass 40 6th surface Outgoing surface 42 of cover glass 40 It calls like the 7th surface. Further, the interval is the distance (mm) between the surface and the next surface.

(Effect of this embodiment)
As described above, in this embodiment, the sagittal depth l of the concave surface 12 on the image side of the meniscus concave lens 10 is made deeper than the radius r of the opening of the concave surface 12, thereby having a wide field of view and a low distortion meniscus concave lens. Is realized. For this reason, the super wide-angle optical system 1 having a field angle of 120 ° or more can be configured by the two lenses of the meniscus concave lens 10 and the biconvex lens 20. Therefore, according to the present embodiment, the size in the optical axis direction of the optical system 1 can be shortened as the number of lenses is small, so that the super wide-angle imaging lens can be miniaturized.

  Further, since the positive diffraction grating 25 is formed on the image side surface 22 of the biconvex lens 20 constituting the rear group, chromatic aberration can be suppressed without increasing the number of lenses.

  Further, since the aperture stop 30 is disposed between the meniscus lens 10 and the biconvex lens 20, an optical system in which the exit pupil distance is increased, the light incident angle on the imaging surface is reduced, and the peripheral portion of the imaging is bright. It is 1.

  Here, Table 2 shows a comparison between the optical system 1 of this embodiment and the conventional three-lens super-wide-angle optical system 200 shown in FIG. Here, the optical system 200 is designed as an imaging lens for a 1/4 inch CCD so that it can be compared with the optical system 1 of the present embodiment.

[Embodiment 2]
In the optical system 1 according to the second embodiment of the present invention, the arrangement of the meniscus concave lens 10, the diaphragm 30, the biconvex lens 20, the cover glass 40, and the imaging plane 50 constituting the same is the same as in the first embodiment. Only the surface data and the distance between each surface is different. Therefore, although description of a common part is abbreviate | omitted, the characteristic is Fno / 2.4, f = 1.14, and an angle of view is 138 degrees.

In constructing such an optical system, in this embodiment, each lens surface is represented by one surface: an aspherical surface K = −2.0130.
Two surfaces: aspherical surface K = −0.63544
4th surface: spherical surface 5th surface: aspherical surface K = -40.90
Coeff on r4 -0.1042
Coeff on r6 0.1336
Coeff on r8 -0.06060
Coeff on r10 0.01527
Diffraction grating φ = −55.5ρ ²
As shown in FIG.

  Table 3 shows data of each surface in the optical system according to the second embodiment. FIG. 6 shows spherical aberration, astigmatism, and distortion of the optical system according to Embodiment 2.

  Even in this configuration, the sagittal depth l of the concave surface 12 on the image side of the meniscus concave lens 10 is deeper than the opening r of the concave surface 12, so that the meniscus has a wide field of view and low distortion. A concave lens is realized. For this reason, the super wide-angle optical system 1 having an angle of view of 120 ° or more can be configured by the two lenses of the meniscus concave lens 10 and the biconvex lens 20, and the same effects as in the first embodiment can be obtained. .

[Embodiment 3]
In the optical system 1 according to the third embodiment of the present invention, the arrangement of the meniscus concave lens 10, the diaphragm 30, the biconvex lens 20, the cover glass 40, and the imaging plane 50 constituting the same is the same as in the first embodiment. Only the surface data and the distance between each surface is different. Therefore, although description of a common part is abbreviate | omitted, the characteristic is Fno / 2.8, f = 1.3, and an angle of view is 128 degrees.

In constructing such an optical system, in this embodiment, each lens surface is represented by one surface: an aspherical surface K = -1.742.
Two surfaces: aspherical surface K = −0.6744
4th surface: spherical surface 5th surface: aspherical surface K = -19.124
Coeff on r4 -0.0857
Coeff on r6 0.1126
Coeff on r8 -0.03664
Coeff on r10 0.006636
Diffraction grating φ = −16ρ ² −12.7ρ ⁴
As shown in FIG.

  Table 4 shows data of each surface in the optical system according to the third embodiment. FIG. 7 shows spherical aberration, astigmatism, and distortion of the optical system according to Embodiment 2.

  Even in this configuration, the sagittal depth l of the concave surface 12 on the image side of the meniscus concave lens 10 is deeper than the opening r of the concave surface 12, so that the meniscus has a wide field of view and low distortion. A concave lens is realized. For this reason, the super wide-angle optical system 1 having an angle of view of 120 ° or more can be configured by the two lenses of the meniscus concave lens 10 and the biconvex lens 20, and the same effects as in the first embodiment can be obtained. .

  In the present invention, the sagittal depth of the concave surface of the meniscus lens is larger than the radius of the opening of the concave surface, so that the field of view is wide. Accordingly, since the front lens group can be constituted by this single lens, the optical system can be constituted by two lenses by arranging a convex lens on the image side of the meniscus lens. Therefore, the dimension of the optical system in the optical axis direction can be shortened, and the optical system can be downsized. Further, since the sagittal depth of the concave surface of the meniscus lens is considerably deep, it is possible to configure an ultra-wide-angle optical system having an angle of view of 120 ° or more.

It is a block diagram of the optical system for imaging which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the specific structure of the optical system for imaging which concerns on Embodiment 1 of this invention. It is sectional drawing of the meniscus concave lens used for the optical system shown to FIG. 1 and FIG. It is sectional drawing of the biconvex lens used for the optical system shown to FIG. 1 and FIG. 6 is a graph showing spherical aberration, astigmatism, and distortion of the optical system for super wide-angle imaging according to Embodiment 1 of the present invention. It is a graph which shows the system spherical aberration, astigmatism, and distortion of the optical for super wide angle imaging which concerns on Embodiment 2 of this invention. It is a graph which shows the spherical aberration, the astigmatism, and the distortion of the optical system for super wide-angle imaging according to Embodiment 3 of the present invention. It is a block diagram of the conventional optical system for super wide angle imaging.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical system 10 Meniscus concave lens 20 Biconvex lens 25 Diffraction grating 30 Diaphragm 40 Cover glass 50 CCD imaging surface

Claims (5)

In a meniscus lens in which a convex surface is formed on one surface and a concave surface is formed on the other surface,
The meniscus lens is characterized in that the sagittal depth of the concave surface is larger than the radius of the opening of the concave surface. An optical system using the meniscus lens according to claim 1 as a meniscus concave lens having concave power,
An optical system comprising: the meniscus concave lens and a convex lens disposed on the image side with respect to the meniscus concave lens. In claim 2,
An optical system, wherein a diaphragm is disposed between the meniscus concave lens and the convex lens.   4. The optical system according to claim 2, wherein the angle of view is 120 ° or more.   5. The optical system according to claim 2, wherein a positive diffraction grating is formed on an image side surface of the convex lens.

Images