WO2005101084A1 - Fixed-focus lens - Google Patents

Abstract

A fixed-focus lens (200) capable of removing chromatic aberration without enlarging the dimension in the direction of optical axis comprising a first lens (10) of resin molding, a diaphragm (50), and a second lens (20) of resin molding arranged in this order. A diffraction grating (B) for removing chromatic aberration on and off the axis is formed on the incident surface of the second lens (20) on the side of the diaphragm (50). The diffraction grating (B) has a circular concentric blaze shape wherein the level difference of the blaze shape is 2 μm or less and the pitch is 10 μm or above. Consequently, primary diffraction efficiency is high in the entire visible wavelength region.

Description

 Specification

 Fixed focus lens

 Technical field

 The present invention relates to a small fixed-focus lens that can be mounted on a camera-equipped mobile phone or a digital camera. More specifically, the present invention relates to a technique for eliminating chromatic aberration. Background art

 [0002] While digital cameras have become widespread, the number of models equipped with a digital camera in a mobile phone has rapidly increased, and there is a sign that a mobile phone with a camera will be standardized. Therefore, the market power is required to have higher definition, that is, an increase in the number of pixels, and the demand for thinner is also increasing. These features are one of the added values of mobile phones and the like. It is becoming.

 [0003] Here, in a fixed focus lens used for a camera, since white light is targeted, on-axis and off-axis chromatic aberrations become a problem. Therefore, in a conventional fixed focus lens, a combination of convex and concave refraction lenses is used.

 Disclosure of the invention

 Problems to be solved by the invention

[0004] A digital camera for a mobile phone is always required to be thinner in terms of space, and even with a fixed-focus lens for a high number of pixels, the number of lenses is reduced as much as possible. It is necessary to shorten the overall length. However, if the chromatic aberration is eliminated by combining the convex and concave type refracting lenses as in the related art, there is a problem that V cannot be shortened. Another problem is that the weight of the digital camera cannot be reduced.

 [0005] In view of the above problems, the fixed focus lens system employs a method that has never been adopted so far, thereby eliminating the chromatic aberration without enlarging the dimension in the optical axis direction. It is to propose a focusing lens.

 Means for solving the problem

In order to solve the above problems, according to the present invention, in a fixed focus lens in which a plurality of lenses are arranged in a lens axis direction, at least one of the plurality of lenses has chromatic aberration. Characterized in that a diffraction grating for removing the light is formed.

In the present invention, since a diffraction grating for removing chromatic aberration is formed on the lens surface of the lens constituting the fixed focus lens, it is necessary to remove chromatic aberration by combining a convex type and a concave type refractive lens. Absent. Therefore, the number of lenses can be reduced. Further, since the diffraction grating is formed on the lens surface, it is not necessary to arrange the diffraction grating between the lenses. Therefore, the dimension of the fixed focus lens in the optical axis direction can be reduced.

[0008] In the present invention, the diffraction grating is a blaze grating. With this configuration, high V and diffraction efficiency can be obtained over the entire visible wavelength range, and chromatic aberration can be effectively removed.

In the present invention, it is preferable that the diffraction grating has a first-order diffraction order. With this configuration, high diffraction efficiency can be obtained over the entire visible wavelength range, and chromatic aberration can be efficiently removed.

 In the present invention, it is preferable that the blazed grating has a step of 2 μm or less and a pitch of 1 μμηι or more. If the step is 2 / zm or less, it is possible to suppress a decrease in diffraction efficiency due to the step. When the pitch is 10 / zm or more, generation of unnecessary orders of diffracted light can be suppressed. In addition, with the blazed grating, mold production and resin molding can be performed efficiently, and high dimensional accuracy can be ensured.

 [0011] In the present invention, when a stop is arranged so as to be sandwiched between the two lenses, the diffraction grating is formed on a lens located on the object side with respect to the stop to reduce axial chromatic aberration. Remove. In other words, when axial chromatic aberration is generated without forming a diffraction grating, it is preferable to form a diffraction grating on a lens located on the object side with respect to the diaphragm to efficiently remove axial chromatic aberration. .

 In the present invention, when a stop is arranged so as to be sandwiched between the two lenses, the diffraction grating is formed on a lens located on the image side with respect to the stop, so that axial chromatic aberration and axial chromatic aberration are reduced. Alternatively, a configuration in which off-axis chromatic aberration is removed may be employed. In other words, if a diffraction grating is not formed, and if axial chromatic aberration and off-axis chromatic aberration occur in the state V, the diffraction grating is formed on the lens located on the image side with respect to the stop, and the axial chromatic aberration is formed. It is preferable to efficiently remove off-axis chromatic aberration.

In the present invention, the diffraction grating is one of two lenses sandwiching the stop. It is preferable to be formed into a lens! / ,.

In this case, it is preferable that the diffraction grating is formed on a lens surface facing the stop. With this configuration, chromatic aberration can be efficiently removed.

In the present invention, it is preferable that, of the plurality of lenses, the lens on which the diffraction grating is formed is a resin molded product. In the case of glass molding, it is necessary to fabricate a mold by processing it into a super hard material. However, in the case of resin molding, the mold can be produced at low cost by processing a normal Ni-P plating layer.

[0016] In the present invention, it is preferable that the number of the plurality of lenses is four or less, preferably two or three. As described above, if the number of lenses is smaller than that of a normal focus lens, the size of the fixed focus lens in the optical axis direction can be significantly reduced.

 Brief Description of Drawings

FIG. 1 is a configuration diagram of a fixed focus lens according to Embodiment 1 of the present invention.

 FIG. 2 is a graph showing lens performance (spherical aberration, astigmatism, distortion) of the fixed focus lens according to FIG. 1.

 FIG. 3 is a configuration diagram of a fixed focus lens according to Embodiment 2 of the present invention.

 FIG. 4 is a graph showing lens performance (spherical aberration, astigmatism, distortion) of the fixed focus lens according to FIG. 3.

 Explanation of symbols

[0018] 10 First lens

 20 Second lens

 30 Third lens

 50 aperture

 100, 200 fixed focus lens

 A, B diffraction grating

 BEST MODE FOR CARRYING OUT THE INVENTION

A fixed focus type fixed focus lens to which the present invention is applied will be described with reference to the drawings.

[Embodiment 1] FIG. 1 is a configuration diagram of a fixed focus lens of a fixed focus type for a digital camera for a mobile phone or a small digital camera according to Embodiment 1 of the present invention. FIG. 2 is a graph showing the spherical aberration, astigmatism, and distortion of the fixed focus lens of the present embodiment.

 As shown in FIG. 1, the fixed focus lens 100 of the present embodiment is composed of three lenses. That is, a first lens 10 made of a resin molded product, a second lens 20 made of a resin molded product, and a third lens 30 made of a resin molded product are directed from the object side toward the imaging surface 80. In this order, a power glass 70 is arranged on the image forming surface 80 side of the third lens 30. Further, an aperture 50 is arranged between the first lens 10 and the second lens 20.

 In the present embodiment, each surface of each optical element is referred to as shown below. Therefore, the object is located on the entrance surface side of the first lens 10 and the image is located on the exit surface side of the third lens 30.

 [0023]

 First lens 1 0 incident surface 1st surface 1

 Exit surface of first lens 10 Second surface 2

 Aperture 5 0 3rd surface 3

 Second lens 20 incident surface 4th surface 4

 Outgoing surface of second lens 20 Fifth surface 5

 Third lens 30 entrance surface 6th surface 6

 Emission surface of third lens 30 Seventh surface 7

 Cover glass 7 0 incident surface 8th surface 8

 Exit surface of cover glass 70 9th surface 9

In the focus lens 100 configured as described above, each surface is designed as described below. In the design data 2, K, Α4, Α6, Α8, Α10, and A12 indicate aspheric coefficients, and Ρ2 indicates the square coefficient of the optical path difference function. The additional amount of the optical path length due to the diffractive lens structure is given by the optical path difference function φ (h ) is, φ (h) = (P h 2 + P h 4 + P h 6 + - ·) is defined by chi lambda, set

 2 4 6

Total data 2 shows the squared coefficient. Design data l

 Radius of curvature Surface spacing

Object infinity infinity

Front 1 1 1.577 281 0.93 509

Side 2 2 13.73688 0.102979

3rd page 3 Infinity 0.473139

4th '4-1-1. 34098 1.019013

5th page 5 1 0.96554 0.2

6th 6 5.0888317 0.5

Side 7 7 1-231809 0.7

8th page 8 Infinity 0.55

9th page 9 Infinity 0.065

Statue infinity 0

Design data 2

First side 1 Second side 2

 Κ 0 Κ

 Α4 — 0.00674 A4 — 0.04 7 34

A 6 0.000 677 A6 0 00 5 4 87

A8 0. 00066 A8 0 .3 7 3 97

A 1 0 1 0.01163 A 1 0 0 8 1 3 8 14

A 1 2 1 0.0005 A 1 2 0 .5 7 9 8 1

P 2 0 P 2 ― 2 0.9 7 36 4th surface 4 5th surface 5

 K 0 K ― 1

 A4 ― 0 .1 1128 A4 0 06 3 7 5 9

Λ 6 ― 0. 33 496 Λ 6 ― 0. 1 2 1 0 7

A 8 0 793502 A8 0 13 4 2 6 2

A 1 0 ― 0 .20327 A 1 0 0 00 2 5 5 7

A 1 2 ― 1.2 22443 A 1 2 ― 0.

P 2 0 P 2 0 6th surface 6 7th surface 7

 K 0 ― 6. 9 5 3 4

A4 ― 0.224 276 A4 0.12 2 94

A 6 0 1 3054 A6 0 04 8 9 57

A8 0 .02872 A8 0 .0 1 8 2

A 1 0 ― 0 .00 166 A 1 0 0 00 4 8 78

A 1 2 0 000 605 A 1 2 ― 0. 0 0 0 66

P 2 0 P 2 0 As described above, in the present embodiment, a diffraction grating A for removing axial chromatic aberration is formed on the exit surface (second surface 2) of the first lens 10 located on the side of the stop 50. The diffraction grating A eliminates axial chromatic aberration that has occurred without using it. Here, the diffraction grating A has a concentric blaze shape, the step of the blaze shape is 2 / zm or less, and the pitch is 10 / zm or more. High folding efficiency. Note that setting a step with reference to the approximate center wavelength of the visible wavelength contained in the target white light to obtain a high first-order diffraction efficiency corresponds to the step of 1.1 to 1. Therefore, a step of at least 1,6 / zm is sufficient, and in this embodiment, the step can be increased by 2 / z in order to increase the power over the entire visible wavelength range and to prevent the step from becoming unnecessarily high. Set to zm or less.

 In the focus lens 100 configured as described above, the spherical aberrations at the wavelengths of 436 nm, 476 nm, 567 nm, 597 nm, and 656 nm are shown by solid lines L11 to L15 in FIG. 2, and astigmatism is shown by the solid lines L21 to L15. As shown by L25 and dotted lines L31 to L35, and the distortion factor is shown by solid lines L41 to L45, as a fixed focal length lens system of a fixed focus type for digital cameras for mobile phones of about 3 megapixels and small digital cameras. The axial chromatic aberration has been improved to a level sufficient for the measurement.

 As described above, in the present embodiment, since the diffraction grating A for removing chromatic aberration is formed on the lens surface (second surface 2) of the first lens constituting the fixed focus lens 100, There is no need to remove chromatic aberration by combining a concave and a refractive lens. Therefore, the number of lenses can be reduced. Further, since the diffraction grating A is formed on the lens surface, it is not necessary to arrange the diffraction grating between the lenses. Therefore, since the fixed focus lens 100 can be composed of only three lenses 10 to 30, the dimension of the fixed focus lens 100 in the optical axis direction can be greatly reduced to 5 mm to 5.5 mm.

 Since the number of lenses is small and all the lenses 10 to 30 are made of resin molding, the weight of the focusing lens 100 can be reduced, and a digital camera for mobile phones or a small digital camera can be used. It is suitable for use as a fixed focus type fixed focus lens system for cameras.

[0030] Further, since the diffraction grating A is formed in a blaze shape and has a V, the diffraction grating A is high in the entire visible wavelength range. Since the second diffraction efficiency is obtained, chromatic aberration can be efficiently removed. In addition, the step size of the blaze shape of the diffraction grating A is 2 μm or less and the grating pitch is 10 μm or more, so that mold production and resin molding can be performed efficiently and high dimensional accuracy is secured. You can do it. Furthermore, since the step surface is substantially coincident with the direction of the light beam entering the vicinity of the step, the loss of efficiency due to the step is minimized.

 [0031] Furthermore, since the first lens 10 on which the diffraction grating is formed is a resin molded product, the cost of a mold for manufacturing the first lens 10 is low. In other words, when a glass molded product is used, it is necessary to manufacture the mold by carburizing it with a superhard material. However, in the case of resin molding, the mold is manufactured at low cost by processing the normal Ni-P plating layer. it can.

 [Embodiment 2]

 FIG. 3 is a configuration diagram of a fixed focus type fixed focus lens for a digital camera for a mobile phone or a small digital camera according to Embodiment 2 of the present invention. FIG. 4 is a graph showing the spherical aberration, astigmatism, and distortion of the fixed focus lens of the present embodiment.

 As shown in FIG. 3, the fixed focus lens 200 of the present embodiment has two lens powers. That is, the first lens 10 made of a resin molded product and the second lens 20 made of a resin molded product are arranged in this order from the object side toward the image forming surface 80, and the image forming surface 8 of the second lens 20 is formed. On the 0 side, a cover glass 70 is arranged. An aperture 50 is arranged between the first lens 10 and the second lens 20.

 In the present embodiment, each surface of each optical element is referred to as shown below. Therefore, the object is located on the entrance surface side of the first lens 10 and the image is located on the exit surface side of the second lens 20.

 [0035]

 First lens 1 0 incident surface 1st surface 1

 Exit surface of first lens 10 Second surface 2

 Aperture 5 0 3rd surface 3

 Second lens 20 incident surface 4th surface 4

 Outgoing surface of second lens 20 Fifth surface 5

 Cover glass 70 0 incident surface 6th surface 6

 Exit surface of cover glass 70 0 7

In the fixed focus lens 200 configured as above, each surface is configured as described below. [0037] Design data i

 Radius of curvature Surface spacing

 Object infinity infinity

 Front 1 1 1.1 9 8 7 1

 Side 2 2 1.28 68 0.1

 Surface 3 3 Infinity 0.1 5

 4th page 4 1 1.94 3 2 1.6

 Page 5 5 1. 1.294 2 1.7

 Surface 6 G Infinity 0.5

 7th page 7th limit 0.3 5 3

 Image Infinity 0 Design data 2

 First side 1 Second side 2

 K 0. 4 79 1 7 1 K 3.8 2 5 5 5

A4 0 A4 -0 0 8 9

 A6 0 A6 0.4 3 1 3 1 8

A8 0 A8 0

 A1 0 0 A 1 0 0

 P 2 0 P 2 0 4th surface 4 5th surface; i

 K 3 7.44 9 5 K 0

 A4 0.703 1 6 A4 0.02 5 3 3

A6 1. 242 304 A6 -0 0 3 7 1 7

A8 0 A8 0.0 2 7 4 2 6

A 1 0 0 A 1 0 -o .0 0 9 2 5

P 2 ― 4 7.74 6 5 P 2 0

As described above, in the present embodiment, a diffraction grating B for removing axial chromatic aberration and off-axis chromatic aberration is formed on the entrance surface (the fourth surface 4) of the second lens 20 located on the side of the stop 50. It has been. That is, the diffraction grating B eliminates the axial chromatic aberration and the off-axis chromatic aberration that have occurred without using it. Here, the diffraction grating B has a concentric blazed shape, the step of the blazed shape is 2 μm or less, and the pitch is 10 μm or more, and the first-order diffraction efficiency over the entire visible wavelength range. Is high. In the focal lens 200 configured as described above, the spherical aberrations at the wavelengths of 436 nm, 476 nm, 567 nm, 597 nm, and 656 nm are shown by solid lines L11 to L15 in FIG. As shown by L25 and dotted lines L31 to L35, and the distortion factor is shown by solid lines L41 to L45, as a fixed-focus lens system of a fixed-focus type for digital cameras for mobile phones of about 1 megapixel and small digital cameras. The on-axis chromatic aberration and off-axis chromatic aberration are improved to a sufficient level.

 As described above, in the present embodiment, since the diffraction grating B for removing chromatic aberration is formed on the lens surface (fourth surface) of the second lens 20 constituting the fixed focus lens 200, the convex type There is no need to remove chromatic aberration by combining the lens with a concave refraction lens. Therefore, the number of lenses can be reduced. Further, since the diffraction grating B is formed on the lens surface, the diffraction grating does not need to be arranged between the lenses. Therefore, since the fixed focus lens 200 can be constituted by the two lenses 10 and 20, the dimension of the fixed focus lens 200 in the optical axis direction can be reduced to 5 mm to 5.5 mm. Also, the number of lenses is small and resin molded products are used for lenses 10 and 20! Therefore, the weight of the fixed-focus lens 200 can be reduced.

 Further, since the diffraction grating B is formed in a blazed shape, a high first-order diffraction efficiency can be obtained in the entire visible wavelength range, so that chromatic aberration can be efficiently removed. In addition, since the step of the blaze shape of the diffraction grating B is 2 m or less and the grating pitch is 10 m or more, it is possible to efficiently perform mold production and resin molding, and to secure high dimensional accuracy. For example, the same effects as in the first embodiment can be obtained. Furthermore, since the step surface is substantially aligned with the direction of the light ray entering the vicinity of the step, the loss of efficiency due to the step portion is minimized.

 [Other Embodiments]

 In the above embodiment, the present invention is applied to a fixed focus lens of a fixed focus type for a digital camera for a mobile phone or a small digital camera. However, the present invention is used for an optical device that does not perform recording such as a surveillance camera or a television camera. The present invention may be applied to a fixed focus lens. Industrial applicability

In the present invention, since a diffraction grating for removing chromatic aberration is formed on the lens surface of the lens that forms the fixed focus lens, the color is obtained by combining convex and concave refractive lenses. The number of lenses can be reduced as compared with the case where aberration is removed. Further, since the diffraction grating is formed on the lens surface, the diffraction grating does not need to be arranged between the lenses. Therefore, the dimension of the fixed focus lens in the optical axis direction can be reduced.

Claims

The scope of the claims  [I] A fixed focus lens in which a plurality of lenses are arranged in a lens axis direction,  A fixed focus lens, wherein a diffraction grating for removing chromatic aberration is formed on at least one of the plurality of lenses.  [2] The fixed focus lens according to claim 1, wherein the diffraction grating is a blazed grating.  3. The fixed focus lens according to claim 2, wherein the diffraction grating has a first-order diffraction order.  [4] In claim 2, wherein the blazed grating has a step of 2 μm or less and a pitch of 2 μm. Fixed focus lens characterized by being 10 μm or more. [5] In claim 1, the diaphragm is arranged so as to be sandwiched between the two lenses,  The fixed focal length lens, wherein the diffraction grating is formed on a lens located on the object side with respect to the stop to remove axial chromatic aberration. [6] In claim 1, the stop is arranged so as to be sandwiched between the two lenses,  The fixed focus lens, wherein the diffraction grating is formed on a lens located on the image side with respect to the stop to remove on-axis chromatic aberration and off-axis chromatic aberration. 7. The fixed focus lens according to claim 5, wherein the diffraction grating is formed on one of two lenses sandwiching the stop. [8] The fixed focus lens according to claim 7, wherein the diffraction grating is formed on a lens surface facing the stop. 9. The lens according to claim 1, wherein, of the plurality of lenses, the lens on which the diffraction grating is formed is A fixed focus lens characterized by being a resin molded product. [10] The fixed focus lens according to any one of claims 1 to 6, wherein the number of the plurality of lenses is four or less.  [II] The fixed focus lens according to claim 10, wherein the plurality of lenses are two.  12. The fixed focus lens according to claim 10, wherein the plurality of lenses is three.