CN102466856A - Two-element optical imaging lens - Google Patents

Abstract

The present invention provides a two-lens optical imaging lens, which comprises, in order from the object side to the image side along the optical axis: an aperture stop; a first lens of positive refractive power which is a plano-convex lens, and the image side surface is convex; a second lens with negative refractive power which is a meniscus lens, and the object side surface is concave, and the image side surface is convex.

Description

Two-element optical imaging lens

technical field

The present invention relates to a two-element optical imaging lens, especially a lens for small cameras or mobile phones using image sensors such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), and provides A wide-angle, long back focus and low-cost optical imaging lens composed of two lenses.

Background technique

With the advancement of technology, electronic products are constantly developing towards the direction of thin, light, small and multi-functional, and electronic products such as: digital still camera (Digital Still Camera), computer camera (PC camera), network camera (Network camera), mobile phone (Mobile phones) and other devices already have imaging devices (lenses), and even devices such as personal digital assistants (PDAs) also have the need to add imaging devices (lenses). In order to be convenient to carry and meet the needs of humanization, the imaging device not only needs to have good imaging quality, but also needs to have a smaller volume and lower cost. Due to the narrow field angle, the captured image is too small, and the imaging lens with a large viewing angle can improve the shooting quality of electronic products and meet the needs of users.

There are two-lens, three-lens, four-lens, and five-lens types of imaging lenses used in small electronic products. However, considering the cost, the two-lens type uses fewer lenses, and its cost more advantageous.

The existing two-element optical imaging lens has many different structural designs, but the differences or technical features between them are determined by the changes or combinations of the following factors: the shape design of the corresponding fit between the two lenses Different, such as the first and second lenses are meniscus shape lenses, bi-convex and bi-concave respectively; or the corresponding convex/concave directions of the two lenses are different; Or the diopters (refractive power) corresponding to the two lenses are different in positive and negative; or the relevant optical data between the two lens groups/lenses, such as fs (the effective focal length of the imaging lens system), di (the i Distance between), Ri (radius of curvature of each optical surface i), etc., satisfy different conditions; as can be seen from the above, in terms of the design of the optical imaging lens of the two-mirror type, the prior art is in the technical field of designing optical imaging lenses, Different changes or combinations are produced for the application of various optical purposes, and because of the different shapes, combinations, functions or functions of the lenses used, they can be regarded as novelty and innovative steps.

In recent years, in order to be used in small cameras, camera phones, PDAs and other products, the imaging lens requires miniaturization, short focal length, and good aberration adjustment. Among various miniaturized two-lens imaging lens designs, the design of the first lens with positive diopter, the second lens with positive diopter or other combinations is most likely to meet the miniaturization requirements, such as US2005/0073753, US2004 /0160680, US7,110,190, US7,088,528, US2004/0160680; European patents EP1793252, EP1302801; Japanese patents JP2007-156031, JP2006-154517, JP2006-189586;

However, the volume of the optical imaging lens disclosed in these patents should be further reduced. For the larger field of view design required by users, such as US2008/0030875 using a combination of positive and negative diopters, US20030/0197956 using a combination of negative and positive diopters, US5,835,288 using a combination of biconcave and biconvex lenses, Japanese patents JP08-334684 and JP2005-107368 use a combination of positive or negative-positive diopters to increase the viewing angle; or such as Japanese patent publication number JP2004-177976, European patents EP1793252 and EP1793254, US patents US6,876,500, US2004 /0160680, US7,088,528, Chinese Taiwan Province patent TWI266074, etc. use a combination of plus-plus diopters.

The above-mentioned optical lenses have a common feature, that is, the back focal length is very short. The shortcoming of short back focal length is that when the size of electronic products continues to shrink, the size of the lens will also shrink accordingly, so the back focal length will also be proportionally shortened. In the optical lens, two objects, an infrared filter and glass, are still arranged. These two objects have a fixed thickness. When the optical lens shrinks, the proportionally shortened back focus cannot place the infrared filter and glass because of the narrow space.

In order to have a design with a larger field of view and a longer back focus, it is an urgent need for users. For this reason, the present invention proposes a more practical design to be easily applied to electronic products such as small cameras and camera phones.

Contents of the invention

The main purpose of the present invention is to provide a kind of two-lens optical imaging lens, which is arranged along the optical axis from the object side (object side) to the image side (image side) and includes: an aperture stop (aperture stop); A first lens of positive refractive power is a plano-convex lens with a convex image side; a second lens with negative diopter is a crescent lens with a concave object side and a convex image side.

Wherein, the two-element optical imaging lens can further satisfy the following conditions:

0.49≤BFL/TL≤0.53 (1)

Wherein, BFL is the back focal length of the two-element optical imaging lens, and TL is the distance from the aperture stop to the imaging surface.

Again, the two-element optical imaging lens can further satisfy the following conditions:

65°≤2ω≤80° (2)

Among them, 2ω is the maximum field angle.

Moreover, the first lens and the second lens can be made of plastic.

Thereby, the present invention can achieve a wide-angle effect, and expand the imaging angle of small cameras and mobile phones; and the combination of the two lenses can achieve a long back focal length, so as to improve the applicability of the imaging lens.

Description of drawings

Fig. 1 is a schematic structural view of a two-mirror optical imaging lens of the present invention;

Fig. 2 is a schematic diagram of the optical path structure of the first embodiment of the present invention;

Fig. 3A and Fig. 3B are the imaging field curvature and imaging distortion diagrams of the first embodiment of the present invention;

Fig. 4 is a schematic diagram of the optical path structure of the second embodiment of the present invention;

5A and 5B are field curvature and imaging distortion diagrams of the second embodiment of the present invention;

Fig. 6 is a schematic diagram of the optical path structure of the third embodiment of the present invention;

7A and 7B are diagrams of field curvature and imaging distortion of imaging according to the third embodiment of the present invention.

Explanation of reference signs: 1-optical imaging lens; 11-first lens; R1-(first lens) object side; R2-(first lens) image side; S-aperture stop; 12-second lens; R3-(second lens) object side; R4-(second lens) image side; 13-infrared filter; 14-image sensor; d1-optical axis first lens object side to image side distance; d2 - distance from the image side of the first lens on the optical axis to the object side of the second lens; d3- the distance from the object side of the second lens on the optical axis to the image side; d4- the distance from the image side of the second lens on the optical axis to the object side of the infrared filter ; d5- the distance from the object side of the infrared filter on the optical axis to the image side; d6- the distance from the image side of the infrared filter on the optical axis to the image sensor.

Detailed ways

In order to make the present invention more definite and detailed, the structure and technical features of the present invention are described in detail as follows in conjunction with the following diagrams:

With reference to shown in Fig. 1, it is a schematic structural view of a two-lens optical imaging lens 1 of the present invention, which is arranged along the optical axis Z from the object side (object side) to the image side (image side) and includes: an aperture stop S, a first lens 11, a second lens 12, an infrared filter (IR cut-off filter) 13 and an image sensor (image sensing chip) 14; The light rays pass through the first lens 11 and the second lens 12 first, and then pass through the infrared filter 13 to be imaged on the imaging surface (image) of the image sensing chip 14 .

The first lens 11 is a plano-convex lens, which has a flat object side R1 and a convex image side R2, and has positive diopter. The first lens 11 can be made of a plastic material with a refractive index N _d greater than 1.5, and its image side R2 is an aspheric surface.

The second lens 12 is a crescent lens, which is an aspheric lens with a concave surface on the object side R3 and a convex surface on the image side R4, and has a negative diopter. The second lens 12 can be made of a plastic material with a refractive index N _d greater than 1.6, and its object side R3 and image side R4 are both aspherical.

The aperture stop (aperture stop) S belongs to a pre-diaphragm, which can be attached to the object side R1 of the first lens 11; the infrared filter (IR cut-off filter) 13 can be a lens, or A thin film with infrared filtering function is formed by coating technology; the image sensing chip (image sensing chip) 14 includes CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor).

When taking an image, the light of the object to be photographed first passes through the first lens 11 and the second lens 12, and then passes through the infrared filter 13 to be imaged on the image sensor 14. After optical combination of the optical surface curvature radius of the first lens 11 and the second lens 12, aspheric surface, lens thickness (d1 and d3) and air gap (d2 and d4) of the imaging lens 1, the field viewing angle can be greater than 68°. Its aspherical surface formula (Aspherical Surface Formula) is the following formula (3)

$\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; ch</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, c is the curvature, h is the lens height, K is the cone coefficient (Conic Constant), A4, A6, A8, A10, A12 respectively four, six, eight, ten, twelve aspheric coefficients (Nth Order Aspherical Coefficient) .

By the above-mentioned structure, the optical imaging lens 1 of the present invention can have a larger field of view and a long back focus, which satisfies formula (1) or formula (2); moreover, the optical imaging lens 1 of the present invention can Further effectively correct aberrations and reduce the chief ray angle.

Hereby enumerate preferred embodiment, and explain as follows respectively:

<First embodiment>

Please refer to FIG. 2, FIG. 3A, and FIG. 3B, which are respectively a schematic view of the optical path structure of the first embodiment of the two-lens optical imaging lens 1 of the present invention, and a diagram of field curvature of imaging and distortion of imaging. .

The following table (1) lists the optical surface number (surface number) numbered sequentially from the object side to the image side, the radius of curvature R (unit: mm) (the radius of curvatureR) of each optical surface on the optical axis, and the optical surface number. The on-axis surface spacing d (unit: mm) (the on-axis surface spacing), the refractive index N _d of each lens, and the Abbe's number (Abbe's number) v _d of each lens.

Table I)

*Denoted as aspheric

In Table (1), the optical surfaces marked with * are aspherical optical surfaces, optical surface 2 and optical surface 3 respectively represent the object side R1 and image side R2 of the first lens 11, optical surface 4 and optical surface 5 respectively represent The object side R3 and the image side R4 of the second lens 12, Fno is the focal length ratio (fnumber) of the optical imaging lens 1, f is the effective focal length of the optical imaging lens 1, and 2ω is the maximum field angle of the optical imaging lens 1. The following table (2) lists the various coefficients of the aspheric surface formula (3) of each optical surface:

Table II)

In this embodiment, the first lens 11 is made of a plastic material with a refractive index N _d1 of 1.50 and an Abbe number v _d1 of 55.00; the second lens 12 is made of a plastic material with a refractive index N _d2 of 1.60 and an Abbe number v _d2 of 29.30 made of plastic material; the infrared filter 13 is made of BK7 glass material.

The effective focal length f of the two-element optical imaging lens 1 of this embodiment is 1.0352 mm, the focal length f ₁ of the first lens 11 is 0.6869 mm, and the focal length f ₂ of the second lens 12 is -50.0205 mm. On the optical axis, the distance TL from the aperture stop to the imaging surface of the image sensor 14 is 2.0804 mm, and the back focal length BFL of the two-element optical imaging lens 1 of this embodiment is 1.0414 mm; that is,

BFL/TL=0.5006; 2ω=68°

Conditional expressions (1) and (2) can be satisfied.

As shown in the above table (1), table (2) and Fig. 2 to Fig. 3A and Fig. 3B, it can be proved that the two-element optical imaging lens of the present invention can effectively correct the aberration, so that the two-element optical imaging lens 1 It has high resolution, wide angle and long back focus, which improves the applicability of the present invention.

<Second Embodiment>

Please refer to FIG. 4 , FIG. 5A , and FIG. 5B , which are respectively a schematic view of the optical path structure, field curvature of imaging, and distortion of imaging in the second embodiment of the two-element optical imaging lens 1 of the present invention.

The following table (3) lists the number of optical surfaces sequentially numbered from the object side to the image side, the radius of curvature R of each optical surface on the optical axis, the distance d between each surface on the optical axis, and the refractive index N of each lens. _d . The Abbe number v _d of each lens.

Table (3)

*Denoted as aspheric

The following table (4) lists the various coefficients of the aspheric surface formula (3) of each optical surface:

Table (4)

In this embodiment, the first lens 11 is made of a plastic material with a refractive index N _d1 of 1.50 and an Abbe number v _d1 of 55.00; the second lens 12 is made of a plastic material with a refractive index N _d2 of 1.60 and an Abbe number v _d2 of 29.30 made of plastic material; the infrared filter 13 is made of BK7 glass material.

Lens of Embodiment 2 The effective focal length f of the optical imaging lens 1 is 1.0317 mm, the focal length f ₁ of the first lens 11 is 0.7234 mm, and the focal length f ₂ of the second lens 12 is 23.6486 mm. On the optical axis, the distance TL from the aperture stop to the imaging plane of the image sensor 14 is 2.0606mm, and the back focal length BFL of the two-element optical imaging lens 1 of the present embodiment is 1.0737mm; that is,

BFL/TL=0.5210; 2ω=67.76°

Conditional expressions (1) to (2) can be satisfied.

As shown in the above table (3), table (4) and Fig. 4 to Fig. 5A and Fig. 5B, it can be proved that the two-element optical imaging lens of the present invention can effectively correct the aberration, so that the two-element optical imaging lens 1 It has high resolution, wide angle and long back focus.

<Third embodiment>

Please refer to FIG. 6 , FIG. 7A , and FIG. 7B , which are respectively a schematic view of the optical path structure, field curvature of imaging, and distortion of imaging in the third embodiment of the two-element optical imaging lens 1 of the present invention.

The following table (5) lists the number of optical surfaces sequentially numbered from the object side to the image side, the radius of curvature R of each optical surface on the optical axis, the distance d between each surface on the optical axis, and the refractive index N of each lens. _d . The Abbe number v _d of each lens.

Table (5)

*Denoted as aspherical

The following table (6) lists the various coefficients of the aspheric surface formula (3) of each optical surface:

Table (6)

In this embodiment, the first lens 11 is made of a plastic material with a refractive index N _d1 of 1.50 and an Abbe number v _d1 of 55.00; the second lens 12 is made of a plastic material with a refractive index N _d2 of 1.60 and an Abbe number v _d2 of 29.30 made of plastic material; the infrared filter 13 is made of BK7 glass material.

The effective focal length f of the two-lens optical imaging lens 1 of the present embodiment is 0.8792mm, and the focal length _f1 of the first lens 11 is 0.6193mm, and the focal length _f2 of the second lens 12 is 5.0496mm; The distance TL from the diaphragm to the imaging surface of the image sensor 15 is 1.9386 mm, and the back focal length BFL of the two-lens optical imaging lens 1 of this embodiment is 0.9818 mm; that is,

BFL/TL=0.5064; 2ω=78.6°

Conditional expressions (1) and (2) can be satisfied.

As shown in the above Table (5), Table (6) and Fig. 6 to Fig. 7A and Fig. 7B, it can be proved that the two-element optical imaging lens of the present invention can effectively correct aberrations, so that the two-element optical imaging lens 1 It has high resolution, wide angle and long back focus.

The above are only preferred embodiments of the present invention, and are only illustrative, not restrictive, of the present invention. Those with ordinary knowledge in the technical field understand that many changes, modifications, and even equivalent changes can be made within the spirit and scope defined by the claims of the present invention, but all will fall within the protection scope of the present invention.

Claims (6)

1. A two-lens optical imaging lens, characterized in that it is arranged along the optical axis from the object side to the image side and includes: an aperture stop; a first lens with positive diopter power, which is a plano-convex lens with a convex image side; and A second lens, with negative diopter, is a crescent lens with a concave surface on the object side and a convex surface on the image side. 2. The two-element optical imaging lens as claimed in claim 1, wherein the two-element optical imaging lens satisfies the following conditions: 0.49≤BFL/TL≤0.53 Wherein, BFL is the back focal length of the two-element optical imaging lens, and TL is the distance from the aperture stop to the imaging surface. 3. The two-element optical imaging lens as claimed in claim 1, wherein the two-element optical imaging lens satisfies the following conditions: 65°≤2ω≤80° Among them, 2ω is the maximum field viewing angle. 4. The two-element optical imaging lens according to claim 1, wherein the image side of the first lens is aspherical. 5 . The two-element optical imaging lens as claimed in claim 1 , wherein the convex and concave surfaces of the second lens are aspherical. 5 . 6. The two-element optical imaging lens as claimed in claim 1, wherein the first lens and the second lens are made of glue.

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