Image capturing optical lens system   

Abstract: This invention provides an optical lens system comprising: a first lens element with positive refractive power; a second lens element with negative refractive power; a third lens element with negative refractive power having a concave object-side surface and at least one of the object-side surface and the image-side surface thereof being aspheric; a plastic fourth lens element having at least one of the object-side surface and the image-side surface thereof being aspheric; a plastic fifth lens element having a concave image-side surface, at least one of the object-side surface and the image-side surface thereof being aspheric, and at least one inflection point is formed on at least one of the object-side surface and the image-side surface thereof. By such arrangement, photosensitivity and total track length of the system can be reduced, and the aberration and astigmatism of the system can be effectively corrected. Moreover, high image resolution can be obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 100120114 filed in Taiwan, R.O.C. on Jun. 9, 2011, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image capturing optical lens system, and more particularly, to a compact image capturing optical lens system used in electronic products.

2. Description of the Prior Art

In recent years, with the popularity of portable electronic products having photographing function, the demand of compact imaging lens system has grown. Generally, the sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS device (Complementary Metal Oxide Semiconductor device). Furthermore, advances in semiconductor manufacturing technology have allowed the pixel size of sensors to be reduced and therefore lead compact imaging lens systems to higher resolution. In the meantime, the demand for better image quality is also increased.

A conventional image capturing lens system equipped on a portable electronic product is in various design of two-lens element, three-lens element, four-lens element or five-lens element, such as the one set forth in U.S. Pat. No. 7,365,920. However, with the popularity of high level portable electronic products, such as smart phone and PDA (Personal Digital Assistant), the demand for the pixel size and image quality of compact imaging lens system increase fast, and the conventional lens system with four lens elements can no longer satisfy the imaging lens systems of even higher level. Moreover, a conventional image capturing lens system having five lens elements usually adopts different assemblies of positive or negative refractive power or has a cemented doublet lens element. This kind of five-lens element lens system frequently has the drawback of excessively long total track length so that is not suitable for compact electronic products

Inasmuch as the foregoing, a need is continuously existed for a lens system with good image quality and moderate total track length and is suitable for compact and portable electronic products.

SUMMARY

The present invention provides an image capturing optical lens system, in order from an object side to an image side comprising five lens elements with refractive power: a first lens element with positive refractive power; a second lens element with negative refractive power; a third lens element with negative refractive power having a concave object-side surface and at least one of the object-side surface and the image-side surface thereof being aspheric; a fourth lens element having at least one of the object-side surface and the image-side surface thereof being aspheric and made of plastic; and a fifth lens element having a concave image-side surface, at least one of the object-side surface and the image-side surface thereof being aspheric, at least one inflection point is formed on at least one of the object-side surface and the image-side surface thereof and made of plastic; wherein a curvature radius of the object-side surface of the second lens element is R3, a curvature radius of the image-side surface of the second lens element is R4, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, a curvature radius of the object-side surface of the fourth lens element is R7, a curvature radius of the image-side surface of the fourth lens element is R8, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element is T45, an axial distance between the second lens element and the third lens element is T23, and they satisfy the following relations: −5.0<(R3+R4)/(R3−R4)<−0.75; −5.0<(R5+R6)/(R5−R6)<−0.8; −5.3<R7/R8<6.5; and 0.1<(T34+T45)/T23<1.8.

On the other hand, the present invention provides an image capturing optical lens system, in order from an object side to an image side comprising five lens elements with refractive power: a first lens element with positive refractive power; a second lens element with negative refractive power; a third lens element with negative refractive power having a concave object-side surface and at least one of the object-side surface and the image-side surface thereof being aspheric; a fourth lens element with positive refractive power having at least one of the object-side surface and the image-side surface thereof being aspheric and made of plastic; and a fifth lens element with negative refractive power having a concave image-side surface, at least one of the object-side surface and the image-side surface thereof being aspheric, at least one inflection point is formed on at least one of the object-side surface and the image-side surface thereof and made of plastic; wherein a curvature radius of the object-side surface of the second lens element is R3, a curvature radius of the image-side surface of the second lens element is R4, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, the image capturing optical lens system further comprises a stop, an axial distance between the stop and an image plane is SL, an axial distance between the object-side surface of the first lens element and the image plane is TTL, and they satisfy the following relations: −5.0<(R3+R4)/(R3−R4)<−0.75; −5.0<(R5+R6)/(R5−R6)<−0.8; and 0.70<SL/TTL<0.93.

By such arrangement, photosensitivity and total track length of the system can be reduced, and the aberration and astigmatism of the system can be effectively corrected. Moreover, high image resolution can be obtained.

In the aforementioned image capturing optical lens system, the first lens element has positive refractive power and thereby can provide significant positive refractive power needed for the system and is favorable for reducing the total track length thereof. When the second lens element has negative refractive power, the aberration provided by the first lens element can be effectively corrected. Also, the chromatic aberration can be favorably corrected. When the third lens element has negative refractive power, the third lens element can correct the aberration and chromatic aberration and reduce the sensitivity of the system along with the second lens element. When the fourth lens element has positive refractive power and the fifth lens element has negative refractive power, a positive-negative telephoto structure is formed so that the back focal length of the system is favorably reduced as well as the total track length of the system.

In the aforementioned image capturing optical lens system, the second lens element has a concave object-side surface and a convex image-side surface so that the astigmatism of the system can be favorably corrected. When the third lens element has a concave object-side surface, the astigmatism of the system can be favorably corrected. When the fifth lens element has concave image-side surface, the principal point of the system can be positioned away from the image plane so that the total track length thereof can be shortened for keeping the system compact. In addition, when at least one inflection is formed on at least one of the object-side and image-side surfaces of the fifth lens element, the angle at which light projects onto the image sensor from the off-axis field can be effectively reduced so that the sensing efficiency of the image sensor can be improved and the off-axis aberration can be corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an image capturing optical lens system in accordance with a first embodiment of the present invention.

FIG. 1B shows the aberration curves of the first embodiment of the present invention.

FIG. 2A shows an image capturing optical lens system in accordance with a second embodiment of the present invention.

FIG. 2B shows the aberration curves of the second embodiment of the present invention.

FIG. 3A shows an image capturing optical lens system in accordance with a third embodiment of the present invention.

FIG. 3B shows the aberration curves of the third embodiment of the present invention.

FIG. 4A shows an image capturing optical lens system in accordance with a fourth embodiment of the present invention.

FIG. 4B shows the aberration curves of the fourth embodiment of the present invention.

FIG. 5A shows an image capturing optical lens system in accordance with a fifth embodiment of the present invention.

FIG. 5B shows the aberration curves of the fifth embodiment of the present invention.

FIG. 6A shows an image capturing optical lens system in accordance with a sixth embodiment of the present invention.

FIG. 6B shows the aberration curves of the sixth embodiment of the present invention.

FIG. 7A shows an image capturing optical lens system in accordance with a seventh embodiment of the present invention.

FIG. 7B shows the aberration curves of the seventh embodiment of the present invention.

DETAILED DESCRIPTION

The present invention provides an image capturing optical lens system, in order from an object side to an image side comprising five lens elements with refractive power: a first lens element with positive refractive power; a second lens element with negative refractive power; a third lens element with negative refractive power having a concave object-side surface and at least one of the object-side surface and the image-side surface thereof being aspheric; a fourth lens element having at least one of the object-side surface and the image-side surface thereof being aspheric and made of plastic; and a fifth lens element having a concave image-side surface, at least one of the object-side surface and the image-side surface thereof being aspheric, at least one inflection point is formed on at least one of the object-side surface and the image-side surface thereof and made of plastic; wherein a curvature radius of the object-side surface of the second lens element is R3, a curvature radius of the image-side surface of the second lens element is R4, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, a curvature radius of the object-side surface of the fourth lens element is R7, a curvature radius of the image-side surface of the fourth lens element is R8, an axial distance between the third lens element and the fourth lens element is T34, an axial distance between the fourth lens element and the fifth lens element is T45, an axial distance between the second lens element and the third lens element is T23, and they satisfy the following relations: −5.0<(R3+R4)/(R3−R4)<−0.75; −5.0<(R5+R6)/(R5−R6)<−0.8; −5.3<R7/R8<6.5; and 0.1<(T34+T45)/T23<1.8.

When the relation of −5.0<(R3+R4)/(R3−R4)<−0.75 is satisfied, the curvature of the second lens element is more suitable for favorably correcting the aberration of the system; preferably, the following relation is satisfied: −2.5<(R3+R4)/(R3−R4)<−1.05.

When the relation of −5.0<(R5+R6)/(R5−R6)<−0.8 is satisfied, the curvature of the third lens element is averted from being excessively large, and thereby the astigmatism of the system can be corrected favorably; preferably, the following relation is satisfied: −2.5<(R5+R6)/(R5−R6)<−1.05.

When the relation of −5.3<R7/R8<6.5 is satisfied, the curvature of the fourth lens element is averted from being excessively large, and thereby the aberration of the system can be corrected favorably.

When the relation of 0.1<(T34+T45)/T23<1.8 is satisfied, the interval between each lens element in the system is more suitable, which is favorable for not only the arrangement and assembly of the lens elements but also the organization of the space in the system for keeping the system compact.

In the aforementioned image capturing optical lens system, a focal length of the fourth lens element is f4, a focal length of the fifth lens element is f5, and they preferably satisfy the following relation: −1.3<f4/f5<−0.7. When the above relation is satisfied, both the refractive power of the fourth lens element and the fifth lens element are more suitable for effectively correcting the aberration and astigmatism of the system.

In the aforementioned image capturing optical lens system, an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, and they preferably satisfy the following relation: 28<V1−V2<45. When the above relation is satisfied, the chromatic aberration of the system can be corrected favorably.

In the aforementioned image capturing optical lens system, an Abbe number of the first lens element is V1, an Abbe number of the third lens element is V3, and they preferably satisfy the following relation: 28<V1−V3<45. When the above relation is satisfied, the chromatic aberration of the system can be adjusted and corrected favorably.

In the aforementioned image capturing optical lens system, the curvature radius of the image-side surface of the fourth lens element is R8, a focal length of the image capturing optical lens system is f, and they preferably satisfy the following relation: −0.5<R8/f<0. When the above relation is satisfied, the back focal length can be effectively enlarged for ensuring that the system has enough back focal length for placing other elements.

In the aforementioned image capturing optical lens system, a focal length of the image capturing optical lens system is f, a focal length of the third lens element is f3, and they preferably satisfy the following relation: −1.3<f/f3<−0.2. When the above relation is satisfied, the refractive power of the third lens element is more suitable for distributing the positive refractive power of the first lens element, and thereby the sensitivity of the system can be reduced; more preferably, the following relation is satisfied: −1.0<f/f3<−0.3.

In the aforementioned image capturing optical lens system, the system further comprises a stop, an axial distance between the stop and an image plane is SL, an axial distance between the object-side surface of the first lens element and the image plane is TTL, and they preferably satisfy the following relation: 0.70<SL/TTL<0.93. When the above relation is satisfied, the arrangement of the stop can provide telecentricity, which is favorable for averting from the occurrence of shading so that the sensing efficiency can be improved.

In the aforementioned image capturing optical lens system, a central thickness of the second lens element is CT2, a central thickness of the third lens element is CT3, and they preferably satisfy the following relation: 0.3<CT2/CT3<1.05. When the above relation is satisfied, the arrangement of every lens element in the system is more suitable for not only the manufacture and assembly of the lens elements but also obtaining better image quality.

In the aforementioned image capturing optical lens system, a curvature radius of the object-side surface of the fifth lens element is R9, a focal length of the image capturing optical lens system is f, and they preferably satisfy the following relation: −1.0<R9/f<0. When the above relation is satisfied, the high order aberration can be adjusted.

In the aforementioned image capturing optical lens system, an axial distance between the object-side surface of the first lens element and the image plane is TTL, half of a diagonal length of an effective photosensitive area of the image sensor is ImgH, and they preferably satisfy the following relation: TTL/ImgH<2.0. When the above relation is satisfied, it is favorable for keeping the system compact in order to be equipped on portable electronic products.

On the other hand, the present invention provides an image capturing optical lens system, in order from an object side to an image side comprising five lens elements with refractive power: a first lens element with positive refractive power; a second lens element with negative refractive power; a third lens element with negative refractive power having a concave object-side surface and at least one of the object-side surface and the image-side surface thereof being aspheric; a fourth lens element with positive refractive power having at least one of the object-side surface and the image-side surface thereof being aspheric and made of plastic; and a fifth lens element with negative refractive power having a concave image-side surface, at least one of the object-side surface and the image-side surface thereof being aspheric, at least one inflection point is formed on at least one of the object-side surface and the image-side surface thereof and made of plastic; wherein a curvature radius of the object-side surface of the second lens element is R3, a curvature radius of the image-side surface of the second lens element is R4, a curvature radius of the object-side surface of the third lens element is R5, a curvature radius of the image-side surface of the third lens element is R6, the image capturing optical lens system further comprises a stop, an axial distance between the stop and an image plane is SL, an axial distance between the object-side surface of the first lens element and the image plane is TTL, and they satisfy the following relations: −5.0<(R3+R4)/(R3−R4)<−0.75; −5.0<(R5+R6)/(R5−R6)<−0.8; and 0.70<SL/TTL<0.93.

When the relation of −5.0<(R3+R4)/(R3−R4)<−0.75 is satisfied, the curvature of the second lens element is more suitable for favorably correcting the aberration of the system; preferably, the following relation is satisfied: −2.5<(R3+R4)/(R3−R4)<−1.05.

When the relation of −5.0<(R5+R6)/(R5−R6)<−0.8 is satisfied, the curvature of the third lens element is averted from being excessively large, and thereby the astigmatism of the system can be corrected favorably; preferably, the following relation is satisfied: −2.5<(R5+R6)/(R5−R6)<−1.05.

When the relation of 0.70<SL/TTL<0.93 is satisfied, the arrangement of the stop can provide telecentricity, which is favorable for averting from the occurrence of shading so that the sensing efficiency can be improved.

In the aforementioned image capturing optical lens system, a focal length of the image capturing optical lens system is f, a focal length of the third lens element is f3, and they preferably satisfy the following relation: −1.0<f/f3<−0.3. When the above relation is satisfied, the refractive power of the third lens element is more suitable for distributing the positive refractive power of the first lens element, and thereby the sensitivity of the system can be reduced.

In the aforementioned image capturing optical lens system, an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, and they preferably satisfy the following relation: 28<V1−V2<45. When the above relation is satisfied, the chromatic aberration of the system can be corrected favorably.

In the aforementioned image capturing optical lens system, an Abbe number of the first lens element is V1, an Abbe number of the third lens element is V3, and they preferably satisfy the following relation: 28<V1−V3<45. When the above relation is satisfied, the chromatic aberration of the system can be adjusted and corrected favorably.

In the aforementioned image capturing optical lens system, a central thickness of the second lens element is CT2, a central thickness of the third lens element is CT3, and they preferably satisfy the following relation: 0.3<CT2/CT3<1.05. When the above relation is satisfied, the arrangement of every lens element in the system is more suitable for not only the manufacture and assembly of the lens elements but also obtaining better image quality.

In the aforementioned image capturing optical lens system, the lens elements can be made of glass or plastic material. If the lens elements are made of glass, the freedom for distributing the refractive power of the image capturing optical lens system can be increased. If plastic material is adopted to produce the lens elements, the production cost will be reduced effectively. Additionally, the surfaces of the lens elements can be aspheric and easily made into non-spherical profiles, allowing more design parameter freedom which can be used to reduce aberrations and the number of the lens elements used in an optical system. Consequently, the total track length of the image capturing optical lens system can be effectively reduced.

In the present image capturing optical lens system, if a lens element has a convex surface, it means the portion of the surface in proximity to the optical axis is convex; if a lens element has a concave surface, it means the portion of the surface in proximity to the optical axis is concave.

In the present image capturing optical lens system, there can be at least one stop, such as a glare stop or a field stop, provided for eliminating stray light and thereby promoting image resolution thereof.

Preferred embodiments of the present invention will be described in the following paragraphs by referring to the accompanying drawings.

FIG. 1A shows an image capturing optical lens system in accordance with the first embodiment of the present invention, and FIG. 1B shows the aberration curves of the first embodiment of the present invention. The image capturing optical lens system of the first embodiment of the present invention mainly comprises five lens elements, in order from an object side to an image side:

a first lens element 110 made of plastic with positive refractive power having a convex object-side surface 111 and a convex image-side surface 112, the object-side and image-side surfaces 111 and 112 thereof being aspheric;

a second lens element 120 made of plastic with negative refractive power having a concave object-side surface 121 and a convex image-side surface 122, the object-side and image-side surfaces 121 and 122 thereof being aspheric;

a third lens element 130 made of plastic with negative refractive power having a concave object-side surface 131 and a convex image-side surface 132, the object-side and image-side surfaces 131 and 132 thereof being aspheric;

a fourth lens element 140 made of plastic with positive refractive power having a concave object-side surface 141 and a convex image-side surface 142, the object-side and image-side surfaces 141 and 142 thereof being aspheric; and

a fifth lens element 150 made of plastic with negative refractive power having a concave object-side surface 151 and a concave image-side surface 152, the object-side and image-side surfaces 151 and 152 thereof being aspheric, and at least one inflection point is formed on the image-side surface 152 thereof;

wherein an aperture stop 100 is disposed between the first lens element 110 and the second lens element 120;

the image capturing optical lens system further comprises an IR filter 160 disposed between the image-side surface 152 of the fifth lens element 150 and an image plane 171, and the IR filter 160 is made of glass and has no influence on the focal length of the image capturing optical lens system; the image capturing optical lens system further comprises an image sensor 170 provided on the image plane 171.

The detailed optical data of the first embodiment is shown in TABLE 1, and the aspheric surface data is shown in TABLE 2, wherein the units of the radius of curvature, the thickness and the focal length are expressed in mm, and HFOV is half of the maximal field of view.

TABLE 1 (Embodiment 1) f = 4.03 mm, Fno = 2.80, HFOV = 35.1 deg. Focal Surface # Curvature Radius Thickness Material Index Abbe # length 0 Object Plano Infinity 1 Lens 1  1.513050 (ASP) 0.553 Plastic 1.544 55.9 2.66 2 −28.260900 (ASP)  −0.013 3 Ape. Stop Plano 0.120 4 Lens 2 −3.718500 (ASP) 0.230 Plastic 1.640 23.3 −7.31 5 −18.573700 (ASP)  0.516 6 Lens 3 −5.081700 (ASP) 0.354 Plastic 1.640 23.3 −10.42 7 −21.929200 (ASP)  0.253 8 Lens 4 −3.107100 (ASP) 0.840 Plastic 1.544 55.9 1.98 9 −0.875450 (ASP) 0.333 10 Lens 5 −3.208200 (ASP) 0.361 Plastic 1.535 56.3 −1.84 11  1.478520 (ASP) 0.700 12 IR-filter Plano 0.210 Glass 1.517 64.2 — 13

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