US 8,508,863 B2Granted

Image lens system

AssigneeLargan Precision Co., Ltd.

InventorsHsiang-Chi Tang, Po-Lun Hsu, Ming-Ta Chou

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Abstract

This invention provides an image lens system comprising: a first lens element with positive refractive power; a second lens element with negative refractive power having a concave object-side surface and a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric and made of plastic; a third lens element with positive refractive power; and a fourth lens element with negative refractive power, and at least one inflection point is formed on at least one of the object-side and image-side surfaces thereof; wherein, the region of the image-side surface of the second lens element near the optical axis is concave, but the off-axis region thereof is convex. By such arrangement, not only the photosensitivity and total track length of the system can be reduced, but also better image quality can be obtained.

Claims22

Dependent claims

An image lens system, in order from an object side to an image side comprising four lens elements with refractive power:

a first lens element with positive refractive power having a convex object-side surface and a convex image-side surface;
a second lens element with negative refractive power having a concave object-side surface and a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric, and made of plastic;
a third lens element with positive refractive power having a concave object-side surface and a convex image-side surface, both the object-side and image-side surfaces thereof being aspheric, and made of plastic;
and
a fourth lens element with negative refractive power having a convex object-side surface and a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric, made of plastic, and at least one inflection point is formed on at least one of the object-side and image-side surfaces thereof;
wherein the region of the image-side surface of the second lens element near the optical axis is concave, but the off-axis region of the image-side surface of the second lens element is convex;
wherein a focal length of the first lens element is f1, a focal length of the fourth lens element is f4, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, and they satisfy the following relations:
0.6<f1/|f4|<1.4;
and
1.0<T12/T23<4.5.

7 more elements

An image lens system, in order from an object side to an image side comprising four lens elements with refractive power:

a first lens element with positive refractive power having a convex object-side surface and a convex image-side surface;
a second lens element with negative refractive power having a concave object-side surface, both the object-side and image-side surfaces thereof being aspheric, and made of plastic;
a third lens element with positive refractive power having a concave object-side surface and a convex image-side surface, both the object-side and image-side surfaces thereof being aspheric, and made of plastic;
and
a fourth lens element with negative refractive power having a convex object-side surface and a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric, made of plastic, and at least one inflection point is formed on at least one of the object-side and image-side surfaces thereof;
wherein a focal length of the first lens element is f1, a focal length of the fourth lens element is f4, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, a focal length of the image lens system is f, a focal length of the second lens element is f2, an entrance pupil diameter of the image lens system is EPD, and they satisfy the following relations:
0.6<f1/|f4|<1.4;
1.3<T12/T23<4.0;
−0.9<f/f2<−0.4;
and
1.6<f/EPD<2.4.

8 more elements

An image lens system, in order from an object side to an image side comprising four lens elements with refractive power:

a first lens element with positive refractive power having a convex object-side surface and a convex image-side surface;
a second lens element with negative refractive power having a concave object-side surface and a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric, and made of plastic;
a third lens element with positive refractive power having a concave object-side surface and a convex image-side surface, both the object-side and image-side surfaces thereof being aspheric, and made of plastic;
and
a fourth lens element with negative refractive power having a convex object-side surface and a concave image-side surface, both the object-side and image-side surfaces thereof being aspheric, made of plastic, and at least one inflection point is formed on at least one of the object-side and image-side surfaces thereof;
wherein a focal length of the second lens element is f2, a focal length of the fourth lens element is f4, an axial distance between the first lens element and the second lens element is T12, an axial distance between the second lens element and the third lens element is T23, a curvature radius of the object-side surface of the fourth lens element is R7, a focal length of the image lens system is f, a refractive index of the second lens element is N2, a refractive index of the fourth lens element is N4, and they satisfy the following relations:
0.75<f2/f4<1.5;
1.0<T12/T23<4.5;
0.1<R7/f<0.8;
and
|N2−N4|<0.18.

8 more elements

Dependencies are inferred from the claim text.