BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a lens assembly.

Description of the Related Art

The current development trend of a lens assembly is toward miniaturization. Additionally, the lens assembly is developed to have high resolution capability in accordance with different application requirements. However, the known lens assembly can't satisfy such requirements. Therefore, the lens assembly needs a new structure in order to meet the requirements of miniaturization and high resolution at the same time.

BRIEF SUMMARY OF THE INVENTION

The invention provides a lens assembly to solve the above problems. The lens assembly of the invention is provided with characteristics of a shortened total lens length, a higher resolution, and still has a good optical performance.

The lens assembly in accordance with an exemplary embodiment of the invention includes a first lens, a second lens, a third lens, a fourth lens and a fifth lens, wherein the first lens, the second lens, the third lens, the fourth lens and the fifth lens are arranged in order from an object side to an image side along an optical axis. The first lens has positive refractive power and includes a convex surface facing the object side and a concave surface facing the image side. The second lens has negative refractive power. The third lens has positive refractive power and includes a convex surface facing the object side. The fourth lens has positive refractive power. The fifth lens has negative refractive power and includes a concave surface facing the image side. The lens assembly satisfies 5<(R11+R12)/(R21+R22)<15, wherein R11is a radius of curvature of the convex surface of the first lens, R12is a radius of curvature of the concave surface of the first lens, R21is a radius of curvature of the object surface of the second lens, and R22is a radius of curvature of the image side surface of the second lens.

In accordance with the invention, the lens assembly satisfies: −2<f/f5<0, −2.5<f5/f1<0, wherein f is an effective focal length of the lens assembly, f1is an effective focal length of the first lens, and f5is an effective focal length of the fifth lens.

In accordance with the invention, the lens assembly satisfies: 0.4<BFL/TTL<0.55, wherein BFL is an interval from the concave surface of the fifth lens to an image plane along the optical axis and TTL is an interval from the convex surface of the first lens to the image plane along the optical axis.

In accordance with the invention, the lens assembly satisfies: 10 mm<f3+f4<15 mm, wherein f3is an effective focal length of the third lens and f4is an effective focal length of the fourth lens.

In accordance with the invention, the lens assembly satisfies: 0<R41/R11<2, wherein R11is a radius of curvature of the convex surface of the first lens and R41is a radius of curvature of the object side surface of the fourth lens.

In accordance with the invention, the lens assembly satisfies: −5<f/f2<−3, wherein f is an effective focal length of the lens assembly and f2is an effective focal length of the second lens.

In accordance with the invention, the lens assembly satisfies: 10 mm<f45<15 mm, wherein f45is an effective focal length of a combination of the fourth lens and the fifth lens.

In accordance with the invention, the first lens is a meniscus lens, the second lens is a biconcave lens which includes a concave surface facing the object side and another concave surface facing the image side, and the fourth lens is a biconvex lens which includes a convex surface facing the object side and another convex surface facing the image side.

In accordance with the invention, the lens assembly satisfies: −5<(R31+R32)/(R41+R42)<2, wherein R31is a radius of curvature of the convex surface of the third lens, R32is a radius of curvature of the image side surface of the third lens, R41is a radius of curvature of the convex surface of the fourth lens, and R42is a radius of curvature of the another convex surface of the fourth lens.

In accordance with the invention, the fifth lens is a biconcave lens and further includes a concave surface facing the object side.

The lens assembly in accordance with another exemplary embodiment of the invention includes a first lens, a second lens, a third lens, a fourth lens and a fifth lens, wherein the first lens, the second lens, the third lens, the fourth lens and the fifth lens are arranged in order from an object side to an image side along an optical axis. The first lens has positive refractive power and including a convex surface facing the object side. The second lens has negative refractive power. The third lens has positive refractive power and including a convex surface facing the object side. The fourth lens has positive refractive power. The fifth lens has negative refractive power. The lens assembly satisfies −1<R21/R22<−0.5, wherein R21is a radius of curvature of the object side surface of the second lens and R22is a radius of curvature of the image side surface of the second lens.

In accordance with the invention, the lens assembly satisfies: −2<f/f5<0, 10 mm<f3+f4<15 mm, wherein f is an effective focal length of the lens assembly, f3is an effective focal length of the third lens, f4is an effective focal length of the fourth lens and f5is an effective focal length of the fifth lens.

In accordance with the invention, the lens assembly satisfies: −2.5<f5/f1<0, wherein f1is an effective focal length of the first lens and f5is an effective focal length of the fifth lens.

In accordance with the invention, the lens assembly satisfies: 0.4<BFL/TTL<0.55, wherein BFL is an interval from the concave surface of the fifth lens to an image plane along the optical axis and TTL is an interval from the convex surface of the first lens to the image plane along the optical axis.

In accordance with the invention, the lens assembly satisfies: 5<(R11+R12)/(R21+R22)<15, wherein R11is a radius of curvature of the convex surface of the first lens, R12is a radius of curvature of the image side surface of the first lens, R21is a radius of curvature of the object surface of the second lens, and R22is a radius of curvature of the image side surface of the second lens.

In accordance with the invention, the lens assembly satisfies: 0<R41/R11<2, wherein R11is a radius of curvature of the convex surface of the first lens and R41is a radius of curvature of the object side surface of the fourth lens.

In accordance with the invention, the lens assembly satisfies: −5<f/f2<−3, wherein f is an effective focal length of the lens assembly and f2is an effective focal length of the second lens.

In accordance with the invention, the lens assembly satisfies: 10 mm<f45<15 mm, wherein f45is an effective focal length of a combination of the fourth lens and the fifth lens.

In accordance with the invention, the first lens is a meniscus lens and further includes a concave surface facing the image side, the second lens is a biconcave lens and includes a concave surface facing the object side and another concave surface facing the image side, and the fourth lens is a biconvex lens and includes a convex surface facing the object side and another convex surface facing the image side.

In accordance with the invention, the lens assembly satisfies: −5<(R31+R32)/(R41+R42)<2, wherein R31is a radius of curvature of the convex surface of the third lens, R32is a radius of curvature of the image side surface of the third lens, R41is a radius of curvature of the convex surface of the fourth lens, and R42is a radius of curvature of the another convex surface of the fourth lens.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

