(1) Field of the Invention
The present invention relates to the field of optical lenses, and more particularly to an imaging lens module capable of lowering the sensitivity of tolerance of a system to improve the yield rate, and providing a better imaging quality.
(2) Description of the Prior Art
At present, digital carriers having a dynamic or static photograph function such as PC CAM, DSC or DVD and DV, etc tend to be designed with a light, thin, short, small and innovative structure, and thus the structure of components is miniaturized, particularly a lens module for controlling the photographing definitely requires such miniaturization for enhancing the weight and compactness of a digital carrier.
Digital video (DV) with static and dynamic photographing functions is a typical example of implementing the miniaturization to home appliance.
Due to the light and easy-to-carry features, the DV market has replaced the V8, Hi8 market in a few years. Although the DV available in the market comes with two major selling points respectively, the light and compact design and the high pixels to enhance its competitive edge, the high pixels emphasized by the present DV or other digital carriers is adversely affected by a poor camera design, and thus the sensitivity of tolerance of the system is too high, and the imaging quality of the DV is affected, and a poor yield rate is resulted.
Therefore, it is an important subject for manufacturers and designers to provide a high pixels four-lens optical lens module that can improve the imaging quality to meet the market requirements of digital carriers.
The primary objective of the present invention is to provide a high-quality imaging lens module formed by four lenses and capable of lowering the sensitivity of tolerance of an imaging system to improve the yield rate of the imaging lens modules.
To achieve the foregoing objectives, the present invention provides an imaging lens comprising a fixed diaphragm and an optical module, and the optical module comprises first, second, third and fourth lenses arranged from an object side to an image side in the sequence of: the diaphragm; the first lens being a double-convex lens; the second lens, having a negative refractive power and a concave surface disposed towards the object side, and at least one surface being an aspheric surface; the third lens, having a positive refractive power and a meniscus lens with a convex surface disposed towards the image side, and at least one surface being an aspheric surface; the fourth lens, having a convex surface disposed towards the object side, and a wavy surface disposed towards the image side and a concave surface disposed towards the image side near the optical axis, and at least one surface being an aspheric surface.
The structural design of the imaging lens module will now be described in more detail hereinafter with reference to the accompanying drawings that show various embodiments of the invention.
Referring to
In two preferred embodiments of the imaging lens module in accordance with the present invention, the imaging lens module comprises a fixed diaphragm 1 and an optical module disposed along an optical axis and in a sequence from an object side A, and the optical module comprises first, second, third and fourth lenses L1, L2, L3, L4, arranged from an object side A to an image side B in the sequence of: the diaphragm 1;
the first lens L1, being a double-convex lens, and the surface of the first lens L1 being an aspheric surface, for enhancing an imaging quality;
the second lens L2, having a negative refractive power and a concave surface disposed towards the object side A, and at least one surface being an aspheric surface;
the third lens L3, having a positive refractive power and a meniscus lens with a convex surface disposed towards the image side B, and at least one surface being an aspheric surface; and
the fourth lens L4, having a convex surface disposed towards the object side A, and a wavy surface disposed towards the image side B and a concave surface disposed towards the image side B near the optical axis, and at least one surface being an aspheric surface.
In the optical module composed of four lenses in accordance to the system of the invention, a first plane glass 2 is disposed behind the fourth lens L4, having a filtering infrared effect. In addition, a second plane glass 3 is installed before the image side B for providing an effect of protecting the light sensor and used for image sensors of different packages and providing a better imaging quality. Further, the image side B refers to a light sensor for capturing images, and the light sensor is a CCD or a CMOS.
In the imaging lens module of the invention, the optical module pre-installs the diaphragm 1, and then the first lens, second lens, third lens and fourth lens, and the surfaces of the second lens, third lens and fourth lens are designed as aspheric surfaces. In addition to the function of reducing the number of high resolution camera lenses, the invention also maximize the effect of suppressing the aberration, and thus the overall design of the optical module can greatly lower the sensitivity of tolerance of the system and enhance the yield rate to obtain a better imaging quality. Further, the pre-installed diaphragm 1 satisfies the conditions and requirements of an incident angle, which is helpful to the production of camera lenses and provide a high yield rate.
In the invention, the optical module of the imaging lens module must satisfy the following conditions:
0.5<f/TL<1
where, TL is the distance from the diaphragm 1 to the imaging surface B, and f is the focal length of the whole lens module;
where, f12 is the overall focal length of the first lens L1 and the second lens L2, and f is the focal length of the whole lens module; and
where, f34 is the overall focal length of the third lens L3 and the fourth lens L4, and f is the focal length of the whole lens module.
In the imaging lens module of the invention, the optical module satisfies the aforementioned conditions before the sensitivity of tolerance of the optical module can be lowered to enhance the yield rate. In the meantime, the imaging quality of the optical module is optimized. On the other hand, if the optical module is below or above each of the aforementioned conditions, there will be no significant effect on the sensitivity of tolerance of the optical module, the yield rate, and the imaging quality.
The schematic views of the aberration of the invention illustrate a non-point aberration, a distorted aberration and a spherical surface aberration as shown in
Referring to
The value of F. No. ˜the F value shows the parameter of brightness. The smaller the value of F, the higher is the brightness.
Angle of viewing˜2ω
Focal Length˜f; and f is the overall focal length (mm) of the optical module, and 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 listed below are numbers of lenses counting in a sequence starting from the object side; and the surface numbers 2, 3 represent two surfaces of the first lens L1, and the surface numbers 4, 5 represent two surfaces of the second lens L2, and the surface numbers 6, 7 are two surfaces of a third lens L3, and the surface numbers 8, 9 are two surfaces of the fourth lens L4, and 10, 11, 12, 13 represent two surfaces of the first plane glass 2 and the second plane glass 3 respectively.
Since both surfaces of each lens of the optical module of the invention are aspheric surfaces, the shape of the aspheric surfaces must satisfy the conditions of the following formula:
where, z is the value of a reference position with respect to a vertex of the surface along the optical axis and at a position with a height h;
k is a conic constant;
c is the reciprocal of a radius of curvature; and
A, B, C, D, E, G . . . are coefficients of high level aspheric surfaces.
With the pre-installed diaphragm and the installed first lens, second lens, third lens and fourth lens, the sensitivity of tolerance of the system can be lowered to enhance the yield rate and obtain a high imaging quality.
While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.