Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
2000-02-24
2001-10-02
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C359S642000
Reexamination Certificate
active
06297915
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image pickup lens and particularly, to a single image pickup lens which is used in an image pick-up device, e.g., a CCD camera, utilizing an image pickup element such as CCD, CMOS and the like mounted on a potable computer, a visual telephone and the like, and which can be reduced in size and weight.
2. Description of the Related Art
In recent years, multimedia have been developed remarkably, and for example, the demand for a CCD camera mounted on a portable computer, a visual telephone and the like is being increased remarkably. Such a CCD camera is required to be mounted in a limited space and for this reason, it is desired that the CCD camera is small in size and lightweight.
Therefore, it is also desired that an image pickup lens used in such a CCD camera is likewise small in size and lightweight.
A so-called single-lens system employing a single lens is conventionally used as such an image pickup lens system.
There is such a conventionally known image pickup lens in a single-lens system, which is disclosed, for example, in Japanese Patent Application Laid-open No.6-88939 and the like.
The known image pickup lens is formed so that the radius of curvature of a second face of the lens is set in a range of 0.5 to 0.63 times the focal length thereof, and the Abbe constant is set smaller than 50.
In the conventional image pickup lens disclosed in Japanese Patent Application Laid-open No. 6-88939, however, in an image pickup element used presently in relatively many fields, an intended effect can be provided, but recently, a further reduction in size of the image pickup element is desired. For example, if the entire optical system is reduced in size in the use of a lens for an image pickup element having a size as small as ⅙ inches or ⅛ inches, the radius of curvature of a second face of the lens is set in a range of 0.5 to 0.63 times the focal length thereof. This results in a problem that the curvature of a second face of the lens is extremely large and hence, it is extremely difficult to process the lens and further, the lens is dim. Moreover, another problem is that the spherical aberration and the coma are increased, because the curvature of the second face of the lens is increased.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an image pickup lens which can be reduced in size and weight and can be produced easily.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an image pickup lens which is a biconvex lens, at least one of faces of which is formed into an aspherical shape, so that the following conditions (1) and (2) are satisfied:
(1) |R
2
|/f≧0.65
(2) |R
1
|>3 |R
2
|
wherein R
1
is a radius of curvature of the face of the lens on the side of an object; R
2
is a radius of curvature of the face on the side of an image pickup element board; and f is a focal length of the single lens.
With the above arrangement, the lens satisfies the conditions represented by the expressions (1) and (2). Therefore, the aberration can be corrected sufficiently, and a good processability can be provided. Moreover, the radius of curvature of the second face can be prevented from being too increased by limiting it in a relationship with the first face of the lens, thereby ensuring a sufficient back focal length.
As a result, even when a lens for a small-sized image-pickup element is formed, the lens can be produced easily, while maintaining an optical performance such as a required angle of view and the like. In addition, the focal length relative to a required angle of view of an optical system can be decreased and consequently, the reduction in optical performance can be minimized.
According to a second aspect and feature of the present invention, in addition to the first feature, the lens is formed from a resin having a high refractive index.
With the second feature, since the lens is formed from a resin having a high refractive index, the focal length of the lens can be shortened, while maintaining the curvature of the lens.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5418649 (1995-05-01), Igarashi
patent: 5900994 (1999-05-01), Otomo
patent: 5917661 (1999-06-01), Tochigi
Kaneko Isamu
Saito Tomohiro
Enplas Corporation
Epps Georgia
Koda & Androlia
O'Neill Gary
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