Imaging lens

#Conventionally, an imaging device using an image pickup device, such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), has been known. In such an imaging device, an image of an object is formed on an image pickup device and electronic signals from the image pickup device are processed in order to create image data that may be recorded or further processed to provide an image for viewing. Miniaturization of the image pickup devices has been progressing in recent years in order to make the entire imaging device smaller.

#In particular, the miniaturization of module cameras for inputting picture images in cellular phones and digital still cameras (hereinafter referred to as digital cameras) has been remarkable in recent years. Conventionally, the imaging lens used in small imaging devices has been a small, single lens component in order to achieve the desired small size and portability desired. Additionally, in recent years, the performance capabilities of image pickup devices has been improved, and small image pickup devices with higher pixel densities have been developed without increasing the size of the image pickup device. Associated with the realization of higher pixel density, higher optical performance of the imaging lens used with the image pickup device is demanded. However, a small, single lens component does not satisfy the optical performance requirements needed.

#Recently, in order to obtain tolerable optical performance for image pickup devices having a high pixel density, consideration has been given to increasing the number of lens components of the imaging lens. However, while increasing the number of lens components enables improvement of the image quality, it is disadvantageous from the standpoint of increasing the overall length of the imaging lens, and may result in the small size and portability of the imaging device being lost. Conventionally, an imaging lens with a high optical performance that is suitable for mounting in a small, image pickup device having a high pixel density has not been fully developed in terms of satisfying the desired miniaturization requirements and providing a satisfactory image quality.

#The present invention will become more fully understood from the detailed description given below and the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention, wherein:

#FIG. 1 shows a cross-sectional view of the imaging lens according to Embodiment 1;

#FIG. 2 shows a cross-sectional view of the imaging lens according to Embodiment 2;

#First, definitions of the terms “lens element” and “lens component” that relate to the following detailed description will be given. The term “lens element” is herein defined as a single transparent mass of refractive material having two opposed refracting surfaces, which surfaces are positioned at least generally transversely of the optical axis of the imaging lens. The term “lens component” is herein defined as (a) a single lens element spaced so far from any adjacent lens element that the spacing cannot be neglected in computing the optical image forming properties of the lens elements or (b) two or more lens elements that have their adjacent lens surfaces either in full overall contact or overall so close together that the spacings between adjacent lens surfaces of the different lens elements are so small that the spacings can be neglected in computing the optical image forming properties of the two or more lens elements. Thus, some lens elements may also be lens components. Therefore, the terms “lens element” and “lens component” should not be taken as mutually exclusive terms. In fact, the terms may frequently be used to describe a single lens element in accordance with part (a) above of the definition of a “lens component.”

#A general description of the preferred embodiments of the imaging lens of the present invention will now be described with reference to FIG. 1 that shows Embodiment 1. In FIG. 1, the lens elements are referenced by the symbols L1 and L2, in order from the object side of the imaging lens. Similarly, the radii of curvature of the lens elements are referenced by the letter r followed by a number denoting their order from the object side of the imaging lens, from r1 to r4.

#In accordance with the definitions of “lens component,” and “lens elements” above, in the thirteen preferred embodiments of the imaging lens of the present invention described below, lens elements L1 and L2 are also lens components. Thus, the present invention may variously be described in terms of lens elements or in terms of lens components.