1. Field of the Invention
The present invention relates to an imaging lens for use in imaging equipment using an imaging element such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor).
2. Description of Related Art
An imaging element such as CCD and CMOS, recently, has been greatly reduced in size and increased in the number of pixels. For this reason, the main body of the imaging equipment and the lens mounted on the main body of the imaging equipment have been also required of reduced size and higher performance. Also, to correspond to the imaging element with pixels increased in number, the imaging lens is also requested to have a telecentric characteristic, that is, it is requested that an incident angle onto the imaging element is near to parallel to an optical axis (namely, the incident angle onto the imaging element is near to perpendicular to the imaging element). In the related art, for example, most of imaging lenses mounted on a cellular phone with a camera are composed of three lenses; however, in order to cope with the increased number of pixels, there is a tendency toward larger number of lenses. In an imaging lens disclosed in JP-2005-208236, a second lens disposed second from the object side is a negative lens, the surface of which on the object side is concave.
However, in the imaging lens disclosed in JP-2005-208236, there is room for improvement with respect to the chromatic aberration thereof and the like. Also, in an imaging lens composed of four lenses, in order to secure the telecentric characteristic, it is expected that an aperture stop is disposed on the object side as much as possible. In this case, when, as in the imaging lens provided by JP-2005-208236, the object side surface of the second lens is concave, the manufacturing sensitivity thereof is high and, therefore, for example, when the position of the lens is shifted in the manufacturing process thereof, the image surface thereof is easy to vary.