In recent years personal computers have become very popular. Now, digital cameras that enable photographed picture information to be easily processed are rapidly becoming popular.
More compact and inexpensive digital cameras are being demanded; therefore, it is especially urgent to provide a more compact and inexpensive photographic lens for such cameras. To respond to these requirements, the inventor of the present application has developed a single focus lens that is formed of only three lens elements, as disclosed in Japanese Patent Application 2001-156653. This single focus lens is formed of, in order from the object side, a first lens element having at least one surface aspheric and which has a weak refractive power, a second lens element of positive refractive power and having its image side surface convex, and a third lens element having at least one surface aspheric and which has a weak refractive power. Although the above-mentioned prior art can meet the requirement of being compact and inexpensive, additional improvements are required from the standpoint of aberration correction in order to provide a higher-quality model of single focus lens. Furthermore, as compared with a conventional compact camera that uses film, the design of a lens for a digital camera is much different not only because of the electronic image sensor that receives the image in a digital camera being much smaller, but also because it is necessary in digital cameras to have the light rays be incident onto the image sensor roughly perpendicular to the detecting surface of the image sensor. Further, a high aperture efficacy and a long back focus are required in digital cameras.