| 摘要 |
According to the present invention, a small-sized double-lens imaging optical system whose chromatic aberration is corrected even at a super wide angle of 150° or more can be provided. The double-lens imaging optical system of the present invention includes a concave lens, and a convex lens having a diffraction grating provided thereon, and satisfies the following conditional expression (1): 4.5<P1=(1−f/fa)·&ngr;d<9.0  (1). Herein, f is an effective focal length of the double-lens imaging optical system; fa is an effective focal length of the double-lens imaging optical system excluding the diffraction grating; and &ngr;d is an Abbe number of the material of the convex lens with respect to the d-line. As a result, chromatic aberration can be well corrected even with respect to rays entering at high angles of view.
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