| 摘要 |
PROBLEM TO BE SOLVED: To obtain a wide-angle photographic lens which is small in size and light in weight and has good image forming performance by providing an apherical surface which is thicker at its peripheral part than when the lens surface is constituted to curvature nearby the optical axis, and satisfying specific conditions. SOLUTION: This lens is composed of a 1st lens with positive power, a 2nd lend with positive power, a stop, a 3rd lens with positive power, a 4th lens with negative power, and a 5th lens with positive power in order from an object side. This lens has at least one aspherical surface which is thicker at the peripheral part than when the lens surface is composed to curvature near the optical axis and satisfies the conditions shown by the expressions. In the expressions, fi (i=3, 4, and 5) is the focal length of an (i)th lens, (f) is the focal length of the whole system, andνj (j=1, 2...5) is the Abbe number of a (j)th lens. The aspherical surface of this wide-angle lens is used preferably as its 5th lens.
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