| 摘要 |
PROBLEM TO BE SOLVED: To obtain a compact and inexpensive lens achieving excellent performance even with near infrared light. SOLUTION: This wide-angle lens is constituted of a 1st lens 1 having negative power and a 2nd lens 2 being a biconvex lens in order from an object side. One or more lens surfaces are made aspherical. When it is assumed that the focal distance of an entire system is (f), the focal distance of the 1st lens is f1 and the focal distance of the 2nd lens is f2, the lens satisfies conditions f<|f1|<1.25f and 0.85<=|f2/f1|<=1.15. Thus, an excellent image is obtained both with visible light and the near infrared light, because Petzval's sum and chromatic aberration are small even though the 1st and the 2nd lenses are made of the same material though two lenses have only to be required, a surface-to- surface distance between the lenses is short and the lens is compact and has the wide angle of view.
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