| 摘要 |
PROBLEM TO BE SOLVED: To achieve satisfactory optical performances from infinite distance to near distance with a long back focus with F number of about 4 and a half field angle of about 45°in a retro-focusing wide angle lens system including, in order from an object side, a first lens group having negative refractive power, a diaphragm, and a second lens group having positive refractive power. SOLUTION: In the wide angle lens system, the first lens group includes a negative meniscus lens with the convex surface turned to the object side, a flat convex lens or double convex lens with the convex surface turned to the object side, two negative meniscus lenses with the convex surface turned to the object side, a positive lens, and a cemented lens composed of a positive lens and a negative lens, which are located in order from the object side. The second lens group includes a cemented lens composed of a negative lens and a positive lens, and a positive meniscus lens with the convex surface turned to an image surface side, which are located in order from the object side. COPYRIGHT: (C)2009,JPO&INPIT
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