| 摘要 |
PROBLEM TO BE SOLVED: To provide a wide-angle lens which has small distortion, a small chromatic aberration, and small variation in performance against variation in projection distance although the lens has long back focus. SOLUTION: The lens has a 1st lens group 11 with negative refracting power, a 2nd lens group 12, and a 3rd lens group 13 with positive refracting power in sequence from long conjugate distance, and the 2nd lens group 12 has less refracting power than the 1st lens group 11 and 3rd lens group 12; when the power is varied from a long distance to a long distance, the 1st lens group 11, 2nd lens group 12, and 3rd lens group 13 move along the optical axis, the air gap between the 1st lens group 11 and 2nd lens group 12 decreases, and the air gap between the 2nd lens group 12 and 3rd lens group 13 increases. An aperture diaphragm 16 is positioned between the 2nd lens group 12 and 3rd lens group 13 and 4<bf/f<6 is satisfied, where bf is the air-converted back focus of the wide-angle lens corresponding to an infinite distance and (f) is the focal length of the wide-angle lens. COPYRIGHT: (C)2004,JPO
|
