| 摘要 |
PURPOSE:To reduce the size, price and weight of the titled optical system by fixing 1st and 3rd groups, moving only a 2nd group in its optical axis direction so that the system can photograph as a wide angle system and a telescopic system at both ends of the 2nd group and their near positions and focusing an object defocused by the movement of the focus due to the movement of the 2nd lens. CONSTITUTION:In the optical system consisting of plural lens groups, i.e. the 1st positive group L1, the 2nd negative group L2 and the 3rd positive group L3 arranged successively from the object side, the 1st and 3rd groups L1, L3 are fixed and only the 2nd group L2 is allowed to move between the 1st and 3rd groups L1, L3 in the optical axis direction. Thereby, the optical system having two focal distances for wide angle and telescopic focuses at both end parts of the movement and their upper parts can be obtained. Consequently, a change on a screen can be obtained as compared with a single focusing lens, the weight, size and price of the optical system can be attained without expanding the size like a converter or zoom type and the optical system appropriate for a VTR image pickup can be obtained.
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