| 摘要 |
PURPOSE:To obtain a telephoto lens in which the variation of aberration resulting from the movement of the lens is suppressed and the aberration is excellently corrected, by making a lens system to satisfy prescribed conditions in a lens system composed of three groups having positive, positive, and negative refracting powers in order from the object side. CONSTITUTION:In a lens system composed of three groups having positive, positive, and negative refracting powers in order from the object side, the 1st group is composed of four lenses arranged in the order of negative, positive, negative, and positive from the object side or of three lenses arranged in the order of positive, negative, and positive, and the 2nd group is composed of two lenses of negative and positive. The 3rd group is composed of three lenses arranged in the order of negative, positive, and negative or positive, negative, and negative from the object side. Focusing operation is performed by moving the 2nd group from the image side to the object side and conditions (1)-(5) are satified. The F, F1, and F1.2 of the conditions (1)-(5) represent the focal lengths of the whole system, 1st group, and the composite system of the 1st and 2nd groups, respectively. The D1 represents the air space between the 1st and 2nd groups and R0 and Ri are the radii of curvature of the 2nd group lenses at the side nearest to the object and the image side, respectively. The D3 is the air space between the 2nd and 3rd lenses of the 3rd group. When such a lens system is used, a telephoto lens in which the variation of aberration resulting from the movement of the lens is reduced and the aberration is excellently corrected is obtained. |
