| 摘要 |
PURPOSE:To suppress fluctuation in the full aperture value in the zoom position of an intermediate region during zooming and to improve spherical aberration by setting the full aperture F-number so that the axial luminous flux of said number passes the periphery of the aperture of a stopper in a specific zoom range. CONSTITUTION:Zooming is accomplished by moving the 1st lens group I and the 2nd lens group II on the optical axis and an aperture diaphram is provided in the 2nd lens group. A stopper is disposed between the 2nd lens group II and the 3rd lens group III. A full aperture F-number is so set that the axial luminous flux of said number passes the periphery of the aperture of the stopper in the entire zoom range from 0.9Z to Z where the zooming magnification is designated as Z. Since the full aperture F-No. is determined by the bore of the stopper in the range from 0.9Z to Z zooming magnification, the luminous flux for an error difference can be cut by the stopper and therefore the full aperture performance is satisfactorily maintained. |
