| 摘要 |
PURPOSE:To stabilize the optical performance and to make simple the mirror frame construction by being composed of the first group to have the positive power and the focusing function, the second group to have the negative power and the variable function, the third group to have the positive power and the variable power function and the fourth group to have the positive power and the variable power function. CONSTITUTION:A zoom lens is composed of the first to fourth groups, and satisfy respective conditions of inequalities (1)-(4) (Provided that f1 and f2 are respectively the focus distance of the first and second groups, fw is a focus distance of all systems at the wide edge, beta2T and beta2W are respectively the magnification of the second group at the telephoto edge and the wide edge, beta3T and beta3W are respectively the magnification of the third group at the wide edge and beta4T and beta4W are respectively the magnification of the fourth group at the telephoto and wide edges.). Thus, for the zoom lens, the minimum picture angle is 19 deg. or below, the maximum picture angle is the large zoom ratio which exceeds 60 deg., the maximum aperture ratio is the lens system of F/3.5 for the wide edge and F/4.68 for the telescope edge, the aberration is satisfactorily corrected and both whole length and outer diameter come to be compact.
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