| 摘要 |
PROBLEM TO BE SOLVED: To provide an imaging optical system constituted so that an object-to-image distance is fixed and the fluctuation of F-number is reduced even if varying imaging magnification, and also, to provide an optical apparatus using the imaging optical system. SOLUTION: The imaging optical system is provided with at least a variable power optical system Z provided with a first positive group G1, a second negative group G2, a third positive group G3, a fourth positive group G4 arranged in this order from an object side, and an aperture diaphragm S arranged between the third group G3 and the fourth group G4, and for varying the power by changing a distance between the first group G1 and the second group G2, a distance between the second group G2 and the third group G3 and a distance between the third group G3 and the fourth group G4, and the power is varied while keeping the object-to-image distance fixed, and also, the imaging optical system satisfies the following conditional inequalities in at least one variable power state, ¾En¾/L>0.4 and ¾Ex¾/¾L/β¾>0.4. Provided that En denotes a distance from the object side first lens surface of the variable power optical system Z to the incident pupil of the imaging optical system, L denotes the object-to-image distance of the imaging optical system, Ex denotes a distance from the image side last lens surface of the variable power optical system Z to the exit pupil of the imaging optical system,βdenotes the magnification of the whole imaging optical system. COPYRIGHT: (C)2004,JPO&NCIPI
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