| 摘要 |
A zoom objective includes four lens groups of which the first and fourth groups are stationary, while the second and third groups are movable independently of each other. Focus adjustment of one of the second and third groups is followed by zooming relative movement of the latter two. To maintain a constant zoom ratio throughout the entire focusing range, the relative movement of the second and third groups is controlled to effect monotonic variation of the magnifying powers of the second and third groups by means of the following formulae as embodied in a microcomputer. Zoom Ratio=Z[S1, X1, X2(S1, X1)] dZ/dS1=O wherein S1 is the object distance; and X1 and X2 are the amounts of movement of the second and third groups with zooming respectively.
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