| 摘要 |
A zoom image-forming optical system used in combination with an infinity-correction objective lens, the zoom image-forming optical system including: a tube lens for condensing a luminous flux from the objective lens to form an intermediate image; and a relay lens with a zoom function for projecting the intermediate image onto an image plane. The relay lens includes a first lens group with positive power, a second lens group that belongs to a movable group with positive power, a third lens group that belongs to a movable group with positive or negative power, and a fourth lens group with negative power, in this order from the intermediate image side. The zoom image-forming optical system changes its magnifying power by moving the second lens group and the third lens group in an optical axis direction.
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