| 摘要 |
A varifocal optical system having at least two lens units A and B, the lens unit A being axially moved to vary the magnifying power, and, while it is moving, the refractive power of the lens unit B being continuously varied to compensate for the displacement of the position of the image surface caused by the variation of the magnifying power of the lens unit A, wherein variation of the refractive power of the lens unit B is made so as to maintain the constant position of a front principal point of the lens unit B when the lens unit A is in front of the lens unit B, or a rear principal point of the lens unit B when the lens unit A is at the rear of the lens unit B, relative to the image plane of the entire system.
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