| 摘要 |
The invention provides a stereoscopic imaging optical system that has a total optical length enough short to be well fit for electron image microscopes. The stereoscopic imaging optical system comprises, in order from its object side, one objective lens OB and a plurality of zoom imaging optical systems ZI. Each zoom imaging optical system ZI comprises, in order from its object side, a positive first group G1, a negative second group G2, an aperture stop AS, a positive third group G# and a positive fourth group G4. The second group moves on an optical axis for zooming, and the fourth group moves on the optical axis in association with the second group for correcting an image position fluctuation incidental on zooming. Conditions (1) and (2) are satisfied: Condition (1) is concerned with the imaging magnification at a low zoom ratio end of the whole of the groups on an image side with respect to the aperture stop, and Condition (2) is concerned with the ratios about a difference between the positions of the fourth group at a low zoom ratio end and a high zoom ratio end and a difference between the positions of the second group at a low zoom ratio end and at a high zoom ratio end.
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