PROBLEM TO BE SOLVED: To provide a stereoscopic imaging optical system that has a total optical length enough short to be well fit for electron image microscopes.SOLUTION: The stereoscopic imaging optical system includes, 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 includes, in order from its object side, a positive first group G1, a negative second group G2, an aperture stop AS, a positive third group G3 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.COPYRIGHT: (C)2010,JPO&INPIT【課題】電子画像顕微鏡に適した光学全長の短い立体撮影光学系。【解決手段】物体側から順に、1本の対物レンズOBと複数本の変倍結像光学系ZIからなる立体撮影光学系において、変倍結像光学系ZIは、物体側から順に、正の第1群G1、負の第2群G2、明るさ絞りAS、正の第3群G3、正の第4群G4からなり、第2群G2が光軸上を移動して変倍し、第4群G4が第2群G2に連動して光軸上を移動して変倍に伴う像位置変動を補正すると共に、低倍端における明るさ絞りより像側の群全体の結像倍率に関する条件式(1)と、第4群の低倍端と高倍端で位置の差と第2群の低倍端と高倍端で位置の差との比に関する条件式(2)と満足する。【選択図】図1
