This paper starts with a description of the usability and the optical layout of an Abbe or Telescope type surgicalmicroscope for stereo optical and stereo digital imaging. Most important optical characteristics for stereoscopic imageaquisition are emphasized. Afocal Galilei-type optical zooms are the heart of all modern stereo microscopes forindustrial, bioscience and surgical applications. Two type of such zooms are described:Type 1: two separate optical channels, one for each stereoscopic view and.Type 2: one common optical channel for both stereoscopic views each guided off-axis.Type 1 zooms have the advantage of compact size and high optical quality. Their downside are tight tolerances andadjustment of optical members required for a good binocular performance. Type 2 zooms are always good at binoculareven for standard tolerances but suffer from magnification dependency of the stereoscopic perception and from nonsymmetricalvignetting. Design examples are provided and some important aspects of aberration correction arediscussed. As a vignetting-free system, one afocal commom optical channel Kepler-type zoom design example isproposed.Finally, some advanced surgical microscope setups suitable for two stereoscopic observers in one microscope havingdifferent stereoscopic perspectives on the magnified object are shown. The Type 2 common optical channel zoom ofGalilei or Kepler type is the best choice if a variable rotation position of a stereoscopic co-observer is required.
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