Afocal zoom lenses for stereo surgical microscopes

This paper starts with a description of the usability and the optical layout of an Abbe or Telescope type surgical microscope for stereo optical and stereo digital imaging. Most important optical characteristics for stereoscopic image aquisition are emphasized. Afocal Galilei-type optical zooms are the heart of all modern stereo microscopes for industrial, 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 and adjustment of optical members required for a good binocular performance. Type 2 zooms are always good at binocular even for standard tolerances but suffer from magnification dependency of the stereoscopic perception and from non-symmetrical vignetting. Design examples are provided and some important aspects of aberration correction are discussed. As a vignetting-free system, one afocal commom optical channel Kepler-type zoom design example is proposed. Finally, some advanced surgical microscope setups suitable for two stereoscopic observers in one microscope having different stereoscopic perspectives on the magnified object are shown. The Type 2 common optical channel zoom of Galilei or Kepler type is the best choice if a variable rotation position of a stereoscopic co-observer is required.