The #21 mount set adapts specific shutter housing types to a Zeiss type microscope configured with the Zeiss type Axiovert Ring Dovetail Mounts. No modification to the microscope should be necessary. A filter area is also provided to allow the user to install an optical filter between the light source and the shutter housing. The housed versions of the VS, LS, and XRS series shutters, as well as the CS25 and CS35, can be configured with this mount set type. A clearance cutoff (1.38 in / 35.1 mm from aperture center) is provided with the VS series only.