The #21 mount set adapts specific #2 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. All shutter types (LS or VS - excluding the CS45) can be configured with this mount set type. A clearance cutoff (1.38in/35.1mm from aperture center) is provided with the VS series only.