Success at last! I have managed to successfully take photos using my Phil Dyer and Watec video cameras on the Zeiss IM microscope. I obtained a second hand Diagnostic Instruments C-mount adapter from ebay which fits directly into the ocular/eyepiece tube without any need for a collar/clamp. There are Zeiss clamps – mainly they attach to the phototube attachment on a trinocular head (but I don’t have one of those).
Diagnostic instruments HR070-CMT C-mount to microscope adapter:
Phil Dyer video camera on Zeiss IM microscope using DIagnostic Instruments adapter:
Watec 120-N camera on Zeiss IM microscope using Diagnostic Instruments C-mount adapter: