The Hertel & Reuss CN-hf microscope looks identical to the CN-fl model (link here: https://www.microscopeparts.eu/microscope/19 ).
The photo shows the two microscopes side by side; the CN-hf model is the one with the round opening inside the arm.
The CN-fl model was also available with a base without illumination - for use with a mirror or external illuminator.
These models could be equipped with an angled mirror mounted in the base, allowing the use of a large HAPRO halogen illuminator (link here: https://www.microscopeparts.eu/part/00662 ).