The Hertel & Reuss CN-fl microscope looks identical to the CN-hf model (link here: https://www.microscopeparts.eu/microscope/226 ).
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.
For these models, an angled mirror mounted in the base could be purchased, allowing the use of a large HAPRO halogen illuminator (link here: https://www.microscopeparts.eu/part/00662 ).