Look i say this, but remember i barely know anything here. Still not sure even sure how all those parts are connected. But for setting up Kohler illumination it looks to be essential.

Yesterday I properly aligned the light source on my microscope and wow it was a tremendous improvement in available light. Feels at least 50% brighter.

https://evidentscientific.com/en/microscope-resource/knowledge-hub/techniques/darkfieldsetup