The lamp is centered and Kohlered according the book and way to bright. I mostly limit it to less than 2V (it goes to 12V) and it is rather red then.
The first thing I wanted to try was the lomo OI-2, a 1950 cardioid darkfield condenser that I fitted to the Nikon, using most of an earlier condenser adapter. Pictures and a description of this very condenser are in Ivan Vysokovskikh's museum, a website that deserves interest of those with Russian microscopes. Google translate (to English!) does a quite decent job here to make it accessible for us mere mortals.
This worked quite well, in line with its specs much better wet (glycerin) than dry. There's an almost magic flash of light when the immersion fluid catches on the slide.
For no reason I then changed the illuminator and held the new epi-lighthouse to the trans-illuminator's light port. Surprisingly, at once I got ultra-bright DF images! I cannot say I do understand this. When I measure the light with my camera, the 50W halogen lamp results in two stops more light than the epi-leds in that same position. Nonetheless the darkfield images are duller. With the led light it was too bright to see at places.
I could not bring the epi light's leds far enough to front to get them in focus with the telescope. I centered it to the maximum output as measured by the camera. This must have resulted in an imperfect collimation by the collector lens. This couldn't possibly be helping lighting the DF, could it?
Anyway, I wonder if another led lamphouse wouldn't be much preferable to the halogen lamp.
Wim