Into the darkness

I've been playing with darkfield microscopy - poor man's phase contrast. Darkfield uses obliqe illumination as a cheap optical trick to increase the contrast of transparent and traslucent specimens. It can produce dramatic images with dark backgrounds and usually features prominently in microscope photography competitions such as Nikon's Small Worlds. I started out with the somewhat translucent furca of a handy Isotomurus unifasciatus specimen. On the left is my conventional setup of top plus bottom illumination, post processed; on the right darkfield transillumination, both stacked with Zerene: 

The problem here is that inserting the darkfield disc into the light path lengthens the exposure time 20-fold and the image quality suffers as a result. Looking at the non-transparent abdomen of the same specimen (conventional illumination):

Darkfield plus supplemental top light:

I think this is the better result, but clearly I need to find some transparent specimens to get maximum benefit from darkfield.