Dark field microscopy is the art of using indirect light to illuminate specimens under your microscope lens; because the light is indirect, it doesn’t shine into the microscope, and the specimen appears to be floating brilliantly against a night-black background.
Image via Wikimedia Commons, on which Uwe Kils has quite a few wondrous images.
I decided to look up dark field microscopy after seeing this photograph of fruit fly sperm that looks like a study from Vincent Van Gogh’s Starry Night. The technique seems to be the same, on a small scale, as the way the moon is lit by the sun.