Darkfield microscopy is a technique in which the illumination light does not make it into the objective... unless a specimen diffracts/scatters some light. The background is black, if the mask is of the appropriate size, with all of the information coming from the scattering object. Diatoms are one of the best subjects for this technique - prepared stained slides rarely give better images in darkfield than with brightfield illumination (which the light from the condenser does make it into the objective directly.)
These images are successively more magnified views of a prepared slide of diatoms. For comparison, the brightfield image of the same section is shown. All images are taken with an Eclipse E200, with a simple opaque sticky dot on the blue filter at the bottom of the condenser, for darkfield illumination.
Notice that high magnifications (100x) are generally more difficult, but noticeably so with darkfield. Also, the exact position of the light cone from the condenser (the condenser stage position) is more critical than many other techniques.
Next is a macro photograph of lacewing eggs on a pine needle. Investigation with darkfield microscopy shows that the little white dots on the end of each egg is actually a little button, perhaps connected with one or more "wires" to the body of the egg. These are very challenging subjects with any illumination I have tried thus far. The darkfield images are at 10x BD Plan for the first three and 40x BD Plan for the last one, which shows the "wire". All images are single exposures.
Also with episcopic-darkfield (BD Plan 5x objective), we see a small burr which stuck to my pants leg. This is a focus stack with Zerene Stacker (PMax) of 297 images.
for navigation!