Dark-field Microscopy

Basic setup
Similar to a bright field but it is modified by a dark field stop just below the condenser, just above the light source. The dark field stop is just  the condenser, and blocks the light in the center of the lightsource so that the only light that goes through is around the edges. That light is then bent by the condenser and diffacts off the specimen. None of the light goes directly from the light source into the objective, so if there is no specimen, the image will be very dark. The specimen in this method will be illuminated against a black background

Uses
A dark field microscope is useful because it increases the contrast of the image and does not use stains. The lack of staining means that it can be used on live specimens and that one can observe the motility of the organism as well as its correct morphology. Usually, the stains and enzymes used in labs can distort the shape of the organism, but that isn't an issue with dark field microscopy. This method can also be used to see organisms that are hard to stain, such as Treponema pallidum, spirochetes, and mycoplasma.

The one downside is that it's not possible to see the inclusions, or internal details of the cell