Dark field microscopy

Dark field microscopy (dark ground microscopy) describes microscopy methods, in both light and electron microscopy, which exclude the unscattered beam from the image.

Light enters the microscope for illumination of the sample.
A specially sized disc, the patch stop (see figure) blocks some light from the light source, leaving an outer ring of illumination.
The condenser lens focuses the light towards the sample.
The light enters the sample. Most is directly transmitted, while some is scattered from the sample.
The scattered light enters the objective lens, while the directly transmitted light simply misses the lens and is not collected due to a direct illumination block (see figure).
Only the scattered light goes on to produce the image, while the directly transmitted light is omitted.

For live samples, no staining needed. But low light levels.