Page "Microscopy" Paragraph 19

The use of oblique ( from the side ) illumination gives the image a 3-dimensional appearance and can highlight otherwise invisible features.

A more recent technique based on this method is Hoffmann's modulation contrast, a system found on inverted microscopes for use in cell culture.

Though Oblique illumination suffers from the same limitations as bright field microscopy ( low contrast of many biological samples ; low apparent resolution due to out of focus objects ), it may highlight otherwise invisible structures.