The production of orbital angular momentum (OAM) using an electrically-tunable q-plate, spiral phase plate or spatial light modulator, as well as a phase mask that can act as a spatial frequency filter, provides a simple, efficient method of edge contrast in biological, objects and medical sample imaging for histological evaluation of tissue, smears, PAP and histopathological samples. An OAM instrument produces OAM situated at the Fourier plane of a 4F lens system, similar to the use of a high-pass spatial filter, allows the passage of high spatial frequencies and enables the production of an image with highly illuminated edges contrasted against a dark background for both opaque and transparent objects.