Hi everyone! I've seen these explanations on the affiliated website of truevisionmicroscopes.com which is livebloodlabs.com. Hope these could bestow more informations to some of the forum members:

Phase contrast microscopy imaging techniques allow normally clear transparent blood cells to appear with increased contrast. This gives the advantage of seeing greater surface detail. Differences in refractive indices of the specimen alter the phase of the light waves. This phase shift is translated into differences in light intensity, effectively allowing better viewing contrast.

Darkfield microscopy imaging techniques provide a method to view features in blood not normally shown with phase contrast and brightfield illumination. This method illuminates the specimen from the side, not from behind, so the background is black. Minute features of the blood are shown in a glowing light as it reflects off their surfaces.

Brightfield microscopy imaging techniques are used in dry layer blood analysis. Light is transmitted through the specimen, and the resulting image is clear and bright. Although it is an excellent technique for examining dry blood, it fails to provide the images in live blood that are necessary for a proper evaluation.

For light microscopy it depends on what you want to demonstrate. There are various staining techniques that stain different nuclear & cytoplasmic components different colours. Not so useful for RBC's of course, but very useful for classifying some of the lymphomas etc. especialy the immunologigal methods, plus the demonstration of blood borne parasites.