A Liquid Crystal Multifilter System for Diascopic Microscopy

Abstract

Various subjects such as protozoa, plant and animal cells, and the like are nearly transparent when viewed with ordinary brightfield diascopic illumination. Light is only weakly absorbed in these nearly transparent subjects so that they are not differentiated from the background light that illuminates them. In the past, various image contrast-enhancing techniques have been used to render these subjects visible and more easily studied. Dyes such as hematoxylin and eosin have been used to respectively stain the nuclei and cytoplasm of cells for improved visualization. A number of illumination- and light-processing techniques are also used to improve visualization with or without staining of subjects. These techniques include darkfield, Rheinberg, oblique, monochrome, polarized, phase-contrast, differential-interference-contrast, and intensity-modulation-contrast illumination. Each of these techniques requires its own add-on microscope accessory, and many accessories must be adjusted to match the numerical aperture of the objective lens being used. Because of these encumbrances, microscopists often pass up an opportunity to quickly view a subject in a variety of perspectives. This article describes the Diabloc™ Optic Multifilter (DOM), a digital illumination filter for diascopic microscopy. It switches between brightfield, darkfield, Rheinberg, oblique, and monochrome illuminations by the simple rotation of a knob. Adjustments for different colors and different numerical apertures of objective lenses in darkfield and Rheinberg illuminations are also done by rotating a knob. With our apparatus, a microscopist can quickly move among these contrast-enhancing methods and see what they would otherwise miss. The following paragraphs describe the physical setup for the diascopic contrast-enhancing methods encompassed in the DOM.