The Gradient Contrast Illuminator, when mounted in lieu of the OEM condenser in infinity-corrected microscopes, provides contrast enhancement similar to that achieved by DIC, phase contrast, and other contrast-enhancement methods.  The IS-GCI is rotated in the OEM condenser mount until contrast is maximized.  The top of the condenser is threaded for the attachment of oil and dry condenser lenses.  It doesn't attenuate as much light as typical contrast methods, providing more light / superior contrast for high-magnification contrast imaging.