(Science: microscopy) Essentially an Abbe condenser in which the upper lens element is fixed and the lower movable. The lower lens may be used to focus the illumination between the elements so that it emerges from the stationary lens as a large diameter parallel bundle. The field of low-power objectives may thus be filled without removing the top element. at the opposite extreme it can be adjusted to have a numerical aperture as high as 1.3.
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... are many ways to increase and decrease contrast in a microscope. The condenser iris is but one of them. Clear blue filters or various other colored ... recently introduced by Zeiss of Germany is VAREL Contrasting or Variable Relief Contrasting . This has the combined features of COL and Phase ...
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