Optimized Transillumination
in the Microscope

"Correct illumination of the microspecimen is the single most important aspect of critical microscopy and photomicroscopy. Fully 80 percent of all photomicrographs submitted for contests and exhibitions are rejected because of improper illumination of the microspecimen. Another 10 percent of the photomicrographs reflect improperly adjusted aperture diaphragms". [Photography through the Microscope, Eastman Kodak Company, 1988, Ninth Edition]

Dr. August Köhler published a paper in 1893 that described a method to obtain the highest intensity of even illumination from a nonhomogeneous source. Applying the "Köhler" method requires the control of 2 iris diaphragms in the light path: the Field and the Aperture. The Field eliminates all stray light by restricting illumination to the actual area under observation. The Aperture controls the cone of light transilluminating the sample so it fills the aperture of the microscope objective, thus optimizing depth of focus and image contrast.

The relationship of diaphragm position and objective lens magnification can be seen above. In an incident light system, the light is directed to the back of the objective lenses. In the transmitted light system, the light is directed to a substage condenser lens with a numerical aperture that approximates the highest numerical aperture of the objective lenses. The substage condensor is automatically lowered to expand the illumination field when low numerical aperture objective lenses are in use. The entire assembly is motorized to provide remote focus capability. The PC-Scope is calibrated to adjust the diaphragms to their proper settings automatically as a function of objective lens selection.


The Next-Generation of Optical Microscopy
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