Transparent specimens, which are almost invisible when viewed in the stereomicroscope using traditional brightfield illumination techniques, often assume a pseudo three-dimensional appearance with stark contrast when viewed in oblique illumination. This interactive tutorial explores variations in specimen contrast produced by Nikon's Oblique Coherent Contrast (OCC) illumination system designed to optimize contrast in transmitted stereoscopic microscopy. The OCC illumination system is available for Nikon's Common Main Objective design stereomicroscopes.
The tutorial initializes with a randomly selected specimen appearing in the virtual microscope port, and being illuminated with brightfield axial light. To translate the sliding diaphragm, use the mouse cursor to move the Diaphragm Position slider to the right. The current illumination mode (brightfield, oblique, or darkfield) is displayed above the slider bar and changes to match new modes when the diaphragm position is altered. As the slider is moved from left to right, the illumination mode progresses from brightfield, through various degrees of oblique illumination, finally ending in darkfield mode. Changes in specimen appearance in the virtual microscope viewport coincide with alterations made to the illumination mode.
A drawing of the optical pathway for oblique coherent contrast illumination is presented beneath and to the right of the microscope viewport. Translation of the Diaphragm Position slider also invokes a shift of the illumination from brightfield to varying degrees of oblique illumination through the optical pathway drawing. To select another specimen, choose a new candidate from the Choose A Specimen pull-down menu.
Matthew Parry-Hill and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.