Koehler illumination in conoscopic observation

Hello,

On a Nikon scope of type L-Ke the illumination
is truly of the Koehler type. The filament of the
tungsten light is imaged onto the diaphragm of
the condenser lens and is centered and clearly
visible at the back focal plane of the objective
when viewed through a Barlow lens.

Koehler illumination is considered to be an ad-
vantage for most types of observation. It is of
apparent disadvantage when one wishes to ob-
serve the interference figures formed by bire-
fringent crystals using the conoscopic form of
observation in polarization microscopy. In that
case the interference pattern formed by the
crystal is superimposed upon the image of the
lamp's filament causing difficulty in clearly seeing
it..

Does anybody know of a way to get around this
problem? One might think of a diffusing filter
someplace in the path of illumination. If this is
a feasible approach where would one place this
filter and what kind should one use?

Thanks for any suggestions
GR.


use conoscopic observation of the
interference figures formed by birefrigent crystals in the
manner


.

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