Hello group.
 
I'm using a Zeiss microscope to examine a thin film of auto-fluorescent
polyurethane cast onto a glass coverslip.  The objective is a Nikon 1.30
glycerol immersion.  Images obtained in reflected mode seem reasonable but
transmitted images are sharp only in the periphery.  In the center of the
field there seems to be a circular haze extending 1/3 of the way out to
the edge.  This occurs at every setting of the condenser, and I can see
the haze through the binocular.  Any ideas?
 
Rik G.