Thanks to Jim for raising an issue that has long been a question I have
never heard an adequate answer to.  What exactly are the beads that people
use for these measurements. I presume they are not hollow spheres but a
semi-solid or open matrix.  Are they optically transparent?  I doubt it.
If not, then how can you expect to get clean data from the far side of teh
sphere-ie the top of the object away from the light source.  It has always
seemed to me that the only way you could accurately do this is to make
spheres out of a refractive index matched material and then resuspend those
beads in fluorescent dye and image the black holes. Haven't I seen "isn't
science cool" demonstrations of materials that disappear in water due to
index matching?  ANyone know what material has that property?  Dave
 
Dr. David Knecht
Department of Molecular and Cell Biology
University of Connecticut
U-125
Storrs, CT 06269
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