>I'm unconvinced that the number obtained is actually useable.
 
With the testing I've done on our Bio-Rad MRC-600, I've found that the
tilted-mirror method and doing axial resolution testing with a fluorescent point
source (.121 micron latex spheres labelled with a flurochrome) yields similar
results.  Not EXACT, but similar.  So, in answer to your statement, I would say
that the numbers you get help you to characterize the optical section thickness
you are obtaining at different pinhole settings with your various lenses.  This,
in turn can be used to set your increment (step size on your stage drive) to a
setting which should be much more optimal than merely arbitrarily setting it
with no regard to this number.
 
What we've done is to take these readings, make a table of lenses and pinhole
settings and their resulting measured optical section thicknesses and recommend
a increment setting for users interested in reconstructions.  This is usually a
multiple of pixel resolution (Field Width/number of pixles = resolution per
pixel) that is close to but less than the measured optical section thickness.
 
In this way, by adding interpolations, we can be much closer to optimal
reconstructions (based on our measurements) than we would be by guessing.
 
It's not a perfect solution, but it's done well for us.
 
Charles Thomas
Program Assistant
Integrated Microscopy Resource
University of Wisconsin
(608) 263-8481