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>--- You wrote:
>I have had some success with flow cytometry standard beads.  They
>do bleach out, but are abundant enough that each measurement can be made on a
>new one.  FCSC makes very well characterized beads.  I think they are now
>owned by BANGS
>--- end of quote ---
>David and others,
>We have used beads often for sensitivity checks  --- we like the
>Rainbow ones from Spherotech.  I think, however,  that  standard
>plastic slides would be lots better.  No problem with bleaching.  A
>full field to survey each time. No focus issues.  And the
>possibility of getting the slides at many defined "concentrations."
>All we need now is some company prepared to make the slides for us
>at defined and low intensities.....any offers?
>
>Alice
>Alice L. Givan
>Englert Cell Analysis Laboratory
>of the Norris Cotton Cancer Center
>Dartmouth Medical School
>Lebanon, New Hampshire NH 03756
>tel 603-650-7661
>fax 603-650-6130
>[log in to unmask]

Sorry for the slow response but just noted the comment about "no
focus issues".  I think that this is not quite true.

Assuming that you are using an oil lens, and have it oil-coupled
through a 170 micrometer coverslip to the plastic, you should be able
to use the specimen as a  "z-step" resolution test specimen (i.e.,
you can measure z-sharpness, rather that being able to "resolve" two
nearby horizontal planes).

However, the moment you focus into the plastic, you will produce
spherical aberration which will reduce signal strength. Then what you
get WILL depend on focus position, unless the plastic RI is close to
1.52.

Cheers.

Jim P.
--
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Prof. James B. Pawley,                             Ph.  608-263-3147
Room 223, Zoology Research Building,               FAX  608-265-5315
1117 Johnson Ave., Madison, WI, 53706              [log in to unmask]
"A scientist is not one who can answer questions but one who can
question answers."  Theodore Schick Jr., Skeptical Enquirer, 21-2:39