Kevin,

Check the LEICA MICROSYSTEMS web page: http://www.llt.de/tips.html

There is a paragraph on: Imaging of fluorophore plated polystyrene beads

In this article it is stated that the beads indeed act as an additional
(and non-ideal) spherical lens producing spherical aberrations.

Guenter
----------------------------------


At 09:32 17.05.00 +0200, you wrote:
>Hello everyone,
>
>recently we've been observing polystyrene microspheres of about 15µm
>diameter with a 10X NA=0.45 lens and have seen some strange effects. We're
>using the MRC1024 system of Biorad. When scanning the microsphere in the z
>direction (iris set as small as possible: 0.7mm), it was visible over about
>220µm (!), while in the xy-plane, the diameter was indeed ~15µm. When using
>a 60X NA=1.4 oil immersion lens, the visibility in the z direction was
>reduced to ~60µm. This suggests that the observed effect has to do with a
>lens effect of the microsphere itself which apparently depends on the
>entrance angle of the light into the microsphere. I know that confocality
>decreases with decreasing NA of the objective lens, but can this account for
>what we've seen?
>
>Does anyone know an explanation for this, or has anyone seen this before?
>Any suggestions will be greatly appreciated.
>
>Thanks,
>
>Kevin Braeckmans, physicist
>Lab. General Biochemistry & Physical Farmacy
>Ghent University
>Harelbekestraat 72
>9000 Gent
>Belgium
>Tel: +32 (0)9 264.80.78
>Fax: +32 (0)9 264.81.89
>E-mail: [log in to unmask]
>http://gmserv.rug.ac.be/biofys/braeckmans.html
>

----------------------------------

----------------------------------
Dr. Guenter Giese
MPI fuer Medizinische Forschung
Abt. Biomedizinische Optik
Jahnstr. 29
D-69120 Heidelberg
Phone (Germany or 0-)6221-486-320
Fax   (Germany or 0-)6221-486-325
e-mail: [log in to unmask]
------------------------------------------