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Hi Scott,

To reiterate what everyone else has been saying, even relatively small  
fluctuations in temperature can have a significant impact on focus.

To provide an example:  I was in an air-conditioned lab over the  
summer and as the air-conditioning turned off and on, the change in  
focus due to thermal expansion was on the order of a micron for a  
1-1.5 deg. C change in temperature - this happened at a period of  
about 200 seconds with the specimen going in and out of focus.

Because I use an older spinning disk unit (without infinity-corrected  
optics) that's no longer sold or supported, many of the "autofocus"  
options available on newer infinity-corrected scopes were not an  
option for me.  Therefore, to compensate for thermal drift, I  
regularly sampled two areas from the CCD image every ten seconds and  
used a metric (e.g. contrast) to determine the z-position and then  
corrected using the piezo.  This was not the most elegant solution -  
most modern "autofocus" options are faster and run parallel to the  
image acquisition - however, it works reasonably well for my  
application (imaging of semiconductor layers) and is pretty cheap.

With this in mind, how often do you need to capture an image - do you  
need continuous video or snapshots?

Hope this proves useful.  Good luck!
-Joe



On Sep 18, 2008, at 8:56 AM, Scott Howell wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> All,
>
> Have new faculty coming aboard and a major application will be 48 hour
> timelapse studies in 96 well plates using multichannel collections.
> Therefore my question is how critical is it to have a system that has
> a perfect focus mechanism to meet this application? Are there decent
> work arounds if the perfect focus is not used? Have never actually
> worked with this type of system so would like input on this matter
> from the list. Thanks.
>
>
> Scott J. Howell, Ph.D.
> Manager, Imaging Module
> Visual Sciences Research Center
> Case Western Reserve University
> 2085 Adelbert Rd.
> Institute of Pathology Room 106
> Cleveland, Ohio 44106
> 216-368-2300
> http://www.case.edu/med/vsrc/

------------------------------------
Postdoc, Physics Dept.
Optoelectronics Group
Mt. Holyoke College
ph: (413) 538-2263
http://www.mtholyoke.edu/~jsummers/