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Dear Deborah,
If you are going to do critical measurement, I recommend calibrating the
system. When I was microspectrophotometry specialist at one company, we
used the back of a business card to establish pure white (255) (actually,
for critical measurements, it is better to use a cake of freshly
preciptated barium sulfate) then closed the shutter and all other available
sources of ambient light to establish absolute black (0). At another
company, we had a special fluorescing plate with 4 sectors on it. One was
bare, giving us a maximum value and the other three were varying degrees of
neutral density filter, producing a more accurate 4 point
calibration. We've been approached by someone to make a similar plate, but
have not done so at this time. If there is sufficient interest, we can get
that plate produced.
Hope this is helpful.
Best regards,
Barbara Foster
Microscopy/Microscopy Education
313 S Jupiter Rd, Suite 100
Allen, TX 75002
P: 972-954-8011
W: www.MicroscopyEducation.com
P. S.
Need a good general reference or light microscopy text? Call us today to
learn more about "Optimizing LIght Microscopy". Copies still available
through MME... even for class-room lots ... and we give quantity discounts.
At 07:06 PM 5/2/2005, Guy Cox wrote:
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Actually PMTs can be pretty linear devices, so long
>as one is not operation at very high or low voltages.
>There is an effect which boosts the gain slightly
>in the midpoint of the range but proper circuitry
>can eliminate that. It's very clearly explained
>at the following reference:
>
>http://www.osa-opn.org/
>view_file.cfm?doc=%24(%5C%3F-J0%20%20%0A&id=%24)%3C%3B'IP%20%20%0A
>
>NB this is a long link and will probably have a
>line break so you may need to 'reconstruct' it.
>
>The paper mentioned is interesting in its own right,
>too - it concerns the early days of lasers.
>
>Guy
>
>
> > Dear Deborah--
> >
> > I think that the dynamic range can be linear only if one is using photon
> > counting. I'm not sure that's even possible on some systems.
> >
> > Good luck!
> >
> > Martin Wessendorf
> >
> >>> When the gain and offset of the detectors are correctly set and no
> >>> averaging is used, is the 0 to 256 dynamic range linear on a confocal
> >>> image?
> >>>
> >>> Many thanks!
> >>> Deborah Wessels, Ph.D.
> >>> W.M. Keck Dynamic Image Analysis Facility
> >>> Room 14 BBE
> >>> Department of Biological Sciences
> >>> University of Iowa
> >>> Iowa City, IA 52245
> >>>
> >>> phone: (319) 335-2883
> >>> FAX: (319) 335-2772
> >
> > --
> > Martin Wessendorf, Ph.D. office: (612) 626-0145
> > Assoc Prof, Dept Neuroscience lab: (612) 624-2991
> > University of Minnesota Preferred FAX: (612) 624-8118
> > 6-145 Jackson Hall, 321 Church St. SE Dept Fax: (612) 626-5009
> > Minneapolis, MN 55455 E-mail: [log in to unmask]
> >
>
>
>--
>Associate Professor Guy Cox
>Electron Microscope Unit,
>University of Sydney,
>NSW 2006, Australia
>
>Phone:+61 2 9351 3176 Fax:+61 2 9351 7682
>http://www.guycox.net
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