[Fwd: photons vs. photoelectrons?]

[Johannes Helm]

Dear John,

you can, anyway, recalculate the actual number of detected photons from
the photon statistics and the pixel intensities provided you have a linear
relationship between the actual number of detected photons and the resp.
pixel values, which, however, is a sine qua non for any reasonable
comparable measurements of the type discussed here.
Ref. e.g.

Helm, Patwardhan, Manders,
A study of the precision of confocal, ratiometric, Fura-2-based [Ca2+]
measurements,
Cell Calcium 22(4):287-298

(Watch out for the appendix, where this specific question is addressed;
this appendix is "hidden" at the very end of the paper).

Best wishes,

Johannes

--
P. Johannes Helm, M.Sc. PhD
Seniorengineer
CMBN
University of Oslo
Institute of Basic Medical Science
Department of Anatomy
Postboks 1105 - Blindern
NO-0317 Oslo

Voice: [phone]
Fax: [phone]

WWW: folk.uio.no/jhelm




---------------------------- Original Message ----------------------------
Subject: photons vs. photoelectrons?
From:    "John Oreopoulos" <[hidden email]>
Date:    Fri, April 16, 2010 16:04
To:      [hidden email]
--------------------------------------------------------------------------

The recent release of the Photometrics EMCCD "eVolve" camera which has the
ability to output images with pixel values that correspond to
photoelectron counts (instead of arbitrary digital count units) has me
wondering a bit something. The idea behind this camera, as I understand
it, is that having images reported in terms of photoelectrons instead of
counts (ie: an absolute scale vs a relative scale) will allow a better
comparison of image data between labs around the world, and even for
single user comparing images acquired with a particular microscope from
day to day. Seems reasonable to me and sounds like a pretty good idea.
What I'm confused about is that I've seen some papers in the literature,
mainly those that deal with single-molecule studies, that report image
data in terms of actual photons detected. Is there a difference, and more
importantly, can someone explain to me the advantage of using photon
counts vs. photoelectron counts?

(No commercial interest for Photometrics)


John Oreopoulos, BSc,
PhD Candidate
University of Toronto
Institute For Biomaterials and Biomedical Engineering
Centre For Studies in Molecular Imaging