This is completely true but, while early systems did not provide adjustable beam expansion, most modern ones do.  In case of doubt go to maximum expansion - you'll lose some light but there's usually plenty to spare (unless you are using a green He-Ne).  Then you get a reasonable approximation to homogeneous illumination with most objectives - close enough, anyway, given all the other potential confounding factors.

                                      Guy



Optical Imaging Techniques in Cell Biology
by Guy Cox    CRC Press / Taylor & Francis
    http://www.guycox.com/optical.htm
______________________________________________
Associate Professor Guy Cox, MA, DPhil(Oxon)
Electron Microscope Unit, Madsen Building F09,
University of Sydney, NSW 2006
______________________________________________
Phone +61 2 9351 3176     Fax +61 2 9351 7682
Mobile 0413 281 861
______________________________________________
     http://www.guycox.net
-----Original Message-----
From: Confocal Microscopy List [mailto:[log in to unmask]] On Behalf Of Arwed Weigel
Sent: Friday, 20 February 2009 10:37 PM
To: [log in to unmask]
Subject: Re: Resolution for fluorescence, brightfield and luminescence

All these formulas for confocal microscope resolution assume a homogeneously illuminated back-aperture, which is not always the case in commercially available microscopes due to the Gaussian intensity profile of the excitation laser beam. Therefore, the lateral resolution of a confocal microscope can even be worse than of a widefield fluorescence microscope with arc-lamp illumination.

--
arwed weigel
abteilung fuer neurophysiology und zellulaere biophysik universitaet goettingen humboldtallee 23
37073 goettingen

phon +49 (0)551 3912201
fax  +49 (0)551 398399

No virus found in this incoming message.
Checked by AVG. 
Version: 7.5.552 / Virus Database: 270.11.1/1961 - Release Date: 19/02/2009 6:45 PM
 

No virus found in this outgoing message.
Checked by AVG. 
Version: 7.5.552 / Virus Database: 270.11.1/1961 - Release Date: 19/02/2009 6:45 PM