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When I look at transmission curves for good dichroic mirrors in their pass band I can't see how it would be impossible to achieve such a gain from just changing a dichroic mirror (unless it was bad to start with). Good dichroic pass about 80-90% . IMO such a gain could only be achieved if the wavelength of interest is very close the the transition region of the dichroic or the dichroic in question was not very good... It may be that the term 'dichroic' may have included the barrier filter properties where higher losses may occur. The very best barrier filters transmit ~80% but some may  be <50%. Some sample transmission/barrier curves that support this view can be examined at

http://www.chroma.com

I have no commercial interest in that company by the way.

Regards Mark Cannell



"Alice L. Givan" wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> With regard to the Leica AOBS, Martin Hoppe says that "detailed comparisons can be found in the Leica SP2 AOBS brochure."  It may be me,  but I can't find any of those detailed comparisons.  The page on the AOBS in that brochure shows two images,  one with a conventional beam splitter and the other with the AOBS.  The one derived from a system with an AOBS is brighter --- but no details are given as to whether the two images were done on the same instrument (probably not) and what the details were with regard to  PMT voltages, objectives, laser power, etc.   In addition, the spectra that are shown in the brochure are just diagrams -- showing that in theory one can broaden the  spectrum of collected light with an AOBS.
>
> If indeed the AOBS does offer "25-45% increase in sensitivity versus a dichroic element,"  we still need to know whether that means that the AOBS is 45% better than a dichroic or whether this is the overall increase in sensitivity in the whole system. In other words, we need to know what proportion of the sensitivity problem in a system  results from the dichroic element.  If the dichroic element provides only a small problem in the goal of high sensitivity,  then removing the dichroic element and replacing it with an AOBS will only provide a small increase in overall sensitivity.
>
> Don't get me wrong  --- the AOBS sounds wonderful.  But we are still waiting for those details.  And, of course, I believe that the reason we don't have those details is that we are still waiting for someone to come up with a measurable definition of confocal sensitivity.  Correct me if I am wrong on this.
>
> Alice
>
> Alice L. Givan
> Englert Cell Analysis Laboratory
> of the Norris Cotton Cancer Center
> Dartmouth Medical School
> Lebanon, New Hampshire NH 03756
> tel 603-650-7661
> fax 603-650-6130
> [log in to unmask]