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Ykn

Hi, Stefan

Your assumption would be true if the light behaved symmetrically but in 
actual fact, the condenser sets up the illumination for interaction with 
the specimen, therefore we should consider its NA; then the light interacts 
with the sample and all sorts of things happen (diffraction, refraction, 
scatter, fluorescence, etc) that affect the angle of light exiting from the 
sample, so we need also to include the NA of the objective, independently.

Another reminder: the NA written on the condenser is only the full NA; 
closing the condenser aperture iris limits that to the real, working 
NA.  As a result, there is a big difference between the theoretically 
possible R, derived from your equation, and the real, working R.  Also, if 
there is an iris in the objective, same thing.

Rule of thumb: The NA of the condenser should meet or exceed that of the 
objective.

Hope that 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 for the Fall? 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. Call Ken Piel at (972)954-8011.




At 06:19 AM 9/12/2005, Stefan Gunnarsson wrote:
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Hi all,
>
>I also have a  very basic question on microscopy theory:
>
>The Rayleigh criterion states that resolution d=0.61*lambda/NA. Taking the 
>condenser lens into account this (in the textbooks) becomes d= 
>1.22*lambda/(NAo+NAc). But shouldn't it be d= 0.61*lambda/NA with 
>whichever NA is the smallest of the two?
>
>tia
>Stefan
>
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++
>Stefan Gunnarsson
>Uppsala universitet                                     Uppsala University
>Evolutionsbiologiskt centrum                    Evolutionary Biology Centre
>Enheten för biologisk strukturanalys            Microscopy and Imaging Unit
>Norbyvägen 18A
>SE75236 Uppsala, Sweden                 Tel & Fax: +46 - 18 471 2638
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++