1.3   Objective Magnification & Numerical Aperture.  

The greater the numerical aperture of an objective the larger is the light gathering cone angle and the greater is the information gathered by the objective.  In other words better N.A. gives more light and hence brighter fluorescence with better resolution.  If everything else is equal (not the case in most situations in the real world) a lens with a high magnification will spread the collected light over a greater area, which reduces the light intensity.  For example a 100X objective will produce an image 2.5x dimmer than a 40X objective of same N.A. and same light transmission.  The partially compensate for this dilution of lighter, higher power objectives tend to have larger N.A.s and smaller working distance.

Last updated 07/31/03

					© 1998-2003 Michael Chua, Cell & Molecular Physiology, UNC.  All rights reserved.
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