microscope lenses explained

A really good overview of NA etc

http://www.mellesgriot.com/products/machinevision/lef_6.htm 

Quite technical

http://www.microscopyu.com/articles/optics/objectiveproperties.html 

http://micro.magnet.fsu.edu/primer/anatomy/fieldcurvature.html 

http://www.ezmicroscopes.com/index.php/5000-Binocular-Microscope-with-Semi-Plan-Objectives.html

Comments

[microscope objectives]

Thanks for sharing the links. It really helps me.