try this https://www.microscopyu.com/microscopy- ... l-aperture
. Pay particular attention to the the first sentence of the paragraph, immediately following the first diagram in the article.
or this http://microscopy.berkeley.edu/courses/ ... cs/na.html
this second article introduces the Rayleigh criteria, which shows how the resolution of an oil immersion objective under oiled conditions used with an oil immersion condenser under un-oiled conditions will be greater than the resolution of an oil immersion objective under un-oiled conditions used with an oil condenser under un-oiled conditions. In other words, the condenser does not limit the resolution of the the objective down to the condenser's working level.
The resultant resolution of an optical system in any case, is also determined by the internal design of the objective. In other words, the objective N.A. is not the only final arbiter of resolution. In some cases, the lack of adherence to an objective's immersion requirements results in a great loss of resolution and in others, such a lack of adherence results in only a minor loss of resolution.