Editing Refractive index (section)

===Microscope resolution===
The [[optical resolution|resolution]] of a good optical [[microscope]] is mainly determined by the [[numerical aperture]] ({{math|''A''{{sub|Num}}}}) of its [[objective lens]]. The numerical aperture in turn is determined by the refractive index {{mvar|n}} of the medium filling the space between the sample and the lens and the half collection angle of light {{mvar|θ}} according to Carlsson (2007):<ref name=Carlsson>{{cite report |first = Kjell |last = Carlsson |year = 2007 |title = Light microscopy |url = https://www.kth.se/social/files/542d1251f276544bf2492088/Compendium.Light.Microscopy.pdf |access-date = 2015-01-02 |url-status = live |archive-url = https://web.archive.org/web/20150402122840/https://www.kth.se/social/files/542d1251f276544bf2492088/Compendium.Light.Microscopy.pdf |archive-date = 2015-04-02 }}</ref>{{rp|6}}
<math display="block"> A_\mathrm{Num} = n\sin \theta ~.</math>

For this reason [[oil immersion]] is commonly used to obtain high resolution in microscopy. In this technique the objective is dipped into a drop of high refractive index immersion oil on the sample under study.<ref name=Carlsson/>{{rp|14}}