When used in light microscopy, oil immersion is a technique used to increase the resolution at higher magnifications. Immersion oil should only be used with oil immersion objectives.A small drop of immersion oil is placed on top of the cover slip and seals the space between the specimen and the oil immersion objective. When using immersion oil an increase in the numerical aperture is observed, providing increased resolution.
When you are finished using the immersion oil be sure to clean the objective lens to prevent the immersion oil from hardening on the objective.
