Oil Immersion Microscopy increases the refractive index of a specimen when used properly. With limited disadvantages, slides prepared with oil immersion techniques work best under higher magnification where oils increase refraction despite short focal lengths.
Microscope immersion oil is used in light microscopy to improve imaging. The use of microscope immersion oil as part of a microscope lens system will produce a brighter and sharper image than a similar design not using immersion oil.