why must oil be used with oil immersion lens
Education in Microscopy and Digital Imaging Oil Immersion and Refractive Index. One way of increasing the optical resolving power of the microscope is to use immersion liquids between the front lens of the objective and the cover slip. Most objectives in the magnification range between 60x and 100x (and higher) are designed for use with immersion oil. Good results have been obtained with an oil that has a refractive index of n = 1.518, which is close to the refractive index of glass. All reflections on the path from the object to the objective are eliminated in this way.