Why do we need to use oil immersion for the 100x magnification?

Question

Why do we need to use oil immersion for the 100x magnification?

Answer 1

if u dont use immersion oil for the 100x magnification the lens will get all scratched up from rubbing right on the slide

Answer 2

When light passes from a material of one refractive index to material of another, as from glass to air or from air to glass, it bends. Light of different wavelengths bends at different angles, so that as objects are magnified the images become less and less distinct. With "dry" objective lenses this loss of resolution prevents using magnifications of above 400x or so. With oil immersion, the oil eliminates the air between the coverglass and the objective lens, and so reduce the distortion.