The effect of refractive index of the mounting medium on the apparent diameter of latex particles and glass fibres

The diameters of latex particles were measured in different media with a light microscope. The microscope was fitted with a filar micrometer eyepiece and, for measurement, the cross-wire was set on the centre of the dark line forming the edge of the image. Electron microscopy was used for comparison. Good agreement between light and electron microscopy was obtained using media of relative refractive index (n(D) object/n(D) medium) between 1.06 and 1.08. With higher relative refractive indices the light microscope underestimates dimensions for particles 4-17 mu diameter and overestimates for particles 2.7 mu diameter.