Lens-ocular association
Light microscopy

The microscope is an optical instrument associated with an observer's eye, and it is this last element in the instrumental chain that forms the final image. It is therefore the eye's limit of perception that ultimately limits the instrument's qualities. The work of A. Arnulf showed that, for a given field luminance, the eye's limit of perception varies according to the diameter of its pupil; he defined a function: the resolving efficiency of the eye σ, equal to the product of the eye's angular limit of perception ε and the diameter Φ_o of its pupil, indicating between which limits this pupil should be diaphragmized for the limit of perception to be the best. For average luminances encountered in microscopy, for which the natural diameter of the pupil...