We consider the axial resolution of confocal optical systems employing high numerical aperture objective lenses for the cases when the specimen refractive index is both higher and lower than that of the immersion medium. In the latter case a spherical aberration‐like phase shift is introduced when the objective lens numerical aperture is greater than the refractive index of the specimen which leads, inter alia, to an asymmetrical axial response with higher side lobe levels. Theoretical and experimental results are presented.

We consider the form of the interference term image in scanning interference microscopes employing finite sized coherent and incoherent detectors. We show, inter alia, that for the case of incoherent photodetectors the interference term image in scanning confocal and scanning conventional systems behave identically in all respects including optical sectioning.