Contrast in confocal scanning microscopy with a finite detector

The optical properties of a general scanning microscope are determined within the framework of Fourier imaging theory. For a simple model optical system, with Gaussian lens and detector apertures, the contrast transfer function can be expressed in terms of elementary functions. The theory predicts that spatial resolution and depth discrimination vary continuously with detector aperture and that defocus phase contrast is present in transmission images obtained with a symmetric objective, collector lens confocal microscope.