Webb, R. H.
Confocal optical microscopy. Reports on Progress in Physics 59: 427-471 (1996).

Confocal optical microscopy is a technique for increasing the contrast of microscope images, particularly in thick specimens. By restricting the observed volume, the technique keeps overlying or nearby scatterers from contributing to the detected signal. The price for this is that the instrument must observe only one point at a time (in the scanning laser version) or a group of separated points with very little light (in the disc version). This paper describes how the confocal advantage comes about and how it is implemented in actual instruments.