Optical sectioning and fast optical focussing in microscopy

The fundamental property, which any optical microscope that is to be used to finally produce three-dimensional images of a volume specimen must possess, is the ability to image efficiently (and infocus) only those regions the specimen that lie within a thin section in the focal region of the microscope. In order to image a three-dimensional volume of a thick specimen it is necessary to take a whole series of such thin optical sections as the specimen is moved axially through the focal region. There are many methods to produce optical sectioning of which the confocal optical system is just one. We shall review these methods and describe a particularly convenient method of implementation that uses white light illumination and real-time image formation and can lead, amongst other things, to enhanced optical sectioning.