The key advantage of confocal scanning microscopy is that it allows a high resolution image to be obtained of
a very thin slice of a thick object. This optical sectioning pmperty, which is completely absent in conventional
microscopy, arises because we adopt a scanning approach. We use a point source and a point detector in
order to image a single point of the object. An image of the whole field is then built up by scanning. It is the
presence of the point detector which leads to the rejection of detail from portions of the object outside the focal
region of the objective lenses. There are two main methods of achieving the scanning required to image the
entire field and this paper will be concerned with the factors which affect the strength of the optical sectioning
which may be achieved by these two methods.