The Role of the Pinhole in Confocal Imaging Systems

Abstract

Confocal scanning microscopes are particularly attractive by virtue of their enhanced lateral resolution, purely coherent image formation and optical sectioning (Wilson and Sheppard, 1984). It is probably the latter property which is most useful as it gives rise to the ability to image a thick specimen in three-dimensions. This is possible because the optical system images information only from a thin region in the neighbourhood of the focal plane. This permits us to store many image slices in a computer to give a three dimensional data set which describes the object. There are now many sophisticated computer software systems available to display this data in various ways. Obvious examples include the extended focus technique (Wilson and Hamilton, 1982) in which we merely add up (integrate) the images from various depths to provide an image of greatly extended depth of field. We may also produce images where object height is coded as brightness or combine the whole data set to provide an isometric view of the object, Figure 1. It is ;also possible to use false color to label features of interest or, by simple processing, to obtain stereoscopic pairs (van der Voort, 1985). Other forms of image display are discussed in Chapter 10.