The Extended-focus, Auto-focus and Surface-profiling Techniques of Confocal Microscopy

The extended focus and auto-focus techniques of confocal microscopy, which can be used to give greatly increased depth of field, are compared. These methods rely on the use of high numerical apertures, so that the paraxial approximation is found to give inaccurate theoretical image predictions. An improved approximation is discussed and compared with exact high-angle calculations. The confocal surface-profiling technique, which allows non-invasive investigation surface topography is also considered.