Optical microscopy with extended depth of field

A method is described that allows the depth of field in optical microscopy to be extended, in principle without limit, while high-resolution, diffraction-limited imaging is retained. Experimentally, an extension of more than two orders of magnitude has been achieved. The images are found to be of high optical quality, and this is borne out by theoretical predictions. The resolution is shown theoretically to be similar to that in a conventional microscope of the same numerical aperture, and for some criteria an improvement is obtained.

On the use of local statistical properties in focusing microscopy images

Techniques to extract focus properties of microscopy images are many and varied. Many of them, however, rely on the summation of local statistical properties. Presented here is an examination of conventional focus determination algorithms, and a new method based on planar histograms of these local statistical properties. It is shown that this new method provides finer discernment of the focus properties of an image, and provides a means to extend the focus of an optical microscopy system.

Use of objective lenses with slit pupil functions in the imaging of line structures

We consider the imaging of line structures in confocal imaging systems and show that some advantages result if we employ a slit pupil function in one of the lenses. As an example it is found that the gradient of the image of a straightedge is 17.8% sharper than in a traditional confocal microscope. Another attraction is that theoretical imaging calculations are often possible in terms of simple analytic functions. Experimental results and images are presented which are compared with traditional confocal systems as well as those employing incoherent slit detectors.

Imaging in scanning microscopes with slit-shaped detectors

We consider the imaging in scanning microscopes employing point and slit-shaped detectors in both the bright-field and fluorescent mode. In particular we consider the three-dimensional aspects of the imaging and show inter alia that acceptable, albeit asymmetrical, images result from a slit detector system at low levels of defocus. The situation becomes worse as the defocus is increased although acceptable extended-focus and isometric images are still possible in some cases.

Three-dimensional imaging in confocal systems

We discuss the origin of the three-dimensional imaging characteristics of confocal optical systems. Several methods of information display are considered. The important practical question concerning the correct choice of limiting detector aperture is also considered.

Effect of detector displacement in confocal imaging systems

Confocal imaging systems rely on the use of an accurately positioned axial point detector. We discuss in this paper the effects on the various imaging modes of using a misaligned pinhole. We pay particular attention to the form of the transfer function and the depth discrimination property. A simple model of a thick edge type object is introduced, and it is found that in certain cases a degree of detector offset may be used to advantage in determining the position of the edge.