Imaging properties of annular lenses.

An improvement in resolution in a conventional microscope has been shown to result if an annular condenser is employed. Here Fourier imaging in the presence of defocus and special aberration is considered, and the image of a straight-edge calculated. Imaging in confocal microscopes is superior to that in conventional microscopes and may be further improved by the use of one lens with annular aperture. Again Fourier imaging with defocus and spherical aberration is considered, resulting in an imaginary part being introduced into the transfer function. The straight edge response is very sharp.