Blanca, C. M., Bewersdorf, J. and Hell, S. W.
Single sharp spot in fluorescence microscopy of two opposing lenses. Applied Physics Letters 79: 2321-2323 (2001).

We demonstrate theoretically, experimentally, and in an imaging application the possibility to generate a single predominant sharp diffraction maximum in the effective point-spread function of a fluorescence microscope that coherently uses two opposing lenses. This is achieved through binary pupil filters that preclude the origination of the unfavorable strong interference side maxima that are otherwise present in these systems. Mathematical postprocessing, which has so far been a prerequisite to gain artifact-free images, is now optional or obsolete.