Theoretical versus experimental resolution in optical microscopy

The aim of this article is to compare experimental resolution under different conditions with theoretical resolution predicted using electromagnetic diffraction theory. Imaging properties of fluorescent beads of three different diameters (0.1 mum, 0.2 mum, and 0.5 mum) as well as imaging properties of four different fluorescence-stained DNA targets (ABL gene, BCR gene, centromere 6, and centromere 17) are studied. It is shown how the dependence of the resolution on object size varies with wavelength (520 nm versus 580 nm), type of microscopy (wide-field, confocal using Nipkow disk, confocal laser scanning) and basic image processing steps (median and gaussian filters). Furthermore, specimen influence on the resolution was studied (the influence of embedding medium, coverglass thickness, and depth below the coverglass). Both lateral and axial resolutions are presented. The results clearly show that real objects are far from being points and that experimental resolution is often much worse than the theoretical one. Although the article concentrates on fluorescence imaging using high NA objectives, similar dependence can also be expected for other optical arrangements. (C) 2001 Wiley-Liss, Inc.