Schmidt, MMSchmidtNagorni, M.M.NagorniHell, StefanStefanHell2017-09-072017-09-072000https://resolver.sub.uni-goettingen.de/purl?gro-2/1999Fluorescent objects closer than the diffraction resolution limit can be distinguished in far-field microscopy provided they feature different emission spectra. Utilizing the superior axial resolution of 4Pi-confocal microscopy of 100-150 nm, we investigate the precision with which fluorescence objects with subdiffraction axial distance can be measured in the far field. At a wavelength of 820 nm distances on the order of 60 nm between beads and a monomolecular Langmuir-Blodgett layer were determined with a precision of 1.2 nm within 3.2 s. The reduced spatial extent of the 4Pi-confocal point-spread-function improves the precision of colocalization measurements in double stained specimens and opens up the prospect on far-field fluorescence profilometry with (sub) nanometer height resolution.enjournal_article10.1063/1.11506850000879068000203144382