Abstract: The invention concerns a method and devices for far field microscopy and flow fluorometry for geometric distance measurements between object structures, i.e. measurement structures, marked with fluorochromes, whereby the distances can be smaller than the half-intensity width of the principle maximum of the point spread function. In this method, the measurement structures are marked with fluorescent dyes with different or identical spectral signatures, according to their distances. Calibration targets with defined dimensions and arrays are marked with the same fluorescent dyes. Calibration targets and measurement structures are prepared separately or together on an object support and investigated microscopically or flow fluorometrically.