Figure 1: Schematic drawing of the (HR-)OPFOS setup: light from a green (GL) or blue laser (BL) passes through a Keplerian beam expander (BE) with spatial filter, a field stop (FS), and a cylindrical achromat lens (CL) which focuses the laser along one dimension within the transparent and fluorescent object (O). A two-axis motorized object translation stage (OTS) allows scanning of the specimen and imaging of different depths. The fluorescence light emitted by the object is projected onto a CCD camera by a microscope objective lens (OL) with fluorescence color filter (CF) in front. The focusing translation stage (FTS) is used to make the objective lens focal plane coincide with the laser focus.