Fluorescence illumination is performed laterally with a laser 'lightsheet', i.e. a plane of light traveling exactly along the image plane, originating from a 90 degrees angle respect to the detection axis. The Lightsheet is fixed and the sample is scanned through it to perform 3D imaging. The geometry allows for sample rotation, long working distance for large samples, excellent optical sectioning at low NA. Long term Live imaging is one of the major possibility because Phototoxicity is dramatically reduced by the optical geometry: the sample is not illuminated outside of the image plane during acquisition.