 This introduced an illumination scheme into fluorescence microscopy, which has already been used successfully for dark field microscopy under the name ultramicroscopy.In this type of microscopy, the illumination is done perpendicularly to the direction of observation (see schematic image at the top of the article).The expanded beam of a laser is focused in only one direction by a cylindrical lens, or by a combination of a cylindrical lens and a microscope objective as the latter is available in better optical quality and with higher numerical aperture than the first.