1. A system comprising: a first laser source which irradiates activation light for activating a part of a plurality of photoswitchable entities into a state able to emit light; a second laser source which irradiates excitation light for exciting at least a part of the entities activated by the activation light; an optical system comprising an optical component configured to produce astigmatic aberration on at least a part of light emitted from the entities excited by the excitation light, a detector which detects at least a part of light that passes through the optical component; and a controller which calculates three-dimensional positional information of at least a part of the entities that emit light detected by the detector based on information regarding the astigmatic aberration to construct at least one image including three-dimensional information.