The principle of OPRA. The figure shows the imaging process of one point source at different times. The fluorophore is placed at the point of origin in the sample plane (a). The emitted photons are imaged to different positions in the image plane (b) according to the excitation positions s. If the general magnification of the microscope is neglected and the intermediate magnification is m= 0.5 the photons are reassigned to half the distance between the nominal excitation position s and the position of the detected photon without intermediate magnification. In normal scanning microscopy the photons are always assigned to position s. Note that the brightness changes of the green emitter caused by the variation in excitation are not shown in this scheme.