In microscopy, the Rayleigh criterion is a measure of the resolving power of the instrument, determined by how close together (as an angular distance) two points in an object can be resolved when images by the system. Remembering that intensities for an incoherent system simply add, for a given aperture diameter, d, and wavelength (lambda), plot a cross-section of the image produced from two point sources in the object plane when the peak of the image of one point source is at the first zero of the Airy disk of the other point source.