The problem of calculating what a diffracted wave looks like, is the problem of determining the phase of each of the simple sources on the incoming wave front. It is mathematically easier to consider the case of far-field or Fraunhofer diffraction, where the point of observation is far from that of the diffracting obstruction, and as a result, involves less complex mathematics than the more general case of near-field or Fresnel diffraction. To make this statement more quantitative, consider a diffracting object at the origin that has a size a . For definiteness let us say we are diffracting light and we are interested in what the intensity looks like on a screen a distance L away from the object. At some point on the screen the path length to one side of the object is given by the Pythagorean theorem