What is Fraunhofer diffraction? When both the diffracted and incident waves are collinear or plane, Fraunhofer diffraction occurs. This situation is easy enough to obtain, merely make the distances from the source to the to the slit or obstacle causing the diffraction to the observation point large enough to neglect the curvatures of the incident and diffracted light. This can be expressed, according to Fowles, as follows:
This is the differentiating factor between Fresnel (an approximation when the light source is relatively close to the diffraction aperture) and Fraunhofer diffraction patterns. The variables above are identified in the picture below adopted from Fowles:
Fraunhofer diffraction can be explained by the Fresnel-Kirchoff equation taking into
account several approximations. The intensity of the pattern seen at Up
would be governed by the equation 
which describes how one obtains the diffraction pattern by
integrating the phase of the light over the slit seen above. This equation will be
adopted and tailored to fit several specific examples of Fraunhofer diffraction that we
study in this experiment.