   ==Editing of Fourier Optics Page==  This page has recently been edited by someone who does not understand Fourier optics.  The paraxial approximation is completely irrelevant and discussion of transfer function is maybe nice, but not central to understanding the basic concept.  Plus, the time-domain wave equation is not appropriate for this subject; only the frequency domain wave equation is relevant here.  Furthermore, you don't have to assume a solution to the wave equation, you can actually derive it from first principles using separation of variables, as in section 1.4.  Sections 1.1, 1.2, & 1.3 should be removed, as they only confuse the presentation.