I was looking at previous exams and I saw a question with single slit diffraction. Please look at picture on the website: http://www.physicsforums.com/showthread.php?p=4807732#post4807732
So, this made me think: "Wow, I never thought single slit diffraction could be applied in 2D with one pattern horizontal and the other vertical."
Then, I thought why is there no diffraction patterns along all the surface of the viewing screen. Can anyone explain why? The textbook I am using emphasizes how when a wave enters a boundary place, each point sends out its own spherical wavelet in 3D. So, why don't we see that on the viewing screen?