Ok, I read that diffraction only occurs when wavelength is larger than than the obstacle/opening. But then I find an equation looking like: sin(theta) = wavelength/width opening For determining the diffraction. Now if the wavelength has to be larger than w for diffraction to occur, why is it that if you apply this to the above equation an error will occur?(note: if wavelength > w then the result will be greater than 1, and sin ^ -1 of any number greater than 1 = error) Sorry if the answer is really obvious or something, it's just that this concept is driving me insane, my physics teacher wasn't really able to help much either with the understanding. Please someone respond soon.