Thank you for your suggestions. #1: I made this more clear by saying that this holds for a lens with focal length f ... when d=f. #2: I made the distinction b

Thank you for your suggestions. #1: I made this more clear by saying that this holds for a lens with focal length f ... when d=f. #2: I made the distinction between the DFT and CFT more clear. I never say they're the same thing, but that they are closely related. #3: I added a paragraph about the complexity of the FT. Thank you for mentioning that. #4: I didn't want to include the derivation -- I wanted to show the end result. I pointed the readers to Goodman if they want the derivation. I also addressed the paraxial approximation in the footnotes as well.