My favorite example of using a lens for a FT is creating a dark field image. You just put a small beam block in the center of a pupil plane and block all of the

My favorite example of using a lens for a FT is creating a dark field image. You just put a small beam block in the center of a pupil plane and block all of the low frequency components. You end up with bright lines only at the edges of things which are the high frequency components of the image. Also "google images" isn't an image source, and just because you found something on the internet doesn't mean it is free to use.