Fourier transforms of images (2017)
An optical lense is essentially transforming the image into fourier space and back again. The radius of the lense (approx) is a limit to the spacial-frequencies, i.e. some frequencies are clipped off. In the image plane, the signal has been backtransformed - however, some frequencies were lost due to the aperture.I.e. the fourier transform explains, why apertures limit the resolution of optical devices. It is not only absolute brightness, but fundamentally an information-bottleneck.