The third lens corrects the distortion from the first two and flattens the rays onto the image plane. From US Patent US20170299845A1 Then we abruptly go to something like this. Look at the lenses.

GINKGO is an Lens Distortion Correction IP capable of up to 192° angle correction. It comes with factors that can adjust zoom and un-distortion strength. It can also perform viewpoint transformation ...

An OpenGL ES barrel shader for correcting lens distortion. Some of the demos peak at around 25-30 frames per second on a Pi 3. Not too shabby.