Pushes the middle of the picture out toward you, like a fisheye lens or a reflection in a spoon.
Each pixel works out how far it is from the centre, and that distance is put through a power. The consequence is that distance is not scaled evenly: near the middle it stretches, near the edge it compresses. Everything the picture contains therefore gets pulled outward from the centre, with the middle magnified most.
strength sets how pronounced it is. aspectLens decides whether the bulge is a circle or follows the shape of the frame, which matters on a widescreen canvas: with it off the bulge becomes an oval and matches the picture's proportions.
pinch() is the same effect with the sign reversed. rotation only does anything visible when the bulge is not circular, since there is nothing to see turning otherwise.