Every once in a while, when photographing a fast jet at transonic speeds, you might get something in the background that allows the diffraction caused by the formation of shockwaves to be visualized.  I have posted about that here.  I was in Vancouver and shooting the floatplanes taking off from the harbor (since it is a Canadian harbor, perhaps I should write harbour).  As I was looking through the images zoomed in to check on sharpness, I realized that there was a visual effect of a similar nature.  (If you think this is a Schlieren effect, it is not.  That is a technique that involves a certain type of lighting to show the density differences but should not be applied to every time you see it in the wild.)

I don’t know whether what is showing up is the result of shocks forming on the props as they spin rapidly or just the tip vortices causing a similar effect.  You can often see diffraction in trailing vortices.  Whatever the reason, as you look above the aircraft at the patterns of structures on the shoreline beyond, you can clearly see some interesting effects.  Since the props are spinning fast and there is an overlap of the wakes from each pass of a blade, the shapes are rather complex.  Now I know that this is a thing, I might be tempted to take a longer lens and see what I can get in more detail of this interesting visual effect.