It's similar to lens flare: lens manufacturers go to great lengths to reduce lens flare (there's a limit to what they can do though), and in VFX/CG we often add

It's similar to lens flare: lens manufacturers go to great lengths to reduce lens flare (there's a limit to what they can do though), and in VFX/CG we often add them for effect in movies, both for full-CG stuff and even on top of plate footage from cameras which didn't even have much (if any) lens flare in the first place.