I'm trying to get my head around perspective. If you look at the animation in Wikipedia :
You can see that the cube looks very distorted, then the edges go more parallel.
From my understanding, the distorted version is when the camera is very close to the cube, and the less distorted version is when the camera is further away.
But if the camera is further away, why does the cube not appear smaller?
Is this something to do with keeping the "field size" constant? Is the field size a flat area? Or part of the area of a sphere? It looks as though you can see more stuff in the background and foreground when you're zoomed out compared to zoomed in, so how can you know that you're keeping the "field size" constant?