This might be a little diffiuclt to explain but stay with me.
A camera by default is perspective. Imagine you are facing
the inside of a cylinder, to the right and left of the camera frame
the walls of the cylinders appear higher than the middle bit does,
which is how perspective works.
What I want to do is to distort the image so that the wall
appears to be the same height without dipping in the middle. I
don't want to use ortographic as that will render models the same
size no matter the distance, I want the walls to get closer as you
approach them, but without the dips.