but in the video there was camera paning left and right.. you said that con/chem/trail looked straight.. I think if you paned non fisheye camera to the left and right of it it would still look straight.. just like when we see it.. is this effect due to fisheye lenses? or that effect when compositing panoramic images?
It IS straight. The curved effect here is because you can't render a 180 degree scene with straight lines.
You should try this:
Sit on the floor about two feet from the middle of a wall (the longer the better), and look up at the corners of the room. See how the ceiling line goes UP from each corner when you look at that corner. Trace the line by pointing at it - you can see after a while how the line visually seems to go up and then curve down, just like these contrails do.
Go give it at go.