first, sorry for my english. I know that is a big problem in most cases.
What i try to achieve is a linear transition from two keyframes.
I can obtain it in the camera movement (with easy in/out set to off) but not in FOV aperture that seems always smooth.
I try to show you what i would.
(this is lightwave 3D preview)
And this is a graph timeline from the 2 keyframe
I hope it's more clear now.