[NB: I’m copying the following from another of my post about perception of speed at the peripheral vision/edges of the screen. This in itself has nothing to do with the topic you’re raising, but I find it interesting nonetheless because it explains some key differences in zoom/camera implementation]
Zoom and Camera focal length are old problems with all Flight Simulator product.
Rewind back to FS9/FSX: I’ve always find the 3D projection wrong because it wasn’t based on recreating a virtual focal length, but in fitting a computer screen like any other Direct3D game which is applying a perspective transformation based on the window size, not based on a fixed focal length.
I’ve been looking back at my experience with X-Plane 11 in 2D then in VR and I think there might be a simple explanation in the end, which can be easily experimented:
- Use the simulator in a window filling 1/4 of your monitor.
- Stretch the window horizontally back and forth.
With X-Plane:
- Perspective projection doesn’t changes while resizing the window and the focal length (as with a camera lens) doesn’t change either so that relative sizes of objects is constant.
- The objects relative sizes don’t change with distance.
- The view keeps the horizontal FOV constant and you’ll change only vertical FOV (the vertical / horizontal ratio is getting smaller).
With P3D5:
- Perspective projection changes as if you’re changing camera lens focal length.
- The objects relative sizes change with their relative distance to the aircraft.
- The view zooms in our out
With FS2020:
- Perspective projection doesn’t change while resizing the window
- The objects relative sizes don’t change with distance.
- The view keeps the vertical FOV constant and you’ll change horizontal FOV.
Comparing all these:
- P3D5 is all wrong. It is distorting the objects depending on the window width/height ratio.
- X-Plane is right. There is no distortions whatsoever and you can calibrate the view so as to use the zoom, instead of the window width/height ratio, to simulate the focal length.
- FS2020 is right, but the problem is that with a fixed vertical FOV, it introduces distortions the wider the window.
IMHO, these distortions to the edges are most likely the root cause of the difference of perception to the aircraft speed, because it is a lot induced by peripheral vision cues, and because of the distortions, the objects are appearing moving faster to the edges than closer to the center.