Actually it's the Focal length in millimetres that I really want, but the accurate Field of view in degrees for the ARCamera would also do. It also it doesn't seem I'm getting the correct resolution/aspect for the ARFrame as the ARFrame is cropped and resolution it gives me is for the full image.

This is driving me absolutely nuts. I have rebuild the icon assets a gazillion times. All works fine on the iPhone, iPad refuses to show the icons. Guh!

Alright, turns out the issue is with adding audio to the ARKit session. No solution yet but at least found the cause.