Thanks heaps for the info.
My personal calculations for my FOV were way off. Don't know what I was thinking.
Ron Wodaski's CCD calculator is amazing!
It agreed very well with images I have taken of the same targets.
It turns out my Orion EON refractor 85mm , F/L 560mm (with ZWO ASI1600) has a FOV 81.9 x 108.3 arc minutes.
This agrees with Joe's formula.
Very clever Joe!
It also means I need another scope
