To clarify, you can convert between different field types as Christian said. If you have field information in degrees, just select Angle in the Type field, as is shown in the graphic above.

As for the Image Simulation, you may use Angle or Object Height fields, but Angle has some difficulties in interpretation, particular at large angles. I would look at the Image Simulation help page, particularly the discussion portions near the bottom in a section titled ‘Comments on using field angles’. As Christian mentioned, converting into object height may help (assuming your object is not at infinity) using the conversion tool in the Field Data editor.