I see you have a place to enter the scope focal length - but there is also a button providing access to the ascom telescope setup. The ascom info is good because it has aperture and secobs - along with focal length. I would like aperture, secobs, and focal length in the fits header. Right now fl comes from the special entry in the telescope control panel - so it could be redundant or conflict with ascom values.
I propose getting aperture and secobs from ascom, and using the fl from the control panel unless it is zero - in which case you get fl from ascom. Then place aperture and secobs in the fitsheader.