Note: '(1)' and '(2)' and '(3)' have been added by me to the above quotes so I can reference them below.

(1) This is precisely why the RFOV must not be called the AFOV (which is the mistake that Baader seems to have made if my assumption regarding their reported values is correct).

(2) That Baader does "apparently" report the RFOV (albeit with the just stated caveat) for two of its eyepiece series indicates (by my admittedly broad and sweeping extension) that it is in fact a real quality of every eyepiece. The concept is practical and can be used to calculate highly correct results, so it is clearly not purely fictitious and arbitrary in the fashion of the popular "Majesty Factor".

I will however grant the concession that the reporting of an eyepieces RFOV in no way means that the eyepieces AFOV should not also be openly reported. In fact with both numbers reported, loads of detail can be calculated regarding the inherent distortions present in the design, so both must be reported.

(3) As to directly measurable being the end all criterion for being real, I give you string theory, dark energy, and dark matter. Their effects are perhaps measurable, though they themselves are directly undetectable. They can however be mathematically expressed to explain real world (OK, universe) phenomenon. The RFOV can likewise be mathematically expressed to explain real phenomenon. The only difference is that the former can not be precisely stated (the +/- 3-sigma being huge), but the latter can be precisely stated (the +/- 3-sigma being small).