[Wavytone]

John, generalisms like the one you quoted simply aren't valid for all.

Some of Al Naglers patents are over 40 years old, hardly “modern”. The Smythe lens used in many is a much older idea. Let alone the Erfle and it’s SWA variants, or plossls - still in production and still a good match for newtonians. And the text you quoted... is, well, not exactly recent either.

What’s more recent raytraces of several key designs confirm there are significant variations and that Nagler in particular was using field curvature and sone negative coma to partially compensate these in fast newtonians, while being entirely acceptable in slower scopes without coma and with opposite field curvature - notably f/10 SCTs fir obvious reasons in the US, and to a lesser extent refractors. At f/13 or f/15 (Maksutovs) almost anything looks fine - not only a ramsden eyepiece, even a single element glass sphere used as an eyepiece.