Clive them not recognizing vignetting in the upper part of the picture is easy to explain they don't know anything about the technical aspects of photography not really when I studied art history with an emphasis on photo history there were two lectures about the technical aspects of the medium both of them non compulsory so very few students attended them. Text analysis where texts about photography were dissected were compulsory lectures.
The same thing applied to general art history a lecture by one of europe's top conservators and art historian about technique, formulas and the more technical aspects of art was non compulsory and again since it was non compulsory no students (loved the lectures). And again an art history lecture by a prof who was reading mostly philosophical hogwash from a book was compulsory. Some of the most quoted authors in photo history are philosophers not photographers not even art historians or artists but philosphers. The problem is that most of today's profs and students only have book knowledge because that's what's expected from them. I also admit that a very small percentage recognized vignetting once it was pointed out to them. This is also the reason why I think that art history should be taught both by process historians as well as classic art historians we need both.
I am also a HCB fan except for some pictures that is. The colored ones in this thread do exactly what they are supposed to do and are not bad imo.