Well, it feels like months since I posted regularly but now that work-related deadlines have passed and my jaunt up Kilimanjaro has been achieved (photos here:
http://www.flickr.com/photos/paulaj2/sets/72157622425660535) I have returned to the discipline of study. And after the wide open spaces of Tanzania what could be more disciplining than rectangles?!
They don't really need an explanation save to say that the course notes are absolutely right - you have to be very careful where you stand to take photos of rectangular things, and sometimes things like the rugby posts below which look rectangular, turn out not to be after all when positioned against the constraints of the frame.
