Confuses me too!!Originally Posted by g0tr00t
I would say the instructor was asked a question, and not knowing the answer, tried to create something.
A wide angle lens on a single-lens reflex camera tends to be more complex ... requiring more elements (read: retrofocus). That usually means more air-to glass surfaces... and less efficiency. Very little less efficiency. DAMNED little less efficiency.
It may be of concern in certain photometric (read wild scientific) applications. but for anyone with a modicum of sanity, it means *nothing* in any type of photography in which the most fastidious photographers - as we know them - might be involved.