There is no clear information in the books (or accio quote) on what people could see as far as the lake task (people clearly saw the Dragon one).
However, we know from GoF's description of Quidditch World Cup that magical world has special binoculars that show things which in our world Google dubbed Augmented Reality and Google TV - they can freeze/slow the action down, they can overlay maneuver and player details on the image etc...