Having Mary Ellen Mark take photos on the set of Planet of the Apes is a little like John Updike writing an episode of Alf. She’s arguably the most renowned photojournalist of our time, and her award-winning pictures — such as her portraits of Seattle street children — are among the most keen images of American life ever put on film. (Many can be seen in 1999’s American Odyssey, Aperture.) But then, that’s exactly why EW sent her to the Mojave Desert to snap shots of actors in monkey suits: We knew her lens would see something no other photographer would.

”Taking pictures on a set is like documentary photography,” says Mark. ”You’re capturing the mood that the director has established.” And nobody does it better than Mark, whose images from Apocalypse Now and Marathon Man are as searing and vivid as the films themselves. Given the uncompromising tone of her work, it’s no wonder that Mark, 61 (who lives in New York City with her husband, director Martin Bell), says, ”Photographing celebrities is very difficult — to get something more than what they show to the public.”

What Mark manages to do with those celebrated profiles, though, is astonishing. ”Photography is like a big puzzle,” she says. ”I’m always asking myself, ‘What are the elements of a great photograph?’ I still haven’t figured it out. I guess that’s why I’m still taking pictures.”