From Open Culture:
To Warhol biographers Tony Scherman and David Dalton, the Screen Tests are serious works of art, the product of Warhol’s “ingenious conception of a mid-twentieth century portrait.” In Pop: The Genius of Andy Warhol, they write:
When movies were invented, their critics claimed there was one thing they couldn’t do: capture the soul, the distillation of personality. Ironically, this turned out to be one of film’s greatest capacities. Operated close up, the movie camera lets us read, perhaps more clearly than any other instrument, a subject’s emotions. As his hundreds of sixties, seventies, and eighties photo-silk-screen portraits attest, Warhol was compelled to portray the human face. The Bolex let him home in on flickering expressions and shifting nods, a near-instant raising and lowering of eyebrows, a quick sidelong glance, pensive and thoughtful slow noods, or a three-minute slide from composure into self-concious giddiness–fleeting emotions that neither paint nor a still camera could capture. Andy’s ambition for the Screen Tests, as for film in general, was to register personality.
Warhol’s method was to load 100 feet of film into the camera, place it on a tripod, press the button, and leave it running–sometimes even walking away–until the film was gone. It was like a staring contest he couldn’t lose. Each roll took almost three minutes. In Dylan’s case two rolls were exposed: one for a wide view, the other a close-up. The short clip above includes footage from both rolls.