Fit out the stage for theater productions.
The Director of Photography heads up the camera and lighting divisions of a film set. You are in charge of how the movie will be captured on film, which places the artistic and technical decisions that define an image squarely in your hands. In many ways, a Director of Photography holds the greatest artistic license on set: Your shots set the the context for the action that happens within.
This is an artistic, technical, and managerial endeavor. The Director of Photography decides what angles and shading will dramatize a scene to the appropriate degree: Should you shoot the characters walking toward the camera or away? What depth of field do you want to frame the shot?
You use your technical knowledge to execute your artistic decisions. You dictate what type of film and lenses are to be used, the shutter angles, focus and depth of field, and so on. You work with the electrical departments to acquire and arrange the necessary lighting. Finally, you indicate on the script where things should be zoomed in, where the cameras are to move, and cues to the crew on when to start and stop filming.
Off of the actual set you oversee how the film is processed and make sure nothing you worked so hard to capture is lost through careless handling.