filming once it was dark outside, planning to take a break for several hours and finish filming during sunrise. He started by alternating between focal lengths of 50 mm and 55 mm. After roughly of film, he moved each of the lengths apart by 5 mm, to 45 mm and 60 mm, then 40 mm and 65 mm, and so on. He marked off lengths in intervals of 5 mm on a piece of tape and gradually moved the lengths farther apart throughout filming. He manually recorded each frame, and without the use of a cable release his fingers became swollen from holding the shutter button. The process took longer than he had expected; he took only one break to use a restroom and held his head under water to keep awake. Analysis and interpretations Watching Serene Velocity produces the appearance of motion and other optical effects, positioning it as a cinematic version of op art. Gehr has noted that the effects of watching the film vary significantly based on which part of the screen the viewer focuses on. The composition of the screen is divided into five sections: the ceiling's fluorescent lights and exit signs; the doors, water fountains, and ashtrays on the left and right walls; the reflections on the floor; and the doors in the center of the frame. The perspective lines point to the center of the frame, which would normally be the center of interest, but the motion along the margins of the frame draws attention away. Viewing the images as flat, two-dimensional spaces transforms the work into an abstract, flashing sign. Focusing on individual features of the successive images produces the illusion of motion. The illusion of depth perception can transform the image into an upright pyramid pointing into or out of the screen. Ken Jacobs emphasized this sense of thrusting and described Serene Velocity as a "sexual metaphor, or sex-become cinema", and J. Hoberman described it as a "piston-powered mandala". Critics have often evaluated Serene Velocity as a metacinematic work. Noël Carroll pointed to the simplified procedure with which it was photographed as an example of minimalist cinema. Carroll wrote that the film, with its lack of movement, is an argument for "the impression of movement" as the essential characteristic of cinema. Critics have drawn parallels with Andy Warhol's 1964 film Empire, an extended, continuous shot of the Empire State Building. Both films