Camera techniques

12 drawings per second

Frédéric Back used a standard animation practice known as 'twos' or 'double-framing,' in which 12 drawings make up one second of film. Since a second of film normally consists of 24 frames, this means shooting each drawing twice. Double-framing is generally used in animation except for quick movements that call for 24 drawings per second. For some scenes, Back would use multiple exposures.

'Two-pass' (double exposure) technique

'Double exposure' means just that: exposing a piece of film twice to have two different images appear in the same frame. The lens aperture must be reduced by 50% to avoid overexposing the image; shooting the same piece of film twice at 50% exposure produces the same quality of image as shooting it once at 100% exposure. In Frédéric Back's 'two pass' method, the same sequence, shot twice at 50% exposure, is offset by one frame the second time around. (Keep in mind the animation practice of double-framing.) In the resulting film sequence, every second frame contains a composite of two images: the image in the previous frame, and the image in the upcoming frame. In animation, this produces the illusion of extremely fluid motion-and is essentially only used when such a quality of motion is needed.

[Vidéo] Frédéric Back explains the 'two-pass' technique.
Credit: Radio-Canada, Horizon 2000, 1984, 00:40

'Four-pass' (staggered mix) technique

The 'four-pass' technique is essentially a series of cross-fades. Each frame presents a triple exposure: the 'main' image plus two 'ghost' images (the image from the previous frame, and the image from the next frame). Here, the lens aperture is reduced to 25%. The two 'ghost' images are shot at 25% exposure, while the main image is shot twice (amounting to a 50% exposure). Together, the four 'passes' result in a full (100%) exposure. This technique, which Back and his cameramen called a 'staggered mix,' was particularly effective at conveying the movement of the water in The Mighty River.


[Document: D_1735]

[Illustration] Diagram drawn by Frédéric Back to help explain the 'staggered mix' technique.

Computer-assisted camera

Up until 1979, each movement of the camera or animation stand called for complex calculations that the cameraman had to execute manually and verify frame by frame. "To make it easier on the cameraman, we had to limit our ambitions with regard to mechanical movements," notes Frédéric Back. The invention of a computer-assisted camera greatly simplified the task, allowing the camera movements to be accurately calculated and pre-set. When one shot was complete and the cameraman lifted the glass plate to change drawings, the computer automatically prepared the exposure, framing and movement for the next shot. "The computer allowed me to develop complex procedures without overly taxing the nerves of cameramen Claude Lapierre and Jean Robillard."
F.B.


[Document: DA_0934]

[Illustration] Example of calculations used.


[Document: P_1122]

[Illustration] Caricature by Frédéric Back.

"I often used pans to describe space, and it was more interesting to do these camera movements at an angle that would produce a certain perspective and help viewers forget about the mechanical nature of the animation. This was particularly useful in The Mighty River, in which I tried to recreate the movement of the waves."
F.B.

[Vidéo] Frédéric Back and Jean Robillard explain the complicated procedure of setting up a sequence to be shot.
Credit: Radio-Canada, La semaine verte, 1993, 02:07