Magazine article American Cinematographer

Cinema Workshop

Magazine article American Cinematographer

Cinema Workshop

Article excerpt

SHUTTERS

Most light meters are calibrated on the basis of a motion picture camera having a shutter opening of 180 degrees. One revolution of the shutter is 360 degrees, so a 180-degree opening means that the shutter is open for exactly one-half-acycle and closed for the remaining onehalf. This yields an exposure time of 1 /48 second at 24 fps. However, not all cameras employ a 180-degree shutter.

The closed portion of the cycle allows the film to be advanced and registered precisely. The shutter can open only after the film has come to a complete halt and must close before the film begins to move to the next frame. The camera designer would theoretically like to have as large a shutter opening as possible. This would increase exposure time and be most helpful in low-light situations. There are several cameras that do employ shutter openings larger than 180 degrees. A shutter opening of 230 degrees will yield an exposure increase of 1/3-stop, while a 2/3-stop exposure increase will result from a 285-degree shutter.

There is, of course, a definite tradeoff. In the case of a 285-degree shutter, the film must be advanced and registered in the remaining 75 degrees of the cycle (285° + 75° = 360°). Since the more conventional 180-degree shutter provides 180 degrees of cycle for pulldown, the 285-degree camera must advance the film almost two-and-a-half times faster than the 180-degree camera. Obviously, this requires greatly increasing the velocity and acceleration of the film during pulldown, which not only places greater stress on both the camera movement and the film, but also jeopardizes a steady image. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.