Cinematography-Theory-And-Practice

frame rate at which the camera is operating. The open section of therotating shutter assembly is referred to as the “shutter angle” and ismeasured in degrees. Sensibly, most shutters are half open and halfclosed, which makes the shutter angle 180°. Some shutters are 165°and many are adjustable (Figure 10.33).With the camera operating at 24 fps and a 180° shutter, the exposuretime is 1/48th of a second (1/50th at European 25 fps). This iscommonly rounded off to 1/50th of a second and is considered thestandard motion picture exposure time.Exposure time can then vary in two ways: by changing the framerate (which is common) and by varying the shutter angle (which isless common). Exposure is determined by this formula:Shutter speed for 180° shutter =12 x fpsExposure in seconds =shutter opening (degrees)360 x frames per secondExposure Time — Shutter Speed versus Shutter AngleTo calculate exposure on shots where the camera is ramping (changingframe rate and thus shutter speed during the spot), here is a quickcomparison of exposure times when expressed in 1/xx secondsversus xx degrees.These calculations are based on 24 fps, which is the most frequentlyused frame rate for narrative filmmaking (30 fps is more often usedfor sports). To convert shutter speed to shutter angles at 24 fps:(24 x 360) / Time shutter is open24 x 360 = 8640 / (xx where xx is 1/ xx sec)Thus, the equivalent shutter angle for 1/50 sec shutter speed is:8640 / 50 = 172.8 (172.8 degrees shutter angle)Table 10.6 shows shutter speed and the equivalent conversion indegrees:ShutterSpeedShutterAngle1/32 2701/48 1801/50 172.81/60 1441/96 901/120 72Some cameras (such as the RED) have variable shutter speeds from1/32 to 1/2000, or the equivalent shutter angles. To find a shutterspeed that relates to a particular shutter angle, do the calculation inreverse. At 24 fps the equation would be:(24 x 360) / Shutter Angle(e.g., 8640 / xx, where xx is xx degrees).So the shutter speed for 144 degrees:8640 / 144 = 60cinematography208