Shutter Speed vs. Shutter Angle

Converting from Film-speak to Digital and back again

Have you ever wondered what the difference is between the way a video camera calculates shutter (fractions of a second) and the way a film camera calculates shutter (in degrees)? If so, then this article is just for you. Here’s what you need to know…

Default Exposure Time – Speed vs Angles
Following up on the question about exposure time when in ramps, here is a quick comparison of exposure times when expressed in 1 / xx seconds v’s xx degrees. Calculations are at 24 fps.

If you want to convert shutter speed to shutter angles at 24 fps the math is:
(24 x 360) / Time Fraction (i.e 8640 / xx where xx is 1/ xx sec)

So the equivalent shutter angle for 1/50 sec shutter speed is:
8640 / 50 = 172.8 (i.e 172.8 degrees)

Here’s a handy cheat sheet with seconds and the equivalent conversion in degrees:
1/32 = 270
1/48 = 180
1/50 = 172.8
1/60 = 144
1/96 = 90
1/120 = 72

The camera’s Sync Scan function permits any shutter speed in the range 1/32 – 1/2000 (or equivalent angles) – i.e these are not preset speeds but fully variable.

To find a shutter speed that relates to a known shutter angle, do the math in reverse. At 24 fps the equation would be:
(24 x 360) / Shutter Angle (i.e 8640 / xx where xx is xx degrees).

So the shutter speed for 144 degrees:
8640 / 144 = 60 (i.e 1/60th sec)

Another cheat sheet with degrees and the equivalent conversion to seconds:
270 = 1/32
180 = 1/48
178.8 = 1/50
144 = 1/60
90 = 1/96
72 = 1/120
45 = 1/198
22.5 = 1/348
11 = 1/696
8.6 = 1/1000

So there you have it. Expect a pop quiz on Friday, now go study. And in the event you suddenly forget the information it will always be right here to access, now doesn’t that make you feel better. Now quit reading and go shoot something!

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[…] in a DSLR camera, that same shutter in a cinema camera would be a 172.8 degree shutter angle. Pro Video Coalition has a great breakdown on how to get an accurate calculation of both shutter speed and shutter angle. Here’s a quick […]