180° Shutter Angle – Why I don’t use it for 50/60p
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What is 180° Shutter?
Shutter Angle stems from early movie cameras which had a spinning disk between the lens and the film. Part of the disk would be removed letting the light though when it passed between the lens and the film. As the disk rotated the light was stopped by the closed part of the disk and the film was advanced to the next frame ready for the next exposure as the open part came around again.
As movie cameras became more advanced it was possible change the size of the opening in the rotary disks to allow more or less light to hit the film, this is where the term shutter angle comes from. A 90° shutter would expose the film for a quarter of the disks rotation, likewise a 180° shutter would expose it for 1/2 the rotation. The effect of having bigger shutter angles would be more motion blur in moving subjects. Over time 180° shutter angle became the normal choice for motion blur levels and thats what we have become accustomed to as viewers.
Here’s a great explanation on WiKiPedia if you’re interested in finding out more about shutter angle.
With modern digital cameras we don’t have to worry about spinning disks and advancing film anymore but we still want viewers to have a that familiar viewing experience. Most people still advise exposing each frame for half the time it’s in place as per a 180° shutter. On modern cameras that means setting the shutter speed to half the frame-rate. For example if shooting 25 frames per second, you set the shutter speed to 1/50th Second.
The 180° Rule!
The “180° rule” in filmmaking has absolutely nothing to do with shutter speed! Over the past few years I’ve heard the phrase used more and more in relation to shutter angle. The 180° rule in filmmaking is actually all about spatial awareness & camera placement.
Now obviously shutter speed is an important exposure choice in the same way aperture and ISO are, however it’s not a rule! Many filmmakers change shutter angle (shutter speed) to create a feeling of tension or to better portray an ethereal moment. One famous example is Saving Private Ryan where 45° and 90° shutters were used to make action scenes look more gritty and frightening.
Shutter Angle / Shutter Speed do effect exposure but what they really control is the amount of motion blur and you are not forced to stick to 180°!
180° Shutter with 50p
I’ll start this section by saying while I’m using 50p shooting and 25p timelines as an example, the same would also apply to 60p shooting for 30p timelines.
If you’re shooting 50p in camera and using that on a 50p timeline to be delivered at that frame-rate then using 180° shutter at 1/100 is likely the right choice. Likewise if you’re shooting at 50p for a 25p timeline and you know that all of your footage will be slowed down by 50% in post production then again 180° shutter would likely be the normal choice.
Where things get complicated though is when you shoot at 50p for a 25p timeline knowing that your footage could be played back at normal speed. When you shoot at 50p with a 180° shutter of 1/100th and play it back at normal speed on a 25p timeline half of the frames are dropped. What you end up with is 25p footage with a 90° Shutter Angle because each frame is only exposed for 1/100th of a second. If you’re going for that Saving Private Ryan look then thats fine, but if you want a normal amount of motion blur then you need to read on!
360° Shutter for 50p
If I’m shooting at 50p knowing that some of my footage will be used for normal speed playback and some will be 50% slow-mo I’ll generally choose a 360° shutter of 1/50th. The result is that any clip played back at normal speed on a 25p timeline will have the equivalent of 180° shutter angle, ie each frame is exposed for 1/50th of a second.
The compromise with this approach is that any clips slowed down to 50% on the 25p timeline will have a 360° shutter angle with more motion blur than usual. The thing is though, because these clips are slowed down to half speed you rarely notice and in some ways it can make the slow motion footage look even smoother!
Give it a try!
It’s always good to experiment with camera settings before shooting something important so I’d recommend going out and shooting something moving with 50/60p Try some shots with 180° shutter and some with 360° and then see how they look on a 25/30p timeline. Make sure to come back and leave a comment letting me know what you find!