The idea behind the 180 degree rule is a simple one, and it fits the aspect of the continuity of your shot when more than one object or person is involved. What the 180 degree rule will help you to do is maintain the screen direction for objects that are in your scene.
The first thing you need to do is establish an imaginary line of action, a straight line which intersects the two subjects. The idea is to keep your camera on one side of this line within a 180 degree angle. The diagram below should help you to understand this.
When put into perspective, if you are capturing video of two people in conversation using various shots, keeping to one side of the action line will result in 1 actor speaking towards the right hand side of the frame, and the other talking to the left hand side, creating the impression that the two people are speaking to each other. If you start varying shots on alternating sides of the action line then it can become confusing to the audience who each person is talking to. The other aspect that plays in to this is the background that is being used in the video. If you keep to one side of the action line, the background will always be the same, if you start to cross this line, the background will be different in different shots creating the impression that the conversation is happening in different locations.
So what happens when you incorporate three subjects into the video? The first thing you need to think about is how those subjects are situated in the shot. The way that it would work best is if they are stood in a triangular formation with each of them facing the centre of that triangle. Use the diagram below as an example.
Using this example, you will now have three action lines intersecting any two subjects at one time. Initially you will most likely use an establishing shot to show all three subjects in the frame, and then break into close up shots when any two subjects are talking to each other.
It is best practice to keep the camera to one side of the action lines. That way you will preserve the continuity of the shots as the subjects are talking to each other and the background that is behind them. When the conversation between subjects move from one to another, incorporate a shot of that person physically moving their eye line from one subject to the other before utilising your new action line, to make it obvious to the person watching the video that the conversation has changed.
If you need any support with your video content requirements, please do not hesitate to contact us on 01404 548405 or jack@cosmic.org.uk