When you position the camera for a dialogue scene, the key is to keep the camera on one side of the imaginary axis along this straight line for the duration of the scene. Why? For many films, the goal is to keep the viewer focused on the action of the scene, keeping them keyed into what is happening with the actors. Obeying the 180 rule maintains continuity — along with following a solid shooting script — so the viewer is not distracted by inconsistencies in spatial relationships.
A cutaway across the line when filming a scene breaks continuity, potentially disorienting or confusing the viewer. But sometimes that confusion is helpful.
How do you visualise this? The answer is simple, says director Whit Ingram: “Watch films, observe the 180 rule and then go out and practice.”
When to hold the line and when to break it.
Making the decision to maintain the 180 line is a critical one and whatever you choose to do, be intentional.
Hold the line.
Preserving the 180 line is critical when you want the focus to be on actors or movement within a scene. When you reverse cut from one over-the-shoulder shot to the other, keep the camera on one side of the line to maintain continuity and keep things consistent for the audience.
Break the line.
One of the most important aspects of acknowledging a convention is knowing when to break it. Many filmmakers make an intentional choice to break continuity and disorient the audience. By jumping across the line, you can cause a shift in perspectives.
But before you think about crossing the line, ask yourself why. There are many reasons to do this — a jarring battle scene, a power change in a conversation or presenting an alternative perspective.
For a lesson in disoriented continuity, look no further than Stanley Kubrick’s The Shining. Multiple scenes in the film break the 180 line to get the viewer inside Jack Nicholson’s character’s own mental disorientation. There are cuts from the right side to the left, so characters in conversation switch sides of the screen. The effect, like Kubrick’s many jump cuts, is unsettling — precisely the right choice for a horror film.
Technical details and stylistic choices.
The beauty of the 180 rule is that there’s no special filmmaking equipment required to practise it. You can maintain the same degree of continuity with an iPhone camera or a three-camera set-up — a multi-camera set-up used to simultaneously film a scene from different angles. The main thing to keep in mind is the structure and flow of your scene.