Post Production: Understanding Continuity in Editing
Continuity editing is the dominant editing technique found in narrative feature films, television shows and web content. It is used to unify a series of disconnected shots into a scene that plays out in a logical fashion. Movies and television are relatively new mediums of story telling completely different from anything we've ever seen before. Part of what makes them so unique is that editing allows the viewer to see a wide shot cut to a close up--something our eyes don't see in real life. This could make a story hard to follow, but continuity editing combined with solid narration allows the viewer to easily get immersed in the story.
The 180 Degree Rule and Spatial Continuity
The first rule that any filmmaker needs to learn before he picks up his camera is the 180 degree rule. Adherence to this rule is necessary to maintain continuity in your scene. What you do is create an imaginary line across your set that you will not cross with the camera. This way if the actor is on the left side of the frame and the actress is one right side in the master shot, they will stay in those established positions throughout the scene as the medium shots and close ups are editing together.
If the camera crossed the line and the actress appeared frame left and the actor frame right, then this would cause the audience to become disoriented because the established spatial continuity had been violated. Once the spatial distance and positions has been established, you should not violate it if you want to maintain continuity.
Cutting on the Action and Temporal Continuity
Entire scenes and montages can move between time, but the shots that compose the scene should have temporal continuity. An individual scene needs to feel as if it is happening right now in real time. The most common way of maintaining this illusion is to cut your shots on actions so that they match up to each other.
For example, let's say that we're editing two shots together of a man throwing a football. We can start with the close up where he begins to throw the ball and then cut to the wide shot where we see the ball leaving his hand and traveling across the field. We would want to cut the two shots together so that they meet at a point when the man's arm is in the same position. This way the action appears to be seamless when edited together.
Breaking the Rules
Not everything in your movie needs to be edited to the continuity style. Montages are a common example of a sequence of shots not edited for continuity. Instead they are put together to show a great passage of time while having a psychological effect on the audience by progressing the story.
Even some of the most celebrated filmmakers break the rules. In Jean Luc Goddard's 'Breathless', the director uses jump cuts to show the passage of time. But, if you plan on making a career in filmmaking, you should first learn the rules before you decide to break them.