In professional productions, the applied 180° rule is an essential element for a style of film editing called continuity editing. However, sometimes this rule will be purposely broken in order to create the sensation of disorientation.
In filmmaking, the 180° rule is a basic guideline that states that two characters (or other elements) in the same scene should always have the same left/right relationship to each other.
If the camera passes over the imaginary axis connecting the two elements together, it is called crossing the line. The new shot, from the opposite side, is known as a reverse angle.
An example of continued use of the 180 degree rule occurs throughout a considerable amount of The Big Parade, a 1925 drama about World War One. In the sequences leading up to the battle scenes, the American forces (arriving from the west) are always shown marching from left to right across the screen, while the German troops (arriving from the east) are always shown marching from right to left.
Left to right is often shown as more powerful as that’s the way we read.
This affects movement and continuity and can cause confusion when
a character changes point of view eg, in Lord Of The Rings, Gollum has a conversation with himself or with his other
personality. Because the filmmakers use the 180 degree rule, and have the
"good" on the left facing the ‘evil’ on the right " looking face
on at one another, these characters will be identified as the same person from
the audiences perspective which will highlight confusion. This effect builds
gradually during the scene. He is shown starting to turn his head, though the
camera changes angles mid-turn. As the argument between the split-personalities
grows, the editing gradually changes to using jump cuts, not showing Gollum turning his head.
Lauren Gibbens