Continuity in Film: Rule of Thirds

The guideline proposes that an image should be imagined as divided into nine equal parts by two equally spaced horizontal lines and two equally spaced vertical lines, and that important compositional elements should be placed along these lines or their intersections. This creates more tension and creates a more interesting composition rather than just putting things in the centre. Ideally, the points of interest should occur 1/3 or 2/3 of the way up or across the frame. Usually, the lower third or upper third line will be where the horizon sits, whilst the primary focus of the shot will remain on an intersection point.

The main reason for using the rule of thirds is to discourage the subject from being at the centre, or prevent the horizon from "dividing" the picture in half. When the subject is placed in 1/3 of the frame, the remaining 2/3 of the frame balances out the subject with some sort of context. This is because, if you have 2/3 of the frame to use, you can fill it with all sorts of visual aesthetics that can help aid the storyline.

Continuity in Film: Shot Reverse Shot

Shot reverse shot is a film technique where one character is shown looking at another character (often off-screen), and then the other character is shown looking back at the first character.The shots you should have for a basic shot reverse shot are: a two-shot of the characters usually in wide or medium shot; an over the shoulder shot on character A; and an over the shoulder shot on character B. Shot reverse shot is used with the 180-degree rule.

For example, in a shot-reverse shot sequence of two characters having a conversation, the first shot is a character looking towards the second character (who is offscreen). The second shot would be a shot, from the reverse angle, of the second character looking back at the first character. The shot-reverse-shot sequence will cut between these shots and will usually include a wide or establishing shot to break them apart. 

Continuity in Film: 180 Degree Rule

The 180-degree rule states that two characters in a scene should maintain the same left/right relationship to one another. The rule states that the camera should remain on the same side of the invisible axis. This is because the axis connects the characters; by keeping the camera on one side of the axis for every shot in the scene, the first character is always on the right of the second character and vice versa. This helps to not disorient the audience.

For example, in a dialogue between two characters, if the camera remains on one side of the axis, the relationship between the two characters will continue from shot to shot, even if one of the characters is not on screen. Moving the shot to the other side of the characters will reverse the order of the characters from left to right will confuse the audience into thinking the characters are talking to themselves instead of to each other. Another example is in a car chase. If a vehicle leaves from the right side of the frame during the first shot, it should then re- enter from the left side of the frame in the next shot. Leaving from the right and entering from the right will also create a sense of confusion within the audience. 

When the camera passes over the invisible axis, it is called crossing the line and the shot becomes a reverse angle. A reverse angle will disorient the viewer by showing an opposing viewpoint of the scene, by altering the perspective of the scene and the relationship between the characters established in the original shot. To avoid this disorientation of the audience, the camera could move in the scene to show the audience that it is from a different angle or viewpoint.