Glossary: Axis of action
In the continuity editing system, the imaginary line that passes from side to side through the main actors, defining the spatial relations of all the elements of the scene as being to the right or to the left. The camera is not supposed to cross the axis at a cut and thus reverse those spatial relations. In other words, the axis of action ensures that relative positions in the frame remain consistent. Also called the 180° line.
From Casablanca
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Frame 1: As Ilsa arranges flowers in the right foreground,
Rick opens a bottle of champagne in the left background
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Frame 2: The next shot reverses the angle but still
obeys the axis of action since Rick remains on the left and Ilsa remains
on the right
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Frame 3: Rick and Victor speak in a conventional over-the-shoulder
shot/reverse-shot sequence
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Frame 4: Rick and Victor speak in a conventional over-the-shoulder
shot/reverse-shot sequence; these shots obey the axis of action
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Frame 5: The next shot crosses the axis line: notice
that Rick is now on the left and Victor is on the right
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Frame 6: After a few intervening shots, the camera
position returns to the original axis of action
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