Dedicated crew team for one production department — camera, lighting, editorial. Each unit reports to department head and handles assigned shooting sequences.
You know the drill: The Line Producer divides the crew into specialized teams, each with its own area of responsibility and hierarchy. That's a unit — no more, no less. On a major feature film, multiple units work in parallel to save time and handle shooting schedule segments more efficiently. The camera unit is on Set A shooting dialogue scenes, while the second unit is out gathering establishing shots or action material. The VFX unit handles green screen sequences in separate rooms. Each unit has a leader — for camera, it's the cinematographer or DoP; for lighting, the gaffer; for grip, the key grip.
The unit structure is less a creative choice than an organizational necessity. On an average feature film, the typical setup is: The A-unit, under the director, with the main actors; the B-unit for secondary scenes, doubles, inserts. Sometimes a C-unit is needed for vehicle shots or stunt sequences. Each unit has its own equipment, its own crew, its own daily rhythm. This means the 1st Assistant of the A-unit coordinates with the A-camera assistant, while the B-unit operates independently with its own focus puller. Confusion is detrimental — therefore, clear role definitions are essential.
In practice, you need strong unit leadership, otherwise the system collapses. A weak second-unit leader produces unusable material that doesn't fit in the edit or needs to be reshot — a waste of time. That's why experienced cinematographers are often assigned to the B-unit on large productions. They understand the aesthetic of the main film and can make independent decisions without constantly asking the Director. The unit structure also works for commercial productions: while the main production films a hero product, the packshot unit shoots close-ups in parallel. In the edit, all materials come together — seamlessly, with good coordination.
Important: Unit work requires trust and standards. If the A-unit works with a certain lighting setup and the B-unit with another, it will be noticeable in the edit. That's why technical meetings are held between unit leaders before shooting begins. Lighting setups, focal lengths, and focus methods are defined. This isn't creative, but it's necessary. The unit remains relevant throughout post-production — if touch-ups are needed (reshoots, green screen extensions), you know exactly which unit was responsible and how they work.