Format in which the film plays in cinema—1.85:1, 2.39:1 (Scope), IMAX. The screen, not the camera, determines final delivery.
The screen dictates, not your camera. This is the first lesson every DoP must internalize when considering projection formats. What you see on the monitor is irrelevant—only how the material will look in the cinema later matters. The projection format determines the visible image area and thus the entire composition of your shots. You must already know during the shoot whether the images will later be shown in the classic Academy format (1.37:1), the standard 1.85:1, Cinemascope (2.39:1), or even IMAX. This is not optional—this is your foundation.
In practice, this means: you typically shoot in 16:9 or native 4K (which is usually wider), but your camera data sheet already accounts for which edges will be cropped later. This is called overscan or safe area. For a Scope film (2.39:1), you crop heavily from the top and bottom—this changes your entire image design. A wide shot that works wonderfully in 1.85:1 can appear empty and awkward in Scope because the vertical space is missing. Conversely, an IMAX film needs more headroom and footroom, more breathing room in the composition. Your camera movements need to be filled differently.
The practical problem: you often don't know the final format until after shooting begins or have to work with multiple options. Then, the focus puller helps you with appropriate masks in the viewfinder, or you mark the safe area lines in the monitoring systems. Many major productions today shoot "Scope-protected"—meaning you ensure that the image content still works in 2.39:1, even though you are technically recording wider. This is pure safety and good craftsmanship. Conversely, if a director needs a specific width, you must truly fill it. A Scope film that feels like 1.85:1 indicates poor preparation—and it shows immediately.
Also consider the edit: the editor must know which format was originally shot. Incorrect safe areas in the rough cut lead to cut-off heads and lost details. You will clarify the exact boundaries later with the colorist. IMAX blow-ups require even more attention—here, material is usually upscaled from 35mm, and your original image composition must withstand the extreme enlargement.