Shutter

The shutter — this is the mechanical or electronic aperture directly in front of the sensor or film plane — determines how long light falls onto the emulsion or chip. For each individual shot, this aperture opens and closes: it does not regulate the amount of light (that's the iris's job), but the duration of the exposure. This is the fundamental difference that many beginners confuse.

The 180° rule — this has been standard since the analog film era and holds true to this day — means that the shutter is half open. At 24 frames per second, this results in an exposure time of approximately 1/48 second. This setting creates natural motion blur that appears familiar to the human eye. Shortening the shutter to 90° or less makes movement appear staccato, jerky — good for horror or action with aggression. Opening it to 270° or more makes everything appear velvety smooth and blurred, as if underwater. This is a deliberate aesthetic choice, not a mistake.

In practice: In bright light and with fast films (like 800 or 1600 ISO), a smaller shutter is your ally — 90° or 135° — to avoid overexposure without having to close down the iris too much. In backlight or with very dark subjects, you often need 200° or 240° to gather enough light. Digital cameras offer flexibility here; with cameras like the RED or ALEXA, you can switch between mechanical and electronic shutters — the electronic one is maintenance-free, while the mechanical one is considered by some to be more cinematic because it creates physical rotations and brings with it specific behavior regarding flicker or fast pan movements.

Important: The shutter interacts directly with your shutter speed and thus with motion blur and flicker behavior. If you are working with artificial light (50Hz or 60Hz), you must synchronize your shutter setting and frame rate to avoid flicker. A 180° shutter at 24fps with 50Hz light can already become critical. This is not an academic detail — you'll notice it in the final image.