An ND filter reduces the amount of light reaching the sensor without shifting color, which lets you keep a wide aperture for shallow depth of field, or a slower shutter speed for natural-looking motion, in bright conditions where correct exposure would otherwise force a narrow aperture or a very fast shutter. The 180-degree shutter rule is the common guideline of setting your shutter speed to roughly double your frame rate, for example around 1/50 second at 25 fps, to produce motion blur most viewers read as natural, but it is a creative starting point rooted in film camera convention, not a technical requirement, and there are legitimate reasons to shoot outside it.

Translate Angle and Frame Rate

Shutter angle as a concept comes from rotating disc shutters used in film cameras, where the size of the open segment of the spinning disc determined how long each frame was exposed relative to the frame rate. Digital video cameras do not have a physical rotating shutter, but the same math is kept as a convention for describing exposure time relative to frame rate. Frame rate, how many frames are captured per second, is a separate value from shutter duration, how long each individual frame’s exposure lasts, and the 180-degree relationship simply sets shutter duration equal to half of one frame’s time.

  • At 24 fps, 180 degrees works out to roughly 1/48 second, commonly rounded to 1/50 in practice.
  • At 30 fps, 180 degrees works out to roughly 1/60 second.
  • At 60 fps, 180 degrees works out to roughly 1/120 second.

These are typical, rounded figures used in everyday practice rather than exact universal values, since fractional frame rates shift the precise math slightly, and the convention is meant as a practical starting point rather than a fixed formula that must be hit exactly.

Set Aperture for the Scene

A workflow that avoids fighting your own settings decides depth of field and motion rendering first, then uses an ND filter to bring exposure down to the correct level afterward. Choose the aperture value that gives you the depth of field you want for the shot, and choose the frame rate and shutter angle you want for how motion should render, since both of these are creative and technical decisions in their own right, not brightness controls.

Once aperture and shutter are set for the image you want, use ND filtration to correct the resulting exposure rather than opening the aperture wider or speeding up the shutter to compensate for brightness, either of which would undo the depth of field or motion choice you just made deliberately. It is also worth remembering that pushing a lens to its widest aperture can affect other optical characteristics, such as vignetting or edge sharpness, on some lenses, which is another reason to pick aperture for the image first and correct brightness with an ND filter second.

Handle Flicker and Changing Light

Flicker under artificial lighting, most often from AC-powered fixtures including many LED lights, happens because those lights vary in brightness at a rate tied to the local electrical supply frequency, and it can show up as visible banding or pulsing in footage when your shutter speed and frame rate do not align well with that light’s flicker cycle.

An ND filter does not address this, since it only reduces the total amount of light reaching the sensor, it does not change the timing relationship between your shutter and the light source’s flicker. Before a shoot under artificial lighting, verify the local electrical frequency, check whether the specific fixtures on location are labeled flicker-free, and test your planned frame rate and shutter combination on-site rather than assuming one shutter setting eliminates every possible flicker source.

Break the Convention Deliberately

A narrower shutter angle, meaning a faster shutter speed relative to frame rate, reduces motion blur per frame, producing a crisper, more staccato look that is often chosen deliberately for fast action, sports-style coverage, or a harsher, hyper-real feel. A wider shutter angle, a slower shutter speed relative to frame rate, increases motion blur, producing a softer or more fluid look sometimes used for a specific emotional tone, though it also raises the risk of unwanted softness on anything moving quickly through the frame.

There is also a purely technical reason to deviate from convention: in very low light, some productions widen the shutter angle specifically to gather more light per frame, when adding further ND is not the issue and opening the aperture further is not desirable for depth of field reasons, accepting more motion blur as the trade-off for adequate exposure.