Variable ND filter
Also known as: VND, variable neutral density, fader ND
A neutral density filter you can twist to adjust how much light it blocks, so you keep a natural shutter speed as the light changes without swapping filters.
Updated
What it means
A standard ND filter blocks a fixed amount of light, such as ND8 or ND32. A variable ND uses two polarizing layers: turning one against the other changes how much light passes through, typically across a range of several stops. One filter can replace a whole set.
Filmmakers use it to keep the shutter speed near the 180-degree rule in bright light, which gives natural motion blur. As clouds pass or you move between sun and shade, a quick twist keeps exposure where you want it.
Variable NDs are common on mirrorless and cinema cameras, and smaller versions exist for drones and action cameras.
How it works in practice
Set the shutter speed first, usually around twice the frame rate, then turn the filter until the exposure looks right. Many variable NDs have marked stops or hard stops at each end, which make settings repeatable.
For drones, fixed ND sets are more common because you cannot twist a filter mid-flight, but variable versions help on the ground and on handheld cameras where conditions change quickly.
Combine it with manual ISO for full control, so the camera does not fight the filter by changing gain. Note the filter position for each setup, so you can return to it quickly.
What to watch out for
At the strongest settings, many variable NDs show an X pattern, a dark cross or uneven darkening across the frame, caused by the polarizing layers. Ultra-wide lenses make it worse. Stay within the marked range, and prefer fixed NDs for very wide action cameras.
Cheap variable NDs add color casts, softness or flare. A quality filter matters more here than with many accessories, because every flaw sits directly in front of the lens for every shot.
Because it uses polarizers, a variable ND can also change reflections and sky color like a CPL, which may or may not be what you want.
How RawClip handles it
RawClip does not change exposure or motion blur. Footage with natural motion blur from a well-set filter cuts together smoothly, and the AI arranges the best moments into your highlight synced to music.