Variable ND filters vs other ND types: are they worth it?

A variable ND filter is worth it if you shoot video in changing light and want to adjust exposure by turning a ring instead of swapping filters. It's less ideal for wide-angle lenses, very strong reductions, or long-exposure stills, where variable NDs can show an X-shaped dark pattern and color shifts. For stills and drones, fixed ND filters usually give cleaner results.

Variable vs fixed vs square ND — Each ND type trades convenience for image quality or flexibility. Variable NDs are fastest for video; fixed filters avoid the cross-polarization X-pattern.

How a variable ND works

A variable ND stacks two polarizing layers. Rotating the front one changes how much light passes, like turning a dimmer. That's why one filter covers a range of strengths. It's also why problems appear at the strong end: as the polarizers approach full cross, darkening becomes uneven, especially on wide lenses.

Pros and cons

Pros

One filter replaces several.
Fast to adjust while filming, so you can keep a 180-degree shutter as clouds pass.
Works well with a fixed frame rate and shutter for video.

Cons

X-pattern (cross-polarization) near the maximum setting.
Uneven darkening on wide-angle lenses, and sometimes on skies, because of the polarizing layers.
Possible color cast and some loss of sharpness from two glass elements.
Usually needs hard stops or markings to avoid the "bad" end of the range.

Tip: stay inside the marked range, and if you see an X or a dark band, back off or switch to a fixed ND.

Other ND filter types

Fixed screw-in ND: one strength per filter (ND8, ND64, ND1000). Simple, with no polarizer side effects. Screws onto the lens thread.
Square or rectangular filters in a holder: a holder mounts on an adapter ring for each lens size, and filters slide in. Lets you stack ND and graduated ND (to darken only the sky). The landscape standard.
Magnetic filters: snap onto a magnetic base ring for quick swaps. Convenient, but check that the base ring doesn't vignette on wide lenses.
Drop-in and clip-in filters: some cameras and lens adapters take filters inside the mount or a slot.
Gel filters: thin sheets cut to size, used on lighting and some cine setups. They scratch easily and aren't the "ND paper" some searches imply. For lenses, glass or resin is the norm.
Drone ND filters: small clip-on sets made for one drone's camera, like DJI's ND sets for the Air 3S (ND8/32/128) and Mavic 3 Pro (ND8/16/32/64). Weight and fit matter on a gimbal, so use the set made for your model.

Rings, adapters, holders and cases

Step-up rings let one larger filter fit smaller lens threads (for example a 67 mm filter on a 58 mm lens). Buy filters for your largest lens and step up.
Adapter rings attach a square filter holder to each lens thread size.
Filter cases (pouches or hard boxes) keep filters clean and scratch-free. Store them separate from loose items in your bag.
Lens hoods may not fit over some filters; check before you buy.

Variable ND vs fixed ND: which to buy

Mostly video on a mirrorless camera: a quality variable ND, used in its middle range.
Long-exposure stills: fixed ND (ND64 and ND1000). See ND filters for long exposure.
Wide landscapes with bright skies: a square system with ND and grad ND.
Drones: the fixed ND set made for your drone. See which ND filter for drones.

For the basics of stops and numbers, read ND filter numbers explained.