ND filters cut the amount of light entering the lens so you can keep a slower shutter in bright sun; CPL filters cut reflections off water and glass. They solve different problems and are not interchangeable. In Egyptian daylight an ND16 is the general-purpose starting point.
What an ND filter is for
Natural-looking video depends on shutter speed being roughly double the frame rate — about 1/60s at 30fps. In bright sun a camera cannot achieve that without overexposing, so it raises shutter speed instead. The footage becomes sharp frame-by-frame but stuttery in motion, which reads as "digital" and unnatural.
An ND filter is effectively sunglasses for the lens. It reduces light so the correct shutter speed becomes usable again, restoring natural motion blur.
Choosing a strength
- ND8 — overcast, shade, early morning.
- ND16 — the default for bright Egyptian daylight.
- ND32 / ND64 — midday sun, desert, open water and sand, where reflected light adds significantly.
What a CPL filter is for
A circular polariser removes reflected glare. Rotate it and you can watch reflections on water or glass disappear, revealing what is beneath. It also deepens sky contrast and saturates colour.
The key point: this cannot be replicated in editing. Once glare is recorded, the detail behind it was never captured. A polariser works optically, before the image exists.
When to use one
- Filming over water, where you want to see into it.
- Shooting through car windscreens or shop glass.
- Landscapes where you want a deeper sky.
Using both
Some kits combine ND and CPL in one filter, which is convenient but fixes the polarisation strength to whatever rotation you set. For most action-camera use that trade is worth it.
One caution: a polariser's effect varies with angle to the sun. On a fast-moving camera that changes constantly, so sky darkening may pulse through a shot. For driving and riding footage, plain ND is often the safer choice.
See Camera Lens Filters and DJI Action Camera Accessories.
Fitting, stacking and keeping them clean
Action camera filters clip or screw directly over the lens housing, so they are sized per model rather than by thread diameter as on a conventional camera. A filter for one generation frequently will not seat on the next.
Avoid stacking two filters. Each additional layer of glass adds reflections between surfaces, which produces flare and reduced contrast — particularly shooting toward the sun, which is most of the time outdoors in Egypt. If you need both effects, buy a combined ND/CPL rather than stacking.
Store filters in a slotted case rather than loose in a bag. Loose glass in a bag with sand is how filters get scratched, and a scratched filter shows in every frame shot through it — the same problem as a scratched lens, at a fraction of the cost to fix.
Frequently asked questions
Do I need filters for photos too?
Less so. Photos can use a fast shutter without looking wrong, so ND matters mainly for video. CPL helps both.
Will a filter reduce sharpness?
A good glass filter has no visible effect. Cheap resin filters can soften the image noticeably.
Which single filter should I buy first?
ND16 for video in Egyptian daylight; CPL if you mostly shoot around water.