Variable ND filters: how to nail exposure outdoors
If your daytime footage looks like a phone video, the fix is almost always a variable ND. It lets you keep a cinematic shutter and shoot wide open in bright light instead of stopping down to f/16. Here's how to use one properly.
- Keep shutter at ~2× your frame rate; change the ND, not the shutter.
- A variable ND lets you stay wide open in daylight for shallow depth.
- Stay within the marked min-max to avoid the dark 'X'.
Watch: using a variable ND
A clear, practical demo of dialling in a variable ND for photo and video — what to watch for and how it changes the look.
Why you need one
For natural motion, set shutter to roughly double your frame rate (the 180° rule — 1/50 at 25fps). In daylight that overexposes badly. A variable ND is sunglasses for your lens: it cuts light so you can hold that shutter and your chosen aperture without blowing out.
- 24/25fps → 1/50 shutter. 50fps → 1/100. Keep the shutter, change the ND.
- It also lets you stay at f/2.8 in sun for shallow depth of field.
Avoid the cross-polarisation 'X'
Variable NDs work by rotating two polarisers. Push past their range and you get an ugly dark 'X' across the frame and weird colour shifts. Stay within the marked min-max, and pick a quality filter sized to your widest lens with step-up rings for the rest.
- If you see an X or magenta cast, you've turned it too far — back off.
- Rent one ND that fits your largest thread and use step-up rings on smaller lenses.
- A matte box with ND trays is the cleaner option on cine glass.
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