How and when to use ND filters (and what the numbers mean)

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Things to look for in an ND filter

Materials & coatings
A number of factors affect the quality – and the cost – of a filter. Resin, glass and polyester can all be used to manufacture filters. Polyester is the cheapest option, but gives poorer quality results. A variety of advanced coatings are used to reduce lens flare and ghosting, while black almite frames and rimmed glass further reduce reflections. Thin, shallow-profile frames help to reduce vignetting.

Screw-in or slot-in?
Circular filters are small, lightweight and easy to fit, but lack versatility as ‘stacking’ soon leads to vignetting problems, and each filter only fits a specific diameter lens. Square slot-in filters require an adapter and holder, which means extra kit to carry around. They’re initially fiddlier to set up, but they’re more adaptable as you can easily stack ND filters for increased exposure times, or add other types of filters, such as ND grads or polariser.

Adaptor & step-up rings
You can easily fit a slot-in filter system to different lenses by purchasing inexpensive adaptor rings for each lens size you own. For screw-in filters, buy a filter to match the largest lens you own and buy step-up rings so you can fit it to smaller lenses.

PAGE 1: How to use ND filters
PAGE 2: When to use ND filters
PAGE 3: Things to look for in an ND filter