Enrico Marega Interactive photography course
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ND filters and polarisers

Two filters change the photo in a way post-processing can’t imitate: the ND, a dark glass that lengthens the exposure, and the polariser, which removes reflections and darkens the sky.

1Simulator

ND filter: long exposures by day

Turn the filter dial, from ND2 to ND1000, and watch the shutter speed get longer: the sea turns to silk, the clouds stretch out, passers-by disappear.

2Simulator

Polariser: rotate the filter

Choose the scene, the sea or a shop window, and turn the filter ring: watch the sky darken and the reflections disappear from the water and the glass.

How to work out the exposure time with an ND

1Simulator Each ND filter cuts a certain number of stops: ND8 cuts 3, ND64 cuts 6, ND1000 about 10. Each stop doubles the exposure time. If without the filter you would shoot at 1/125, with an ND1000 you need 1/125 × 1024, which is about 8 seconds.

Some compacts have a built-in ND filter that you switch on from the menu: the Ricoh GR IV has a 2-stop one, the Fujifilm X100 a 4-stop one.

The polariser: sky, water and glass

2Simulator The polariser darkens the sky most when the sun is at 90 degrees to the direction you’re looking in, that is, off to the side. It cuts 1 to 2 stops of light and you adjust it by rotating it while you look through the viewfinder.

2Simulator It doesn’t only work on the sky: it also removes reflections on shop windows and car windows and on water. The reflection almost disappears when you look at the surface at an angle, about 30–40 degrees; if you look at it straight on, the filter can do little. On shiny metal, however, it doesn’t work.

Key points

  • ND: each stop of filter doubles the exposure time. ND8 = 3 stops, ND64 = 6, ND1000 ≈ 10.
  • Long exposures need a tripod and, if possible, the self-timer or a remote release.
  • The polariser removes reflections from water, shop windows and car windows and darkens the sky: maximum effect with the sun to the side and looking at the glass at an angle.

Try it yourself

If you have an ND filter, photograph a fountain or the sea at 1/250 and then with the filter, lengthening the exposure by the number of stops it cuts. If you don’t, try at sunset with the lowest ISO and the aperture at f/16.

Post the result and tag me @enrico.marega, or send it to me by DM: I’d love to see how you tackled it.

Quick check

Without a filter you shoot at 1/60. You fit an ND64 (6 stops). What shutter speed do you need?
You want to photograph the inside of a shop window without the reflections of the street. What do you do?
When does the polariser darken the sky the most?