How to use a polarising filter


To learn how to get the most from a circular polariser

Time: 10 minutes

Skill level: Beginner 

Kit needed: D-SLR, Circular polariser

Circular polarisers are among the most important filters you can buy for your camera. They are pretty much essential for landscape photography as they enable you to give skies extra punch, and help to reduce glare and reflections on shiny surfaces. 

Polarisers work by filtering out so-called polarised light (ie light waves travelling in a single plane, rather than in all directions). When light reflects off a non-metallic surface (such as water) it becomes partially polarised, and a polarising filter can be rotated so that it blocks this polarised light, but lets light waves travelling in other planes pass through. This helps to reduce glare on everything from sweaty faces to waxy leaves, and allows the natural colours and details to show through.  

Similarly, some of the light from the sky is polarised, and filtering out this component of the light darkens the sky. Clouds are less affected, which is why they often look so white and fluffy against the darker blue sky. For our full round-up of circular polarisers, turn to page 106. 

STEP BY STEP: Do the twist


Circular polarisers attach to the front of your lens, so your filter’s diameter will need to match that of your lens’s filter thread. If your lenses vary in diameter, you can get step-up rings that enable you to attach your filter to any lens. These can also help reduce vignetting (see far right). 


Be aware that a circular polariser will reduce the amount of light entering the lens by a stop or two, so you’ll need to set a slower shutter speed or a wider aperture to let in more light, and ensure an accurate exposure 


It can be tricky to predict how a polariser will affect a scene. Holding the filter up to the sky will allow you to preview the effect, but it’s far easier to see any effect by looking through your camera’s viewfinder as you rotate the filter when it is attached to the lens. 


Polariser filters are most effective if you shoot at 90 degrees to the sun. (Basically, keep the sun to one side of you to get the bluest skies possible.) Stay safe, though: make sure that you don’t look directly at the sun through the viewfinder while searching for the sun’s position. 


Another potential issue with circular polarisers is that they can cause vignetting (a darkening of the image corners), especially on wide-angles lenses at wide apertures – in effect, the edges of the filter frame become visible at the very corners of the image. The obvious solution is to use a polariser with a slimmer frame, but generally speaking, the slimmer the frame, the more expensive the filter (see page 106 for more on this). 


Once your filter’s in place and you’re standing at the right angle to the sun, you might think you’re all set to take the shot, but you can still boost the sky some more. Rotate the front ring of the filter to maximise the intensity of the polarising effect. 


As mentioned in the introduction, polarisers increase the contrast and saturation of your images, especially in blue skies, but take care: with wide-angle lenses, the strength of the polarising effect can vary across the frame, so it can sometimes look a bit uneven. 


By reducing the reflections from, say, a shallow river, a polariser can help cut through the glare to reveal the rocks in the riverbed below; this effect is more noticeable on still water when the sun is 30-60 degrees above the horizon, but it’s also apparent on moving water.