HOW TO USE A Polarising filter


 dull days Small change, big difference - a polariseradds magic to your shots

LEE FROST: The polariser is the most ver satile filter, killing sever al birds with one stone and making a massive difference to your images. Some photographers reckon they no longer need one because anything a polariser does can be achieved in post-production. "Poppycock, ’I say! The only way to get the true effects of a polariser is by using one, so ignore the sceptics and see the evidence here for yourself.

When light from the sun bounces off a reflective surface, it becomes polarised; scattering light rays. Polarisers block most of these rays, only allowing those travelling in one direction to pass through. As most light in the sky is polarised, it means blue skies are deepened and white clouds are more dramatic. Also, glare is reduced on non-metallic surfaces such as foliage, increasing colour saturation, and reflections are reduced or eliminated in water and glass.

It s easy to control the effect of the polariser as you can see it through the viewfinder as you ro:ate the filter. You ll see the sky darken then lighten as you rotate, glare disappear then reappear; when you re happy with the effect, you simply stop rotating. To get the ceepest blue sky, the sun needs be 90° to the lens; if the sun is behind you. or you shoot into the light, you ll see little change. The same applies to dull days; the sun needs to be shining to get the full effect. Take care when using lenses wider than 24mm, too, as polarisation will be uneven and the sky can be darker on one side. You can even it out in post-production, but realistic results a e hard to achieve.

The reduction of glare can be clearly seen when shooting landscapes - colours suddenly seem so much richer. But don t limit your use of a polariser to landscapes; it works brilliantly on architectural subjects, as well as colourful abstracts, because glare is reduced on all non-metallic surfaces. It will also reduce glare on dull days, so if you re shooting woodland scenes in overcast or wet conditions, your polariser will get rid of the sheen’on wet leaves and colours will appear much stronger. To reduce reflections with a polariser, the angle between the reflective surface and your lens axis should be around 30°. It can take trial and error to find that angle, though partial suppression of reflections is often sufficient, so you needn t be spot on.

Polarising filters reduce the light entering your lens by two stops. This means if you were using an exposure of l/125sec at f/11 without a polariser, the exposure would drop to around l/30sec at f/11 once you ve added one. The light loss will be accounted for automatically by your DSLR, so you don t need to compensate, but you do need to be aware of it because the shutter speed can become slow, increasing the risk of camera shake when handholding. That said, this light loss can be a benefit in situations where you want to use a slower shutter speed as the polariser acts like a 0.6N D filter. When shooting waterfalls and rivers, for example, the polariser not only gives you a slower shutter speed to blur the water, but also removes reflections from the water, and glare from wet rocks and surrounding foliage. It s a win-win situation!

 SETTING UP: I use a 105mm screw-on Heliopan Circular Polariser Slim Mount.

The polariser screws to the 105mm threaded ring on the front of my Lee Filters filter holder. I align the polariser by rotating it on the front of the holder or by rotating the holder itself - while looking through the camera s viewfinder to see the effect. This method is preferable when also using an ND grad filter as it means I can align the grad first, then rotate the polariser to achieve the desired effect.

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