Polarising Filters

A polarising filter is used to remove reflections from a shiny surface and make blue skies darker, but there are many other uses for this versatile accessory. Nina Bailey takes a look at how many subjects can be improved by polarisation.

The image on the left shows the classic effect that a polarising filter can have on the sky in a landscape photograph.

However the correct technique is essential to get results like this.

Polarising Filter Types

Any Polarising filter used on an Autofocus camera must be of the circular type. This does not mean that it is round in shape, but is designed to mimic the natural polarisation of light therefore avoiding the problems that can occur in optical systems. The older linear type interferes with both the auto focusing and exposure systems on Autofocus cameras. Focusing on an Autofocus camera works by the light travelling through a partially translucent coating on the cameras reflex mirror. This bounces off a sub mirror to arrive on to the auto-focusing sensor.

If a linear polarising filter is used it is possible for the filter to polarise the light in such a way that when it arrives at the sub mirror it is unable to pass the correct quantity through due to the cross polarising effect caused by the sub mirror.

Polarising filters are available from a range of manufacturers such as Hoya, B&W and Cokin. All manufacturers use different depths of filter mount. Generally the lower the cost of the filter the thicker the mount becomes and the higher risk of vignetting occurring.

All polarising filter have no coatings – this would defeat what a polarising filter does. They also have quite soft surfaces that mark easily, so when not on the camera lens they should be kept in the protective case they were supplied in.

A polarising filter must be used on it’s own. Filter such as UV and Skylight must be taken off as they cause two potential problems.

1. The extra depth will cause vignetting on many lenses

2. The coatings and filtration provided by these other filters can reduce or eliminate the effect generated by the polarising filter.

The photographs on the right show the traditional use of a polarising filter to remove reflections from shiney surfaces

How polarising filters work

A polarising filter only allows light to enter the lens in a specific direction whilst absorbing other light. If used for its traditional role of removing reflections, by polarising the light reflected from the surface it permits the actual subject to be viewed without reflections.

When removing reflections the optimum polarisation effect will be achieved with the camera at a 30^o ~40^o angle to the subject. The effect will be greatest when using a short telephoto lens as the whole picture area can be within the optimum angle. When using wide-angle lenses much of the subject is outside this and therefore not all reflections will be removed.

By rotating the polarising filter different parts of the subject can often be polarised changing the overall effect. The polarising effect gradually builds in intensity as the filter is rotated and gradually goes away again. This allows the degree of polarising effect to be varied.

Darkening Skies With Polarising Filters

Polarising filters are used a great deal to darken skies giving the images we are used to seeing in holiday brochures. Normally depicting a golden beach with deep blue sky and small fluffy white clouds. The degree of polarisation varies according to many things. If shooting the sky near the horizon the polarisation effect will be less than if shooting the sky immediately above you. The part of the world you are photographing will also make a big difference to the effect as the sun’s angle varies. The more overhead it is the less effect you get. The nearer the horizon the more dramatic the effect can become. It is possible with the right condition and shooting situation to make the sky turn virtually black, Not natural but it can make architectural details look stunning against it.

To obtain this effect you need to shoot with the camera at approximately 90^o to the sun where the effect is at its maximum. If used when the sun is directly behind or in front of you there will be little or no visible effect.

The lens used will affect the overall appearance of the scene. A moderate Wide angle (35mm or 28mm) works best as the amount of sky captured in the photograph is quite large and the polarising effect works to its best advantage with a large expanse of sky well above the horizon.

An often-suggested way of finding the maximum polarising is to turn and face the sun. Put your arm out in front of you pointing at the sun. Hold your hand as if hitching a lift and turn you hand through 90^oin either direction. Your thumb will then be pointing at the area of greatest polarisation.

Problems Using Polarising Filters

Care also has to be exercised with the choice of lens. Wide-angle lenses can give very dramatic effects when used with a polarising filter fitted. However when using wide-angle care needs to be taken to ensure that the sky is polarising evenly.

In this example a 17mm lens has been used. This has produced a very uneven effect on the sky, as the entire scene does not lie in the area where the polarising effect is strong. We also see here evidence of another problem common when using polarising filters on extreme wide-angle lenses. The corners are just beginning to show darkening where the filter due to its deeper mount than a normal filter, has caused part of the image to be cut off and therefore vignetting on the final result.

Shooting at the incorrect angle can also produce uneven polarisation. In this example the wide-angle lens has captured half the sky polarised but half remains light where the polarising effect has not worked.

Long telephoto lenses may not give the expected results as although it is easier to use them at an appropriate angle, the area of sky often visible in the photograph may have so much haze or pollution that the effect is almost non visible. If shooting from a low angle looking up then this ceased to be a problem and dramatic results can be achieved.

Polarising filers are normally sold for removing reflections – and sometime for intensifying a blue sky. They can be used for much more than this.

Increasing Colour Saturation

Polarising filters can be used to increase the colour saturation of vividly coloured subjects. The shooting angle needs to be ideally 30^o ~40^o angle to the subject.

Most manmade surfaces are reflective; by using a polarising filter to remove these surface reflections it is possible to produce very saturated colours giving an eye-catching result. This can also work in cities where tall shiny skyscrapers can be made to look dramatic by controlling the level of reflections from there surfaces.

Landscape Photography

When shooting distance views the amount of haze present often spoils the overall effect making the image dull and lack lustre. By using a polarising filter, if the angles are right it is possible to cut though the haze, which is causing the reflected light to flatten the image and thereby increase the colour saturation of the scene.

In this example the polarising filter has cut through the blue haze making the scene look much clearer. It has also increased the colour saturation and the contrast of the scene. The foliage in the foreground has also intensified in colour giving life to the foreground in the image.

We tend to think of reflections occurring in man made objects such as cars & windows. We also think of using polarising filters to remove the reflections on a lake or the sea to make the water deeper in colour. In fact water is a very reflective substance. Even the smallest coating on a surface will give it a high gloss and make it highly reflective.

In this example the water on the rocks is reflecting the sunlight back towards the camera angle. This is masking the rich colours of the algae growing on the rocks. With the polarising filter set, the bright reflections are removed and the colours and more saturated.

Natural History Photography With A Polarising Filter

One of the lesser-known uses is with macro or close up photography to remove reflections from foliage and to intensify colours in the image. This also works when shooting in woodland areas and allows colours to be intensified.

Without the Polarising filter this shot is very dull and lacks colour. With a Polarising filter the colours intensify and the scene becomes interesting. The effect works equally as well when shooting close in removing the shine of the leaves revealing a rich vivid green. The same technique can be used to remove reflections on flower petals especially useful with some macro photography.

Site designed and managed by Enigma Media Solutions Ltd

[an error occurred while processing this directive]