Polarisers - a guide to using polarising filters

Updated 26 March 2010

Digital photography enables us to recreate most filters effects that we used to produce using optical attachments on our cameras. But there's one filter that should still be in every photographer's gadget bag. Let's forget the crazy world of multi-images, the colourful starbursts and the dreamy diffusers - the essential item you should own is a polarizing filter. A genuine polarizing filter can have a dramatic effect on your photographs, but it won't ruin them, which is one common criticism of special effects filters, such as spot colours and multi images.

The classic effect a polarising filter has on the sky. Left shows a non polarised photograph and right with a polariser attached. Notice the saturation in the sky, making it vivid blue, but also the improved detail in the foliage and blooms, that give the picture more clarity.

How they work
Polarising filters work by suppressing surface reflections from non-metallic objects, by blocking the rays. The amount of suppression depends on the angle of the reflected light, the rotation of the filter and the amount of polarisation. You also see an increase in colour saturation, as the glare caused by the surface reflections often lightens the subject.

Polarsing filters are perfect for landscape photography. Here a warm tone version was used which has made the picture look more like a summer's day.

Some image editing software suggests it can offer the same results as a polarizing filter, but it misses the mark. A digital polarizing filter can enhance contrast and colour saturation, but it can't remove the reflections caused by light - well not yet anyway!

Here sunlight has caused glare on the varnished wooden sign which can be reduced when a polarising filter is used.

Photos of non-metallic surfaces aren't the only subjects that benefit from the use of a polariser. Light reflected from water and glass is also polarised and using a polariser enables the photographer to see through the glass or water.

A polarising filter used on water kills reflections, allowing you to see below the surface.

Another essential use of a polariser is for creating those rich blue skies that are normally seen in travel brochures and on postcards. Light scattered from a blue sky is polarised, making many blue skies look drab, add a polariser to the equation and you will produce a lovely dramatic blue sky.

How they attach
There are three types of polarizing filter. The most basic is a sheet of polarizing gel, which you would need to cut to size and hold over the lens or mount in a gelatin holder. Then we have precut and mounted versions, made by the likes of Jessops and Cokin, that slot into a filter holder and mount onto the front of the lens. The third option is the round type that has a sheet of polarising material sandwiched between two pieces of optical glass. The screw-in variety has a rotating front ring so you can adjust the filter while looking through the viewfinder until the reflections are reduced. The holder variety is usually round and can be rotated in the holder.

Ten top tips on using polarising filters

• When shooting to prevent reflections, it's best if you are at an angle of around 35 degrees to the reflective surface.

• A polariser can be attached on top of an existing UV protective filter, but if you do so, be aware that the depth of the filter rims may cause a small amount of vignetting (darkening of the edges) on wider-angle lenses. And as there are more glass to air surfaces the image quality could be degraded. So where possible it's better to remove any other filter and just attach the polariser.

• When shooting skies ensure you shoot at the best angle - for rich blue skies move around so that the sun is at 90 degrees to the subject - anything more or less and the saturation is reduced.

• Avoid using a polarising filter on a lens wider than 28mm as the effect can look false because only a proportion of the sky will be deeply polarised.

• Watch the exposure. A polariser has a neutral grey look, which won't affect colour, but does reduce the amount of light reaching the film/CCD. If your camera has through-the-lens metering it will calculate the exposure difference automatically, which is roughly two stops.

• Use two polarisers together as variable neutral-density filter with between two and nine stops light reduction.
   
• Use two polarisers one over the light source behind a plastic subject and one on the camera for a cross polariser effect.  There's a technique how to do that here: Cross Polarisation

• When using a polarising filter on an older camera that doesn't have TTL viewing hold it up to your eye and rotate until the filter is showing the best effect. Then mark the uppermost point of the rim with a china graph pencil or tape, screw it onto the lens and rotate so that the tape or mark is at the uppermost position. Some filters have a white line mark already printed on the rim which can be used as a gauge.
   
• Buy a slim version for use on a wide-angle lens to prevent the mount causing vignetteing
   
• Don't use a polariser when shooting through an aircraft window, you will record distracting patterns in the window.

There's one incident when a polariser should not be used. Here I increased the colours in the sky and made the ground look more saturated by using the polariser (left), but look at the rainbow pattern. This is caused by the material used in the windows and has produced the cross polarised effect.

Which polariser?
Linear or circular? Square or round? Take a look at our polarising filters buyers' guide. 

Visit Park Cameras to see the range of filters they stock.



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