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Polariser filter guide - Peter Bargh explains what polarising filters are and how they work.
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.
Linear or circular? Square or round? Take a look at our polarising filters buyers' guide.