Guide To Buying A Polarising Filter

A polarising filter is a key part of any photographer's collection, but knowing what type to go for can be a minefield if you're a filter novice. We've created this article to give you the options and let you decide what's best for you. 

Without a polariser 

What is a Polariser? 

A polariser is a filter that helps to cut reflections from non-metallic surfaces, such as water and windows. So, they will enable you to see to the bottom of a pond, for example, or through the window without reflections blocking the view. They also increase density in the sky or on foliage by absorbing reflected light, resulting in deeper colour tones.

Linear or Circular?

There are two varieties  of polariser - linear and circular. Although they're both physically round, a linear variety can have an effect on the autofocus or metering accuracy of any camera that uses a semi-silvered mirror or prism to split the light entering the viewfinder. This is known as a beam splitter and is used by most modern SLRs to calculate exposure and focusing distance.

As a rule use a circular filter if you have an autofocus camera or a manual focus model with a spot meter.

With a polariser 

Screw in or system filters?

You need to decide whether to buy a round, screw mount filter like those from Hoya or a system version that slots into a filter holder, like the Cokin system. Round ones are often easier to adjust and feel better built. They're also more compact to carry around. The disadvantage is larger sizes are more expensive and, if you have two lenses with different filter thread sizes, you may need to buy two filters, whereas a system type would just need another adaptor ring for the filter holder.

The filter holder type can also cause vignetting when used on some larger thread wide-angle lenses. Equally, a larger filter holder may prevent vignetting when used on a smaller thread wide-angle.

So, which are the latest available polariser filters?

We'll take an example from both Hoya and Cokin to answer this question. 

Hoya

Hoya's PL/PL CIR filter is an effective polariser available in 37, 40, 43, 46, 49, 52, 55, 58, 62, 67, 72, 77, 82, 86 and 95mm sizes. It won't affect the colour balance of a shot and provides colour and contrast enhancement. 

Cokin

Cokin produce the PURE Harmonie Circular Polariser. They claim it's the thinnest and lightest polarising filter in the world. It has a factor of only 1 f/stop when attached to the lens. It uses EVERCLEAR 5 Coating Technology, which repels water, oil, dust and grime and is also scratch resistant. 

For more information on both Hoya Ns Cokin filters, take a look at the Intro 2020 website.