Polarising filters: Should you choose a CPL or linear polariser option?

Can’t decide between a CPL or linear polariser filter? With our expert advice, you’ll learn just what’s right for you.

Gobe HQ   |   AUSTRALIA


 

Polarising filters offer a number of benefits for the landscape or outdoor photographer. If you’ve decided to use them, you’ll soon discover that there are two types to choose from – CPL and linear polarisers. 

What are the differences between CPL and linear polariser filters, and which one should you choose? This is a very common photography query.

Before working out which type of polarising filter is right for your camera, understand what polarisation is all about. 

Essentially, polarisation refers to the way in which light behaves or moves as it hits your lens. Light forms waves as it travels. When it is reflected off non-metallic surfaces, this light is bounced and scattered making the waves move in different directions. With polarisation, light is oriented in a single direction, making it predictable and not random.

Polarising filters work by cutting out the reflected light that travels at different angles. This brings lots of benefits. Reflections, glare and haze are reduced, while colour saturation, contrast and intensity are enhanced. This filter is especially revered by anyone who shoots images of sky, water or vegetation.

 

 

When a polarising filter is on the end of your camera lens, you can easily and conveniently turn it. This lets you control light exposure levels.

Many people assume it’s the filter’s shape that determines whether it’s a CPL or a linear polariser. But, this isn’t the case at all. In fact, both filters are circular and look the same. When used appropriately, they both deliver the same fantastic image-enhancing results for your photography.

The actual difference between these polarising filters is how they each modify light waves that pass through them.

Linear polarisation refers to light waves that are vertically or horizontally polarised. Therefore, a linear polarising filter only allows horizontal or vertical light waves to enter the filter when it is rotated.

Circular polarisation relates to light waves that move in a circular direction, leading to left-handed or right-handed polarisation. A circular polarising lens filter, or CPL, therefore, filters circularly polarised light. But, it is also sensitive to linear polarised light. A CPL filter is basically a linear polariser, but with an extra glass element behind it. This glass is called a quarter wave plate, and it circularly polarises light. When light hits the light meter, it gives accurate exposure results.

 

Image—Anthony Awaken

 

What does this mean in practical terms, when deciding whether to buy CPL or linear polarising filters? 

Whether you choose a CPL filter or a linear polariser is largely down to the type of camera you own. In general, CPL filters are more versatile than linear types. CPL filters are suitable for all digital cameras, but a linear polariser won’t work on DSLR cameras.

If you own a modern DSLR camera, it will probably have a partially reflecting mirror. The presence of this partially reflecting mirror can cause metering errors if you use a linear polariser with a DSLR camera. A CPL filter does not interfere with the lens metering system, however, so is the right choice of polarising filter for a DSLR camera.

Therefore, if you own an old compact camera that is unlikely to have a partially reflecting mirror (but instead has a fully reflecting mirror to reflect all polarisations with equal density), you can use either a linear polariser, or, indeed, a CPL filter.

A linear polariser also won’t work on a camera that has autofocus.

If you’re not sure which filter to use for your camera type, check the instruction manual that your camera came with. Whether you choose a CPL or linear polariser, always buy good quality polarising filters from a reputable source, to ensure the best image-enhancing results.