A Beginner’s Guide to Polarizing Filters (CPL)

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Everything you need to know about polarizing filters and why you should consider adding these valuable tools to your photography toolkit.

Words and Photography by Urth HQ

What Is A CPL Filter?

A circular polarizer/linear (CPL) filter is an easy-to-use, screw-in camera lens filter that alters the appearance of a photo. A CPL filter works by cutting polarised (reflected) light from any angle. Polarised light can often make a photo look washed out, so a CPL filter helps to combat this for more vibrant photos. 

People who love outdoor and landscape photography are particularly fond of polarizing lens filters as they can reduce several unwanted effects like silvery reflections on wet rocks or tree leaves, and enhance the colors, detail, or drama of an image. Essentially CPL filters can bring lacklustre images to life, boosting their richness, color saturation, and contrast.

Shot without a polarizing filter.
Shot with the Urth CPL Polarizing Filter Plus+

Types of Polarizing Filters

There are two types of polarizing filters – a circular polarizing filter and a linear polarizer. The difference between these two types involves how light waves pass through them.

A linear polarizer only lets horizontal or vertical light waves enter the filter as it is rotated. A circular polarizing filter passes circularly polarized light waves through the lens but is also sensitive to linear polarized light. A circular polarizing filter is similar to a linear polarizer but has extra glass behind it called a quarter-wave plate, which circularly polarizes light.

A circular polarizing filter is suitable for all DSLR cameras but a linear polarizer is not. Linear polarizers interfere with auto-focusing functioning and create light metering errors. This means that circular polarizing filters offer great versatility for use with a wide range of camera types.

To learn more, check out our in-depth guide to the differences between circular polarizing filters and linear polarizing filters.

How to Choose the Best Polarizing Filter

Because of the reasons mentioned in the section above, we recommend choosing a circular polarizing filter over a linear polarizer for their versatility and their compatibility with more cameras. 

When deciding which CPL filter to buy, the most important factor to consider is the lenses you’ll be using them on. Let the quality of your lens guide your decision because an entry-level lens filter on a professional lens may affect image quality. 

Urth has two different ranges of filters: standard and Plus+. Our Plus+ professional range is made with German SCHOTT optical glass – considered the best optical glass in the world. If you’re buying a filter for a professional lens or a telephoto lens (focal length >100mm), we recommend you use an Urth CPL filter Plus+. The quality of the German Schott Glass will match the level of sharpness your lens provides without affecting image quality.

If you’re buying a CPL filter for an entry-level or mid-level lens, we recommend our standard CPL Polarizing Filter. It’s more affordable and is still made from premium Japanese AGC optical glass for excellent polarisation. 

The Urth CPL Polarizing Filter.
The Urth CPL Polarizing Filter Plus+.

How and When to Use a CPL Filter

Your CPL filter will cut reflected light but remember that you need to rotate the outer element of your CPL filter to do so. 

To get the maximum polarization from your CPL filter, use the 90-degree rule. To do this, make an L shape using your thumb and index finger. Point your thumb at the sun and wherever your index finger is pointed, that is the angle that will achieve maximum polarisation. 

You can always adjust the level of polarization too. Sometimes full polarisation can be too strong, but it’s subjective.

At full polarization, most CPL filters reduce light coming through your camera lens by 1.33 f-stops, thus darkening your images and adding richer colors for a more visually striking result. This is especially useful if you want to make a sky appear a more vibrant tone of blue, or make clouds stand out against blue skies to add drama and intrigue to a scene.

CPL filters are extremely useful for nature and landscape photography, to reduce reflections and glare from reflective surfaces, such as bodies of water. This can give water surfaces more detail and a see-through effect so you can see fish or wildlife beneath the water. By removing glare or shine off objects, images have increased clarity.

Shot without a polarizing filter.
Shot with the Urth CPL Polarizing Filter Plus+

CPL filters are also useful in architecture or street photography, to reduce reflections, light streaks and glare bouncing off windows. A polarizing filter can effectively eliminate these issues, so that images appear clear and vibrant.

Shot without a polarizing filter.
Shot with the Urth CPL Polarizing Filter Plus+

The effects of a polarizing filter are difficult to reproduce digitally in post-production, so if you want to alter the color balance in your photos in real-time, this filter is indispensable. Rotating the filter to adjust the level of polarization creates different effects on your final image, so you can have a play around onsite and see all the creative opportunities live.

Find out more about why, how, when and when not to use a CPL filter.

Can You Leave a Polarizing Filter on All the Time?

Many landscape or outdoor photographers would be lost without a circular polarizing lens filter and leave them on their lenses 90% of the time. 

However, there are some occasions when they do more harm than good. For example, if you were trying to capture the reflection of a mountain mirrored in the lake below, a CPL filter would remove this reflection, so you’d want to take the filter off in this instance. 

Another thing to note is that CPL filters work most effectively when positioned at a 90-degree angle to the sun. If you use a CPL filter with a wide-angle lens, this covers more than 90 degrees, so it will result in an uneven depth of color in a single scene.

Find out more about the restrictions of using a polarizing filter.

How Much Light Does a Circular Polarizer Cut Out?

Polarizing filters cut out the equivalent of around 1.3 f-stops of light, which means if you’ve got a polarizing filter on you’d need to compensate for 2 f-stops of light by adjusting your shutter speed, aperture setting or ISO to get the same exposure.

An easy way to see the difference is by going into aperture priority mode on digital cameras and checking out the shutter speed reading before and after you put the polarizing filter on. This should give you an indication of the difference in light exposure. Sometimes having the autofocus on can affect the reading, so it’s best to keep your lens on manual focus for this test, especially if you’re not using a tripod. 

Although 1.3  f-stops is the average amount of light a polarizing filter blocks, this can vary according to the scene and your position relative to the light waves coming from your light source. Different multi-coated filters cut out various amounts of light, so make sure to check the details on whatever filter you purchase.

Check out these helpful tips for how to compensate for exposure when using polarizing filters.

CPL Filters Compared to Other Lens Filters 

UV AND CPL FILTERS

UV and CPL filters don’t perform the same task. Whether you choose a UV or CPL filter largely depends on what you want to achieve from your photography as each filter performs a different function. UV filters are often used to remove haze and sharpen details, but they can’t darken the sky or smooth water surfaces as they don’t reduce light from coming into the lens. 

A UV filter doesn’t affect the amount of light coming through your lens like a CPL filter does, so it won’t require you to adjust your shutter speed or aperture. Most photographers use both filters individually for various purposes, although they can also be used together simultaneously. You can read more about stacking lens filters here. 

Find out more about the difference between CPL filters and UV filters here.

ND AND CPL FILTERS

Polarizing filters and ND filters help photographers deal with challenging light conditions to improve image quality, especially when shooting landscape photography. However, polarizing filters and ND filters are not the same thing. 

Both filters are made from thin pieces of protective glass that are easily attached to a camera lens, but they each reduce the amount of light coming into your lens in different ways so it wouldn’t make sense to restrict yourself to using just either a polarizing filter or an ND filter. If you need to reduce light in a scene by more than 1.33 f-stops like a CPL filter does, or you need to reduce light without also removing reflections from a scene, ND filters allow you to reduce light by between 1 and up to 10 f-stops, so you can shoot long exposures and extremely shallow depths of field. 

You can learn more about the difference between CPL filters and ND filters here

Are Polarizing Filters Worth It?

CPL filters have many benefits with no real drawbacks and form an essential part of every landscape and outdoor photographer’s toolkit. Their ease of use, flexible applications and simple mechanics make for a low-risk, high-reward investment towards creating stronger, more captivating imagery.

They can give your photos more depth, drama and intensity without requiring much effort on your part.

To enjoy the many great benefits of a CPL filter, never skimp on quality when you’re shopping for polarizing filters. If you’ve been thinking about picking up your first polarizing filter, have a look at Urth’s line of polarizing filters, all made with premium optical glass and guaranteed to help take your photography to the next level. 

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2021-09-22T02:19:46+00:00Categories: Gear|Tags: |