A circular polarising filter (CPL) is often considered an essential tool for outdoor photography to reduce glare and reflections while enhancing colours and contrast. But does it truly live up to its reputation?

To find out, I put a CPL to the test during a recent short trip, aiming to see if it genuinely makes a noticeable difference to landscape photography.

What is a Circular Polarising Filter?

A circular polarising filter (CPL) is a piece of optical glass that attaches to the front of your camera lens. Its primary purpose is to reduce glare and reflections, enhance colours, and improve contrast by filtering polarised light. Unlike neutral density (ND) or UV filters, CPLs specifically interact with the way light travels.

How does a CPL filter work?

Light waves vibrate in multiple directions. When light reflects off surfaces like water, glass, or foliage, it becomes polarised, meaning the waves align in a specific direction (usually horizontal). A CPL blocks this polarised light, allowing only unpolarised light to pass through, which reduces glare and improves clarity.

A CPL filter consists of two rotating glass elements. As you rotate the filter, it selectively blocks polarised light, allowing the photographer to control the polarisation effect and obtain the desired amount of reflection removal.

Does a CPL filter make a real difference in landscape photography?

I decided to take the Kase CPL III filter into the field to determine whether it makes a discernible difference to my photos. I chose to travel to a nearby lake (see story here) and test it under various conditions. Each time, I shot the same image with 3 different CPL settings, as follows:

CPL with maximum effect
CPL with minimal effect by turning the CPL filter 90 degrees from the maximum effect setting
No CPL effect by removing the filter from the camera lens

Here are the results:

1. Reducing Glare and Reflections

Reflections can obscure details in your photos, especially when shooting through glass, water, or shiny surfaces. A CPL minimises these reflections, revealing underlying textures or colours.

I was surprised to find that the CPL setting with minimal effect seemed to enhance the reflection even more than when the filter wasn’t used at all. Curious about this, I decided to test it again in a different setting the next day.

2. Enhancing Colour Saturation

A CPL intensifies colours, making them appear richer and more vibrant; skies become a deeper, more saturated blue and foliage appears lush and vibrant by reducing light scatter and reflections on leaves.

3. Improving Contrast

By filtering out stray polarised light, CPLs can improve contrast in outdoor scenes. This makes clouds stand out against the sky and adds depth to your images.

An unexpected discovery:

Throughout my tests, I consistently found that, in terms of reflection, colour saturation, and contrast, the image taken without the CPL filter fell somewhere between the two images taken with the filter at opposite settings. I'm unsure whether this is a characteristic of all circular polarising filters or specific to the Kase CPL III. If you have any insights, contact me, or let me know in the comments below.

When to Use a Circular Polarising Filter

CPLs are versatile, but their impact is most noticeable in specific scenarios. Here are some ideal situations for using one:

1. Landscape Photography

CPLs can improve a landscape photo containing water, clouds and/or foliage.
Reflections in lakes or streams may complicate a scene and obscure the stream or lakebed underneath. A CPL will minimise reflections, enabling you to photograph the lakebed and aquatic life.
Glare on leaves can distract a scene and reflect bright light. A CPL can enhance the greens of forests or fields by reducing glare on leaves.
Sometimes you may wish to emphasize clouds in the sky. A CPL can darken skies and make clouds more dramatic.

2. Seascape Photography

Often, a CPL can improve a seascape photo. Beaches are filled with reflective surfaces, from shimmering water to wet sand and rocks. As waves wash up the shore, they leave behind wet surfaces that reflect bright light and create distracting glare. This glare can weaken your composition and make the scene less visually appealing. By minimising these reflections, a CPL allows the natural textures and colours of wet surfaces to stand out, resulting in a more polished and captivating seascape.

3. Urban Photography

When shooting through glass or near reflective buildings, a CPL helps reduce reflections, making urban scenes cleaner and more detailed.

When NOT to Use a Circular Polarising Filter

While CPLs are powerful, they’re not suitable for every situation. Misusing one can lead to unintended issues:

1. Low-Light Conditions

CPLs reduce the amount of light entering the lens by about 1 to 2 stops. This can be problematic in low-light environments, such as:

Night photography
Indoor photography without ample lighting

Using a CPL in these situations may force you to increase your ISO or slow your shutter speed, introducing noise or motion blur. You may need to use a tripod to ensure a sharp image.

2. Ultra-Wide-Angle Lenses

When using ultra-wide-angle lenses, the effect of the CPL can appear uneven, particularly in the sky. This happens because polarisation varies across the wide field of view, leading to unnatural gradients. If your lens covers more than 90 degrees, you’re likely to end up with an uneven polarising effect.

Also, be aware of vignetting with wide-angle lenses. Drop-in filter holders are particularly prone to this issue, because filters can be positioned too far from the lens. Filters that screw on or attach magnetically often offer better results compared to drop-in filter holders, particularly for wide-angle lenses. It may be worth considering a filter with a larger diameter than your lens and using an adapter to fit it.

3. Panoramic Shots

In panoramic photography, the polarisation effect may vary across frames, creating inconsistent skies that can be challenging to stitch seamlessly.

4. Photography of Metallic Surfaces

CPLs don’t significantly affect reflections on metallic surfaces. Using one in such scenarios might not provide noticeable benefits.

5. Rainbows

A rainbow is reflected light, so if you stick a polariser on your lens, the rainbow will vanish.

6. When Natural Reflections Enhance the Scene

Sometimes, reflections add interest or context to a photo. For example:

A reflection of mountains in a calm lake.
The shimmering surface of water during a sunset.
A brightly coloured sky during a sunrise or sunset.

In such cases, using a CPL to eliminate reflections could detract from the image’s overall impact. In these cases, turning the CPL to reduce the effect may create a better result. Or you could blend multiple images during post-processing, one with CPL and one without, to eliminate glare in the foreground, but retain the reflection in the mid and background.

Conclusion

A Circular Polarising Filter (CPL) is a useful tool for outdoor photographers, as it effectively reduces glare and reflections while enhancing colours and contrast. It works by filtering polarised light, blocking reflections from surfaces like water, glass, and foliage, resulting in improved clarity. CPLs are particularly valuable for reducing unwanted reflections and glare, capturing rich, vibrant skies, and boosting contrast, making them useful for landscape, water, and urban photography.

While versatile, it's important to use a CPL thoughtfully. It is most effective when the light source is at a 90-degree angle to the subject, and subtle adjustments can achieve the best results. Over-polarising can result in unnatural skies or eliminate reflections you may want to keep, so moderation is key. Since CPLs reduce the amount of light entering the lens, adjustments to settings like ISO, aperture, and shutter speed may be needed, and a tripod might be necessary for sharp images. Although CPLs are ideal for bright conditions and certain subjects, they should be avoided in low-light environments, with ultra-wide lenses, or when photographing metallic surfaces, as their effects may be uneven or minimal. Furthermore, some reflections can add visual interest, so carefully consider whether to reduce or retain them based on the composition.

My Personal Preference

CPL filters offer unique advantages that can’t be fully replicated in post-processing, particularly when it comes to eliminating reflections. Instead of using one all the time, I recommend applying it selectively when it enhances your composition. Personally, I find a CPL most useful for effects that editing can’t achieve—such as revealing details beneath the water’s surface or reducing glare on leaves. However, when photographing skies, I’ve often found that a CPL can produce undesirable results, so I usually prefer to shoot skies without one. Likewise, when capturing large bodies of water like lakes, I often choose to keep reflections to create symmetry rather than remove them with a CPL.

Circular Polarising Filter (CPL) - What is it and does it make a difference?

What is a Circular Polarising Filter?

How does a CPL filter work?