A polarising filter is one of the few camera filters whose main effect cannot convincingly be recreated in post-processing. The filter reduces certain reflections before light reaches the sensor. As a result, colours become richer, reflections on foliage become less distracting, water surfaces become more transparent and landscapes often appear clearer. A polarising filter therefore remains a valuable tool, especially for landscape photographers.
What does a polarising filter do?
Light travels in different directions. When it is reflected by water, glass, leaves, wet stones or other non-metallic surfaces, some of that light becomes polarised in a particular direction. A polarising filter blocks part of this reflected light.
You can see the effect directly in the viewfinder or on the camera screen. Turn the filter’s front ring and reflections increase or decrease. At the same time, colours may become more saturated and the contrast between a blue sky and white clouds may increase.
The filter does not simply add extra colour. It removes light that obscures details and colours. This distinction is important: anything hidden behind a strong reflection when the picture is taken usually cannot be reconstructed later by image-editing software.
Why Photoshop cannot fully reproduce this effect
In Lightroom or Photoshop, you can adjust contrast, saturation and the brightness of the sky. You can also use a digital graduated mask. But if a reflection prevents the camera from seeing through the surface of water or a pane of glass, the information behind it has not been recorded.
A polarising filter can reduce that reflection when the picture is taken. This can reveal stones beneath the water, details behind glass or the true colour of wet foliage. No slider can recover details that the sensor never saw.
Post-processing remains useful, of course. You can refine the result, especially when you shoot in RAW, but a picture taken with a filter contains different image information from the same picture taken without one.
More than simply removing reflections
In landscape photography, the effect is not limited to water or glass. Grass, leaves, rocks and wet ground all reflect light. Especially after rain, a landscape can be covered in small highlights. These make colours look paler and the image more distracting.
By turning the filter carefully, you can reduce some of that glare. Greens become richer, autumn colours more vivid and textures more distinct. Atmospheric haze may also be reduced in some conditions, giving distant hills or mountains greater contrast.
The effect does not have to be maximised. Partial polarisation often looks more natural than removing every reflection completely.
Practical situation 1: Water
Point the camera at a pond, stream or wet beach and slowly turn the filter. You will see the reflection change. In one position, the water mainly reflects the sky; in another, stones, plants or sand beneath the surface become visible.
The maximum setting is not always the most attractive. With no reflection at all, water can lose its sheen and sense of depth. Turn the filter back until you find a pleasing balance between seeing through the water and retaining some reflection.
Practical situation 2: Forests and wet leaves
In a forest, the difference can be surprisingly large. Leaves and tree trunks reflect light, particularly when they are wet. A polarising filter reduces this glare and deepens the colours. Moss looks greener, tree bark gains more texture and autumn leaves become more intense.
A filter is also useful around waterfalls. It reduces reflections on rocks and water and usually cuts one to two stops of light. That light loss can sometimes help you use a slightly slower shutter speed without an additional ND filter. If you want to blur the water much more strongly, you will generally still need an ND filter for longer shutter speeds.
Practical situation 3: Sky and clouds
A polarising filter can darken a blue sky and make white clouds stand out more strongly. The effect is greatest when you photograph at an angle of roughly ninety degrees to the sun.
A simple way to find the strongest direction is to point your index finger at the sun and extend your thumb sideways. Rotate your hand around your index finger; the direction in which your thumb points roughly indicates the area where the polarising effect is strongest.
With the sun directly in front of or behind you, the effect on the sky is much weaker. Under overcast conditions, the filter can still reduce reflections in the landscape, but it will not suddenly turn the sky deep blue.
Be careful with ultra-wide-angle lenses
With an ultra-wide-angle lens the photograph covers a large area of sky. Because the angle to the sun varies considerably across the frame, the polarisation can become uneven. This may produce a dark patch or band in the sky while other areas remain much lighter.
This effect can look unnatural and is difficult to correct fully afterwards. Check the entire sky, not just the centre of the frame. Turn the filter back slightly if the difference becomes too pronounced. Sometimes the best choice is to photograph without polarising the sky.
Glass, shop windows and car windows
A polarising filter is useful when photographing through a shop window, car window or museum display case. By turning the filter, you can often reduce distracting reflections and show the subject behind the glass more clearly.
It works best when you photograph at an oblique angle. The effect may be limited when shooting straight through a pane. Also bear in mind that laminated or toughened glass can reveal coloured stress patterns when polarised.
The filter behaves differently on metal. Reflections from an unpainted metal surface generally cannot be filtered out in the same way as reflections from water, glass or leaves.
Circular or linear polarising filter?
For modern digital cameras, you will almost always choose a circular polarising filter, commonly referred to as a CPL. The word “circular” refers to the way the light is treated after passing through the filter, not to the filter’s round shape.
A linear polarising filter can interfere with the metering and autofocus systems of some cameras. A CPL is designed to work with modern autofocus and metering systems. For practical use on a mirrorless camera or DSLR, a CPL is therefore the safe choice.
How to use the filter
Screw the filter carefully onto the lens and avoid overtightening it. Look through the viewfinder or at the screen and slowly turn the outer ring. Pay attention not only to the sky, but also to water, leaves, windows and dark areas.
If in doubt, take several pictures at different settings. The maximum effect is not automatically the best effect. Also check your shutter speed and ISO, as the filter generally cuts around one to two stops of light.
If you use a lens hood, it may be more difficult to turn the filter ring. Set the effect first and then attach the hood, or choose a hood that allows you to reach the ring easily.
Filter sizes and step-up rings
The required size is usually marked on the front of the lens with the diameter symbol, for example 67, 72 or 77 millimetres. This measurement is not the same as the focal length.
If you have lenses with different filter sizes, you do not necessarily need to buy several filters. Choose a filter that fits your lens with the largest diameter and use step-up rings for smaller lenses. This is often cheaper and lets you retain the same filter quality.
A step-down ring is less attractive because fitting a smaller filter to a larger lens can cause dark corners.
What should you look for when buying one?
A good polarising filter uses high-quality optical glass and a coating that reduces reflections, colour casts and dirt. Cheap filters may reduce sharpness, introduce a colour cast or be difficult to clean.
For a wide-angle lens, a slim filter mount can help prevent vignetting. Be aware, however, that some very slim filters have no front thread for a lens cap or an additional filter.
Before buying, check the correct filter size, the CPL type and the thickness of the mount. If you use several lenses, it is often better to buy one high-quality larger filter with step-up rings than a cheap filter for every lens.
Common mistakes
The first mistake is always turning the filter to its maximum setting. This can make water look unnaturally flat or the sky too dark. The second is looking only at the centre of the image and missing uneven polarisation in a wide-angle view.
Another mistake is forgetting that the filter reduces the amount of light reaching the sensor. In low light, the shutter speed may become too slow for handheld photography. Also watch out for dirty filters: dust, grease and dried raindrops will reduce contrast again.
A compact cleaning kit for filters and lenses is therefore useful to carry in your camera bag.
Finally, stacking two filters can cause vignetting. Only combine a polarising filter with an ND or protective filter deliberately, and check the corners of the frame.
When should you leave the filter at home?
For night photography and many indoor situations, the additional light loss is usually undesirable. Strong polarisation can also cause problems with panoramas because the sky may have different brightness levels in consecutive images.
With rainbows, the wrong filter position can weaken the rainbow or even make most of it disappear.
With rainbows, the wrong filter position can weaken the rainbow or even make most of it disappear. When reflections contribute to the atmosphere or composition, less polarisation is often more attractive.
A small filter with a big effect
A polarising filter is not a universal solution, nor is it an effect that should automatically be used at maximum strength. It is a tool that lets you determine which reflected light reaches the camera when you take the picture.
That is precisely where its value lies. You can change contrast and saturation afterwards, but you cannot recover details hidden behind reflections. For landscapes, forests, water, glass and wet surfaces, a good CPL filter therefore remains one of the most useful accessories in a camera bag.
