A circular polarising lens (CPL) filter is commonly used by landscape or outdoor photographers to enhance the quality of their images, most notably by affecting colour. A CPL filter is a type of polarising filter made from glass. It can be easily screwed on to a camera lens, to protect it. But, it’s mainly used to block out reflected light travelling at different angles, by rotating the filter.
There are two types of polarising filter – a CPL filter and a linear polariser. The difference between these two types relates to how light waves pass through them.
A linear polariser only lets horizontal or vertical light waves enter the filter when it’s rotated. A CPL filter passes circularly polarised light waves through the lens, but is also sensitive to linear polarised light. A CPL filter is similar to a linear polariser, but has extra glass behind it called a quarter wave plate. This plate functions to circularly polarise the light.
In practical terms, a CPL filter is suitable for all DSLR cameras, but a linear polariser isn’t. This is because a linear polariser interferes with auto-focusing functioning and creates light metering errors. This means that CPL filters offer great versatility for use with a wide range of camera types.
By turning a CPL filter in one direction or the other, you can control how much light your camera lens is exposed to. This produces a number of desirable effects for the photographer, which can improve the quality of an image.
A CPL filter can darken an image, thus adding richer colours 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 to add drama and intrigue to a scene. By boosting colour contrast and saturation with a CPL filter, you can make muted objects appear more vivid and eye-catching.
Photographers also benefit from using a polarising filter when they want to reduce reflections and glare from non-metallic surfaces, particularly water or rocks. This can give water more detail and a see-through effect. By removing glare or shine off objects, such as foliage, images have increased clarity.
Photographers face many problems when shooting through glass, including reflections, light streaks and glare. But, a polarising filter can effectively eliminate these nuisance issues, so that images appear clear.
For panoramic shots, such as mountain vistas or cityscapes, atmospheric haze can make these distant objects less visible on your photo. A CPL filter can help to reduce this haze, making those far-away objects much clearer to see.
The effects of a polarising filter are difficult to reproduce digitally in post-production, so if you want to alter colour balance in your photos in real-time, this filter is indispensable.
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 uneven depth of colours in a single scene.
To enjoy the many great benefits of a CPL filter, never skimp on quality when you’re polarising filter shopping.