Polarising filters are one of the first filters photographers buy, and for good reason. They are used to remove reflections and add contrast and saturation, two very useful properties that can result in clearer, richer images.
About Polarising Filters
Polarising filters block polarised light rays and suppress the reflections they cause. This includes reflections from water, glass, and reflective plastic surfaces, but excludes metallic surfaces. Unless reflections are extremely strong, they can be made almost unnoticeable, though the ability of polarising filters to suppress reflections does also depend upon external factors. These include the extent of polarisation and angle of reflected light.
Removing reflections from surfaces such as water and glass has very useful applications. Polarising filters can help the lens to see through the water, so underwater wildlife, plants, and fish could be captured, for example. Photographing through windows without any unwanted reflections appearing in the image is also possible.
As well as removing reflections, polarising filters also add contrast and saturation. This is a result of the surface reflections adding light. Colours in the image become brighter and richer. Polarising filters are very frequently used to enhance blue skies, turning the dull skies often produced without a filter into the vibrant blue skies as seen by the human eye on a sunny day. This effect can be quite dramatic and enables clouds to stand out beautifully. Grass appears greener, and other bright colours are also enhanced.
Polarising filters continue to be so popular partly because the effects they create are simply not possible in the same way with photo editing software. This applies especially to their ability to remove unwanted reflections, and, to a lesser extent, to adding contrast and saturation. And these effects are not just used for creating weird and wonderful images, but for creating superb-quality images in real everyday use. This makes them essential items in any serious photographer’s kit.
Choosing a Polarising Filter
Factors to think about when choosing a polarising filter include the type of filter, type of fitting, and any special features as well as budget, brand, and filter quality.
Type of Polarising Filter
There are two basic types of polarising filter, classified as circular or linear depending on the mechanism used to polarise light. Circular filters are typically required for digital cameras. This is because linear polarising filters can affect the autofocus, or the beam splitter, which is used to calculate exposure. Whether they are linear or circular filters does not have a bearing on their physical shape, which can sometimes cause confusion. Circular filters are more expensive, so don’t be tempted to purchase a cheaper linear filter.
Type of Fitting
The simplest polarising filters are gel sheets which can be cut to size and either simply held across the lens or placed in a gelatine holder.
Another type is a filter that can be mounted onto the front of the lens with a filter holder and adaptor ring. These can be rotated within the filter holder. They are known as system filters.
The most popular type of polarising filter is one that can be attached directly to the lens. These are known as screw-in or threaded filters. Screw-in filters are convenient and easy to use. They are also compact and easier to transport. They have two rings which both rotate, giving the photographer fine control over the extent of polarising effect.
Features and Filter Quality
There are some useful features of screw-in filters to look out for. If they are to be fitted to a camera without a view mechanism for alignment, a filter with an index mark will help in fitting it. Also useful are little arms used to rotate the filter, especially if gloves are often worn. Filters with slimmer rings are less prone to vignetting than wider rings. Vignetting is when the outside of the image has reduced saturation. Some filters have specialised seals to protect against moisture and are recommended for use in humid environments. With system filters, features to look out for include precise fitting mechanisms and ease of rotation.
Glass filters, which are more expensive, are less prone to scratching than resin. More expensive filters typically have better quality glass and anti-reflective treatments. They also usually have more precise, better quality fittings. There is quite a wide range when it comes to price, so decide how important these factors are when purchasing a filter. It may also depend upon the quality of the lenses as it makes sense to buy a high end filter to enhance the action of a superior lens. Buying from a reputable brand is usually worth any extra expense, though larger brands will often produce a range of differently priced, though all decent enough quality, filters aimed at different types of photographer. Some filter brands are particularly recommended for certain styles of photography, which is where product reviews and photography forums can be helpful.
Using Polarising Filters
Polarising filters work best on sunny days and have less effect on days with more dull weather. They cannot produce vibrant blue skies when the skies are grey and overcast.
Angles are important when it comes to both adding contrast and reducing reflections. For vibrant blue skies, the optimum angle between the sun and subject is 90 degrees. For suppressing reflections, the angle between the camera and reflective surface should be about 35 degrees.
The type of lens used will affect the final image. Clear or UV filters used for protection can cause vignetting on wide angle lenses, and the extra glass and air interfaces can result in reduced image quality. Slim filters can help reduce vignetting. Wide angle lenses in general should be used with caution with polarising filters, especially those with a focal length less than 28 mm, as only a section of the image will be polarised.
Polarising filters block rays of polarised light, suppressing reflections and adding contrast and saturation. Useful applications include photographing though water and glass and making blue skies more vibrant. Polarising filters are popular additions to the photographer’s kit because of these everyday applications and because their effects are difficult to obtain with photo editing software. Factors to consider when buying a polarising filter include its fitting mechanisms and special features as well as general considerations about budget and quality.
The two types of polarising filter are circular and linear, with circular the type almost always used with digital cameras. This is important as linear filters can affect autofocus and beam splitting. Polarising filters come in both screw-in, or threaded, designs and in system designs. Screw-in filters attach neatly to the lens while system filters need to be mounted with a filter holder. Useful features of screw-in filters include index marks to aid alignment, arms to rotate the filter, slimmer profiles to minimise vignetting and specialised seals to protect against moisture. More expensive filters typically have better quality components and superior glass. Read product reviews and visit photography forums to find the best polarising filters to suit the camera and budget.