MINI TEST
Circular polarizers
What are circular polarizing filters and which are the best options? Angela Nicholson investigates…
A circular polarizer is one of the most useful accessories to have in your camera bag and has several possible effects on your photos. At certain angles it will darken blue skies, as well as appear to saturate other colours within a scene. It will also help to reduce unwanted glare from shiny surfaces, and even remove reflections.
Polarizers have long been a popular filter for travel photographers who want to deepen beautiful blues skies. This is best achieved when the sun is at 90 degrees to the lens, as you’ll find that when the sun is directly in front or behind you, there will be little or no effect!
The removal or reduction of reflections can also be a powerful photographic trick. Again, travel photographers like to remove the reflection of a boat floating on a tropical harbour, so the water seems bottomless, and the viewer just wants to dive into it – or at least book a holiday!
Polarizers are easy to use because you can see their effect as you look through the viewfinder or at an LCD screen. All you need to do is attach them to the lens itself and then rotate to get the effect you want. Most polarizers are attached to the lens via its screw-in thread, so just buy the right diameter for the filter size marked on your lens. Others are designed to work with ‘square’ filter systems, which have a special attachment for this circular filter.
Polarizers and light loss
Of course, a polarizer doesn’t come without some drawbacks. Its main one being the reduction of light that you get when attached. This can vary with conditions but expect to lose one stop of light as a minimum and around 2.5 stops as a maximum.
Some screw-in polarizers can also cause a slight darkening (vignetting) at the corners of the frame, but if you buy a good quality, slim filter, this shouldn’t occur. Also watch out for overpolarization of a scene, where already beautifully deep blue skies go almost black. When used with a wide-angle lens, you may also sometimes see uneven polarization, where some areas are darker than others. If this happens, adjust the amount of polarization you apply to keep the sky balanced.