Polarizing Filters or simply Polarizers were second most used filters in the film era, first being the UV filters. Polarizers work on the principle of letting only one plane of light waves to pass through. Remaining planes of light waves are blocked. Earlier polarizers had a single polarizing layer. Then came the autofocus cameras. There were times when the angle of polarized light being let into the lens would not coincide with the autofocus sensors and autofocus used to fail. Circular polarizers were introduced. These had another plate after the polarizing layer to rotate the light. This reduced the problems with the auto-focus systems. Due to their construction method, the circular polarizers show the polarizing effect only when seen from ‘thread side’. When seen from the ‘groove side’ polarizing effect is not seen, instead just a color shift is visible.
(Polarizers in different sizes and thicknesses)
Photographers use polarizers for cutting down reflections and for increasing saturation and contrast.Both linear and circular polarizers work well. Linear polarizers are inexpensive but they are hard to find now a days, even though the present auto-focus mechanisms are capable of easily working with them. Circular polarizers are the ones which are sold at every camera shop and are now simply marketed as polarizers.
When digital cameras became popular, image editing softwares also started making their mark. Photographers now bank on these programs to alter the saturation and contrast. Polarizer use might have been reduced but they are one of the most useful filters even now.
Polarizers are usually neutral in color. They don’t cause any color shift, just a bit of darkening. Some polarizers are however warming in nature and add a little yellow hue. The darkening also varies. The best polarizers cause minimal darkening. I use Hoya HD series polarizers.
Polarizers work wonders with reflections and thereby increase the saturation of foliage and sky. The maximum effect is seen at a particular angle. Excessive polarization is also not good. Some reflections are required to make the scene look natural. I have seen countless photos of boats near the sea beaches, where maximum polarization was used and the boats end up looking like floating in air. Some amount of reflections maintain the natural touch and complete absence of reflections can spoil the image.
(The landscape above is without any polarizing filter being used. The one below has polarizing filter dialed in to give about 2/3 of its effect. The reflections on the water are reduced and foliage looks greener but with slight warm tone)
(Polarizing filter dialed in to give about 2/3 of its effect. The reflections on the water are reduced and foliage looks greener but with slight warm tone. Nikon Df with Zeiss 25 mm lens at f/8.)
I use polarizers for landscapes when I have to cut reflections but I avoid the maximum effect they produce. The maximum effect looks too artificial for my taste in most cases. Sometimes excessive polarization can turn a beautiful looking pond into a muddy puddle. I also use them to cut reflections while photographing buildings and metallic objects. They are useful in portraits too and help reduce reflections from oily skins.
In fact when variable ND filters were not available in the market, I used to use two polarizers and rotate them with respect to each other to get the same variable ND filter effect. Now a days, buying a variable ND filter is a better option.
One question that photographers frequently ask me is the reason for buying ND2 or ND4 filters when polarizers give almost the same reduction in light. This is true. They both darken the image. However, polarizers can be quite annoying at times when changing the camera orientation (vertical to horizontal or the other way round). Further more, if the surface of the subject is curved, polarizer will invariably cut some of the reflections, which may not be what the photographer has in mind. Still, polarizers can be frequently used to replace ND filters, but not always.
Evaluative metering modes (like 3D Matrix on Nikon) may give wrong exposures when dark filters like polarizers are used. I recommend using spot metering or center weighted metering while using such filters. Many photographers stick with evaluative metering and just dial in the required exposure compensation based on the curves available on the camera’s preview screen. Any method that is comfortable is fine as long as the exposure is taken care of.
Exposure compensation is also required when not using ‘through the lens metering modes’ (TTL) available on the camera body. Same holds true with flash units that work independent of the camera settings and readings. If however you are using a manual flash and calculating the exposure using the guide-number and distance, then a correction is required based on the filter factor.
Never use more than one filter on the lens when it can be avoided. More filters mean more chances of flares and reduction in image quality. If you use UV filters then removing them before mounting polarizer is a good idea.
No amount of post-processing or working on image editing programs can give the effect that a properly used polarizer can.
Polarizers can be very attractive to use initially and so there is a tendency to go overboard with them. Here are a few more things to consider while using them –
- When cutting down reflections from water, do not completely do so. Some amount of reflections or shine on the surface of water is natural. Absence of this can give an appearance that there is no water present. I have seen countless images of boats on still water with completely dialed in polarizer effect. The water is not visible and the boats appear to float in air. We don’t want that unnatural look, do we?
- If the water is muddy, reducing the reflections makes it look dirtier than it actually is. Be careful while using polarizers on rivers and sea-beaches after rains!
- As I have discussed earlier, sometimes polarizers can be used to replace ND filters but be very careful when doing so with water. Those fine motion blur lines that are seen in flowing water are also due to reflections or shine. Using a polarizer to reduce available light will also cut those reflections and reduce the places where motion blur can be achieved.
- Using polarizer with ultrawide lenses can lead to artificial looking sky, with one part extremely dark and the other with no polarization effects. I avoid polarizer when I compose landscapes with skies visible across the full frame.
(Motion blur of water in a mountain stream. The photograph on the top used a regular ND filter whereas the one below had a polarizer dialed in to get the maximum effect. Notice the lack of shine on the water surface and increased visibility of the river bed in the second image. 50mm lens at f/16 at ISO 50)