In what situations do you need a polarizing filter?
Architectural photography: buildings, cars, etc. (anything with glass)
When photographing buildings with windows, a reflection of the sky and/or surroundings is often visible. The same problem occurs with other objects with transparent glass, such as bus shelters and cars. Such reflections can disrupt the image or distract attention from the subject. In that case, the use of a polarization filter is a solution.
Studio photography: shiny objects (metal, plastic, etc.)
With glossy materials and structures (for example, metal, plastic, leather) it is usually a challenge to illuminate them evenly in the studio. A polarizing filter can make the difference here. By placing a polarization filter in front of both the lamp and the lens, you achieve a natural effect without remarkably high light reflections.
Nature photography: water, sky, clouds, etc.
A polarization filter is also a much needed tool for photographers who spend a lot of time outdoors, especially in areas with waters. The main function of the polarization filter is to block the reflection of light on water. The result is even so strong that you can see the bottom through the water surface thanks to the filter. The filter can also provide more contrast between the sky and the clouds.
TYPES OF POLARIZING FILTERS
There are 2 types of polarizing filters: linear and circular. The filter I used for this article is a circular polarization filter (CPL filter). I use a circular polarizing filter because a linear polarizing filter interferes with my digital camera’s automatic mode. Automatic exposure and autofocus (AF) only work with circular filters. So if you use an analog or digital camera with AF and/or automatic exposure, then a circular filter is the right choice.
However, many visitors and customers of De Wit Cameras use analogue cameras without AF. They could opt for a linear polarizing filter. This is because the desired polarization effect emerges much more strongly than with a circular filter.
In both cases you have to bear in mind that a polarization filter reduces the brightness of the lens. With cameras with automatic exposure – depending on the settings – this difference can be compensated automatically. With some analog cameras, this difference will have to be corrected manually. Depending on the quality of the polarizing filter, the difference in brightness can be 1 to 3 stops. The better the quality of the filter, the smaller that difference. The choice for a more expensive high-quality polarizing filter is certainly recommended for analog photography.
HOW DOES A CIRCULAR POLARIZING FILTER WORK?
A circular polarizing filter consists of 2 parts, namely a linear polarizing filter and a quarter-wavelength plate. A quarter-wavelength plate is made of birefringent material just thick enough to slow down light waves polarized in one direction after passing through it, relative to light waves polarized in the other direction.
Because the light first falls on a linear polarization filter, the reflections and scatterings are filtered out and only the other oriented light waves remain. Then the transmitted linearly polarized waves are converted to circularly polarized waves by a quarter-wavelength plate set at 45 degrees to the polarization axis.
To put it more simply: the filter ensures that the light on your photo comes from one specific direction. Think, as it were, of a kind of luxaflex. This prevents the rays that come from elsewhere (via reflections) from disturbing your image. In this way, a polarization filter removes indirect lighting and glare from your photos. You can even completely get rid of the image of a television or telephone! You will then see a black screen, as if the device is switched off.
HOW TO USE A POLARIZING FILTER
The back part of a polarizing filter has a screw thread (and the quarter-wavelength plate) that you can use to secure it to your lens. The front part is a rotating ring containing the linear polarization filter. First focus your lens and then turn the filter. This allows you to manually adjust the angle at which the light falls on the quarter-wavelength plate via the linear polarization filter.
The closer you get to the 90 degree angle, the stronger the effect is visible.
WHEN NOT TO USE A POLARIZING FILTER?
Situations where a polarizing filter is not always useful:
Little light
It is better not to use a polarizing filter in dark conditions. Since the filter darkens an additional 1 to 3 stops, the risk of motion blur or noise is high. You then have to add lighting, flash or use a tripod and that can change the atmosphere of your photo.
Rainbow
While the polarizing filter can be rotated in any direction to enhance the colors of the rainbow, this can sometimes create a ripple or unrealistic effect, especially with a wide-angle lens. Turned the other way, the polarizing filter can actually minimize the visibility of the rainbow, making it appear dull and less vibrant. So keeping rainbows colorful and looking good in photos requires fine tuning of the polarizing filter.
Wide-angle lenses or panoramic photos
Be careful with extreme wide-angle lenses. It is best to use a polarizing filter that is as thin as possible. A filter that is too thick sometimes causes extra vignetting. In panoramic photos where the camera is pulled from one side to the other, you will see a dark spot where the light is less transmitted than in other places.