Why You Need a Polarizer

Why You Need a Polarizer

Light meters read; photographers interpret.
— Catherine Jo Morgan

Never have truer words been spoken in the world of photography. Your camera is just a box, with a hole at one end to let light through (focused and distorted by the lens in front of it) and a rectangle of film or an electronic sensor to capture it. If you have a DSLR, it has an electronic light meter that ‘reads’ the light, computes the optimal settings for your exposure, and… click.

However, light meters can be fooled, especially when the light is harsh and uneven or when it’s bouncing and reflecting off multiple objects in your field of view. What you see with your eye can be very different from what your camera renders. More importantly, how you want to INTERPRET your picture can be very different from how your camera chooses to do so.

I use different tools to interpret my picture a certain way, to enhance it to make it more visually appealing. In addition to different lenses for different occasions, lighting accessories, neutral density filters, polarizers, and diffusers are all part of my toolbox. A polarizing filter is an essential part of my landscape and food photography kit. To explain how it works, I need to talk a little physics. I promise to keep it as simple as possible, so indulge me for a few minutes.

Polariser 01.jpg

Ambient light is unpolarized. What this means is that since light is transmitted as 2-dimensional waves, it bounces off multiple objects and strikes your sensor in different planes. Light coming off flat, reflective surfaces can become polarized at low incident angles, which means that the light waves reflecting off leaves, bodies of water, windows and automobile windshields orients itself at a particular angle that can cause unwanted glare in your picture. If you can block this reflected angle from your picture, you can reduce or altogether eliminate glare from your picture. The function of a polarizer is to basically filter light in such a way that only waves ‘polarized’ at a specific angle are allowed to strike your sensor. This angle can be selected using a circular polarizer, and allows you to cut the glare from various objects in your field of view. This is the difference, for example, between seeing the shimmering surface of a lake and being able to see the rocks at the bottom, or seeing the light reflected off a car windshield and being able to see the driver within, or seeing your reflection in a window and being able to look through it at what’s inside.

The pictures below are two unedited, SOOC images (the only post-processing done was setting the same white balance for both images and the conversion from RAW to JPEG) shot through a glass door from a sunlit terrace. The top image is unpolarized, while the lower image was shot using a circular polarizer (see below) oriented to eliminate the reflections in the glass. Aperture and ISO settings for both shots were identical. The lower image had a slower shutter speed to compensate for the stopping power of the polarizer and provide equivalent exposures.

Without polarizing filter

Polariser 03.jpg

Polarized to maximise transmittance through the glass door

The composite image above shows the difference between the shot made with and without the polarizer

Likewise, as seen in the images below, a polarizer can be used to either minimise or maximise reflections from the surface of a body of water. In the images above, a polarizer was used to either enhance the reflection of the mountains and the sky on the lake surface (top image) or accentuate the rocks on the lake bed (bottom image).

Polarized to enhance reflection sky and mountains

Polarized to accentuate features on the lake bed

How a polarizer works can be best explained using the figure below. A polarizer, in simple terms, is rather like a picket fence. Objects oriented along the horizontal axis (red) are blocked by the vertical slats of the picket fence, but those oriented vertically (blue) are allowed through. In a similar manner, a polarizer selects light whose waves are oriented at a certain angle, blocking out everything else. Simply put, you can block the waves of light that reflect off the surface of a lake or a car windshield and cut the glare in your picture by orienting your polarizing filter at an angle that prevents these reflected waves from being transmitted through.

Polarised Light Schematic.jpg

A circular polarizer is essentially a pair of polarizing filters, in which the first filter rotates relative to the second (also known as a quarter wave plate). The rotating filter allows you to select the angle you need to achieve your desired effect. Remember that they come in different sizes to fit different lenses, so do what I do and get one that is as big as or bigger than the diameter of your biggest lens and use step-up rings to attach it to the front of your smaller ones.

Polarizers are also used extensively to create more dramatic skies. Since a polarizer only allows light waves that are polarized at a particular angle to be transmitted through, it essentially filters out the remaining light, thereby reducing the amount of light that strikes your sensor. This has a dual effect: 1) it darkens your picture by 1 to 2 stops, deepening the blue (or sunset reds and yellows) of the sky and, consequently, increasing the contrast between the sky and the clouds, and 2) it cuts the haze by filtering the light bouncing off and diffracted by particulate matter in the atmosphere. This gives the overall picture more clarity and ‘pop’, and makes for a dramatically better landscape.

Polariser 07.jpg

Without polarizing filter

Polarized to accentuate sky

An important fact to keep in mind, particularly for landscapes, is that a polarizer causes a phenomenon called banding when used with wide lenses. The banding gets more apparent as the lens gets wider because of the extensive field of view, and the fact that the extent of polarization at the centre of your frame is different from that at the edges. This isn’t remedied using a longer lens and panning across the landscape because the polarizing effect isn’t evenly applied across the frame, and you will end up with uneven exposure and banding across your stitched panorama. For landscapes, polarizers work best when they’re pointed at 90 degrees to the sun, and when used with a lens longer than 35 mm on a full frame camera. Polarizing filters also find utility in the food photography industry, where they are used to cut strong light reflections off food, plates and silverware.

If you are a landscape photographer, consider getting yourself a polarizer if you don’t already have one. It will quickly become one of the most important pieces of equipment in your kitbag. The extra punch that it will add to your pictures will more than pay for itself.

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