What Are Polarizing Filters in Photography?

Robert G. Mull

Right out of the box, it’s easy to mistake a polarizing filter for something designed to simply protect your lens from getting scratched.

What does a polarizer do, exactly? Is it just a glorified neutral density filter? Far from it, although both are incredibly useful. Here, you’ll find out what a polarizing filter is, and if it’s worth the investment.

What Is a Polarizing Filter in Photography?

A side-by-side polarizer comparison

When the sky is not 15 stops brighter than the landscape that you’re also trying to capture, you’re able to expose everything correctly all at once. If you’ve ever tried taking a landscape photo at dawn or dusk, you can probably attest to the fact that the sky is bright, and that our world is a dark, dark place.

Related: A Complete Guide to the Exposure Triangle in Photography

Polarizing filters in photography help the artist primarily manage three things: reflections, glare and lens flare, and the exposure of the sky. How can a simple glass filter accomplish this without making the rest of the frame too dark to see, though?

What Is Polarization?

The simple answer: light polarization describes the way that the photon travels about its path, en route to your camera sensor. Directly from the sun, daylight is not polarized. Things get a little more complicated when the path of a photon is disrupted somewhere between you and the original source.

Particles in the atmosphere scatter and diffuse each photon, knocking them out of place and causing the photons to “spin” horizontally as they make their merry way to us. This is how they become polarized in a physical sense. What does this property have to do with photography?

In front of the lens, polarizing filters prevent light of a specific polarization from passing through, purely by way of the shape of the path that the photons now travel in. Sometimes, the science behind a piece of equipment is almost cooler than the gear itself.

How Do Polarizers Work?

An ordinary lens admits light indiscriminately, with no regard for each photon’s polarization. Polarizing filters, contrarily, are instead etched with a series of very small lines. These inclusions are responsible for preventing polarized light from reaching the sensor.

How do polarizers work? They block light moving horizontally from entering the camera

With polarizers, it’s all about the angle that the light hits the filter and the degree to which the filter itself has been rotated. This configuration determines how much of the polarized light is absorbed before reaching the sensor.

One of the polarizer's linear inclusions preventing a photon from entering the lens

When the series of lines has been rotated to its most upright, perpendicular position, the majority of the polarized light is absorbed. The light cannot get past lines that are vertical when each photon is moving horizontally in a path that is two-dimensional and totally flat. Horizontal lines allow these flat paths to pass through with no problem.

Rotating the polarizing filter clockwise or counter-clockwise gives you more control over how much polarized light makes it through. This means that you can dampen the appearance of the reflections in your photo without doing away with them entirely. For most polarizing filters, you do so by rotating it on a fixed adjustment ring.

For direct light, the effect of a polarizer will be most apparent when the light is striking the lens at a 90-degree angle. You can orient yourself around your subject to either lean into the effect or lessen it, depending on your vision for the photo.

Polarizers and Reflections

Polarizers are great for more than just outdoor photography. When trying to take photos of something shiny, like a brand new car, a polarizing filter helps us see “through” the glare of the reflection by admitting light selectively. This is the case even when shooting indoors or in a studio setting. How?

When light glances off of a specular surface, its polarization changes on the rebound. The light reflecting off of it falls out of “phase” with the light from the original source, with respect to where you stand with your camera. We are able to adjust the rotation of the filter so that it targets this re-polarized light that the specular surface is trying to convey to us.

The reflections on the car have been reduced with a polarizer filter

Image Credit: Asgw/Flickr

This results in a much more professional final image, devoid of distracting reflections. The color and tone of the subject will also come across more vividly than they would otherwise. The image feels “cleaner” and more to the point.

If you think that your own work is exempt from this principle, you would be incorrect. Even matte or near-matte subjects “reflect” light into the camera. Polarizing this reflected light will do you some amount of good for the same reason described above. Now, the values of the subject itself are no longer hidden underneath stray “reflections.” The results speak for themselves.

Linear Polarization vs. Circular Polarization

There are two types of polarizers: linear polarizers and circular polarizers. If you use an SLR or a DSLR, a linear polarizing filter may inhibit your camera’s means of reading the light for focus and exposure. Cameras that rely on mirrors use polarization to meter the incoming light, which is why circular polarizers were invented.

A linear polarizing filter consists of only one layer of glass characterized with an array of linear inclusions. Circular polarizers include both this first layer as well as a second. The second glass plane re-treats the light, polarizing it circularly and translating it into a form that the camera will be able to interpret.

What is a circular polarizer?

Linear polarizers work the same in both directions. Circular polarizers are a one-way street. When using a linear polarizer, SLRs and DSLRs can’t really “see” the reflections required to meter the light through their own internal set of mirrors without some semblance of the rest of the picture, so to speak. For mirrorless cameras, this won’t be a problem.

Related: Photography Terms All Photographers Should Know

What Types of Photography Stand to Benefit From a Polarizer?

Two landscape photos, one with a polarizer filter and one without

Image Credit: Chripell/Flickr

The truth is, all photographers should probably own a polarizer camera filter. If you fall into any of the following categories, it should definitely be a priority:

  • Landscape Photographers: This is the textbook example of why polarizers are vital. Even back before the days of color photography, black and white landscape photographers made liberal use of polarizing filters to improve the contrast of their photos. Artists were able to capture the detail of the scene while keeping the sky perfectly exposed.
  • Product Photographers: Sometimes, the sheen of an off-screen softbox makes a product look luxe. Other times, it becomes a painfully prevalent distraction. If unwanted reflections are robbing your subject of its charm, a polarizer will almost certainly help you banish the excess light.
  • Fine Art Photographers: One thing is for sure about artistic photographers: we love shiny things, and we love to take photos of our own reflections. Polarizers bring specular objects to life, even under the din of lights that are less-than-suited to photography in an aesthetic sense.
  • Casual Photographers: If you shoot for fun, chances are you’re not devoting a lot of time to planning each photo that you take. Many of us start out by shooting our friends randomly, in broad daylight. A polarizing filter tames the fire of the sun, making each shot that much more Insta-worthy and memorable.

No matter what you’re shooting, polarizers make a huge difference in the appearance of the light and the color that your photo captures. They make every photo worth taking.

Related: Freelensing for Beginners: Tips and Tricks

Polarizing Filters: A Must-Have for Any Photographer

Exposing anything correctly allows your camera to receive a much richer and deeper array of chromatic values. Your contrast is likely to feel more dynamic. Now, no subject is too far out there for you to conquer.

While a graduated filter can achieve a similar effect flat-out, polarizers deal with the problems plaguing outdoor photographers right at the source. It’s a solution that travels with you everywhere, no matter what.

A close-up on a lens.
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