What Effect Does a Polarizer Filter Have?

Polarizer filters can work wonders in spicing up a photo. They can work wonders in cases where cutting through glare will improve contrast and make the colors pop. By reducing the glare of reflections, they can help peer through transparent reflective surfaces. They can deepen the blues of a blue sky, and even with black and white, they can add texture to areas that might otherwise have become blown-out highlights.

They’re especially well suited to outdoor photography because of the way they can counteract the natural glare of sunlight. At the beach, they’ll intensify the color of water, especially when there’s a coral reef or sand not far underneath the surface. They’ll also rescue highlights from bright snow or ice. And even as a general-use tool, they can go a long way to salvaging shooting outdoors in the middle of the day when the sun is at its harshest.

And a true polarizing effect is something that just can’t really be mimicked effectively by post-processing, despite any software filters you see in apps that call themselves polarizers.

There are two elements affecting how much of an effect polarizing filters have. The first is the strength and type of the polarizer filter. Not all polarizers are the same, as you can clearly see in these polarizer filter side-by-side tests.

The other element comes down to lighting conditions, and especially the angle of light. They’re at their maximum strength at 90° to the sun or primary light source, so you’ll get the most effect if the sun is directly behind you. The effect reduces the further away from 90°, which can introduce some inconsistent results on very wide-angle lenses because they span a wide field of view—you end up with banding, which where parts of the sky are a dark, deep blue and other parts are less so.

Real-World Examples of the Effect of a Polarizer Filter

To make it easier to visualize the effect, put together some practical side-by-side examples with before and after, with and without a polarizer. These are using some scenes where the polarizing effect really comes into play: clear blue skies, bright highlights, and water.

All of these were shot with the same camera and lens combinations. They’re shot at the same ISOs and apertures. The only slight differences in exposure settings are due to the little bit of light drop off that the polarizer adds, so the shutter speeds for the polarizer versions are just a shade slower to compensate.

There’s no additional post-processing–I haven’t applied any extra contrast in editing to the polarized versions, for example. And to make the comparison as close as possible, I’ve synchronized the white balance setting in each pair.

Things to Watch Out For When Using a Polarizer Filter

There are some things to watch out for when using a circular polarizer filter.

You’ll lose up to about two stops of light. That’s one reason they can be less useful in marginal lighting conditions. Conversely, they can also be useful if you need to slow down shutter speeds just a touch but don’t want to resort to an ND filter.

They work best with directional light, ideally at 90° to the sun, and don’t work as effectively outside a certain angle range.

Unless you’re using something like the Cokin or Lee filter mount system, it means screwing and unscrewing a filter each time you want to use it.

They don’t work well with most lens hoods.

You’ll also need to adjust the filter for each shot since it consists of two layers of glass and the outside layer rotates.

Adding extra layers of glass can increase the chances of lens flare. Ideally, you wouldn’t be shooting directly at light sources with a polarizer anyway, but the modern coated filters do a pretty good job of reducing flaring.

It’s generally not a good idea to use a polarizing filter when shooting for stitched panoramas. Because the polarizing effect isn’t evenly applied across the frame, if you have blue sky in the frame, you’ll have a lot of trouble avoiding banding across the sky. I’ve put together some examples of why not to shoot panoramas with a polarizer filter.

What to Look for When Buying a Polarizing Filter

There are two classes of polarizing lenses: circular and linear. If you’re using a DSLR with autofocus or anything that meters through the lens, you’ll almost certainly want a circular polarizer. In general, you’ll only want a linear polarizer for manual focus or video cameras.

You need to get the size that matches the thread diameter of your lens. If your lens has a 77mm diameter (usually marked on the lens itself in the form of ∅77), you’ll want a 77mm polarizer. Unfortunately, that means that there’s not a one-size-fits-all screw-on filter, so depending on the lenses you have, you might need to choose which lenses you want to be able to use with a polarizer or buy multiple filters. In some cases, you can use step-up or step-down adapters. If you’re really serious about your filters, you can also get polarizers for Lee and Cokin systems that are more forgiving of lens diameter.

With very wide-angle lenses, adding what amount to extensions onto the end of the lens risks vignetting in the corners of the frame. Buying polarizing filters designated as slim filters reduces that risk, although they are often more expensive.

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