Polarizing Filters: What Are They and Why Do You Need One?

The post Polarizing Filters: What Are They and Why Do You Need One? appeared first on Digital Photography School. It was authored by Darren Rowse.

What is a polarizing filter? And what makes polarizers so special?

In this article, I’m going to tell you everything you need to know about polarizers. I’ll explain what they are, what they do, and how they can help improve your photography. I’ll explain when you might want to use a polarizer, and I’ll also highlight certain situations where a polarizing filter is a very bad idea – so you know exactly when to use one the next time you’re out in the field.

If you’re ready to become a polarizer expert, then read on!

What is a polarizing filter?

A polarizing filter is a piece of glass that goes over your camera lens and reduces haze, reflections, and glare. It also darkens blue skies.

Without getting too scientific, light waves that bounces off water, leaves, glass, and other reflective materials become polarized, which means they vibrate in a special way; polarizing filters are designed to block this polarized light from reaching your camera sensor.

Most photographers use circular polarizing filters, which screw onto the lens and can be rotated to amplify or reduce the polarization effect. So by turning a polarizing filter in one direction, the photographer can block out reflections, and by turning the polarizing filter in the other direction, the photographer can ensure the reflections are clearly visible.

Why are polarizing filters useful in photography?

Polarizing filters are known for three highly visible effects:

1. They reduce reflections, so you can photograph through glass and water.
2. They reduce glare, so you can capture more saturated colors.
3. They cut down on polarized light in the atmosphere, which causes skies to turn a deep, dark blue.

In certain situations, these effects are a big deal. For instance, if you’re photographing a beautiful rocky tidepool, a polarizer can eliminate pesky reflections and reveal the beauty underneath. And if you’re photographing a desert landscape at noon, the polarizer will turn the hazy blue sky into a darker, more evocative color.

In fact, polarizers are used for landscape photography all the time, because you’re often faced with reflective water and foliage. Don’t like the reflections in the water? Use a polarizer. Want to capture more saturated fall colors? Use a polarizer.

And many other genres of photography use polarizers, too. Cityscape and architectural photographers use polarizers to reduce reflections in glass windows and car windshields (though note that polarizers don’t reduce reflections and glare off of metal surfaces, such as the sides of buildings).

Basically, whenever you’re faced with unwanted haze or reflections, you simply screw a polarizer onto the front of your lens. Then, by twisting the polarizer, you can block out the offending light and get much deeper, saturated colors and reduced reflections.

How to use a polarizing filter: step by step

Polarizers are wonderfully easy to use.

First, when you find a scene that requires reflection or glare reduction, simply screw your polarizing filter onto the front of your lens.

Next, look through the camera viewfinder, then slowly rotate the polarizer. As you rotate the glass, watch the areas of your composition with obvious reflective elements.

After a few moments of rotation, you should see the reflections start to fade. Continue to rotate the filter until the reflections have disappeared (or have reached a level that you like).

Then leave your polarizer as it is, and proceed to adjust your other camera settings for the proper depth of field, exposure, etc. Note that you should always set your exposure after applying the polarizing filter, because a polarizing filter blocks out light, which in turn requires exposure compensation.

Another key fact: Polarizing filters don’t always work perfectly. Depending on the angle of the sun and the quality of the light, you may notice significant changes to a polarized image – or you may notice no changes at all.

For the greatest effect, try to keep the sun at a 90-degree angle to your lens. A common trick is to make a finger gun with your thumb and index finger. Then point your thumb at the sun and rotate your index finger in a circle (as if your thumb is the axle and your index finger is the spoke on a bicycle tire). Wherever your index finger points will experience the strongest polarization effect, whereas other areas of the scene will experience the polarization effect to varying degrees.

The problem with polarizers

Now that you’re familiar with the polarization effect, you might be wondering:

Why don’t I just use a polarizer all the time? Can’t I keep it attached to my lens, then rotate it as needed?

The problem is that, in addition to their benefits, polarizers have several drawbacks.

First, polarizers reduce the amount of light that hits your camera sensor and this impacts exposure. Every time you add a polarizer to your lens, you lose light, which means you need to use a slightly slower shutter speed, a slightly wider aperture, or a slightly higher ISO. This is rarely convenient, and in certain situations, it can be a non-starter; what if you’re photographing in low light? A polarizer may cause you to miss the shot thanks to a too-slow shutter speed.

Second, polarizers don’t impact an entire scene equally, especially if you’re using a wide-angle lens. Wide-angle lenses portray so much of the scene that you’ll often get some areas that are highly polarized, and other areas that are much less affected. This can look strange – like blue banding across the sky – and so you may want to avoid using a polarizer in certain wide-angle landscape situations.

Third, while quality polarizers work well, there are plenty of poorly made options out there that will produce unpleasant color casts and reduce image sharpness. So if you do buy a polarizer, make sure it’s a good one. Don’t compromise, even if it means paying $100+ for a nice filter.

When to use a polarizing filter

While you shouldn’t use a polarizer all the time, here are a few situations when it’s a good idea to screw on that filter:

When photographing water

When photographing a scene with water, you’ll often get unwanted reflections, and a polarizer can make all the difference.

For example, when I was snorkelling off the coast of Indonesia a few years back, I took a series of photos without my polarizer. The water looked murky, plus it had a big, unpleasant reflection on the surface.

But when I used my polarizing filter, everything changed; the water become a crystal-clear, bright-blue color, and the shots had far more impact.

Of course, you shouldn’t always apply a polarizing filter to water shots. Sometimes, you’ll want to maintain reflections in a scene – think of a mountain reflecting in a quiet lake – in which case you should leave the polarizer in your bag.

But more often than not, if water is featured in your scene, a polarizer is a good idea.

When photographing a blue sky

The color of the sky can change dramatically with a quick twist of the polarizing filter. A pale blue can turn to a vibrant, deep blue color, though the extent of the effect does depend on the sun’s position.

(Also, a polarizer can cut out a lot of the smoggy haze that you’ll find in city scenes.)

When you’re photographing a landscape on a clear day, it’s often a good idea to at least try using a polarizer, especially if you’re shooting when the sun is high in the sky. The effect is quite striking, and it can even be the difference between a mediocre shot and a great shot.

When photographing trees and leaves

When you think of reflective objects, “leaves” probably isn’t the first item that comes to mind.

Yet leaves are actually quite reflective, and this reflectivity can seriously reduce color saturation.

A circular polarizer is particularly useful when capturing fall colors – professional photographers use polarizers pretty much non-stop when photographing the autumn landscape – because it cuts down on reflectivity and glare, which consequently increases color intensity.

When photographing reflective glass

If you like to photograph buildings or cars, a polarizer can be a big help, assuming you want to emphasize the building/car interior.

Glass is pretty reflective, but a polarizer can do a very nice job of removing those reflections.

(Of course, there are times when you’ll want to keep reflections for an interesting effect. In such cases, keep the polarizer off your lens.)

How to choose a polarizing filter

Most lenses take screw-in filters that attach to the end of the lens barrel, just over the front element.

Because different lenses feature different diameters, you’ll need to take note of the diameter on your specific lens, then buy a polarizing filter with a matching size.

If you have several leness with different diameters, you’ll need to buy several polarizing filters (annoying, I know; the alternative is purchasing step-down filters, but they can be cumbersome and frustrating to work with).

Keep in mind that good polarizers are not cheap – but as I emphasized above, you shouldn’t skimp and buy a poor-quality filter for your top-notch lenses. Instead, pay for a good polarizer made by a reputable brand (Hoya and B+W are two good places to start!).

Polarizing filters: final words

Now that you’ve finished this article, you should know all about polarizing filters and how you can use them for stunning shots!

So if you’re attracted to the power of a polarizer, then consider purchasing one! I guarantee you’ll have a lot of fun with it.

Now over to you:

Have you ever tried a polarizing filter? What was it like? What subjects did you use it on? Share your thoughts (and images!) in the comments below.

The post Polarizing Filters: What Are They and Why Do You Need One? appeared first on Digital Photography School. It was authored by Darren Rowse.