This is why you absolutely need a polarising filter

Filters have largely gone the way of the dinosaur with digital photography. Lens filters, that is. The simple fact of the matter is that they’re just not needed now. We used to need a whole array of filters when we shot film. Solid colours to shift the contrast on black & white film. Variously coloured graduated filters to shift skies warmer. Now, you can do all that in post.

Colour shifts and gradients are pretty straightforward in Lightroom or Photoshop. But one filter that’s still essential is a circular polarising filter. It allows you to do things that are simply impossible in post, even with today’s digital technology. This video from photographer Christopher Frost explains why, with some practical examples.

The task of a polariser is fairly straight forward. The science behind it is a little more complicated to get your head around. But, in short, their primary advantage for photographers is that they allow you to completely cut through reflections.

It’s not all reflections though. Only reflections on non-metallic objects. It’s won’t make chrome suddenly appear dull and flat. But it will take some of the shine off window, water and other objects. This is something that you can’t simply “fix” in post with a slider in Lightroom.

This is why polarised sunglasses are so popular amongst fishermen. They allow them to see through the reflective surface of the lake or river and spot where the fish are. Skiers use polarised goggles for similar reasons, too. To help take the bright reflections off the surface of snow and ice.

They work equally as well with glass, too. This can be very handy for street photographers to remove bright reflections and glare from car windows, for example. Or, to darken a reflective shop window behind your subject.

It will also help to take the shine off a great many things. I use a polarising filter often when I’m location scouting, not because of the benefits it offers with skies (we’ll get to that), but because it reduces the shine on leaves. Instead of having a lot of blinking blown out specs on the trees where the leaves are reflecting the sunlight, I see a wash of bright, vibrant, green.

I tend not to turn it all the way for the trees, though. I do still like a tiny bit of shine, otherwise, they often just look like fake plastic trees.

But, back to the skies. Skies are probably main reason that most people use polarising filters. Especially landscape photographers. To help provide more contrast and richness in skies. And this is why some people say that you don’t need a polarising filter today. Because you can always just grab the blue slider in Lightroom and drag the luminosity down and the saturation up.

And, if that were its only purpose, I’d possibly be inclined to agree. But it’s not, so I don’t. The ability to be able to eliminate unwanted reflections will save you hours in post with the clone stamp tool trying to recreate what the camera couldn’t possibly see. The only way around that is with a polariser.

Christopher prefers Hoya polarising filters, although the last Hoya polariser I used fell apart in my hands while trying to take it off a lens. I’ve since switched to B+W polarisers, and couldn’t be more pleased with the results they offer.

Polarising filters aren’t great for every situation, though. They’re not all that useful if you’re pointing directly towards or away from the sun. Extreme wide angle lenses can produce some strange effects. And polarisers can also make for very bizarre looking people, too. Taking the shine of human skin often tends to make it look quite weird, almost velvet-like.

Quality polarisers aren’t inexpensive, either. If you have lenses with multiple filter diameters, it can get expensive. So, here’s a tip. Buy a 77mm (or an 82mm if you have lenses with filter threads that large). Then get cheap step up rings for the rest of them.

[via Reddit]