A beginner’s guide to polarisers and neutral density filters

Some might have you believe that neutral density and polarising filters aren’t required in today’s modern era of digital photography. That you can replicate their effects in post. No problem, just a couple of clicks, right?

Well, no. While many filters aren’t really required any more (unless you just want to save yourself some time in post), neutral density and polariser filters both offer effects that can’t be accurately recreated in post. In this video, Evan Ranft explains why and how each of these different filters work.

Polarising Filters

First up, polarisers. Typically, they’re often hailed as simply a way to make skies more blue, and sure, you can do that in post by dragging the blue luminosity slider down and saturation slider up. But that’s not all they do. They also eliminate reflections.

They can take shine and glare off non-metal reflective surfaces, like rocks, shiny tree leaves, and even skin. Or they can completely eliminate and let you see right through reflections on glass and water. It’s why fishermen wear polarised sunglasses, too. It’s not so they get those pretty deep blue skies. It’s so they can see through the reflection on the surface of the water at the fish swimming below.

They’re not perfect, though. They’re not going to instantly improve every shot. There are times when you don’t want a polariser. One of the things I mentioned from which a polariser removes shine and glare is skin. And if you remove that reflection completely, it can often give skin a somewhat soft and even velvet-like look. There are plenty of desert scenes shot during Breaking Bad (particularly the last season) where this polariser effect on skin is especially noticeable.

So, don’t always try to eliminate glare & reflection completely. Sometimes we expect surfaces, like skin, to show spekular highlights and when they’re not there it looks odd. You can rotate the filter to only get some of the effect and reduce the highlights, though, without completely eliminating them.

Polarisers can also have issues with ultra wide angle lenses. This is a simple fact of physics, there’s not much you can do about it. You just need to understand that it’s going to happen and figure out whether or not you really need one.

Neutral Density Filters

Neutral density filters have one function but with several implications. Essentially they just cut the visible light entering your lens by a certain amount. Essentially they allow you to show down your shutter. They come rated in stops, and the higher number of stops, the more light they block. There are a number of reasons you might want or need to be able to do this.

You may simply want to capture an image of something happening over a long period of time. Say, clouds rushing across the sky, the blur of a waterfall or people rushing through a city. Long exposures is not all they’re good for, though.

You may be using flash that does not support high speed sync in bright conditions and are limited in shutter speed. Or you might be limited in shutter speed due to shooting video, too.

Neutral density filters will allow you to achieve all of this, and they can’t simply be replicated in post.

Personally, I’m a big fan of Schneider neutral density and B+W polarisers, but there are plenty of options out there.