Filter manufacturers may not really enjoy this post, but the truth is that filters are very antiquated in the world of digital photography. With the incredible abilities of programs like Lightroom, Photoshop, Picasa, iPhoto, and others, you rarely have the need for physical filters anymore. Now, with the click of a button, you can “cool”, “warm”, and color correct your photos after the fact with incredible precision and ease.
However, there are a small handful of filters that are still quite important to have, the effects of which cannot be perfectly replicated in photoshop or similar programs. These include Neutral Density, Graduated, and Polarizing filters. For this post, we’ll be talking about Polarizing filters.
For starters, let’s look at what a polarizer even does. Basically, it’s a piece of glass that has invisible bars to it that only allows light to pass through at a certain angle or range of angles. As you can see from the above graphic, light starts out in all sorts of directions, but then passing through the Polarizer, it is filtered into a more orderly set of wavelengths.
To skip through a bunch of scientific explanation, the basic outcome is two-fold. One, you get rid of a good bit of reflection, and two it produces much deeper shades of blue when photographing skies. Most photographic polarizers are what’s known as circular polarizers, as they can be rotated to produce a gradient of polarizing intensity.
So, when might all this be useful?
Filtering out surface reflection can be very helpful when photographing watery landscapes. But, not just any water…it has to be smooth, highly reflective water. For instance, say you’re photographing breaching humpback whales in choppy water…what will happen? Not much. Sure, the bright glare on the water will be cut down slightly, but frankly, not significantly. What if, however, you’re photographing a lake with river rocks below the surface? Yep! That’s a perfect time to use a polarizer, as long as you want to also capture the rocks below and the water isn’t too deep. Scenes in Glacier National Park are ideal for this, like the below.
But truthfully, what most photographers enjoy most about polarizing filters is their ability to yield more saturated-looking skies.