Before we get onto the ways in which you could use a CPL filter and the situations best suited to it, let’s run through a couple of the basics first.
A CPL filter – which stands for circular polarizer/linear – is a glass attachment that can reduce the glare from reflected surfaces. Although there are various types available on the market, the most popular is the circular model, partly as it can fit easily onto the end of virtually any camera lens.
Beginner photographers often don’t feel the need to complicate their hobby any further than is necessary. However, for those who want to move their skillset forwards, a CPL filter has the potential to turn otherwise unusable shots into professional standard photographs.
It does this by taking what you could call “obstacles”, such as unwanted light, reflections or colour, and reducing them to a certain extent. The ability to do this gives you more control over what appears in your final product. As wonderful as the nature around you is, it’s far better from a photography perspective if you’re the one in charge.
How to use a CPL filter
Although it can take years to fully master the art of using a polarized filter, thankfully the basic concepts are relatively easy to get to grips with.
For starters, the filters themselves are generally available in a range of diameters, so finding one that fits onto your lens shouldn’t prove a strenuous search. Once on, all you need to do is rotate the filter in order to block particular wavelengths from hitting your sensor. This is often dependant on the angle between your subject and the source of light, e.g. the sun. It’s a common belief that pointing the lens at a 90 degree angle to your source produces the best results, and although this isn’t true for all circumstances, it will be for many.
It’s also recommended to not always twist your polarizer to full effect, which can make scenes look unnatural. The point is to fine tune images, not completely alter them – unless that’s your intention.
When to use a CPL filter
There are numerous scenarios we could go through here, so for the sake of space and time let’s narrow them down to a key handful that you’re likely to encounter during your day-to-day snapping.
Removing glass reflections
One of the first things people notice when starting out in photography is how difficult it can be to take photos from the inside of a window. A polarized filter has the ability to reduce all those unwanted light streaks that blur the subject of your shot. It can also do the same for light reflected on water surfaces.
Darkening the sky
Nothing helps give your landscape shot a more forboding sense of tension than a darker, more menacing-looking sky. The same could be said of shots inside where you’re aiming to create a sinister atmosphere. A good CPL filter will enable you to do just this without making the scenario look unnatural.
Removing haze or colour
This example blurs the line between when to and not to use a polarized filter, as you could justifiably want to increase or decrease the amount of both depending on what you’re trying to achieve. In this case, if you’re hoping to show a sky that’s clearer than it actually is, then the CPL would come in handy.
When NOT to use a CPL filter
Despite the above, there are certain circumstances where it might be best to take off the filter and shoot your scene with all the natural light intact.
Reflected light can sometimes enhance a photo, especially if the light itself takes on a colour other than the usual. For instance, if the sky is red in the evening, this can create a vibrant effect that would be best off kept.
Water is transparent and, as such, not always easy to capture through a lens. Because of this, it can be difficult to tell the difference between, say, a wet rock and a dry one. Allowing light to shine off the droplets can overcome this issue.
Under such circumstances, you’ll likely want to reflect as much light as possible as there will be very little illuminating your subject in the first place. A CPL filter in this case would do more damage than good.