What is a Polarizing Filter?
There’s two main types of polarizing filters, linear and circular. Despite their names, both types are usually circular in shape, threading onto the front of the camera lens like a UV filter.
Linear Polarizing Filter
Linear polarizers are traditional in the sense that they were designed to be used with manual focus SLR cameras, when autofocus wasn’t yet a thing. A linear polarizer, much like a circular polarizer, both give the effect of reducing reflections against glass surfaces in addition to improving the color saturation of your image. The main problem with a linear polarizer however, is that it can cause cross polarization against other reflective surfaces, such as mirrors. For instance, if you were to have a mirror or other reflective surface inside of your camera, a linear polarizer could be detrimental to your footage as it can cross polarize the reflected image, leaving the possibility open for your footage to be blacked out. However, since digital cameras in today’s day and age have auto as well as manual focus systems, the more commonly used polarizer is the circular type.
Circular Polarizing Filter
Circular polarizing filters (CP) feature an outer bezel independent from the threaded filter frame that allows the polarizing effect of the filter to be circularly adjusted to the minimum or maximum point of polarization. At the max polarization angle, a circular polarizing filter reduces most direct reflections from water and other reflective surfaces like wet foliage, snow, rocks or desert sand. The result is a clearer image with enhanced color saturation and definition.
What Can a Polarizer Do?
Use a polarizer on a cloudy day and you’ll notice that it has the effect of making the clouds pop, adding contrast and depth to an otherwise flat sky. This is one of the most commonly known reasons for a landscape photographer to use a polarizer, as it has the ability to enhance the look of their content. Polarizing filters can also remove reflections from windows so that you can see through them. They are even useful in creating contrast between clouds in an overcast sky and reducing atmospheric glare. By improving contrast, polarizing filters also enhance saturation. When used at a 90 degree angle to the sun, a polarizing filter has the maximum polarizing effect. By reducing harsh reflected light, the camera is able to pick up softer, diffused light, rendering more true to life colors, especially in landscapes that suffer from overexposure under bright midday sun. Furthermore, a polarizing filter can be used to enhance rainbows. Whenever you are lucky enough to witness a rainbow, it is always first instinct to be able to photograph it; yet, it does not always turn out to be top quality. With the help of a circular polarizer, you can capture a rainbow in an image that will look exactly as how it did in person. However, it is important to beware of the fact that when rotating the polarizer, you can also eliminate the rainbow from your image completely if you turn it too far.
Polarizing filters can be one of the more expensive filters out there, but it’s important to invest in a quality glass or quartz filter so that you don’t hinder the performance of your camera lens by shooting through a low quality filter. A low quality plastic or resin filter will cause more harm than good, adding noise to your scene that’s difficult to fix in post and possibly putting the whole composition out of focus. Be sure to pick up a polarizing filter that matches the quality and performance of your camera lens. At PolarPro, we have hand-crafted the QuartzLine collection by providing unrivaled durability and optical clarity with our fused quartz glass construction. Our circular polarizing filter is a favorite among landscape photographers as the quality speaks for itself when put to the test out in the field.
Common polarizing filter sizes for full-frame digital cameras include 77mm, 67mm and 82mm. If you’re using multiple lenses, you can buy a set of step-up or step-down rings that allow you to use the same polarizer filter on larger or smaller lenses. For example a 67mm-77mm step-up ring mounts to a 67mm camera lens and allows you to use a 77mm polarizer filter. Conversely, a step-down ring of the same value allows you to use a 77mm polarizer filter on a 67mm camera lens. Step-up rings are more common, as step-down rings can cause vignetting or unwanted cropping of your composition. Other popular step-up rings sizes include 52mm-67mm, 55mm-67mm, 58mm-67mm, 62mm-77mm, 67mm-77mm, 72mm-77mm, and 62mm-82mm, 67mm-82mm, 72mm-82mm, or 77mm-82mm. As a rule of thumb, you want to stick within a range of about 20mm when choosing a step-up ring to avoid introducing noise to your composition.
How Does a Polarizer Reduce Light?
It should also be noted that a polarizer filter reduces the amount of light entering a camera sensor by about 1.5 - 3 stops, depending on the angle of polarization. At ninety degrees to the sun, a polarizing filter polarizes the most amount of light. If you rotate the filter another ninety degrees using its adjustment bezel, or change your camera’s orientation to the sun by ninety degrees, the polarizing effect is eliminated. Between these two extremes, one can adjust the filter to achieve the desired amount of polarized light in a scene.
If using a slower lens, polarizing filters can cause blurry images in low light. Using a high quality glass or quartz polarizing filter will produce the clearest results. When buying a polarizing filter and step-up rings for multiple lenses, choose a filter that fits your largest diameter camera lens. The main reason for this is that step-down rings can cause vignetting, so it’s best to use step-up rings to fit larger polarizing filters onto smaller camera lenses. An exception is when using full-frame sized camera lenses and filters on APS-C or Micro Four Thirds camera sensor formats, where those smaller crop sensors eliminate vignetting or clipping of a composition.
Because polarizing filters have the ability to reduce glare and highlights, as well as improve saturation and contrast in ways that can’t be achieved in post editing, these filters remain indispensable for every content creator. And while you may be hard pressed to find a newly manufactured linear polarizer, always choose a circular polarizer when purchasing a new or used filter for a digital (DSLR/mirrorless) camera. For more info on camera filters, like how to align a polarizer filter or ND/PL filters, check out PolarPro’s YouTube channel.
Edited by Carly San Filippo
Written by Scott Fairfax