The polarizer filter (CPL) is probably the only filter that is impossible or very difficult to reproduce in photo processing.
What is a polarizer filter
The essence of the polarizing filter is very simple – such a filter can delay the reflected polarized light. For example, it is possible to catch the reflected light from water, glass.
But the functionality of the filter is not limited to that.
A CPL made of two parts – a movable and a stationary one.
The fixed part of the filter is screwed into the lens filter thread.
The movable part can rotate freely 360 degrees. By rotating the front part of the polarizing filter, the filter is adjusted to a specific type of polarized light.
There are linear and circular polarizing filters. Today, the vast majority of photographers use a circular polarizer or CPL.
The circular polarizer is specifically designed not to interfere with autofocus. When you put the filter on your lens, you’ll find that it can rotate, changing the direction in which the light is polarized.
Visible light, like any other electromagnetic radiation, is a wave. Polarized light is radiation whose waves oscillate in the same plane.
Initially, sunlight is not polarized, that is, its waves do not have a well-defined direction of transverse oscillation. But on the way to the camera, the light is reflected and refracted.
As a result, we have reflections on various surfaces, and a peculiar shroud appears in the sky. A polarizing filter is designed to fix it.
So what is polarization
Imagine a light wave pointing directly into your eye. If you rotate the previous picture 90 degrees, all we will see is an up and down oscillation of the wave. Such a light beam is called a polarized light beam.
So a polarized light is one whose electric field oscillates in one direction only. Vertically in this case. It can also be horizontal, and any orientation, in principle.
How does a polarizing filter reduce glare
Imagine yourself standing on the shore of a lake in sunny weather. Light hits your eyes from all directions, reflecting off the clouds, any surface in the neighborhood. Calm reflected sunlight.
But if you look directly at the water, you see the bright glare from the sun. There’s nothing good about it: it’s blinding.
Fortunately, though direct sunlight has no polarization, but, reflecting from the surface, it is at least partially polarized (at some angles of incidence – completely). And the direction of polarization is parallel to the plane from which the light is reflected.
It turns out that most (if not all) of the light reflected from the surface is clearly polarized. All we have to do is to put on sunglasses with a vertical polarizing filter and thus cut off the glare.
The same sunglasses will allow us to look beneath the surface of the water.
Circular polarizer filter and why is it needed
Besides linear polarization there is another type – circular polarization.
The thing is that electronics of modern cameras cannot work properly with linearly polarized light. Mistakes of exposure metering and focusing are possible.
With light that has circular polarization, there is no such problem, because it is like ordinary natural light.
Oh my God, that’s a lot of theory! OKAY. So let’s put the polarizer on the camera.
How to use a circular polarizer
As I wrote in the beginning, a CPL filter makes the colors in a photo richer and also removes glare from the picture. The increased saturation and contrast are useful when shooting landscapes.
The left picture was taken without the polarizing filter. The right picture was taken with the filter. In the second shot, you can clearly see both the increased overall image contrast and the increased amount of detail in the clouds.
Note that because the filter cut off some of the light, the bottom photo was taken at a slower shutter speed than the top one: 1/125 seconds versus 1/250. The ISO and aperture settings are the same.
Sometimes you can achieve a similar effect in processing (often by spending more time on it), but what you definitely can’t achieve is to get rid of glare and reflections. Using a polarizing filter on the right photo helped remove most of the glare on the windows. This can be pretty darn useful when you need to take a shot through glass, but you can’t catch anything because of the reflections.
The same effect is seen with glare on the water surface. The picture on the right is taken with a polarizing filter.
Of course, sometimes a polarizing filter can make a photo worse with its effect. For example, when you want to keep the haze in the atmosphere or leave out reflections. It all depends on how you want to put it in your hands. And don’t forget that a polarizing filter always darkens the image by about 1.5 f-stops.
The best circular polarizer filter
I personally use and highly recommend the B + W 77mm Circular Polarizer Kaesemann – Xtra Slim Mount (XS-PRO) filter because of its top optics, slim mount, which is essential for wide-angle lenses, and very low light loss of 1-1.5 steps.
You don’t want to put a cheap piece of glass in front of your expensive lens only to be disappointed later with poor image quality and unwanted ghosting and glare. You don’t want to waste money and time on poor quality filters!
I guess I would give one piece of advice – don’t skimp.