Introduction

Polarizers can be broken down into two basic categories: linear and circular. This does not refer to the physical shape of the filter—a circular polarizer can have a square or rectangular shape, and a linear polarizer can have a round shape—but rather to how light exits the filter and whether or not the filter incorporates an additional type of filtration. A circular polarizer can have a square or rectangular shape, and a linear polarizer can have a round shape. A polarizer, in general, is the same thing as a linear polarizer. It functions in the manner that was just outlined to block off polarised light coming from a certain route while allowing non-polarized light to travel uninterrupted. The problem is that the light that was not polarised before it went through the filter is now polarised after it has gone through the filter. The filter, similar to a picket fence, only lets light through that is oscillating in one direction. This is not a problem with the vast majority of film cameras; but, if the camera also has a videotape and receives its image through a beam-splitting prism, the problem arises.

However, this can be problematic for some digital cameras, particularly those with an auto-focus or auto-exposure option. A beam-splitting prism or half mirror is commonly used in these cameras to redirect light from the lens to a separate exposure metre or secondary sensor. If the sole light entering the beam splitter or half mirror is already polarised, the auto-focus or auto-exposure may not work effectively because the intensity of the light entering the beam splitter or half mirror may be misconstrued. This issue can be remedied by using a circular polarizer.

linear polarizer lens

On the rear of a linear polarizer lens is a secondary filter that is called a “quarter-wave plate” or a “quarter-wave retarder” in circular polarizers. This filter is part of the circular polarizer. The light that passes through the filter is essentially depolarized as a result of this wave plate. The light that passes through the polarising filter is “remixed” so that it has a more natural orientation for the beam splitter or partial mirror in the camera. This may appear to be counterproductive, but the polarising filter’s qualities are nevertheless maintained despite this.

This is accomplished by the circular polarizer, which “spins” the linearly oscillating light wave. This is where the term “circular” originates, as the light wave then adopts a circular oscillation rather than a linear one as a result of the circular polarizer’s action. When the wave travels through the quarter-wave plate, it changes its motion so that it no longer oscillates in a single plane but rather rotates about its own axis.

Linear polarizers lens

Linear polarizers can also cause issues with three-chip broadcast/ENG cameras that have dichroic prisms, it is best to use a circular polarizer not only with those cameras but also with the cameras themselves. The use of a circular polarizer does not, in point of fact, have any disadvantages, with the exception of the financial investment required. In most cases, this is the more prudent course of action while using any camera.

Techniques for Applying a Polarizer

Because a polarizer only modifies polarised light when positioned at the correct angle, the filter must be rotatable. As previously mentioned, polarizers can be found in either a circular or square/rectangular form. The threads on the spherical filter allow it to be screwed onto the front of a lens; once attached, the filter can be rotated freely without affecting the threads or the frame.

Some polarizers come in a spherical shape but lack threads, necessitating the use of a matte box with a spherical stage for clamping. Additionally, unique rotating filter stages in a matte box or a rotating filter holder are required for square or rectangular polas. A polarizer can be used in conjunction with any other filter type, and its placement is not critical. In contrast, most matte boxes have moving filter stages at the very back, hence a pola is typically mounted as close to the lens as possible.

Once a polarizer filter is in place, its orientation can be changed by observing the result in the viewfinder or on the screen. The effect of a pola can also be seen with the naked eye. One way to do this is to stand next to the camera and look through the filter while rotating it in front of the eye to get a rough idea of how the desired effect will look. Keep in mind that you don’t have to use a polarizer at peak effectiveness all the time. As a matter of fact, there are contexts in which something may seem implausible or out of place. One of the many great things about polarizers is that you can change the intensity of the effect.