Introduction

Knowing how to apply these unique filters is essential knowledge for any imaginative filmmaker because the effects they produce cannot be simply replicated digitally.

Many of the old-school glass photographic filters have fallen out of favor in the digital age because their effects can be recreated in the color suite with comparable, if not superior, precision and speed. This is especially true with color grads and other color-effect filters, but it is also true with diffusion filters, at least to some extent, and in some situations allowing for greater flexibility with the desired effect.

However, the polarizer is a unique filter whose effects cannot be replicated with simple software manipulation. Some reflections disappear, colors, notable greens, become brighter or more saturated, and the sky darkens (at a specific angle). While a grading suite can be used to darken the sky and boost saturation, only CGI can do rid of annoying reflections.

What is the mechanism of action of a polarizer?

You must keep in mind that light can act both as a particle and a wave. We will be discussing the wave behavior of polarizers. It is true that when light from the sun or an electric bulb is produced, it travels in all directions at once. Light rays that collide with a flat object, especially one with a highly reflective surface, become polarised upon reflection. This means that the light is now mostly emitted in one direction rather than equally in all directions. The reflection of light off the reflecting surface is usually captured by the camera as a bright highlight.

This allows us to employ a polarising filter to isolate the unmixed, single-plane polarised light.

The polarising filter has an absorption layer made of dichroic glass in between two layers of regular glass. The polyvinyl alcohol (PVA) plastic used to create the dichroic layer—also known as “pola foil”—is stretched during production, causing the plastic’s molecules to align in long parallel chains with microscopic gaps between them. To the unaided eye, these chains appear to be completely transparent. Iodine molecules bind to the polymer chains after being dipped in a solution containing the stretched polymer. Light waves traveling perpendicular to the long chains are unaffected by the pola foil’s structure, while those traveling in the opposite direction are absorbed.

Using Polaroid Cameras in Real Life

First, picture two kids clutching the ends of a jump rope that is strung between them; this is the polarizer, and it will change the way the light behaves. A single kid shakes the rope up and down, producing a sinusoidal wave that travels along the rope in a single dimension. To visualize this, picture two kids, one on each side of a picket fence (the parallel chains of the pola foil), hanging from the rope that runs between the slats. If one child shakes the rope up and down, the ensuing wave will travel through the fence’s opening and reach the other child on the other side; but, if the first child shakes the rope side to side, the following wave will be blocked by the fence and won’t travel through.

This is essentially what occurs when using a polarising filter. (A polarizer actually absorbs light travelling in the same direction as the chains and transmits light travelling in the opposite direction, but the fence analogy serves to illustrate the point.) Because the pola foil absorbs light energy, it prevents polarised light from reaching the camera when the molecular lines are turned into the correct orientation. Non-polarized light passes through the filter unaffected, but we’ll get into why that is in a moment. This allows us to see normally despite the fact that we are able to completely block out any and all light reflections off of surfaces.

It has the appearance of magic, although it is based on scientific principles.

Naturally, there are restrictions. It’s not possible to magically eliminate all reflections; rather, the ones that may be eliminated are limited to those that are at a specific angle to the camera. It’s important to note that light doesn’t always reflect off a surface in a precisely polarised manner, so while you might not be able to totally get rid of a reflection, you can at least It drastically reduced intensity. ThThisoesn’t only work on perfectly flat surfaces; it works on a wide range of surfaces.  It is common practice to employ polarizers to reduce the shimmering effect caused by reflections of polarized light on non-flat surfaces, such as water, where the undulation of waves (or wavelets) provides briefly “flat” surfaces.

A pola can also be used to make reflections off of leaves less dazzling. A polarizing lens can be used to lessen the effects of reflections on glass, windshields, and shiny floors. The only reflections that a polarizer can’t diminish are those off of metallic surfaces, because the light isn’t polarized in the first place. The polarizer eliminates the reflection on the automobile door in the next image, but that is because the reflection is coming from the clear coat and not the metal:

how does a polarizer work to darken blue skies?

This has to do with the way oxygen and nitrogen molecules in the air scatter light. The beautiful blue colour of the sky is the result of the greater scattering of blue light than other wavelengths. Polarizing filters can be used to mitigate the effects of this scattered blue light because it is polarized. If the filter is turned so that polarised light is blocked, the sky darkens because there is less scattered light to “pollute” the eye. This effect is most noticeable when the sun is right in the middle of the shot (at a 90-degree angle to the lens). The polarizer lens will have no effect on polarized light when the sun is directly in front of or behind the lens.

Conclusion:

The polarizer is a one-of-a-kind filter whose effects can’t be made to look the same by changing the way the software works. A polarising filter has an absorption layer made of dichroic glass in between two layers of regular glass. The polyvinyl alcohol (PVA) plastic used for pola foil is stretched, causing molecules to align into long parallel chains. It allows us to see normally despite the fact that we are able to completely block out any and all light reflections off of surfaces. 

The effect has the appearance of magic, although it is based on scientific principles.

A polarized lens can be used to lessen the effects of reflections on glass, windshields, and shiny floors. The only reflections that a polarizer can’t diminish are those off of metallic surfaces. A polarizer will have no effect on polarized light when the sun is directly in front of or behind the lens.