Unpolarized light is produced by reflections or travels through a material. This is visible as glare (reflected) or a color cast (after traveling through another medium).

Note: Light is a very technical phenomenon and so is the polarization thereof. The purpose of this guide is to look at the polarization of light in very simple terms. I will thus not attempt to bedazzle you with technical terms and phenomena, as easy as that may be.

Polarized electromagnetic waves are light waves in which the vibrations occur in a single plane (all waves vibrate in the same direction). This is in contrast to unpolarized light which vibrates in multiple planes.

Linearly polarizedlight

Filter brands and models come and go so I’d recommend using Google to get an idea of the ‘best’ CPL filters on the shelf at any given moment. If you cannot afford the ‘best’ (probably most expensive) ones, try to avoid the cheapest ones and purchase one in the mid-price ranges.

Key Lesson: Both square and round CPL filters will do the job. The determining factor when buying it is how easy it is to use and the price. In general, round CPL filters are easier to use but they tend to be of higher quality than square filters, which makes them more expensive.

Some CPL filters incorporate high light transmission glass, letting light pass through by half a stop or more than filters without high light transmission glass. This can be quite important as the average CPL filter may reduce your light by up to two stops.

The CPL filter rotated to its fullest effect. The 11:00 am the sun is 90° to my right and slightly above me. The amount of glare removed is significantly more than when the sun was behind me. Photograph by Tobie Schalkwyk

One can mimic quite a few filter effects in post-processing, but unfortunately, polarization is not one of them. An image is a two-dimensional entity, so post-processing software can’t remove glare and ‘guess’ what is supposed to be behind the removed glare.

The quarter-wave plate is needed to ‘spin’ polarized light before it reaches the mirrors of our DSLR cameras; otherwise, these mirrors may filter out all polarized light, leaving us with unusable/blank images.

Well, unless you need some artistic effect, the nature of unpolarized light (visible as reflections or glare) implies that it might spoil your image. A polarizer gets rid of all reflected light waves (or glare) by only letting light through on a single plane.

Light consists of two waves oscillating perpendicular to one another. That means if one wave oscillates vertically, then the second will oscillate horizontally. One wave is an oscillating electric field and the other is an oscillating magnetic field. It should come as no surprise then that light is also known as electromagnetic waves.

CPL filters produce the best results when the sun is sitting at 90° from the direction you are pointing your lens in. This can vary from 90° to your left, right above you, or 90° to your right (or anywhere in between).

Look through your viewfinder as you rotate the filter and stop rotating when you achieve the desired result. If you find it impossible to get the desired result, the sun may be sitting at an unfavorable position relative to the direction your lens is pointing in (not at 90°).

Circularly polarizedlight

Key Lesson: Polarizers in two basic forms are important to photographers: linear and circular. Linear polarizers do most of the work as desired by us. Circular polarizers are linear polarizers with a quarter-wave plate on the ‘inside.’

Unpolarized light vibrates in multiple planes. An example of this is a lamp. It creates electromagnetic waves that vibrate in all directions.

Linear polarization

CPL filter used to its maximum. The driver is 100% recognizable and the image is softer on the eye in general. Photograph by Tobie Schalkwyk

The second advantage of the round CPL filter is implied by the fact that the CPL filter has to be mounted in such a way that its quarter-wave plate layer is on the ‘inside,’ facing your lens. In round CPL filters, the quarter-wave plate layer is on its screw-in side, making it impossible to mount the wrong way.

Unpolarizedlight

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Key Lesson: Light is an extremely complex phenomenon. We can make it as complex as we want to, but we only need to know a little about it to understand the effect of polarization. Let’s not overanalyze it and rather focus on the results achieved using a polarizing filter plus how to do so.

The advantage of a square CPL filter is that it can be shared between lenses having various lens diameters. The disadvantage is that it might be bulky and ‘in the way’ because it does not sit ‘flush’ with your lens’ round edges.

The advantage of the round CPL filter is that after screwing it into the front of your lens, it becomes part of the lens – almost ‘invisible.’ The lens cap even mounts directly onto the mounted filter, not only making it almost ‘invisible’ but also protecting the filter when not in use.

The CPL filter rotated to its fullest effect. The 11:00 am the sun is slightly behind and above me. Photograph by Tobie Schalkwyk

Well, I have good news for you. There is a solution that, if not removing all of the glare from an image at the time of the shoot, will remove at least some (or most) of the glare. It is called a Circular Polarizer or a Linear (CPL) filter.

Recommended Reading: If you’re interested in learning more about light and how you can use it to improve your photography, grab a copy of Photzy’s bestselling premium guide: Understanding Light Book Two.

Political polarization

Key Lesson: The quality of a CPL filter is mostly determined by protective coatings, the amount of light it lets through, and possible vignetting effects. Do your homework (online) when shopping for one and buy the best you can afford. It will reward you greatly. Remember that unpolarized effects (defects) cannot be ‘fixed’ in post-processing.

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The circular polarizer has a second layer inside the filter, called a Quarter Wave Plate. This filter ‘spins’ the light after it goes through the linear layer before it goes through the camera lens. This eliminates the cross-polarization effect on your camera’s mirror.

Our view of polarized light may thus be somewhat incomplete as we will focus more on the results rather than on the science behind it.

Key Lesson: Light is produced in two basic forms: polarized (straight from a natural source) or unpolarized (reflected or ‘spread’ by a medium it travels through). Sometimes we wish to polarize it to remove glare or to produce ‘cleaner’ (dehazed or more vibrant) images.

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“Can I thus use the cheaper (non-circular) linear polarizer filters on my mirrorless DSLR camera?” Yes, indeed. It appears, however, that it is so difficult to get high-quality linear polarizer filters that most photographers hang on to their (by default higher quality) circular polarizer filters for use with their mirrorless DSLRs.

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The reason why round CPL filters are so popular (and worth the investment) is that it becomes part of your lens. Note the small ridges on the filter’s frame, making it easy to screw onto the lens or unscrew it. The front (smooth) part holds the filter and is rotated to achieve the desired effect. Photograph by Tobie Schalkwyk

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Just like any other commodity in the world, you get low-quality and high-quality CPL filters. In general, price is a good indication of quality, but understandably the bigger the diameter, the more expensive the filter.

Circular polarization

My purpose in this section is not to win any prizes, but to prove a concept. See what you can glean from it and apply it where needed.

In this guide, we will have a look at polarized light, including what it is and why we need to polarize it. We will look at how to achieve this using a Circular Polarizer/Linear (CPL) filter.

From long to short wavelength, the EM spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays.

CPL filter used to its fullest. The portrait is much more visible, and the reflection of the security gate is only vaguely visible. Photograph by Tobie Schalkwyk

No CPL filter was used. It’s almost impossible to see the portrait inside the house. The security gate is not in front of me but to my right. Its reflection is showing up on the glass of the sliding door between me and the portrait. Photograph by Tobie Schalkwyk

The effect of the CPL filter can be seen (the right half). Saturation is better in general, and the sky has changed from dull to a beautiful blue. Photograph by Tobie Schalkwyk

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If you have believed that a CPL is too expensive, just look at the technology and science behind it and think again! It’s great value for money!

polarization中文

A polarizing filter is a great little masterpiece. It is created by sandwiching a dichroic absorbing layer (made of PVA plastic) between two layers of glass. This PVA layer is stretched until its molecules line up in long parallel polymer chains with tiny gaps between them.

Note: The idea is not necessarily to get the maximum effect but rather to get the desired effect. Sometimes the maximum effect would not look pleasing to the eye, or you may want to retain a little bit of glare on a body of water (or window).

Polarization

The disadvantage of around CPL filter is that it screws into the front of your lens. It is thus made for a particular lens diameter so you cannot share it with one of your lenses having a different diameter. A solution may be to buy a CPL filter for your largest lens diameter and mount it on any of your lenses utilizing step-up rings.

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The term ‘circular’ polarizing filter should not be confused with the shape of your filter. Circular Polarizing/Linear (CPL) filters can be purchased in both square and circular forms.

In general, price is a good indication of quality, but understandably the bigger the diameter, the more expensive the filter.

High-quality CPL filters will screw in smoothly into your lens and offer slick filter rotation. It will have grooves on its outside frame so it can be mounted/unscrewed easily.

The frustration was supplemented even further by embarrassment when you had to explain to your (perhaps paying) subjects why these images were not included in the collection at the delivery date.

The stretched PVA layer is then dipped into iodine and the iodine molecules attach themselves to the polymer chains. This allows the resulting pola foil to absorb light waves that are parallel to the polymer chains while letting through waves that are perpendicular to these chains.

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I’m sure that you have encountered a situation at least once, where you have been frustrated by glare/reflections hitting your lens from a body of water, glass, or perhaps another object. When you looked back at your affected images, then you realized that had it not been for the glare, these images would have been awesome.

Recommended Reading: If you’re interested in learning more about light and how you can use it to improve your photography, grab a copy of Photzy’s bestselling premium guide: Understanding Light Book Two.

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