This entry in the "Keppler's Vault" series revisits a 16-page article from the July 1985 issue of Modern Photography that explains how polarizing filters work. Polarizers are among the most misunderstood lens filters, and unlike UV, color, or neutral density filters, their effects depend on the physics of light waves rather than something more intuitive like blocking wavelengths or reducing overall light. The vintage article breaks down the concept simply: light can be polarized (rays aligned in one direction) or unpolarized (rays scattered in all directions), and a polarizing filter only allows light aligned with its orientation to pass through. Since the human eye can't detect polarization, using these filters effectively requires some trial and error, though the article offers guidance—such as positioning the camera at a 90-degree angle to the sun on a bright day for maximum effect, since polarized light is also created by reflections off skin, water droplets, and certain plastics.
The piece includes visual examples showing the impact of polarizers in three scenarios: removing reflections off a car windshield to reveal detail behind the glass, diffusing reflections off water droplets on skin to create a velvety appearance, and revealing an iridescent "birefringence" effect on a plastic tape dispenser. The article also explains the practical difference between linear and circular polarizers—both filter light in the same basic way, but linear polarizers can interfere with an SLR's metering and viewfinder image, whereas circular polarizers use an added "quarter wave plate" to avoid these issues. The original piece reportedly included a chart listing various period SLR models and specifying which type of polarizer each required.
The author praises the article for explaining a technically tricky subject in an accessible way, balancing enough technical detail to explain "why" polarizers work with clear visual demonstrations of their creative effects. While admitting to having lost interest in polarizers earlier in his photographic career, the author credits this vintage piece with reigniting his curiosity, and suggests it may do the same for readers today.
AI-generated summary. May not capture every detail — read the full article below for the complete picture.
Most people understand how lens filters work. Colored filters are used with black and white film to filter out specific wavelengths of the color spectrum to alter the contrast of the image, UV filters filter out ultraviolet light which in some lenses helps to reduce haze (and is also a great way to offer some protection on your lens’s front element), and finally neutral density filters restrict the amount of light passing through the lens, to allow for creative use to add blur to motion or use a wider aperture than a given amount of light would otherwise allow.
Of all the different kinds of lens filters, the one that seems to confuse people the most are polarizers. Light moves as a wave and those rays act differently when passing through a polarizer oriented one way versus another. Through creative use of polarizers, you can achieve effects such as darkening a blue sky, reducing glare on human skin, or enhancing iridescence in some plastics.
For most photographers, a complete understanding of the physics of light is not necessary to use a polarizer. The best way to learn how they work is just to get one and try it out for yourself and see what happens.
If you want to learn more about polarizers, I am sure there are a great deal of books or other online resources that explain how they work, but this being Keppler’s Vault, why not let a 36 year old 16 page article from the July 1985 issue of Modern Photography explain it!
In the simplest terms possible, light is either polarized or unpolarized. When it is polarized, the invisible rays of energy that we perceive as light are lined up in a specific direction. Unpolarized light is not lined up. A polarizing filter is one that only allows polarized light traveling in a specific direction to pass through. Since unpolarized light bounces in all directions, at least some of it lines up with the filter and can pass through. When light becomes polarized either by bouncing off a specific surface, travels in a specific direction, or is artificially polarized via another filter, the orientation of the filter restricts that light from passing through.
Since the human eye cannot detect polarized versus non polarized light, determining when these filters can be used is a bit of trial and error and the Modern Photography article tries to explain where this effect can mostly easily be used. On a bright sunny day, positioning a lens with a polarizing filter at a 90 degree angle from the direction of the sun has the best chance at capturing polarized light. Light reflecting off human skin, droplets of water, and certain plastics can also polarize light.
In the gallery above, we see three examples of scenes with and without a polarizer. Polarized light reflecting off a windshield can be filtered out to better show detail behind the glass, water droplets on a woman’s skin can be diffused giving her skin a vivid, almost velvet-like appearance, and in the case of the tape dispenser, an iridescent effect called birefringence is revealed with a polarizer.
Polarizers can be generally grouped into two broad categories, linear and circular, and the article gives a good explanation about when one is needed versus another. In simple terms, both a linear and circular polarizer accomplish the same thing, filtering out light moving in certain directions. The problem with many SLRs however is that this filtering affect can negatively affect a camera’s ability to meter light and may also cause parts or even all of the viewfinder image to become filtered out as well. With a circular polarizer, a second filter called a ‘quarter wave plate’ takes the filtered light and spins it in a way that eliminates these unwanted in camera effects. In the article is a chart showing many SLRs of the era and which ones require one vs another.
There is a lot more to know about polarizers, how they work, and how they can be used. This article does an excellent job of not getting too technical, while showing the different effects polarizers can achieve while also explaining why it works. I’ll admit to having an early interest in polarizers in my early days of photography, but quickly losing interest in them, but this article has definitely reignited my interest and perhaps it will for you too!
All scans used with permission by Marc Bergman, 2021.