Updated Sept. 25, 2021
If you have bought an old 35mm kit at some point (or five...or fifteen...you'll get no judgment from me ;-)), you have likely encountered a polarizing filter in among the customary packet(s) of lens tissues, bottle(s) of cleaning fluid (either unopened or completely evaporated), a blower brush that develops negative thrust, crummy 2x converter (usually described as a lens ;-)), and a gaggle of other accessories to the crime. Of all that seeming detritus, the polarizer could prove to be the most useful to you in your photographic journey. But like any tool, it can be misused, overused, and in some cases even prove detrimental to your camera's metering or focusing performance, and image quality. So how do polarizers work? How can you maximize their performance? And which type of polarizing filter will be right for you?
What Do Polarizers Do?
Before being able to utilize a polarizer to best effect, a basic understanding of what they do is in order. Hopefully without falling too far down the physics of light rabbit hole ;-). Light waves ordinarily vibrate in all directions. A standard polarizing filter consists of two layers of foil applied to pieces of optical glass that can be rotated in relation to each other. Each layer is arranged like a row of "bars". When both layers are oriented with their "bars" parallel (both vertically or horizontally) to each other, the light passing through is unaffected and remains unpolarized. But when the front layer is rotated 90 degrees in relation to the rear layer, now only the light in a single plane (the vertical or horizontal component, but not both) is permitted to pass through. The basic overall effect is a reduction of glare, and thus a perceived increase in the saturation of colors (blue and green being the most noticeable). Because arrays of vertical and horizontal lines are involved, the term linear polarizer is applied to such a filter. In the process of polarization, the filter also reduces the amount of light transmitted to the film or sensor, thus simultaneously acting as a 1 - 2 stop Neutral Density (ND) filter (the amount of light being absorbed depends on the type of foil used and the degree of polarization applied by the user).
Edwin H. Land, the founder of Polaroid, developed the first practical, cost-effective polarizing foil in the 1930s (thus the origin of the name :-)). One of its earliest applications was for sunglasses. Polarized sunglasses became very popular among pilots, drivers, and fishermen, as they eliminated glare emanating from clouds, roads, water surfaces, even the glass faces of analog instruments in both aircraft and vehicles. Land was obviously very much into photography as well, and sought to apply the principles of polarization of light in that field as well, which led to the development of the screw-in linear polarizer for lenses, among other applications. Linear polarizers for photography were so effective that they remained virtually unchanged until well into the 1960's. But as new technologies, such as beam-splitters, began to find their way into a few SLR meter designs, the limitations of the linear polarizing filter began to become apparent. Beam-splitters act as polarizers themselves and so do not play well with already-polarized light, so a modified method of polarization had to be developed in order to allow them to function as intended. Thus the circular polarizer was born. This type takes the standard two-foil linear configuration and adds a third component called a quarter-wave plate behind the linear films. This plate re-orients the linearly-polarized light into a circular pattern (thus the terminology) that permits the beam-splitter to operate normally while retaining the polarization effect for the image. Okay, that's as much physics as I can take in one sitting ;-). But it will be enough for you to make the decision on whether you will need a circular or linear polarizer for your particular camera system.
Linear vs. Circular - Which Will It Be for You?
This is not as difficult a choice as it may at first seem. The reason it comes up at all is that there are a zillion cheap used linear polarizers out there from decades of production. Circular polarizers have always been more expensive than their linear counterparts due to the added quarter-wave plate component. Nowadays, since all new ILC cameras require circular polarizers, filter manufacturers do not even bother producing good-quality linear polarizers simply because circular polarizers work on every camera type to date. You can still purchase a new linear poIarizer for much less than a top-quality circular version, but it is not a good idea because of other compromises that have been made to cut costs in the construction of such filters. The basic rule is this: if your interchangeable lens camera (ILC) utilizes a beam-splitter for metering and/or phase-detect auto focusing...you will need a circular polarizer for achieving correct exposure and/or auto focus. This includes virtually all digital ILCs. Vintage SLRs with beam-splitters include:
Let's go back to our original scenario: you pick up a non-beam-splitter SLR with an old linear polarizer. Should you bother upgrading? Not necessarily. If it is a good-quality filter in good condition, have at it. But, what determines whether a polarizer (linear or circular) or any other filter is of good quality? Here are a few factors to think about:
By all means, give that old linear polarizer a whirl, but remember that technology has come a long way and good quality modern (say within the last 10-12 years) circular polarizers provide a noticeable boost in anti-reflective performance over their forebears. But drop $80 - $100 USD for just a filter when I got this whole kit for that much? Get real, man. Okay, okay, okay. Here comes a tip or two:
How to Get the Most Out of Your Polarizer
Just like watching the image in an SLR viewfinder snap in to focus for the first time as you twist the focus ring on the lens, so watching a blue sky darken and clouds pop out dramatically as you rotate your polarizer can be intoxicating. Or observing leaves snap into the most intense green or yellow you have ever seen...or seeing paint turn into a deep pool of color on a nice car as you kill reflections with a mere twist of your thumb and forefinger...and pretty you soon you are polarizing everything... everywhere... now all your dreams are in polarized light... and you can't stand in front of a mirror to brush your teeth anymore because you can't stand any reflections anywhere... and welcome to the polarization spiral ;-).
Oh yeah. Been. There. Done. That. It is sooo easy to overdo it with a polarizer. But the beauty of these little gizmos is that is doesn't have to be on OFF/ON, all-or-nothing, Nigel Tufnel "but-these-go-to-eleven" proposition ;-). You have, in the tips of your fingers, the ability to dial in just the right amount of polarization for a given situation. Polarizers are like spices in cooking...they are flavor-enhancers, not the main ingredient, and are at their best when used with a dash of subtlety and a pinch of restraint. Leaving a touch of glare on those wet rocks beside a waterfall, or just a bit of reflection on that pond surface to retain a sense of mystery, or to emphasize a beautiful compound curve on a classic car's fender are just a few examples of tasteful enhancement of an image via polarization.
One also needs to keep in mind that polarizers have limitations. They are at their most effective when used at a 90-degree angle to the direction of your main light source (e.g. the sun), and they gradually lose effectiveness the closer to parallel that they are oriented to said light source. The wider the angle of view of your selected lens, the more a banding effect (lighter and darker strips) between adjoining sections of the image will become apparent as the lens is taking in both those perpendicular (the more pronounced "darker" bands) rays versus the ones closer to parallel to the light source (the polarizer is less effective here, producing "lighter" bands and thus less glare reduction). This effect can be used creatively but more often than not serves as a distraction in the final image.
So, What's It Going to Be?
Modern, top-of-the-line B+W, Hoya, and Marumi (among others) circular polarizers offer the most bang for your buck versus boutique (Singh-Ray, etc.) or OEM (e.g. Canon, Nikon, Zeiss) manufacturers, offering excellent quality for less money. They all have some version of high-transmission foils, hardened glass and multicoatings, and easy-to-clean surfaces. You can pick up a top-quality used or discontinued NOS copy for less than half the price of a new mid-grade version in their respective lineups. A polarizer can easily outlast a number of bodies and is brand-agnostic as far as fitment goes if you ever decide to switch systems. It is also one of the last filter types that has not been successfully cloned for use in the digital darkroom as of yet. That makes it an important part of many a photog's kit today and one that will reward the care you take in selecting it for years to come :-).
Polarizer @ https://en.wikipedia.org/wiki/Polarizer
Understanding Polarizing Filters @ https://ascmag.com/blog
How Circular Polarizers Work @ https://hoyafilterusa.com/pages
The Physics Behind Polarization @ https://schneiderkreuznach.com
Polarizer @ https://schneiderkreuznach.com/en/photo-optics/b-w-filters
Suffers from a quarter-century and counting film and manual focus SLR addiction. Has recently expanded into 1980's AF point and shoots, and (gack!) '90s SLRs. He even mixes in some digital. Definitely a sick man.