The greatest use of polarizing filters is to achieve that "polarizer" sky effect. That polarizer sky effect being the darkened, deep indigo blue sky phenomenon seen when viewing through a polarizing filter rotated to the most dramatic angle.

All photons are polarized. Each is a single one-cycle wave that can be thought of as a sine wave drawn on a sheet of paper. That flat paper represents their "polarization axis". They are emitted from the sun in every conceivable orientation along their direction of travel.

At about 90 degrees around the hemisphere of the sky starting at the sun, the blue light reaching your eyes contains a large proportion of polarized photons. Think of them as waves all oriented in the same direction with their polarization axes now broadside to the direction pointing to the sun.

Blue sky is made of the blue (shorter) photons that have bounced off microscopic particles of airborne matter: Dust. The glancing photon bounces out 90 degrees sideways with its polarization axis perpendicular to what it was before the bounce. Like the piece of paper it was drawn on were folded perpendicular to the photon's travel.

Who would have thought that a microscopic particle of dust would be an effective scatterer of blue photons based on each photon's individual polarization orientation? Huh.

Polarizers let in light mainly oriented along their polarization axis. They reject (absorb, actually) the photons that are perpendicular to their axis. Meaning... They "see" the ones that are waving in one direction and don't see the ones waving 90 degrees in the opposite direction.

So, if you hold a polarizing filter over your camera lens and turn it, at one particular orientation, the sky that is half way from the sun will appear darker. Dramatically darker! It's a great effect, but is that the only way you can get it?

Not if you have the 7 new iNovaFX iPolarizeSky6.atn filters. With these you can have your camera and polarize the sky later. No need to fuss with the filter unless it is absolutely necessary.

You can even run the filter twice or more. Sure, it's going to change anything in the sky-blue-range it's tuned to, and if you need, you can mask the area that will be affected. Got noise? Try running the iColorDeNoise filter first.

You can run the saturation of the blue part of the spectrum by using the selective blue color controls found in the Hue And Saturation control. (Ctrl-U > Ctrl-5 in Windows, Command-U > Command-5 in Mac 9.x and OSX)

Of course, you can use this iNovaFX Photoshop Action Filter on shots you made with that polarizing filter and further enhance the deep contrasty sky effect, but that's a different story.

To be sure, there are advantages to the real polarizing filter. Notice how in the lower image--the real polarizer shot--the glare off the paint around the upper windows is suppressed along with some of the subtle reflection on the lower windows.

But for me, the control these filters give make them worth using. See that little dark spot in the upper left of the real polarizer shot? Mm-hmm. Vignetting. Caused by the Nikon Circular Polarizer filter itself at wide zoom.

Each from iPolar1 to iPolar4 is more generously tolerant of the range of blue they impact. The difference in this particular example is subtle, but you may find that your image responds better to one and not another. 

iPolar5 is very aggressive. Try it for skies that don't yield easily. iPolarPale is for very light skies and iPolar2Taste walks you through the process, letting you sample the sky yourself and adjust the amount of saturation and lightness.

They're also included in all our eBooks

Notice that these only work in the full version of Photoshop 6.0 or above. Why? PS 6 is smarter about color. Yes, they work in Version 7 and CS 1&2, too.