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A study of what a Polarizer does
Posted By: m8o, 06-07-2009, 11:04 PM

This is a series of photos showing what a lens polarizer does over one revolution, in 8 shot increments. The difference from one 45 degree increment to another can be pretty dramatic at a few of the increments, so maybe 22.5 degree increments would be something to try in the future. But this should give you a good idea as it stands.

The photographs were taken off my back deck, across the inlet to all the bays to the South [left of frame] of me [seen here is Huntington bay] around 4pm. They were cropped to 35% of frame, cropping out more of the foreground trees in my backyard above, to the left, and on the bottom of the frame. Focus point was the Lighthouse which is about 2 miles away. The houses in the background are another 1/4 mile further.

Used was my K10D with Sigma 300mm f/2.8 EX DG and the rear drop-in Sigma polarizer supplied with the lens when I purchased it. No TC was used. All shots were taken handheld in Av mode at f/6.3, ISO200. Shutter speed was varied by the camera to keep exposure the same, based on how the polarizer reduced the light more or less as I rotated it around 360 degrees.

All shots were taken within about two minutes, with the same lighting conditions. First shot was with the guide/dot on top of the lens. Next shot was after I turned the polarizer's wheel 45 degrees to the left. Then so on and so on until I made one full revolution in 8 shots.

PP of RAWS done in Lightroom. Landscape sharpening with increased detail setting, high contrast plus some add'l but subtle contrast & brightness curve adjustment. MOST IMPORANTLY, THE WB THE CAMERA CHOSE WHEN IN AUTO MODE, WAS SET TO 'DAYLIGHT' FOR ALL. Use of a Polarizer will cause the camera to change the WB it selected a good deal, and magnify any color cast/alterations the Polarizer creates; most noticeable if you use the unaltered JPGs out of the camera (which is why I am not using them). When I cropped all the images to the same size, I also straightened and re-positioned them the best I could. (Use of a tripod would have been better.) Upon export I resized to 1600 pixels on the long end. They are being shared here resized by the Hosting service Fotki to be 800px wide. You can see the 1600px wide images by clickint the link on each page in the series here:

Aside from the color cast change use of a polarizer brings, much less dramatic as I normalized the WB across all these images, NOTICE THE REFLECTION OFF THE ROOFTOPS OF THE HOUSES TO THE RIGHT OF AND UP FROM CENTER. The latter is perhaps its most important attribute.

Hope this helps understanding what a polarizer can do for you.

(Tho the position of the polarizer dial is only valid relative to the len's rotation, Degree rotation is provided here simply as frame of reference for relative rotation of the polarizer.)

0 Degrees

-45 Degrees

-90 Degrees

-135 Degrees

180 Degrees

135 Degrees

90 Degrees

45 Degrees

Based on the hi-rez images, I think I like the rendering the 90, then -135, then 0 Degree rotation on the polarizer's dial gives me the most...
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06-12-2009, 05:48 AM   #2
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Join Date: Apr 2009
Location: Bath, Ontario, Canada
Posts: 31
Hi: Thanks for this. Certainly the effect on the roof reflections is dramatic. But I am puzzled. I have always understood that a polarizer's effect is relative to its orientation to the sun. In fact as an air navigator I used that effect to determine the aircraft's true heading heading in the high arctic where compasses are not usable and the sun was still below the horizon.

When I use a circular polarizer on my cameras I always use the recommended technique of pointing my forefinger at the sun with my thumb held at a right angle. The rotation of the hand then indicates the plane of maximum polarization. 0 and 180 degrees give zero polarization, 90 and 270 the maximum.

However I am mainly using this approach to deepen the sky tones and have not used it very much to reduce reflections. I assume that the optics are similar and that the same relationships to the source of light would remain valid.
I am heading up north next week, but not to the high arctic, and will study the polarizers effect on lake reflections and leaves.

Thanks again. Hey that is a busy harbour ; no signs of a recession there.

Dick K.
06-14-2009, 12:45 PM   #3
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Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,831
A polarizer's effect is evaluated relative to the reflective surface, not the Sun.

Consider that light is made of waves. Now consider that (simplifying a lot) waves can be vertical or horizontal. Light from a bulb, or the Sun, is made of both those orientations. Some reflective surfaces will reflect light only in one "wave direction" (I'm not talking about where the light will go, I'm saying only the horizontal or vertical waves will be reflected). The polarizer, for its part, rejects one of those directions. So if you rotate it properly, you will be able to reject almost all of the light reflected by such surfaces.

The Sun's orientation will have impact when you are trying to reduce sky haze and deepen the shades of blue. That's because haze is generated by particles in the air, so it's the same effect as the one I explained above, with the particles as reflective surfaces.

Again, this is strongly simplified, but the basics are correct. I hope it helps.

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