How do I use a CPL (polarizer)?

Contrary to my name I really have no clue how to use this thing.

I get the whole 90 degree to the sun using my hand as a gun kinda thing... but what I don't get is why the filter turns? Why would I rotate it?

CPLs are adjustable. Sometimes you don't want/need maximum polarization.

How do you know when it's at max polarization?

It depends what you're doing. Look through the viewfinder or Live View and watch the reflections (if that's what you're trying to prevent). Since my CPL wasn't marked, I mounted it, and held it in front of my computer's LCD monitor and took note of what happened as I rotated it. At full polarization, it looks black. You can use a white-out pen or something to mark that point on both outside rims of the CPL.

I just rotate it until I get the desired effect.

When you think it might help, put it on the camera and rotate it as you look through the viewfinder. You'll either see a change as it turns or be in a situation where it won't help. If you see changes when you turn it, keep going until you like what you see, be it deep blue skies or reduction/enhancement of reflections from non-metallic objects.

crn3371 wrote in post #14147182
I just rotate it until I get the desired effect.

+ a gazillion!

On a more serious note.., Don't worry about 90 degrees to the sun, throwing salt over your shoulder or finding a pair of ruby slippers.

Point your lens, with polarizer mounted, at something with glare. Metal or windshields are very good for this. While looking through the viewfinder, turn the filter until the glare or reflection is minimized. You've now adjusted the polarizer for optimum effect.

Set your exposure and start shooting.

Enjoy your polarizer!

Polarized wrote in post #14146562
Contrary to my name I really have no clue how to use this thing.

I get the whole 90 degree to the sun using my hand as a gun kinda thing... but what I don't get is why the filter turns? Why would I rotate it?

Polarized wrote in post #14146813
How do you know when it's at max polarization?

You need to be careful when using a polarizer. First off, its not the type of filter that you want to keep on your lens 100% of the time. Second, you may not always want "max polarization" dialed in...there's nothing worse than looking at an image with a sky that has been over-polarized (the navy blue color is usually the giveaway). You should be judicious in how much polarization you dial in...think of it as "season to taste" in cooking terms. Rotate until you have the desired effect.

Also, when looking through the viewfinder, be sure to rotate the polarizer in a counter-clockwise direction...this will ensure that it won't accidentally screw off from the lens and fall to the ground (or in the water).

In addition to adjusting the strength of the effect, rotating the filter can adjust where the effect occurs too. If photographing a car, for example, the subject comprises many angles so, at one point of filter rotation, you may kill reflections on the bonnet and windscreen but leave the reflections on the side of the car. Rotating the filter can then move the area affected to kill the reflections in the side windows and bodywork but bring back the reflections in the windscreen etc.

The simplest way to understand what it is capable of doing, is to stick one on your lens and look through it while you play.

When I was using a CPL recently what I saw through my viewfinder looked great but the actual picture was not, it did not make much sense to me.

dsblk93gt wrote in post #14243776
When I was using a CPL recently what I saw through my viewfinder looked great but the actual picture was not, it did not make much sense to me.

In what way was it different? Don't forget that you look through the viewfinder in real life, an image is affected by exposure and other settings.