In this EDU I'll try with the best of my knowledge and limited photos to show you the effects of circular polarizers for your photos... In these examples I'll be showing you Automotive use, and Water use... Circular Polarizers, also known as CPL's allow only certain light rays to pass through it. Depending on the orientation of the filter, it can reduce glare, make greens and blues more saturdated against each other, reduce reflections on water and automobiles, and also can be used as a neutral density filter. CPL's generally have two rings, the threaded ring that threads into your UV"lens protector" filter, or straight onto the lens if you have no UV filter... The second ring allows you to adjust the effect the CPL has, on most Point and shoot cameras you can see this effect via the LCD screen, and on SLR/DSLR you can see it via the viewfinder. note: The CPL should always be the very LAST filter you place on your lens, with the exception of the lens cap (meaning Lens -> UV -> CPL - > CAP ). note 2: When shooting in semi auto or automatic modes (P, TV, AUTO) your exposure will be decreased by a few stops of the aperture, in AV mode your shutter speed will be decreased with a CPL on in low light conditions, in very bright conditions it still may stop it down a bit, but usually not as much. I have posted, above the photos, shooting information. I took the car and mirror photos on Manual, 50mm F/2.0 1/200 at iso 100 The pool was done on P mode - filtered - f/4.0 1/200sec iso100, and unfilterd f/4.5, 1/250 at iso 100 here are some side by side examples of what a CPL will do... With a Car - Reflections greatly reduced, glare greatly reduced, while not 100% gone is a a lot better than normal, you get more paint color than sky. This is especially useful when photographing vehicles in all conditions to reduce background glare, and if you are trying to capture the driver you'll be able to better do so by reducing the glare on the windows... (Paparazzo use this to capture celebs in their cars during daylight hours as it allows a direct through view in most cases) again with a vehicle description.. This is a side view mirror on a GMC Pickup, it's picking up the reflection off of the vehicles window, which is of my neighbors chimney and antenna.. With the CPL on, all it shows is the deep black of my tint. And in this one, a pool... With filter you can see into the water and the floor of the poool better than without the filter... this can be useful when photographing people in the water, fish, animals, etc. A CPL can also saturate sky/trees a lot... Example WITHOUT CPL: EXAMPLE WITH CPL when taking these I turned the CPL to its MAX effect for the greatest difference from filtered to unfiltered Any questions/corrections?