Circular polarizer + UV Filter?

[Axis]

I just purchased a circular polarizer and I took off my UV filter to attach the CP, is this something I should be doing or should I just leave that UV filter on there as well? I'm thinking going through one less plane of glass is better over all but does it really matter?
Using the Polarizer on my Canon 72mm 18-200 lens.

[dakwegmo]

The UV filter will hurt more than helps when stacked with the polarizer. On the wide end of your lens you'll likely see some serious vignetting and as you guessed, image quality will likely be reduced overall with two extra pieces of glass. If you want to keep a filter on all the time, I'd stick with the UV and only switch to the CP when you need it.

[dcclark]

The UV doesn't do much at all. It's only useful (on digital cameras) to physically protect the front of the lens. It doesn't help with filtering UV light, because the sensor already does that for you.

So, keeping the UV filter on does NOTHING useful if you already have a CP on there -- the CP takes over to protect the lens (and does cool stuff as well). As dakwegmo mentioned, it will cause more trouble, too, because of vignetting.

[LeeR]

Don't forget, however, that your CP uses up 1.5 to 2 f-stops; not a big deal if you are shooting landscapes, but a killer if you are trying to shoot a basketball game.