Filter study.. help.

I got my filters and adapter today. I must say that this lensmate 52mm adapter is top notch - fits snug and color appears perfect.

Anyway, I took a couple shots of my boring backyard with nothing, then the hoya uv, then the hoya uv and hoya linear polarizer. Shutter was at 1/250 in all, but I noticed that I had to drop the f down from 8.0 once I put the polarizer on. At 6.3, the picture still appeared a bit too dark. At 4.0, the picture looked almost as if I hadn't used the polarizer at all. The sun was to my left, and I rotated the dot counter clockwise to the sun. Am I using it right (I am new to all of this).

The pictures can be seen here, but don't mind the rest of the page as I've just started building it. Thanks.

http://www.hypokondria​k.net/filter_study.htm

Polarizers cut down exposure from 1-2 stops. So, your stopping down from f8 to f4 (2 stops) sounds about just right.