As a part of my new years resolution to become a better photographer I went to photography shop and purchased a Neutral Density filter. My hopes are that this will improve photographs that are taken in low light and cloudly contions. The only filter I purchased was a +2. I plan to add the the rest of the filter values once I learned to use this filter better. What other light conditions are approriate to use the ND filter and what F-stop and shutter speeds should be used in suck instances? Also I learned recently that I can screw one filter on top of another yet I don't hear much about this what other filter should I use with the ND filter, I was thinking maybe a polarizing. I've also been trying the understand the differences between a graduate neutral density and a neutral density filter if there is one.