Ok I'm a little confused. I did some research but can't come up with a solution. I was under the impression that NDG filters helps compensate the loss of sky or ground detail depending which area your exposing. But apparently a circular polarizer does the same thing? I'm confused at to what the difference between these two filters are and their purposes, and if I need both. (I only want a filter to help maintain strong sky detail). Filters for flare/uv/etc I could care less about.