Hey folks, I just ordered a set of formatt/hitech ND grad filters (.3, .6, & .9). Now, how does one use them? I get the gist of it. You use the DoF preview button and line up/rotate your filter along the horizon. But what if you have stuff that pops over the horizon line, like in this pic... http://patricksmithphotography.com/photoslarge/070211-2361-940.jpg The rocks overlap the horizon line. Why aren't the rocks darker where the fitler would overlay it? He doesn't claim to use 2 exposures, so how is this accomplished without some photoshopping?