Hi, I'm thinking of getting a ND graduated filter to improve my landscape/travel photos. I have the Canon 17-55 f2.8 with a 77mm thread. I also have the 10-22mm which also has a 77mm thread. The choices on Adorama are overwhelming. What are a couple of recommendations that will at least work well with my 17-55? (If it will work with the 10-22 that's a bonus but not essential). Should I get something threaded, or drop-in? ND.6? Here's an example... http://www.adorama.com/TF77CGND6X.html Thanks!