I need some advice on buying GND filters. I have never used any GND filters before. To get ready for some landscape photography I have been reading about them and as I understand, the reason my skys are always washed out is that I am not using these filters. I need to get some advice from those who use it regularly as to what brand and what different strengths (stops) I need to have to cover most situations, without spending a fortune. The only filter I currently have is a Hoya CL polarizer filter.