Originally Posted by
dje
Joe the best form of GND filter system to use is one using square filters that slide into a square frame. They come in various sizes from 67mm to 100mm. You need to buy a system which comprises a filter holder, mounting adapter to suit the filter ring size on your lens, and one or more GND's of various types (1 stop, 2 stop, 3 stop, hard or soft grad etc).
Cokin are a popular lower end brand but the more you pay the better they are. Eg Lee are very good but expensive. Formatt/HiTech are the ones I use and I guess these could be classed as mid-range.
However there is one important proviso - you need to be using a lens whose front element doesn't rotate with focus change. I think your EF-S 18-55 does have a front element that rotates so it would not be a candidate for GND's I'm afraid.
Dave