The difference is that an ordinary ND filter is a solid gray all over, whereas a graduated ND (GND) is clear on one half and gray on the other half (often with a soft transition in the middle). You use an ND for slowing down your exposures, for example, when you want to get motion blur in bright sunlight. You use a GND for situations where there is a large difference in brightness between one area of your image and another, for example, if the sky is bright but the land is shaded and you don't want to either blow out the sky or black out the land. You place the gray part of the GND over the sky to dim it, and the clear part over the land so that it won't be dimmed, resulting in a nice balance.
For GND filters I recommend Cokin P-series filters, which are square pieces of plastic that require a Cokin P holder and an adapter ring for the filter thread on your lens. This has the advantage that the transition area in the GND filter can be moved up and down to be right where you need it.
For ordinary ND filters, Hoya's multi-coated filters are a good balance between quality and price. B+W filters may be better but are more expensive.
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I am not sure the difference or what they will do for me.
For GND filters I recommend Cokin P-series filters, which are square pieces of plastic that require a Cokin P holder and an adapter ring for the filter thread on your lens. This has the advantage that the transition area in the GND filter can be moved up and down to be right where you need it.
For ordinary ND filters, Hoya's multi-coated filters are a good balance between quality and price. B+W filters may be better but are more expensive.
Got bored with digital and went back to film.