Common ND filter

In an ideal world, you'd have a set of ND filters that would give you anything from, say, one to six stops of ND. This isn't always practical though, would be expensive and sometimes isn't even necessary.

You need to consider both the kind of conditions you like to shoot in and what kind of stop you like to shoot at (as well as the native ISO of the camera - the Alexa at ISO 800 would need more ND than an original RED One at ISO 320).

If you like to shoot on sunny, snowy mountains at f/1.4… good luck to you. If it's a typical overcast British day and I wanted to shoot at f/2.8, I may only need two or three stops of ND.

My advice would be to see how much light you have where you want to shoot, and work out from there what would be most useful.