Variable or "Fader" ND Filters

[daveake]

Does anyone here use them? They seem a bit on the expensive side (£50+) for what I assume is a pair of polarizing filters stuck together.

At the moment I carry an ND8 for doing slow exposures but in bright light that's not enough. A stronger filter would be better but then it might be difficult to actually see anything through the viewfinder! Hence I'm considering getting a fader so I can compose and focus, then spin the filter to get the ND level I need.

[SamHH]

I think there are problems with using them at short focal lengths: you get a black cross in the middle of the frame. That has put me off them.