I'm considering whether or not to get an expodisc to use with my D2X. I'd welcome to advice of more experienced people. I notice the price has recently dropped a little in the UK. I always shoot RAW, so I know I can adjust white balance in post processing, but I also know most people advise trying to get it right in camera. I use almost exclusively 17-55DX and 70-200VR, so one 77 mm expodisc will cover both. So what's the consensus? Worth it or not?