I have been pondering for a long while about stumping up for an ND filter and started looking around again for prices etc. One thing I have stumbled across is coatings. I was looking at some B&W 10 stoppers, and they have single coated and multi coated. What exactly does this mean? More uniform light distribution? Better quality glass? From a quick google it seems it is to do with lens flare, but they are generally comparing non coated to multi coated, but how does single coated to multi coated compare?