I purchased some Schneider 4" x 4" ND filters from 2Filter for my medium format camera that I was shooting last weekend. I am amazed at the quality of the filters. Sure, they are darn expensive! I think it is safe to say that you get what you pay for with filters. I agree with Neuro to avoid using variable density filters. I've not had good luck with the ones that I have tried using with my 1D-X.