Just to add my two cents, keep an eye on EBay. All sorts of otherwise hard to find items show up there. As for my preference, I always preferred to put the gel type filters above the condensor. It goes in the drawer, is out of the way and not on the floor (I am a klutz), and if the filter is not in perfect shape, at least it is not in the image path. You can use the hard below-the-lens filters and I have used them, but you have to be more gentle in your handling of them. I did try using "wrong brand" filters for different papers, and the results were less than good. Using Ilford filters with Kodak paper gave me flat, low contrast, "muddy looking" prints. Popping in the Kodak filter, everything was fine. So, if you use Kodak filters, use Kodak paper. If you use Ilford filters, use Ilford filters.