I have just tried a Baader 2" fringe killer with my 4" f/10 Vixen achromat, but the color correction of the achromat is so good that the filter doesn't provide enough improvement to justify keeping it. The filter is like new in box. These go for about $93 shipped new. I am asking $83 shipped. I can take pay pal but add $3 for their fee. Thanks for looking, Bob.