The auxiliary push-on. It's big. But in theory you only lose the 3 or 4% light of the lens-surfaces, and only add his own faults. But, alas, these are big: strong vignetting, and it is not aplanat for sure. And my Sun doesn't fit properly, I have to use felt packings. 23 Febr 2012 I solved this problem with mastic silicone kit (!) Look also flickr photostream erwinruys.
So: the pictures are mùch better without - but the looks! Impressive!