Any particular reason why you haven't gone with the CLS CCD? the UHC is made for visual use primarily
http://www.astronomik.com/en/visual-...hc-filter.html
my understanding is that it won't work well under f4 (f3, f2) i'm not sure how bad it would become however. the filter doesn't have an IR cut so it may impact upon colour. the cls ccd does - i am also not sure why you would not just use the filtered version in entirety vs unfiltered... the concept is a bit different to introducing Ha to an image?
cheers
Russ
ps is your camera modified?