I found this filter to be as good as the Lumicon UHC, but much less cost.
(#05656 Asking $85, normally $129) + $7 Shipping (includes insurance)
Dramatically Improves Views of Emission and Planetary Nebulas
Screws on the the back of your SCT. Excellent condition. Used five times and kept in sealed case. Takes advantage of SCT visual back's threads and works with both 1.25" and 2" accessories and eyepieces.