Field flatener & H-Alpha filter question

[axle01]

Looking to get a good quality field flattener and a H-Alpha filter for a ULT United Optics APO 132 triplet http://www.astronomyalive.com.au/astrophotography/astrophotographic-telescope... (http://www.astronomyalive.com.au/astrophotography/astrophotographic-telescopes/united-optics-ult-132-triplet-apo-refractor-telescope.html)
Any advise would be appreciated.

Alan

[Chris85]

Have you tried the one they offer down the bottom of the link you gave?
"* Option - Field Flattener 68mm for advanced astroimaging"

Chris