Here you go. Christain Buil has measured the Canon 350D built in IR/UV block filter and this gives 19.5% transmission at H-alpha

http://www.astrosurf.org/buil/350d/350d.htm

Meanwhile I've looked up Astronomiks transmission graphs for their filters and a replacement astronomical UV/IR filter gives 95% transmission, while the restorative filter (OWB) takes this back to 30% for H-alpha. I've superimosed the charts to allow you to see this

The H-alpha line is the second from right green spike. The grey area is human eye sensitivity by wavelength (human eyes don't see H alpha well - unless its very bright e.g. observing the sun via solar H-alpha filters). The strong red curve is the astronomical UV/IR cut filter, the paler one is the OWB restorative WB filter