The figures I have seen the Canons (10D/300D/350D/20D etc) allow only 20-25% H-Alpha through. The 20Da allows nearly 70% through and a Hutech moded camera close to 100%. So the improvement is 40% in H-Alpha from a 20Da to a hutech 20D.
Bert, yeah the sensitivity of these cameras is suprisingly good. Have you seen these H-Alpha shots with a modded 20D that were just posted on Digital_Astro?
http://tinyurl.com/bujmr
Now whats this about you loaning your 300 2.8
?
Terry