Using a Canon T3i with full-spectrum mod and IDAS UV/IR cut filter?

Hi Rudy and congrats!

Now, I'm not a narrowband guy, so take my advice with a grain of salt.

For Ha, you don't really need a filter.  Just pull out the red channel from the t3i image and that should be sufficient I think.  Hb does tend towards blue, but if it's just Ha, then the red channel is all you need.  Note that the reason these cameras are modded to capture more Ha is to extend the light transmission into the deep red.  One caveat though, red tends to pull a bit more than just Ha.  If you want a very well defined Ha band, then a narrowband filter would be the way to go, since it limits the bandpass to just a portion of the Ha band.

Bloated stars.  If you use an uv/ir cutoff filter like you mentioned, you should be ok, the stars should be no worse than with an unmodded camera.  However, for very tight stars, a dedicated Ha narrowband filter (like say a 5nm one) will produce smaller stars simply because it cuts off any starlight outside the band.

3.  Yes.  You can either use a front mounted filter (like a 2" ) and use one band at a time.  Or, you can try one of the more expensive filters like the triad series (three or four band) which are multiple bandpass.  The difficulty with those is separating the narrowband channels afterwards.  I believe someone has created a color mapping action though that makes that process easier.  The advantage of those multiple bandpass filters is that you image all bands at the same time, which eliminates filter changes (and refocusing) and also uses all the pixels in the camera at once, since the different bands show up in different colors.

Hope this helps.

Daniel

Glad to help Rudy.  Looking forward to even more awesome images from you.  Loved the ones you've been posting on CN.

Daniel