Maybe the following
Canon EOS Insert Filters (
http://www.telescope-service.de/filt...OS_Klemmhalter ) might be a better option than the Baader style front filter change overs for DSLRs that involve pulling the DSLR apart and which radically change the colour response of the DSLR when used for happy snaps and NORMAL photography ?
.... when I get my 40D I just don't want to go there .... and will take a lot of convincing unless Telescope-Service come up with a AS EOS Korr that suits a 40D.
If I do a mod , I will be sending tbe body to Baader to get the job done PROPERLY !!! That's a big IF. I don't want a $1500 camera stuffed up by an incompetent camera mechanic or my warantee voided.
See below for what's involved with a 350D , I imagine similar for a 40D.
http://www.astrosurf.org/buil/350d/350d.htm
and Baader's information on this process
http://www.baader-planetarium.de/dow...non_dslr_e.pdf is not cheap , 395 Euros + insured traceable postage both ways.
The filter transmission curves here http://www.astrosurf.org/buil/filter...Badder%20UV/IR are interesting , I am looking for the curve for the standard canon 40D front filter (anyone seen one somewhere ?)
If the 40D front filter transmission curve the same as the 350D (or 400D) curve (which passes 25% of Halpha that falls on it , so matched up with a Lumicon Deep Sky Filter or a Lumicon Halpha Pass Filter (and longer exposures ((2x longer), or a suitably higher chip speed setting (2x higher ISO) because only 1/4 the Halpha is getting though the standard canon front filter) will still give a nice response in deep sky photos - I would think.) see graph for standard 400D filter and Baader filter.
http://www.telescope-service.com/baa...anonFilter.gif
Halpha band is very narrow .
My 40D will be used not just for astro imaging.
At this stage I am leaning more towards a 2" Lumicon Halpha or 2" Lumicon DEEP SKY which will be cheaper and I can attach it to the front of my coma corrector , so I can use them with my Minolta 35mm SLR too , and later if I decide to go there later on , with a dedicated CCD imager (one of those SBIG or similar jobs) as well , and I suspect will be just as good at bringing out those nice red gas clouds.