Hi All, just had to post this image my girlfriend took a few days ago using a Modded 40D and a £120 90-300mm lens, can't believe it came out so nice on such aa cheap lens, that said, the red channel was slightly out of focus, although I found this problem even on my more expensive lenses, guess you just can't beat telescope optics!
Anyway, this image was taken at about 200mm F5.6 59x90s
Daniel
:O)
(http://farm3.static.flickr.com/2674/3727277102_178ff2bb10_o.jpg)
Nice image Daniel.
I have found exactly the same red channel problem using standard lenses with a modded camera. I'm pretty sure the problem is that the lenses are not designed to focus Ha as well as visible light. As proof, older lenses often used to have an IR mark - which showed the adjustement that had to be made to the focusing position to bring IR to focus.
A lens (or telescope) designed for a wide bandwidth will have a different design compromise.
Mark