You cannot get a better lens than any Canon Super Telephoto. These have a Fluorite element and ED elements. You also have to pay a premium price. There is no cheap alternative. Even the top Nikon lenses can be dissapointing in their performance for astro images.
I know I am slightly biased. Any zoom will give major CA. Only very good primes may give a reasonable image. When I see an image as good as this from any brand of lens other than Canon, I will be werry werry quiet. Kill the wabbit?
http://avandonkbl.bigblog.com.au/dat...1124131416.jpg
http://avandonkbl.bigblog.com.au/dat...1124131416.jpg
Bert