I'd suggest looking at the Amazon user reviews for each of those brands. I can tell you that Sigma stands out most out of the brands that you listed. Don't expect very good A/F per... http://www.quora.com/Which-is-the-best-500mm-lens-...
It seems that most of the regulars are not used to recommending third party options. Pity - it's the best way to go on your budget. I did a quick check of the selection at B&H and ... http://answers.yahoo.com/question/index?qid=200809...
Bryan, You can't adapt Canon FD or EOS lenses to Nikon F without physically and permanently altering the lens. There may be adapters with optical components that should allow you t... http://answers.yahoo.com/question/index?qid=201101...
