Tokina 400mm ATX SD 5.6 and Tele-Con

I am thinking about getting a 1.4 teleconveter to use with my Tokina 400mm ATX SD lens on my 30D. Has anyone used one with this lens and which one would be the most compatable? Did Tokina make a tele-con? Thanks for your help.
Clay

You'll lose AF and probably not gain a ton over cropping.

Thanks for the advice. Maybe I'll save up for a Tamron 200-500 or Sigma 50-500.

I dunno, is 400 vs 500mm really that much? It's 20% like the difference between 40 and 50mm. I would think you would be just as well off cropping.

The Sigma 50-500 and Tamron 200-500 should not be in the same sentence. BIgma is much better.