I just returned from my annual windsurf trip to Baja. This was my first trip with a canon DSLR (EOS 30D) using a 70-300 canon IS zoom with or without a tamron 2X doubler. The focal lengths 140-600 using the doubler were about right (most shots between 250 and 600, with 450-600 being the most common). I loved the camera, and I could get much better pics than with the point and shoot olympus I have been previously using.

The one problem I had is that the autofocus doesn't work with the tamron doubler (2X). When i returned from the trip, I investigated the canon 100-400 zoom, hoping that I could pair it with a 1.4X teleconverter. Apparently, this just exceeds the limits for auto focus to work.

So--I would really like a zoom with a 200-600 range, but I also really like autofocus. I do like image stabilization as well, but it may not be necesary as most of the windsurf pictures will be in bright sunlight. Small and light is also a big plus (a nice feature of the 70-300 mm lens) so I can go handheld.

Any recomendations about how to proceed would be appreciated.