Or stretch to the 400mm f2.8 for a better contest.

Getting back to your question I'm debating the same choice and think I'll go for the 400m and use a 70-200mm f2.8 with a TC to get the in between ground.

Choccy...

Are you saying that the 400 2.8 is not so good as the 300 2.8 ? . Just interested because I have not heard of any birders using the 400 2.8 before, apart from costing almost 5k it weight 5.37 KG - not a ideal walkaround lens.

Trouble with these big lens you need a tank turret to mount them on :rolleyes:

I know this is an old thread but as I recently got the 300 f4 IS and alread own the 400 f5.6 I thought I'd dig it up (just in case anyone is still pondering). I've had the 400 f5.6 for just over a year and love it, the focusing is very fast and the image quality is excellent (alomst on a par with a 500 f4). People often quote the minimum focusing distance as a negative, but when shooting birds I have yet to find this to be an issue, even at MFD a bird like a robin will be almost frame filling. However for butterflies/dragonflies the MFD can be an issue, which is why I've picked up a 300 f4 (which is also handy at a feeding station). I used to use the 100-400 IS and although it's a good lens for me it would come in third after the other two options. The 300 f4 is definitely more versatile than the 400 f5.6, but if I could have only one it would be the 400... I reckon it's the best walkabout lens for birding available. Here's the reason I love the 400 f5.6...

I agree with Pete,in the prev post.The 400F5.6 is an amazing lens,lightweight,quick to focus,easy to handhold,and a good price,most important.

100-400mm 5.6 for flexibility
400mm 5.6 for ulitmate sharpness in a lightweight lens
Both lenses have a pretty big following for reasons above

RE; bigger glass....there's no real substitute for a nice bright 2.8 aperture, but try hand holding and panning with one before buying. Some get on with them....some don't. No sensible person really 'wants' to handhold a 2.8, but the results justify them (particularly in lower light)