100-400 or 400f/4 or 300f/2.8

I do a lot of walking in jungles and forests where the lighting in marginal at best most of the time. I was using a 100-400L IS (w/7D body). But needed more reach so tried adding a 1.4TC. Problem was I lost AF once past f5.6 and I really need AF with my poor vision. Next tried a 500f4IS+1.4 this was great ...700mmf/5.6 fast AF and super IQ but too heavy to carry with big tripod and ballhead for 1-2 hours. So I'm thinking about getting a 300f/2.8IS because to get the flexability of a fast lense at 300mm or for more reach add a x2.0TC keeping the AF (f/5.6) at 600mm. This setup is lighter in weight but is it hand-holdable? And how good is the IQ?

Anybody else in this situation or have comments?

Have a quick search in the lens samples thread, I don't think you'd go wrong with the 300 at all. Its easy to carry with the right strap all day long.

I run around with the 2x on it about half the time, and I think I'm getting pretty decent shots.

The lens produces arguably the best IQ Canon has in the lineup.

I carry the 300 & converters all day in my backpack when traveling. A very versatile set up. As for weight, that is the max I am comfortable with.

I bought the 400 DO for the same reasons, I travel to Costa Rica several times a year. It is an awesome lens. Works great with TC, I use the 1dMKIII.

Although the 400 is lighter and smaller I think the slight extra of the 300 is worth carrying, increases your range with TCs and the 400 will never be a 2.8 lens....but the 300 makes a superb 420mm f4! Thats my choice....but I got one so i am biased With a 2x you got one hell of a 600mm lens and with both TCs....I still get keepers.

300mm f2.8 has f2.8
can do 420mm f4 and probbaly same quality as 400mm f4 DO. I never tested DO
Can do 600mm f5.6 which is real real good at f8 if needed.

300f2.8 all the way.

+1 on the 300mm 2.8
I have seen on many reviews saying the the 300mm 2.8 is sharper then the 400mm DO comparing both the 300 with a 1.4 and the 400 native.
I would get the 300!

I went with the 300 instead of the 400 because I can always increase focal length with TC's but I also got 300 when longer focal lengths are too long. Plus the af on this thing is fast! I am able to handhold it without any problems. I also have the 100-400. Was planning to sell it but decided to keep it for times when the 300 would be too much to carry around.

Yes, the 300L 2.8 is one of the Canon sharpness super telephoto lenses. If you want soon, try the Sigma 120-300 F2.8.

definitely go with the 300 2.8, one of canon's best
you have 2.8 when you need it, super sharp wide open
works very well with both 1.4 and 2.0

i tried 400 do f4 and wasn't impressed, price quality not the best option.

With Micro adjust AF I find the 300 @ 600mm wide open is sharp, stopping down only helps a little in my case. With the 1.4 TC the is no obvious loss in IQ....to this I will swear my life!

Didn't consider the 100-400 ... try it in the past and I'm one of those that didn't get on with it.

I've got the Bigma 150-500 and its OK (IMHO on a par or better than the 100-400) ... but I'm now craving IQ and the 300 2.8 + tc's will be my setup shortly.