am i being silly ?

[knocker]

i have the feeling i'm confusing myself, i currently have a sigma 70-200 f2.8 and have a 1.4x tc on it's way, however, i am not sure that this setup will be what i want (1.3 crop on my 1dmk2 and 1.6 on the 40d) for my motorsport/wildlife/planes etc (i also have a thing for fast moving things of any description) so i am thinking canon 100-400 L IS 4.5-5.6 for the extra reach but thats a big difference from f2.8 to f4.5, now i have come across the
Sigma 120-400mm f4.5-5.6 APO DG OS HSM for half the price of the canon which i could possibly use the 1.4x with............any help in deciding would be appreciated

 

[Bawbee]

You're not silly but stick with f/2.8 for speed.

 

[Mr_Sukebe]

If you're shooting fast moving objects, good AF is pretty much a pre-requisite, and whilst your 1D will certainly help, a non-Canon lens might not perform aswell as a dedicated Canon unit. Don't get me wrong, I've zero experience of the big Sigma you mention, having said that, most non-Canon lenses tend to AF worse than their Canon equivalent.

 

[ppp]

Get a Sigma 100-300 f4, then you can couple it with your 1.4xTC if required to give 420mm max

 

[sportysnaps]

lenses hold their value very well so invest in the best quality you can afford, and buy a lens for a purpose, not as a jack of all trades.

for the best AF get a canon prime lens 400mm f5.6 / 300mm f2.8 / 300mm f4

many wildlife photographers swear by the 100-400mm but you need good light. in lower light the sigma 120-300 f2.8 is a good option, but is heavy, and slower to focus then a prime lens, but should be faster then the 100-400mm.

 

[david1701]

do you need the reach, with a fast lens you will have a lower iso, that way you can crop more, what about going for the 70-200 f2.8L ?

 

[KIPAX]

so i am thinking canon 100-400 L IS 4.5-5.6 for the extra reach but thats a big difference from f2.8 to f4.5

but the 1.4 on a f2.8 lens will become an f4 so not much of a leap..

 

[HoppyUK]

If you need the reach, you need the reach. Whichever way you go about it, you won't do better than f/5.6 with a 400mm zoom.

Basically, the choice is between the Canon 100-400mm L and the cheaper Sigma. If you can afford the Canon, get that - it will hold its value well. If the price is too much, then the Sigma. They will both take 1.4x extender quite well, and will even AF on your 1D2.