Well, I have owned the really great 100 - 400 (F4 L IS - the old faithfull) and the first version of the 70 - 200 L IS 2.8. Currently have the 70 - 300 L IS and am missing the 400 reach for birds with motion - hence the need for speed. I still have my old but true 40D. I was wondering whether to go for the Sigma 120 - 300 F 2.8 or the second version of the 100 - 400?
I know - it is not yet out. I could not get a grip on the push pull. The IQ tests (according to Digital Picture) show the sigma @ 400 (with extender Y 1.4 (is it as good as the Canon 1.4 version III)) is better than the old 100 - 400.
What does one do? (said with plaintiff, heart felt voice to Canon guru's hoping they will help me with a lens of my choice(a 100 - 400 not push pull with better performance than the first version hopefully constant F4)).
I like the "black" look of the sigma. Specs are good also (just like their specs on the new 18 - 35 (something F1.8 (Sigma are becoming even more of age)).
The new 70 - 200 2.8 L IS (version II) with a 2x converter according, to the Digital Picture, is still not as good as the sigma with a 1.4 x TC.
Canon 100-400 (new version) have not seen a price nor a spec but I expect it will not be a dollar under $2.9k.
May have to go for the Sigma.
What are the considerations?
I have the gear to cover the wider world. I want something with longer reach and better IQ so when I cannot get too close to those very teeny weeny birds, I can still get a good image filling an A4 print.
And yes, if I were to change the old 40D for another!!! But why? 6.5 fps, solid body, reliable. I may get more resolution with another camera. But when is the next 7DII coming or even better, when is the 3D (yes 3D:) going to appear. Now that was a camera! Still have mine: and film. Remember that stuff. Acid, paper, dark rooms, magic appearing before your eyes.
Canon must be reserving the 3D name for something exceptionally good.