It's a nice image for sure, great job! But frankly I think even the lowly Rebel T3 might (emphasize might) have grabbed and locked in servo mode with such a large slow-flying bird against a bright sky like that, even with an STM lens. Cheetahs are a farrrr different story though!!
Do you find the 200-400 / 1DX able to servo track equally well for subjects moving away from the camera really fast (such as a running cheetah), as it can for when they're running toward the camera?
Hi CarlTN, your right of course, in the conditions I shot this Eagle you could have used pretty well anything, either lens or Body, my son was using a 6D on a 70-300L & got as good (I can't say better considering the difference in gear value and my Lads ego & my own). BIF etc are targets of opportunity, I rarely shoot them, although I have a mild fascination with Vultures, again, that's likely because they're big & slow & make the job easy.
Shooting a stooping Eagle with a 600f/4 + 1.4x Converter and getting sharp Images takes some real skill, Gary Samples Images spring to mind when discussing this particular subject, sharp & Beautiful.
I've owned the 70-300L since just after it was released, although I think it's an excellent Lens, Sharp & not heavy, I often found I'de leave it at home in preference to the 70-200f/2.8 L II and that Lenses ability to utilise the 1.4x converter. Now my Lad uses the 70-300L almost exclusively & just loves the Lens, he produces some remarkably good Images from this Lens on the 6D, on these trips with me to Africa he pretty well uses the 6D + 24-70F2.8 L II plus 70-300L, that's a pretty light load in the backpack considering I generally travel with 2 x 1Dx Bodies, 70-200f/2.8 II, 200-400f/4, 600f/4 II & 300f/2.8 II.
My only concern with the 70-300L was not being able to utilise the 1.4x on it, I think Canon made a small error of judgement there, my Lads Images would tend to say no, he does well with his lighter less expensive package. The combo 6D + 70-300L though is not likely to get some of the faster action shots though when compared to the 1Dx + 200-400f/4.
The 200-400f4 is an absolutely wonderful Lens, if I had to have just one lens this would likely be it, 300f/2.8 L II might squeeze it out on sharpness/weight etc, but sheer versatility, the 200-400f/4 is hard to beat.
On Servo Tracking the 200-400f/4 & 1Dx will track just as well in any direction, including away from the Camera, when tracking Cheetah you will loose Lock if the Animal goes behind a Bush or Tree, but I rarely have to Manually re acquire focus lock, in 90% of cases the Lens/Body automatically re acquires, amazing technology in these modern cameras.
But, as I've mentioned in previous Posts, you can get sharper Images at 200/300/400 & 600 Using Primes (I've never owned the 500 so I can't speak for that Lens, but from what I've seen it's in the same Class as the other Large Primes), there's very little in it, but the Primes I feel do provide the marginally sharper Image, but the versatility of the 200-400f/4 makes this Lens almost Magical (taking a word from Steve Jobs when describing the iPad).