Great pictures all!Yes. I was taking pictures of Ospreys near the river just before, during, and after the morning golden hour. Before and during golden hour, I was fighting the speed of the lens because I did not have enough light to nail sharp shots of the constantly moving birds. The f/2.8L IS II would have been perfect.
I've a small question, as this is the f/4 lens and you all have it. Do you ever run into situations in which you wish you had the even wider 2.8 aperture version? If so, what are those situations? Because the DOF from these pictures just looks great as is, and I find it hard to find examples where f/4 wouldn't bring enough. Thanks!
That said, my Osprey shot (above) was taken hand held after golden hour was over, with my arm extended out to get a clear view of the squawking bird, which was partially out of view. I would not have been able to get this shot with the f/2.8 because of the precariousness of how it was taken and the weight of the f/2.8. The f/4 was the right lens for the shot.
As a result of this experience, I got the f/2.8, and I decided to keep both lenses in my bag because both are amazing.
Yes, there are instances where I also wished I had a bigger aperture lens, but it was never for thinner DOF. Like scrappydog mentioned, there are situations where a bigger aperture lens would have enabled you to use a higher shutter speed. Even though your f4IS at 1/40 will deliver sharp results, it cannot help you freeze your subject's movements , you need bigger aperture or higher ISO for that. Since most of the current cameras are capable of producing cleaner pictures in higher ISOs, it won't be a bad decision to go for an f4 lens considering its price and weight advantages.
Apart from brighter viewfinder, there is another advantage of having a max aperture of 2.8, even after fitting a TC you would still have a reasonably faster lens(98-280 f4 with 1.4x or 140-400 f5.6 with 2x). 70-200 2.8 and 2x combo will autofocus in all bodies but f4 and 2x will autofocus only on 1 series(except 1dx as of now) bodies.
On the topic of DOF, it is not dependant on the aperture alone, focal length and subject distance also affects DOF. It is possible to get narrow DOF even at f8 if you are closer to the subject or by using a longer focal length. If you don’t want to move closer or change your focal length, you still need to use bigger aperture to get thinner DOF.
Having said all this, I would get 2.8 only if the prices are the same:).