MrFotoFool said:
Both the Canon and Nikon version are soooo expensive, I have a hard time figuring why anyone would buy one (as opposed to say a 500 f4 or 400 f4 DO or even a 300 f2.8 with external extender). I have only seen it in person one time myself, by the San Diego Zoo staff photographer (at their sister facility San Diego Safari Park).
The Canon 200-400 with internal extender is the lens I dream of
It is a perfect telephoto zoom, because if you wear two bodies, 70-200 and a 200-400 + internal extender, you can shoot any telephoto FL you need without a lens swap. The alternative would be to take a 100-400 on one body, and a big white on another. But a 100-400 is not nearly as good as a 70-200 at the short telephoto end, and some big prime with or without an extender is not nearly as flexible as a zoom that can cover that whole range, and also probably leaves you with a gap, for example, between 400 and 600 (which is a big gap).
Also, not being a super pro, the one (and only) time I've used a big white prime, I had trouble finding, tracking, and composing my subject at 600mm. Sometimes, it's just easier to zoom out a little and rely on cropping in post, in order to capture the subject, if it's moving, especially when the movement is erratic (a hockey player, for example, as opposed to a race car). I'm sure this would be less of an issue for someone who uses super telephotos day in and out though.
But yes, the price is prohibitively high for me -- or at least impossible to justify, for taking pictures of birdies that nobody except me will ever care about. It's hard to imagine a time when there won't be something that's a higher priority for me to spend $10,000+ on. Then again, there are years where I've spent more than that on photography, or other hobbies (though not on a single item).
It is possible, I suppose, that I end up buying one, one day, just to cross it off my bucket list
Then I can sleep with it curled in my arms... my preciousssssss.