That looks like a push-pull zoom, but the hood is wrong for it to be the 100-400, so my guess is the 28-300L.
When I read "28-300L" I thought that must be a typo, and you meant the 70-300L. But then I remembered that the 70-300 is a zoom-ring, not push-pull. So I was confused, because I couldn't remember anything about a 28-300L - that seems quite a remarkable zoom range for the "L=luxury" moniker.
But I took a quick look at the Table of Lenses, and there it is. Not cheap, and I guess I forgot about it because it must also be fairly compromised in terms of IQ (probably at the long-end), but wow, what a range of FL...
shinksma
It's definitely a compromise, but if you need an all-in-wonder I guess it's the one to get, particularly if you have a full frame and 28mm comes a lot closer to being actual wide angle.
