Brant:

For milkyway shots - the wider the lens, the longer the exposure you can use before you start seeing star movement. The rule of thumb for the maximum shutter speed to produce sharp pinpoint stars is: Tv(max) = 500/(Focal Length). For example, at 16mm, the max shutter speed is around 31 seconds which is probably do-able at f/2.8, but now you are wide open with the 16-35mm where the lens is not at its best. For a 24mm lens, the max shutter speed would be 21 seconds which I can typically do at f/1.8 - f/2 with my 24mm f/1.4L and it is not wide open (good thing). I guess my point is: If you are going to use a lens that can only get to f/2.8, then it had better be pretty wide, and it should be good wide open (rokion 14mm f/2.8 seems to hold some good reguard wide open).

Not living in the land of great mountain views and other large vistas, I find 24mm on full frame to be pretty wide; and in many cases, to wide. I thought about the 16-35mm, but for the landscapes I shoot I think it would be too wide. I would like it for the occasional need of an ultra wide, but it just would not get used enough. And I still like my 24-105mm... in fact, I like it even more with the FF. I have actually been thinking about the Sigma 35 f/1.4 Art lens. It would be a pretty good focal length for me and it is good wide open... so I could get to the 15 second max shutter speed wide open for milkyway shots.

Having said all that... I have seen a lot of really great shots with the 16-35mm. I am not sure you go to wrong picking one up.

Pat