FYI for those eager to see the new 16-35 F/4L IS -- a short hands-on video and some sample shots are here:https://www.youtube.com/watch?v=Bl0cTEDzD6k
Most important thing I learned (see 1:30 in the video):
It's internal zooming/focusing if you define that as nothing protrudes past the filter ring of the lens
. But there is no front element that covers the entire lens, so that zooming motion leaves a sliding surface that is exposed to the elements
. If you've shot a 50L, the relationship is similar (but obviously being a prime, that sliding is a focusing motion and not a zooming motion).
For me, that's technically internal zooming/focusing for length
but not for access to dust/moisture
; with (say) a 70-200 lens, that zooming motion is entirely captured behind a front element, which I have to say gives me a little more peace of mind when shooting in the elements.
Yes, normally I would UV or CPL this lens for handheld use anyway, but with an ND grad setup that you use right on the lens, this could be a potential for dust/moisture to get into the lens. Seaside landscape shooters -- do you care about this? (I never bought an ultrawide since I moved to FF, so I don't know if this is similar to the 16-35 F/2.8L or 17-40 F/4L and you've been coping with this limitation for a while anyway...)
He also goes on to say IS doesn't do much in wide angles... for video.
[Cue drum fill.] If it gives me 3-4 more stops of handholdability in low light for my stills, this lens will be golden IMHO.
Links to sample images are here:https://drive.google.com/folderview?id=0BxMcAIja4uORVnRXbG9JVDZ2ckk&usp=sharing