I do a fair amount of travel photography, but must travel quite light since I leave for months at a time to remote destinations (and carry all my equipment on my back). I'm a semi-pro but really enjoy taking photos for personal enjoyment most. The problem: The few lenses I carry with me just aren't cutting it in terms of sharpness and ability to fit the whole scene in my shot.
My travel kit includes a:
-Canon 7D
-50mm 1.4
-17-50 2.8
-70-200 or (usually) 70-300
I mostly shoot travel portraits, but I'd like to do more in-the-moment, full-body portraits with more props/scenery (farmers with animals/equipment, fishermen in their boats, cooks with their food). Instead of just getting a shot from the chest up, I'd really like to focus on the bigger picture, too. For most photos I take, I have just a few seconds or minutes to get the right shot, so fast focusing is pretty important as well as clarity.
What I'm looking for:
-A wide-angle, preferably prime lens that is SHARP (this is the most important factor)
-Something not too far out of my $1,500 limit
-A lens that isn't too bulky or heavy to carry--the smaller the better
-Any brand (though I haven't had good experiences with Sigma)
-A lens with apertures around 1.4-2.0 are ideal; I definitely won't go above 2.8
What are your recommendations? Equally helpful: What would you not recommend? I need a lens that is known for sharpness and clarity--a real professional look and fast focusing are important to me. I of course have some in mind, but wanted your opinions before my final tests. Links to your example photos with recommended lenses are welcomed. Thanks, all!