I travel with my husband and it is hard to have the time to use a tripod.
I just returned from a trip with my T1i, and used the 17-55mm for most of my landscape shots. Even though it has Image Stabilization, most of my shots were on a tripod in order to maximize depth of field, which means small apertures, meaning often very slow shutter speeds.
Here is another solution: Purchase the new Canon G11 for less than the price of a great DSLR lens. It will take up less space and weigh less than the Canon 17-55mm lens!
My brother is a landscape photographer and uses a Pentax system with the FA limited Primes lenses. He recently purchased the G11 to use on trips where he's with other people and would find it inconvenient to carry a lot of gear + tripod.
He has tested the G11 extensively and gives it high marks. He recently wrote, "I plan to do most of the G11 work hand held. The G11 with battery weighs exactly 1 lb."
With the small sensor, he can shoot at f/4, meaning faster shutter speed, and get the same or more DOF than with his Pentax @ f/11. Like our T1i cameras, the Pentax is 1.6 crop.
You can carry the G11 in a small bag for your quick landscape shots! I'm considering getting one as my second camera!
B&H has a rebate through 12/3:
http://www.bhphotovideo.com/bnh/controller/home?O=&N=0&gclid=CIqF-JWS-p4CFY915QodQzDGJg&A=endecaSearch&Ntt=canon%20-g11&Q=
Review:
http://www.dpreview.com/reviews/canong11/
regards,
-rich
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Careful photographers run their own tests.