get the Sigma 10-20 or Canon 10-22 as an addition to the 28-70. Neither is very large or heavy and would serve well for landscapes. They might also be fun to use for some around town shots where the utra-wide perspective can be used as a creative element.I have few cheaper len, but I too use Tamrom 28-75 f2.8 as walk
around len. I am not landscape photographer, but once awhile I do
run into few scenes I wanted wider angle (I do have 18-125) but
usually too lazy to change len just for one shot, so I often skip
it. I do see few landscape photographers post few beautiful wider
scene those made me hungry for sharp wider angle len.
-Gene L.