For me, 24mm isn't wide enough for landscape, the 17mm TS/E is too impractical and Canon's 20mm is junk leaving only the 21mm Zeis.
TS-E is impractical, why? Because it doesn't accept filters easily?
Quote from: NancyP link=topic=19117.msg358110#msg358110 da
Do you find the polarizer useful at 21mm, or does it result in obvious artifact (sky gradient)? Actually, I know that it must, because I have used a polarizer at the 15mm end of a zoom on APS-C, and the effect is noticeable on a plain blue sky. I have been considering whether to buy a polarizer at 82mm diameter, or the 105mm diameter used to mount on the Lee holder - both options are ungodly expensive ($260.00 to $400.00 for B&W XS-PRO Nano "wide"). I suppose that one inconspicuous use of a polarizer on ultra-wide angle lens might be in a shot without significant amount of sky, eg, woodlands shot.
A polarizer can be useful even for WAs. It can be used for water, but I like using it for snow, and in some cases can be used for the sky depending on where the sun is and what effect you're trying to go for. Although, you might find youself using it more if you choose to get a canon/tamron 24-70 in the future.