[obican]

Have a look at the Samyang 12/2. It's even wider, cheaper, smaller and it's probably as sharp as either of those options. If I were to shoot some trees, I'd definitely get the 14/2.8 since it's again, wider, lighter and cheaper. People have been ignoring that lens ever since the 10-24 and other wide angle options came out but that's still as good as a 21mm equivalent lens can get in any system.