How does the Contax N Vario-Sonnar T* 17-35mm f2.8 compare with the Canon EF 16-35mm f/2.8L II?

My main use for the lens is landscape astrophotography for timelapse on a 1DsM3. Because I like to shoot very wide, at night, with the iris wide open, I worry about distortion and softness at the edges of frame.

Are there any other lenses I should be looking at along these lines? I like the idea of a zoom around this focal length, but if there is a really good prime I could shoot with at f/2, for example, that might be the ticket.

Actually, all manual control of focus and iris is fine with me, too, since I always use manual settings for this type of night timelapse photography.

thanks

For low distortion the Sigma 12 24mm is excellent . For sharp corners, Canon don't make anything neither does anyone else for Canon. The new Nikon wide gets rave reviews, I believe it can be used with adaptors.

Kevin.