I've been really noticing the limits of my venerable Canon 16-35mm f/2.8L lens (Mark 1), particularly towards the edges, where the image starts to degrade. Shooting at f/11, focussing directly at the corner of a building recently (closest to my position), I can see clear image degradation towards the top of the subject -- in the upper bricks and top edges. I'm shooting RAW images on a heavy tripod, with mirror-lockup engaged and a shutter release (or 2 second self-timer). I've been comfortable with the lens set at 16mm (as are my clients) and see no need to vary from this focal length too much. It would seem that Canon's TS-E tilt-shift 17mm f/4L lens would be a suitable upgrade for the types of shooting I'm doing, but would like to hear some opinions on the matter. Any Zeiss Milvus 15mm users out there? Is the Canon tilt-shift 17mm my best option for improvement? Opinions and/or thoughts are most welcome.