I had my sigma dc 17-70 2.8-4.5 idling ever since I switched from cropped frame canon 20d to full-frame 5d. I theoretically knew that nothing terrible will happen if I put it on fullframe camera, but something always stopped me.
Now when I switched to the newer version of 5d, I finnaly felt brave enough to try and see what happened. and what happened is that I liked the results. my only complain is that the circle of invisibility (or whatever the technical term is) is not full. It can be helped to a degree with photoshop
Looking at it now, I'd say I should have used two different pictures to form the full circle
More practically, the lens is macro, and even if you deduce the useless black space, it still gives a bigger object size pixel-wise than my current main 24-105 L. Below is 100% crop. It was sharpened a bit during processing, but then save-for-web ate some of it, so what you see is pretty much out-of-camera
All the pink flowers above are sainfoins (http://en.wikipedia.org/wiki/Onobrychis_viciifolia), growing by Sawston bypass - Local reference for those locals that are interested.
No reason for producing an image below at all, except I happened to press ctrl-i :)
all sainfoin pics at shutterstock