20D+580ex+ Sigma 18-50 f2.8 users

I've recently got hold of the Sigma 18-50 F2.8 and it's a stellar piece of glass.

However, I discovered that it back-focuses when used with a 580ex (AF assist on), especially at 18mm. One stop AF (center pt) was used in this test.

If you happen to have the same stuff as I do, you might want to test this out as well. Apparently, this back-focusing issue occurs only when the 580ex is used. Tried my sigma 500DG super and the focusing was perfect.

Let me know if u have this issue too.

regards
DG