I just bought a Sigma 17-70 macro. Where do they measure from, when they say "minimum focusing distance - 20cm/7.9 in."? I was trying to take a close up shot of a couple of items and the lens almost touched the items (1/2 inch) and it would still focus and lock on. If I had the hood it would have touched it. Is this normal? I'm not complaining, I just didn't know what to expect.