Oddly, only one lens backfocuses on my D7000 and it is a Sigma 17-50mm. On my D300s it is fine and all my Nikon lenses are OK on the D7000. However, the Sigma 17-50mm is hopeless. I will do some proper tests at the weekend. I'm wondering it's worth shelling out £49 for the Lenscal or whether just to use my own scheme. So far, I have dialled the Sigma lens to -5, -10, and -20 and all are an improvement on 0! I don't get it why the Sigma doesn't work properly on the D7000 but is fine on the D300s but the moral is probably: use Nikon lenses with the D7000.