I purchased my neighbor's 6 month old, barely used 18-35mm f/1.8 for $600 CDN. Seemed like too good of a deal to pass on. It's front focusing terribly on my 7D so I need to calibrate it. I've used the "Dot Tune" method in the past and am wondering if this will yield me the best results. Who has calibrated their 18-35 using the dock? Just hoping for advice. Be as detailed as possible. Thanks!