So, after reading all of the calibration hype I decided to give it a go. First up was my 18-140 and it appeared to have a significant back focus issue. I adjusted it from -20 to +20 with no adjustment in focus that I could tell. So I tried my 50mm......same deal. Now, let me go ahead and say that this wasn't the most precise calibration, as I was shooting at a 45 degree angle to a tape measure..........but I thought that I would be able to see a focus change between adjustments. I tried every distance from about 14 inches to 10 feet, same thing. I plan to print out or buy a more precise tool than a tape measure, but wanted to ask for your thoughts in the interim.