Not sure how to properly calibrate a zoom lens but for the 15mm the choosen high contrast subject does not need to be further than maybe 30 to 40m away. I found the calibration of the 12mm lens to be most challenging. Not sure why but it took me many tries until I achieved the best possible sharpness. Once I did, all my photos and videos are consistently sharp every time. All I need to do is to tap the infinity mark in GO4 in MF.