Dear It's only the lenses which get changed Accordingly calibration factor will get changed as well Just imagine you have two measuring tape one only with only millimetres and second with centimetres No matter which measuring tape you are using your height will be same by both the tape For example if your height is 1.6 meter there will be 1600 divisions in mm tape and 160 in cm tape but in both the cases you will read it as 1.6 meter I hope it is clear now