How to change a field lens for a fiber laser engraver?

Change a field lens for a fiber laser marking machine and set up ezcad software. The download link for the document of fixing distortion: https://drive.google.com/file/d/1NHoP... 00:00 Beginning 00:22 Replace field lens 01:06 Set up Ezcad 03:18 Find focal length 06:25 Calibrate size 08:11 Fix distortion 10:43 The end