How to check if the focus is normal?

I have a Genmitsu 3030 CNC machine with a 5.5W laser installed on it. Overall, it works normally.
My question is how to check if the focus is normal? LaserGRBL has a focus setting button. After pressing the button, the laser power will be turned on at 3%. When I observe this button through my glasses, I can hardly see the laser. Is this normal? How to check if the focus is normal?