How to set focal length?

[gandyman]

Just want to get start point for the Focal length. Is it the top of the focus lens, the middle, or bottom? Or it set from some other point? Just want to get it as accurate as possible. I have the High quality 18mm ZnSe Focus lens (F50.8mm). As of now it is set 50.8mm from the bottom of the lens to the top of my object. Just want to make sure it is not something like middle of lens to depth of cut or something else I am not looking at correctly.

[bsm2003]

https://buildyourcnc.com/Tutorials/tuto ... cal_length

[gandyman]

Outstanding! Way to easy.

[bsm2003]

You're welcome. It was the best way I found.