Neje A40640II laser lens focus

[Bobchaos (Bob)]

Hi! I got my Neje laser hooked up and running but I can’t seem to find instructions on how to focus the lens. Lightburn has a helpful focus test tool but I’d like to optimize the hardware first. I found out you can screw or unscrew the lens to adjust focus, but there’s no details on which way to turn for what resultor how best to test it without running a full focus test (which requires unhooking the module from my CNC on every attempt). Anyone here with experience adjusting the lens?

I’m hoping to do both cutting and engraving, if that matters.

[MikeyH (Mike Hembrey)]

@Bobchaos

Lightbulb has a helpful focus test

You sure you are in the right forum?

[misken (Melvin)]

Are you sure your laser has an adjustable focus? Most diode laser modules have a fixed focus and the lens can only be unscrewed for maintenance.

[MikeyH (Mike Hembrey)]

@misken

adjustable focus

My 3018 Pro came with a variable focus lens on the 5w module. I was never ever sure if I had it properly focused.

[Bobchaos (Bob)]

The lens is adjustable, says so in the poorly translated manual that came with it, and after some testing I’ve determined screwing it in brings the focal point closer to the lens. There’s no way to measure this other than testing as far as I can tell, but I’ve finally reached a more reasonable focal point, sitting about 20mm from the casing. I’m still not sure how it will impact the length of the “knife” for cutting operations tho, guess I’ll find out soon enough!

[MikeyH (Mike Hembrey)]

@Bobchaos

not sure how it will impact the length of the “knife” for cutting operations

If by this you mean the Depth of Focus, It should not affect that. You are juse moving the focal point up and down.

Lightburn has a Focus Test tool you might find useful. @jkwilborn has provided some good images showing both focus and DOF.

Focus for different Materials

You need a quick review of how lenses work. There are a ton of videos, but I’ll try to simplify it to how I use lenses. Most of the time we see the diagram of a lens with there being a finite focal point. [point-focus-graphic] This is clear but pretty simplistic. Lenses don’t focus to infinitely small. There is an area called the depth of focus (dof). Within the dof, the beam is the same size. [depth-of-focus] Many of the on-line spot size calculators, like this one, will give you an …

[Bobchaos (Bob)]

Extremely helpful thank you! Plus some new vocabulary for me to get acquainted with

I’m using lightburn’s focus test but my initial run had my Z axis come off its tracks while still burning instead of cutting, seems factory defaults have the focus set as far as it goes. If DoF is unaffected then I’m ready to move on to the next set of calibrations thanks!