How to found the best divergence in a 532 nm 200 mW fixed focus module?

[Minamoto Kobayashi]

Hello.
I have some of those 200 mW green modules:

and in one of them I was forced to replace the lens.
Before to replace it, I put the laser at exactly 8.45 meters from a white wall (the max distance available in my apartment). With Laserglow 532 nm goggles on I have measured with caliper a dot of 16mm.
Then I have replaced the lens, and while trying to refocus the module again, I have seen that I can reach a smallest dot at the same distance.
So now I'm in doubt how to procede to obtain again the best divergence available: I must reach the same spot size of the last measurement, or I must found the smallest dot available at a 8.45 meters from the aperture?

With this program:
http://www.buildlog.net/cnc_laser/laser_calcs.htm
I have calculated 1.775 mRad with the original lens config, but I don't know what is the exact distance from aperture to the wall to obtain the best result available.
Any help very appreciated, thanks!

 

[Eudaimonium]

1.7 mRad divergence is perfectly acceptable for a green laser. If you can make the laser perform as good as it did, it's perfectly fine and it will look nice outside.

No need to go with extra effort to reduce divergence, in my opinion.

 

[honeyx]

Then I have replaced the lens, and while trying to refocus the module again, I have seen that I can reach a smallest dot at the same distance.

You probably focused it to a pinpoint at this distance but not to infinite. Or you used a different collimating lens with a longer focal length, which gave you a bigger beam diameter and reduced the divergence.

 

[Minamoto Kobayashi]

Hello. The lens are the same original one, probably I have focused to a pinpoint. My goal is point at best to the infinite, so I think that the only chance is reach again the same spot size from the initial distance. Or point to a open sky and try to reach the best visible focused beam ...

 

[Minamoto Kobayashi]

Well, I have found an optimal focus in a somewhat rudimentary way.
First I have twisted the lens to a X position, more or less near the original position, then I have gently twisted with a toothpick the lens ring in a clockwise direction by 180 degrees. As referral point I have taken the two notches present in the lens ring. For a good reference point I have observed the beam from the aperture to the infinite, keeping my eyes parallel and near to the beam as much as possible. I have seen that the divergence sux, so I have rotated the ring in a anticlockwise direction, and I've seen better divergence. I have repeated the 180 degrees anticlockwise rotation until I have seen the divergence suxx again. So I have inverted again the rotation, but only of 90 degrees. Same soup until I have seen that the divergence suxx one more time, so I have inverted the rotation again of 45 degrees. After some attempts I have find the best divergence available to the infinite .. A very spartan way, but very useful! :beer: Please do not steal me some reputation points for this LOL.

 

[Minamoto Kobayashi]

Ehehe thanks buboniccronic, You writed a reply while I was writing my experience LOL