Quick and easy laser focus correction.

[Marco Polo]

A few of my lasers aren't focused quite right. That is, if I turn the focus knob all the way down, then aim the laser at a 'distant' wall (30' or so away), I can see that the beam has diverged a bit. At this distance the beam should diverge more as I start turning the focus knob out. Instead it shrinks initially, opposite of what is expected.

I cut a few tiny (about 1/8" square) pieces of electrical tape and used them as shims. I laid them flat on the rim of the host body, where the focus knob makes contact when it's turned down. Then I turned down the focus knob, but due to the shims it can't go quite as far as before. In my case the shims made just enough difference to correct the focus and reduce the beam divergence.

The only downside is that turning out the focus knob can ruin the shims. So if you adjust focus a lot, this might not be useful. Maybe try a different shim material, e.g. thin plastic. I mostly use my lasers to point at distant objects at night, which means keeping them focused to infinity most of the time. So, this works for me.

The best part is that it's safe for your lasers, unlike opening them up and trying to adjust the internal optics. It can be a semi-permanent solution if you don't change focus a lot.

Hopefully it works for you, have fun!

 

[xmtgx]

Aluminium tape would hold up much better I would think.

 

[Speedy78]

For every distance you will have a different amouny of "focus" of the lens. They are not designed to be screwed in all the way and focused to the smallest diameter possible at any given distance. You kind of just have to observe the laser (through safety glasses) and adjust the focus until its where ypu need it.