Take a Brunton 7x18 pocket monocular and break out the prisms (they absorb a TON of light) and relocate the smaller lens to the outside and glue it in place. (This is necessary to make it focus properly without the prisms.) The image will now be inverted, but that won't matter unless you wanted to use it as a monocular again.

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Whoa!They are 16$ shipped from amazon. Not bad for a beam expander...I cannot wait to try this (when i have money-cant spend 16$, pathetic, huh?). Thanks for the find/tutorial/post!

That must be what I need to do to my monocular. I didn't know modifications would have to be done.

No prob!

You don't HAVE to take out the prisms, but they waste a ton of output.

Want to post photos of the lens and where it needs to be glued.....im interested

Any photos of results as well?

The lens unscrews from the inside. I think there is some kind of retaining ring that I have since discarded. Glue where indicated in the pic below. I'll try to get some divergence measurements and pics up tonight.

Edit - I'm still at work but I decided to make a graph illustrating the benefit of beam expanders. The original beam diameter I used for the calculations is 1.5mm and the divergence is 1.2 mRad. The expander is a 7x. As you can see, the beam starts off much wider with the expander, but after 9 meters it starts to pay off. At 100 meters the beam without the expander is 12.15 cm wide, but only 2.8 cm wide with the expander!

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Can you take some pictures of the results?

I will try to tonight. It's been raining here and the longest distance in my house isn't long enough to see the benefit of the expander.

How do you attach it to your laser?

It ain't pretty. Pics coming tonight.

EDIT: It is FREEZING here (literally) but I got it done. Pics of spot are at 33 meters. The smaller spot isn't as bright because the laser was not liking the cold weather.

As you can see I simply wrapped the laser and the monoular/expander in electrical tape until it fit into a PVC pipe adapter. Like I said, it isn't pretty, but it's cheap! I usually just hold the laser up to the expander with two hands so both can go back into my pocket.

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WOW -- PVC fittings!!! That's what I use too......
Easy to machine and CHEEP!!!!
Bet that expander won't hold up to an SSY-1
YAG pulse!!
HMike

Probably not. I put it up to my 445 once and it started smoking on the inside. Not sure if that was from reflections or from having it misaligned.

which lens are you taking from where and putting where exactly

on another note couldnt this be turned around to focus the beam too??

not an expert but i think that is what is being done.... not sure why they call it expander though...

It's an "expander" since it increases the diameter of the beam near the laser source. The increased beam diameter improves the divergence so the resulting dot after a long distance is smaller.

Pic attached. Again, if you don't mind reduced output you can leave the monocular as it is and it works just fine. Moving the small lens to the outside is only necessary if you want to remove the prisms that suck up so much laser light.

You don't have to turn it around to focus the beam. All you have to do is adjust the focus on the monocular. You can focus it to a fine point pretty far away actually.

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