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GB 16x diode focusing

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bbb18c1

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Aug 20, 2007
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Today I finally had time to build my laser with the GB diodes.

I have a question about focusing the beam. I put the GB diode in the Aixiz Laser module and the dorcy host. It lights up fine, but I'm not sure about the focusing.

I can get it to focus, but as soon as I move back a bit, the beam becomes huge again. Say If i had the lens focused at 2 feet, and i move to 10 feet, the beam is huge...like the size of my head!

I not sure if thats just how it is, or did I do something wrong. I tried the 5mw diode in a spare Aixiz Laser module and the focus seems to remain fairly constant.

Anyone know why the GB diode and Aixiz Laser module combination does this?

thanks
 





Gazoo

Gazoo

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That's how it is. You focus at two feet or so for burning. But for a nice beam, you need to focus it for distance.
 
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dingle

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This is why when you stand far back from a parabolic mirror you're upside down.

When the light is converging to one point, it makes an incredibly small dot with tons of heat. In physics, this dot is infinitely small. But after the point where all the light meets, the light comes out the opposite side it went in, at the same rate it approached the point. If its focused up very closely than the angle is much higher and diverges much faster after the point.

Thats a bit confusing to say in words, if you'd like i'll draw it in paint.
 
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dingle

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img232.imageshack.us/img232/1008/laserfw1.jpg

Where the lines meet is where its focused to.
 
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stevetexas

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the stronger the lens, the more convergence. these lasers aren't collimated in the conventional sence, they're focused. big difference.
 
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cyclonite

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so how should I focus it if I want to burn an object somewhere across the street?
 
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Greyfox

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You don't. You mount the laser and select a target such as in a lab, and focus to that. Shooting across the street is high risk, and may be illegal depending on where you are.
 
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Skram0

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You can try to focus it across the street, but I may be difficult. I think any focusing past 20 feet or more will take very precision movements of the lens. Just a slight touch to change the focus. Once you let go the slack in the threads and spring will probably jack yer focus anyway.

But do let us know the farthest you're able to burn!
 
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cyclonite

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why can't someone make a colliminator lense which outputs a beam with an extremely small diameter? that way the burning power will be there no matter how far away the object is right?
 
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the_stark

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Well, theoretically, but all the dust and stuff in the air will also suck some of the energy away from the beam.

To quote: "Fog is a weak laser's best friend".... because it allows you to see the beam, when it reflects off the fog particles. But, the beam is shortened because it's being used up every time it hits a particle.

You could probably find a collimater lens which will really lower the divergence (the amount the beam spreads out over distance) but to lower it to something like .2 mRad (which is almost close to perfect across a street) would cost mucho $$$. Also, collimater systems increase the size of the beam, so it's larger but more constant over distance, and a beam reducer would cost more money, if not also raise the divergence again.

So, yes I guess it can be made, but would be very expensive.
 
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Phazonx

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yeah, focus it at something 10 feet or more away and try focusing then. Then you will have a nice beam
 
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cyclonite

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Phazonx,

What should I look for in a beam? How would I know that I have a 'nice' beam?

Sorry sounds a little stupid but I'm very new to this and still waiting for my aixiz laser case to arrive.

Thx.
 
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zerafiel

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Generally, I think you want to burn stuff so you just leave the focus at like a feet or so in front of the lens. You can easily burn stuff even at lower powers just by focusing to a pinpoint.

With a low divergence lens, you can focus to infinity with a small enough beam that might still be able to burn. Mine will burn minimally at long distance but much weaker than a pinpoint focus.

Usually, expanding a collimated beam reduces divergence while making the beam smaller increases the divergence. You can't have it both ways unless you have some uber optics I know not of.
 
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Phazonx

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if you want a nice beam, focus the lens back and fourth until it is teh smallest. If you hit the smallest point and it gets bigger, go back.


for pointing at stars, focus it at the farthes object.
 
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