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Improving Focus

bluestars

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Jun 29, 2010
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Hello all,

Back in 2011, I bought a 445nm ~1W laser from an LPF member. It runs on a 14500 and is built in a little Trustfire F25 host (flashlight review for some detailed pics of the host). It's a sweet little laser, but my needs have changed. In 2011, I was more interested in burning. Five years later, I like nice beam specs - narrow and low divergence. This laser is focusable, but when the focus ring is screwed all the way down, it does not focus to infinity. Instead, it seems to focus "beyond" infinity (whatever that means). I don't understand the optics well enough to know what is happening, so let me describe:
When I screw the ring all the way down, the beam seems to spread quite widely, even when I'm sky-pointing. If I unscrew the ring just a little bit, it seems to be more collomated.

So... what does it mean for something to be focused "beyond" infinity? And is there anything I can do to fix this? I'm pretty sure that it's using an Aixiz lens.

You can see some of my photographs of the laser in this album. I'll try to grab some beamshots that demonstrate my issue tonight.

Thanks!
 
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Sta

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Jan 27, 2014
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Focusing beyond infinity is normal -- it happens with almost every laser if you put the lens too close to the diode. This is because the beam has not spread out enough to be properly collimated by the lens. So it's perfectly normal to have to unscrew the lens a bit.

:)
 

Cyparagon

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Sep 12, 2007
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There's no such thing as "beyond infinity". It's either focused, collimated (focused to infinity), or not focused. If the beam doesn't come to a point at any length along the beam path, that means the lens is too close. If it comes to a point and diverges again, that means the lens is too far.
 
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steve001

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Jun 3, 2007
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There's no such thing as "beyond infinity". It's either focused, collimated (focused to infinity), or not focused. If the beam doesn't come to a point at any length along the beam path, that means the lens is too close. If it comes to a point and diverges again, that means the lens is too far.
There is, but it doesn't mean what it sounds like. It means infinite conjugation or more simply the optimal minimum divergence.
Reply to the red text. That also indicates the lens has collimated the beam optimally, or focused to infinity (and beyond!)
 




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