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large beam expander?

ryanlee

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Rather than use a Newtonian or Keplerian expander, why not just change the collimating lens to something larger with a shorter focal length? It is cheaper, simpler, and smaller.

I found an old mspaint sketch I used to illustrate this a few years ago:



My proof of concept:

what size spot will that method produce at longer distances?
 



RedCowboy

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Mine makes about a 2mm thick line that's about 15mm long at 20 feet and will light a paper lunch bag.

But if I use a 44/G2/6X C pair and 3X BE then I get a spot smaller than a bb at 20 feet that is HOT! Pops a flame kernel on wood and ignites paper instantly.

My point is a larger primary lens will work but not as well as correcting the divergence before expanding the beam.

Note that the 05 diode has 3/4 the divergence of the 44.
 
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Cyparagon

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what size spot will that method produce at longer distances?
The same math applies. If the laser was 1mRad with a 4mm beam, and you switch the collimating lens to have a 80mm beam, the new divergence is 0.05mRad, all else equal.
 

lazeristasUVISIR

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The same math applies. If the laser was 1mRad with a 4mm beam, and you switch the collimating lens to have a 80mm beam, the new divergence is 0.05mRad, all else equal.
That will hold only with $$$$. A one big lens with short focus shall be really good not to spoil divergence.
Otherwise photography lenses would have no professional grade :whistle:
 

Cyparagon

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If you knew even a little bit about photography, you'd know photography lenses have a lot more to worry about besides good focus. There's chromatic aberration, internal reflections, and lost of other things that just don't matter with lasers. A single lens is not good enough for professional photography, but a single lens is perfect for something as simple as laser collimation.
 

ryanlee

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If you knew even a little bit about photography, you'd know photography lenses have a lot more to worry about besides good focus. There's chromatic aberration, internal reflections, and lost of other things that just don't matter with lasers. A single lens is not good enough for professional photography, but a single lens is perfect for something as simple as laser collimation.
who here has a laser using this method so i may see it in practice?
 




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