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Laser+binoculars=amazing divergence!

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lazerguy

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I yesterday figured this out, don't know if anybody else has discovered it yet (probably someone have), but it's amazing!
The dot of my x-85 at 100m is about 15 cm wide. When i shine it through a pair of binoculars with the right zoom adjustment, the dot is about 2 cm wide at that range! that would make a divergence of about 0,3 mrad! :cool: When i usually shine it up in the night sky it's a pretty tight line, but with the binoculars, it is extremely thin!
Could someone tell me why this happens?
 





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toked323

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i think there are 2 lenses in binoculars if i am not mistaking? I think they work like another collaminator
 
Hemlock_Mike

Hemlock_Mike

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A colliminator is a telescope. Some call them beam expanders because they do that too. In basic form, the beam strikes a diverging lens and then is focused by a magnifier. Simple straight line binocs will work best ( not the folded ones).

There are other posts here about collimators.

Mike

The picture below is my sky with home made collimator.
 

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Benm

Benm

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Could someone tell me why this happens?
Click to expand...

Very simply put, you can with optics exchange divergence and beam diameter. If you run a laser through binoculars from the eyepiece, the beam becomes much wider but better collimated (a factor 10 on both is not uncommon).

It works the other way around too, but divergence is so bad that the result is hardly worth using.
 
L

likewhat

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I posted this on some other thing also

The beam divergence is given by this equation

Divergence= wavelength/Pi/waist_size


The divergence is inversely proportional to the beam diameter. So if the smallest spot the beam makes is 1 mm the divergence will be 10 times larger than if the minimum spot size is 1 cm.
 

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steve001

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lazerguy said:
I yesterday figured this out, don't know if anybody else has discovered it yet (probably someone have), but it's amazing!
The dot of my x-85 at 100m is about 15 cm wide. When i shine it through a pair of binoculars with the right zoom adjustment, the dot is about 2 cm wide at that range! that would make a divergence of about 0,3 mrad! :cool: When i usually shine it up in the night sky it's a pretty tight line, but with the binoculars, it is extremely thin!
Could someone tell me why this happens?
Click to expand...

Measure the beams diameter at the lens. Let me know what it is in millimeters.
I ask because you might be focusing the beam rather than optimally collimating the beam.
 
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lazerguy

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Yes steve001, the beam is about 10mm at the lens of the binoculars. when I adjust the zoom, i can get a focal point a around 10 metres where the beam is about 4 millimeters in diameter. So I guess it works like a convex lens with a very long focal length. :p Anyway, very useful to make the beam even more visible at long distances.

I also managed to pop a balloon in about 3 sec. at 20 meters with good zoom adjustment! :eek:
 
VW

VW

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Simple optical effect really. One thing I find cool is shining it through a pair of glasses, where you can see the beam is actually concaved instead of straight...
 
FrothyChimp

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I've used a target spotting scope as an impromptu collimator. Since it is 45x - 60x zoom I can focus the beam at great distances. The nice thing about spotting scopes, binoculars, and telescopes is the optical components tend to be broadband AR coated minimizing reflections from the surface of lenses withing the body of the device. As such they work extremely well.
 
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lazerguy

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Thanks for the link, wow, matches lit from 300 feet! :cool: Imagine setting up a firework some blocks away, and then ignite it with a laser and a telescope! ;D I soo wish that lasers had 0mrad in divergence. At least, in about 20 years, I hope we have pen sized lasers with 0,01mrad. :D Woulddn't that be nice?
 
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cybob101

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if that happened lasers will owned the world. wanna scare some one walk past there house with some fireworks and fire crackers. later set them off with ur 0mrad 1watt blue laser
 
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lazerguy

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You can dream.... :p If a laser didn't diverge, you could ignite a match from one side of the universe to the other. Well, at least theoretically because it would be pretty hard to put the laser on a match tip from lightyears away! ;D
 
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LikeitBright

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lazerguy said:
I yesterday figured this out, don't know if anybody else has discovered it yet (probably someone have), but it's amazing!
The dot of my x-85 at 100m is about 15 cm wide. When i shine it through a pair of binoculars with the right zoom adjustment, the dot is about 2 cm wide at that range! that would make a divergence of about 0,3 mrad!  :cool: When i usually shine it up in the night sky it's a pretty tight line, but with the binoculars, it is extremely thin!
Could someone tell me why this happens?
Click to expand...

Its a basic property of diffraction limited laser beams. The smaller the beam waist the larger the beam divergence. Its a diffraction thing. So expanding the waist of the diffraction limited beam results in a lower divergence. Yeah, its cool eh?
 
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lazerguy

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Thanks for all explainations, NOW I understand what is happening here! :) So, theoretically, you could make something that expanded the beam waist to about 1 meter in diameter, and then have ultra low divergence? If I got it correct, the beam divergence would then be harldy noticeable even on very large distances.

Anyway, I think this is really cool. The bad thing is that my pair of binoculars are pretty old, so there is a lot of scratches etc. on the lenses. This blocks a lot of the light, so if I shine a 100mw laser though it, the power behind all the lenses is estimatedly only 50mw. I wish I had a brand new telescope or something - you could have a lot of divergence fun with it! :cool:
 
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