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Can a green laser pointer with low power be used for star-pointing?

swans

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Whether there is some relations between laser's power and how far the light can reach. Can a green laser pointer with low power like
5mW 532nm Green Laser Pointer Pen be used for star-pointing? Is it bright enough to be luminous in the sky?
 
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ryansoh3

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Generally, laser beams extend indefinitely until something blocks it.

However, some say that the beam stops abruptly in the middle, and I don't think its power affects this distance.

That thread is here: http://laserpointerforums.com/f44/why-does-beam-end-sky-75315.html

To answer your question, a 5mW might be a tad weak. Try going for 30-50mW.

People have found out that this set's greenie is actually around 30-60mW, so I would definitely recommend them.

http://www.amazon.com/QQ-Tech®-Viol...DMSU/ref=sr_1_4?ie=UTF8&qid=1332904374&sr=8-4

Watch out for ridiculously high outputs for ridiculously cheap prices, such as a 200mW green for 20 bucks. They're obviously fake, and are about 20-50mW.

Cheers!
 
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swans

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Thanks ryansoh3. I went for one with 30-50mW at first in fact. But my friends suggest that one with 5mw would be safe and can meet the requirements.
 

ryansoh3

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Thanks ryansoh3. I went for one with 30-50mW at first in fact. But my friends suggest that one with 5mw would be safe and can meet the requirements.
No problem. I just got my 3 pointer Amazon set a few hours ago, and I'll test it out during the night and see if it doubles as a astronomy pointer.

Cheers! :beer:
 

InfinitusEquitas

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10-20mW is ideal IMO, if you are in a place with little or no light pollution. 30-50mW is definitely the perfect range if you're in a city..

With the beam apparently "stopping" in the night sky, there is no difference whatsoever imo, whether you are using a 50mW or 500mW.
 

ryansoh3

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Meh... with the greenie from the Amazon set, you can barely see the beam during the night. Seoul is quite bright during the night but at the same time polluted so the dust particles should be making the beam brighter.

But I will say that if you tell your friends, "You see that beam over there?" while pointing the laser at the sky, they'll be able to see it.

So it's usable, but not as bright as I had hoped.

If you want me to take some beamshots as the human eye sees it, I'll do that.


Cheers! :beer:
 

DrSid

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There is HUGE difference between night in city, and real darkness. Most of the time there is even no point in looking at the sky in big city. There is nothing there, except the most bright objects, and pointing is not necessary.
For real astronomy you need total darkness .. to be kilometers away from cities or any light. Eye is completely adapted to darkness in about 30 minutes in darkness. One glance at street lamp (or Moon for example) will ruin the adaptation. So the laser may even be too strong. Especially in winter, if you breath out (creating visible steam) into the beam, the reflection can be very bright.
Unfortunately I have never tried using laser for pointing in real darkness, so I can't tell what power/color would be the best. 50mW has visible beam even in city.
 
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swans

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No problem. I just got my 3 pointer Amazon set a few hours ago, and I'll test it out during the night and see if it doubles as a astronomy pointer.

Cheers! :beer:
I am looking forward to the result you test. :friend:
 

ryansoh3

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I am looking forward to the result you test. :friend:
:wave: I posted this a few posts back; did you see it?

Meh... with the greenie from the Amazon set, you can barely see the beam during the night. Seoul is quite bright during the night but at the same time polluted so the dust particles should be making the beam brighter.

But I will say that if you tell your friends, "You see that beam over there?" while pointing the laser at the sky, they'll be able to see it.

So it's usable, but not as bright as I had hoped.

If you want me to take some beamshots as the human eye sees it, I'll do that.


Cheers! :beer:
However, as DrSid had stated, the night sky here is quite bright. If you plan on using the pointer in complete darkness in the countryside, it should be brighter.

Do you want me to take some pictures? I'll just have to wait a couple hours for the sun to set. (It's 11:31 AM now.)

Cheers! :beer:
 

swans

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:wave: I posted this a few posts back; did you see it?
sorry, I haven't seen it.

However, as DrSid had stated, the night sky here is quite bright. If you plan on using the pointer in complete darkness in the countryside, it should be brighter.
Do you want me to take some pictures? I'll just have to wait a couple hours for the sun to set. (It's 11:31 AM now.)

Cheers! :beer:
aha! That's very kind of you. I am looking forward to it. :thanks: :D
 

ryansoh3

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ryansoh3

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As promised, here you go. I don't have an LPM so not quite sure of the power.


The settings were: 1 sec, f/3.5, ISO 800

Cheers! :beer:
 
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ryansoh3

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"5mw" laser reaches 75mw? By the way, beautiful night scene. :thanks:
Yeah, Amazon doesn't let vendors sell >5mW lasers, but many of us found out that they were very very over spec.
So you might get lucky and get a 80mW greenie.

Thanks, but it all contributes to light pollution.

Cheers! :beer:
 
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I have one of those amazon pointer greenies. Mine was pretty bright. I wouldn't hesitate to buy another set if mine got lost or stolen some how. My greenie is just about bright enough for star pointing. I'm sure your experience may differ. I'd estimate my pointer to be about 25-30mw due to the fact that it is not much brighter if any over my other 25mw greenies (all of my green pointers except the Amazon ones were metered on a coherent fieldmax)
 
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Flask

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Yeah, Amazon doesn't let vendors sell >5mW lasers, but many of us found out that they were very very over spec.
So you might get lucky and get a 80mW greenie.

Thanks, but it all contributes to light pollution.

Cheers! :beer:
Does being so over spec. like that not open the possibility of eye damage and law suites?
 




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