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405nm owners, visibility inquiry

ColdWelder

ColdWelder

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Guys, I'm curious, what would the visibility of a 405nm beam putting out 100mw be like in a dark sky, i.e. Astronomical use? Would you be able to see it at all?
 





You will be able to see something. But pretty much You will be guessing where the beam is or trying to find it 90% of the time for what your purpose is for.

Get a 5mW Green laser. There usually over spec to ~15-25mW and will be enough for what you are looking for. Unless you are looking specifically for 405nm.?
 
Well I want a subtle color that wont throw off my night vision mainly. Minimizing my visibility to park rangers, etc... would be a nice bonus. ;) I may upgrade the diode to an A140, and drive it at 400ma, I'm sure that would do the trick. But I wonder if the 405 would have any use in that sense? Also, regarding both the A140 at 400ma (not sure what that output will be), and the 405 putting out 100mw, when using these beams for guiding my telescope in very fine increments, will I need to wear my glasses to observe the beam??
 
Yeah I find that red is so bright in contrast to the sky, love a red LED flashlight for observing though. :)
 
To answer your question: a 100mW 405nm laser would not be good. I just checked my 120mW 405nm laser in my relatively dusty house and it is very hard to see the beam. Even if you had the same mW with a 445nm laser, it would be much easier to see just because of the eye's sensitivity to certain wavelengths (see luminous efficacy for scotopic vision).

Also, I wouldn't trust a laser anywhere in the vicinity of me looking through a telescope. What if some damn moth were to intersect the beam?
 
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Badger,
You don't look through the scope with the laser on. You use the laser to point the tube in the right direction and get close to the target object. Then you switch the laser off and guide manually (sometimes with a wideangle eyepiece) to get on target.
 
Yes 123 is right, but that is a funny thought. :) I HAVE had the sh** scared out of me by a jetliner in my FOV. ;) Btw, this laser will be putting out less than 100 mw i think. Would glasses be required for outdoor use/general pointing use? I of course assume they are required for focusing/burning.
 
Oh, well I always see the 'over 5 mw glasses are required' warning. I know the dangers surrounding laser light, but i'm new to owning lasers. Is there a resource for some more practical goggles rules? I'm also curious how laser shows get away with it. Is it because the diffracted beam has diverged to a 'safe' energy density?
 
The main reason for glasses is so you don't catch a reflected beam and blind your self.
I don't wear mine when I use my lasers outside.
As far as laser shows the beams are usually above you or the audience.
The laser show guys could tell you more about that, I am not an expert by no means.
 
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As stated, red lasers preserve your eyes' dark adaptation the best. I find 100mW 650nm is enough to just be able to see the beam on a perfectly clear night, it isn't nearly as defined as even a 5mW 532nm beam. When I receive the batteries needed for my 200mW 650nm handheld I will give it a shot on the next appropriate night and let you know how it is, if you wish. Too bright of 635nm or lower will screw up your dark adaptation. To answer your question about 405 though, it doesn't bother my dark adaptation if <75mW as long as the spot isn't projected off of something close.

As far as 405nm goes, it seems not everyone agrees how visible it is. For example, I can see the beam from my 10mW 405 pointer in a dimly lit room, and quite easily see it when fully dark adapted on a clear night, my wife and all her family cannot see it at all on a clear night, much less in a dimly lit room.

My 50mw 450nm pointer's beam is brighter to my eyes than my 5mW 532nm pointer's beam, and this normally isn't the case. My 5mW 532 is probably overspec as well. I would say it is almost twice as bright even without dark adaptation. All sources I have seen so far, including the calculator suggest that a 50mW 450nm spot should be half as bright as a 5mW 532nm spot, and 450nm beam 80% as bright as a 532nm beam with above stated powers.

I would guess that my eyes' sensitivity is downshifted from what is normal. I do have excellent night vision as well and that would help explain it.

I dont wear my laser safety glasses for under 400mW when outside in the clear, and certainly not when using my lasers for starpointing! If your laser can reflect off of something when pointing it into the sky, you've got a bigger problem than a chance of a specular reflection hitting your eye!
 
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