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Flash Blinded By Green Laser



 
 
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  #11  
Old December 31st 04, 10:57 AM
gubbenimanen
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Hey, what about using a green laser for collimation of a big dobsonian?

Roger Persson

Brian Tung wrote:
....
If you're talking about the concave surface of a telescope mirror, I

of
course agree that shining a green laser down a telescope is

completely
irresponsible. But that's not what we were talking about. We were
talking about possibly using green lasers to blind pilots.

....

  #12  
Old December 31st 04, 10:59 AM
Roger Hamlett
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"Brian Tung" wrote in message
...
Tim Killian wrote:
So tell us, what is the safe distance when someone points a green

laser
in your face? What, you don't know for sure?


Mike need not give a hard lower limit for safe divergence to show the
logical flaw in Gary's argument. My common experience is that the
beams do diverge significantly even after only 100 meters or so, and
while I wouldn't want to stick my eye in the beam path, a few kilometers
seems more than enough to ensure safety.

Yes.
To get a beam closer to parallel, requires a longer laser assembly. I used
to work with lasers that were certified as 'eye unsafe', at over 10km.
They had three features relative to the pointers being discussed. The
first was that they were they were over 2 million times the initial power
(just over 10KW). The second is that they were in the IR (the eye has a
tendency to 'blink' if the light is visible). The third is that the
optical assemblies were just on a metre in length. The actual
specifications for how parallel the beam is from most laser diode
assemblies, are remarkably good for their size, but are still in the order
of tens of arc seconds of divergence, rather than than the sub arc second
levels needed for the beam to be really tight after a few thousand feet.
Remember even one minute of arc, gives a 'spot size' of 1" at 100 yards.

But even if there were a laser beam that *could* be kept that tight,
one needs to show that the green laser pointers are in fact kept that
tight. Experience at tens of meters such as Gary had--as unfortunate
as that was--won't extrapolate to thousands of meters.

Yes. Distance is definately your 'friend' in this regard.
However, I treat any such light, 'with respect', and would avoid any
situation involvng looking directly at such a beam, eevn if it was
certified as 'safe'.
With regards to pilots, the biggest danger, would be in the UK, a pilot
flying 'night VFR'. Compared to the normal instrument flight, a pilot in
this enviroment is dependant far more on 'seeing', and a light that is
completely 'safe', can still have a very significant effect on night
vision. When powerful searchlights are aimed up into the sky, notification
has to be given to the CAA, of this, not because they will endanger the
eyes, but because of the effect on vision.
Unfortunately, these laser pointers, are common, and cheap, and are being
handled by many people as if they are 'toys', yet in some circumstances
can have slight dangers associated with them, and as such need a degree of
responsibility in their use.
The astronomical club mentioned in an earlier post in this regard, has
done the 'right thing', by arranging not to use these when flight is
occurring over the area, and this should be a signal to other groups to
consider similar care in this regard, to help prevent a beaureaucratic
'overreaction', that old be t th detriment of everybody...

Best Wishes


  #13  
Old December 31st 04, 11:30 AM
Mike Simmons
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On Thu, 30 Dec 2004 22:42:02 -0700, Tim Killian
wrote:

So tell us, what is the safe distance when someone points a green laser
in your face? What, you don't know for sure?


I said nothing about a safe distance. I said only that Gary's experience
could not be extrapolated to the distance of an aircraft. Do you disagree
with that?

Laser beams can be collimated, expanded, even focused (theoretically to
a spot 1/4 wavelength in diameter). To make a blanket claim that beam
divergence will always protect bystanders shows you have little real
understanding of atmospheric propagation.


I didn't say that beam divergence will always protect bystanders, nor did
I make any claim, blanket or otherwise. I said the events could not be
equated, and divergence is a major reason. Other reasons include the
windows on the aircraft and atmospheric scattering and/or absorption.

Where did this stuff about focused beams come from? Are you suggesting
that that's what happened in the incident with the airline pilot? Did
someone track the aircraft with a focused laser beam? Do you have any
evidence for this? If not, what's the relevance of the ray gun talk? Are
you saying that because lasers can be focused Gary's experience was the
same as the airline pilot's? Or are you bringing stuff up just to argue?
Your tone is consistent with that.

In fact, what I objected to might be considered a blanket claim made by
Gary -- the apparent assumption that all events would have identical
results despite very different circumstances. You've pointed out that
variable factors can affect the resulting beam. It seems we agree.

As for my understanding of atmospheric propagation, that's pretty much
irrelevant, but I do have some knowledge of how our observatory's adaptive
optics laser behaves in the atmosphere and how much it diverges at the
height of aircraft and beyond. But even without that I'd guess most
people know that laser beams diverge.

Mike Simmons



Mike Simmons wrote:

On Fri, 31 Dec 2004 04:17:33 GMT, Gary Honis wrote:

I've been watching the news channel reports today on green lasers and
the
dangers to pilots. I've also been reading the messages here about
using
green lasers to easily point out objects in the night sky. I don't
own a
green laser pointer but I have a unique opinion of green lasers
because I
was flash blinded by one accidentally turned on by Howie Glatter at a
star
party. When a pilot says he was "flash blinded" by a green laser, I
know
what he experienced and the disorientation that results.



No you don't. The pilot of an aircraft will likely be miles from the
laser. The beam will diverge greatly at that distance. Equating that
(if that's what it was) with your point-blank experience is ludicrous.

Mike Simmons



  #14  
Old December 31st 04, 11:37 AM
Mike Simmons
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On Fri, 31 Dec 2004 08:04:53 GMT, Stuart Levy wrote:

I have a 5mW green laser, and have tried shining it into my own eye --
briefly (1 second or so) but at short range, so that the beam diameter
was smaller than my pupil -- while dark adapted.


You're a brave man, Stuart. I'm glad your experiment turned out alright.

Mike Simmons
  #15  
Old December 31st 04, 03:45 PM
Jax
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"Gary Honis" wrote in message
...

I was flash blinded by one accidentally turned on by Howie Glatter at a
star party.


I would like to hear Howie's response to this message.



  #16  
Old December 31st 04, 04:32 PM
shneor
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I would venture to say that automobiles kill more people every day in
the US than willl ever be hurt by green lasers in the course of 10
years. I don't see anyuone calling for banning cars. Instead, we enact
laws and rules to govern the use of cars. It's the same with green
lasers. Exercise appropriate care in their use and storage to eliminate
the possibility of accidental damage. IMO, it's absurd to ban green
lasers at star parties. Maybe we do need a 10-minute class on their
safe use.

Clear skies,
Shneor Sherman

  #17  
Old December 31st 04, 05:08 PM
Rod Mollise
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When a pilot says he was "flash blinded" by a green laser, I know
what he experienced and the disorientation that results.


Hi:

You do? Well, tell me how some pilot was "flash blinded" by a handheld laser
pointer at 5 or 10k feet? How was it guided? How was it pointed into the
cockpit? What about the tremendous beam dispersion?

I have several friends who are airline pilots, and I respect them tremendously.
But, as they will tell you, when you're tired and immersed in what is basically
a disorienting enviroment, it's very possible to see things that ain't so, from
zooming saucers to laserspots. Unless these incidents were documented with
laser radiation detectors, I wouldn't call them "proven."

If these incidents were a terrorist attack, yes, it's serious, VERY SERIOUS,
but it was NOT done with a 5mw handheld laserpointer.

I don't think they (green lasers) should be used in an environment where they
can irritate other folks, but they are not useless, especially for educators.

I'm very sorry--VERY--that you were injured by a laser flash, but I must also
say this is not a common incident. I've been to plenty of star parties over the
last 5 years or so since the greenies started becoming popular, and I can't
recall somebody creating a problem with one. That doesn't mean that there are
not kooks and careless people out there, just that they must be the exception
rather than the rule among amateurs.

Frankly, I'm afraid I see the beginnings of an anti-green-laser movement not
unlike some segments of the anti-gun movement:

"We don't care if you're a law-abiding citizen who uses that laser/pistol
responsibly. No one should be allowed to have a laser/firearm."

Wouldn't ya know it? I FINALLY get a green laser of my own, and now they're
gonna be OUTLAWED! ;-)


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html
  #18  
Old December 31st 04, 05:20 PM
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Jax wrote:
I would like to hear Howie's response to this message.



The topic was discussed on the Cherry Springs Star Party list, and
Phil De Rosa e-mailed me to ask about it. Phil kindly posted my
correspondence with him to the list in an attempt to clarify the
details. I'll copy Phil's post, which he e-mailed to me:

I know Howie from his attendance at star parties, including ours, and I
was
very concerned when I heard about the laser incident at CSSP with Thom
Bemus. I also banned green lasers from the MDSP, for safety reasons,
but I
didn't ban Howie from selling them. I also use one at our public
starwatches.

I was very curious why I did not hear anything from him after people
were
going back and forth about green lasers after the incident. So I
emailed
him, and following is the thread of emails:

================================================== ====

What happened, if you care to share it with me?


I'm sorry to report that the accident referred to did occur, and
although
it was an accident, I was responsible for it. It was not a green
pointer,
but a collimator. It was early twilight, I just finished collimating my
scope, and two outside visitors from a group that had been invited to
the
party by the park rangers came by and asked me general questions about
astronomy and telescopes. I believed I had turned the collimator
reliably
off by unscrewing the battery cap, and I was holding it in my hand.
Evidently, in gesturing while talking to the guests, the battery cap
jiggled
on and the collimator was pointing backwards. I was unaware it had
turned on
until I heard people calling out. By that time the incident had
occurred.
A am mortified and incredibly bummed out that it happened. I was
most
concerned about Gary, but evidently he is O.K. Fortunately the
collimator
was class IIIa, 5mw , and the contact was momentary, but this shows
that
one cannot be too careful.
I was hoping it would not receive wide circulation, but alas, it is
on
the internet. I will answer e-mail by concerned parties, but I don't
wish to
post anything. It would remind me of gawkers at highway crashes.

Yours, Howie

I would have liked to hear what actually happened sooner,
I think it would have been better if you spoke up at the time.


I don't know what I would be responding to. Do you have any links to
where it was discussed?

Did you at least tell Thom Bemus what happened?


No, but an accident report was filed with the park police, and I
spoke to
them then. I'm pretty sure Thom knows.

Yours, Howie

I think the best thing to do so long after the incident is to let me
forward your explanation to the Cherry Springs List server.


It's up to you, but I think you should only do so if it will serve a
good
purpose and not feed the gossip network. If the thread died down, why
start
it up? If someone recently posted something on it with wrong
information or
assumptions, I could see a reason.
If you decide to, you can post my e-mails to you if you explain that
you
initially e-mailed me, and include your questions and my unedited
responses

Yours, Howie

================================================

I am not excusing the incident, but this could have been ANYONE on the
field, and someone mentioned the incident again. I think Howie has
been in
the doghouse long enough. Apparently, he talks with his hands. Must
have a
bit of Italian in him.....I would have never guessed!


Philip J. De Rosa

York County Astronomical Society


12/31/04 addendum from Howie:
The only positive development to come out this that I know of is
that I've belatedly taken up an idea and suggestion that Frank Bov made
to me a few years ago to place a thin full diameter O-ring between the
collimator battery and the battery cap (Thanks, Frank!). It prevents
inadvertent activation from shakeing and vibration. I'm supplying them
now, and I plan to send them to past purchasers of my collimators.
H.

  #19  
Old December 31st 04, 05:23 PM
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I agree that you can't simply extrapolate the flash blinding
by a nearby laser pointer to flash blinding of a pilot at
large distances (like thousands of feet). Beam divergence
of these inexpensive laser pointers would diverge the beam
to the point that the energy is just too low to do anything
other than appear to the pilot like a tiny green point in the
distance.
Assuming an initial beam size of 2 mm and a beam
divergence of 5 miliradians, at a distance of 40 feet the
beam gets to be 7 mm in diameter. At greater distances
the beam continues to expand so that it can no longer be
completely accepted by the dark adapted eye. For example,
at a distance of 100 feet the beam is 15 mm across and only
23% can enter the dark adapted eye, at 500 feet it is 66 mm
and only 1% can get into the eye. At one mile, the beam is
673 mm across and would require the pilot to use a 26 inch
diameter telescope objective to collect the whole beam (not
just any old concave surface which happened to be in the
cockpit. Not a likely chance occurrence.
What this tells me is that either someone is playing
games with an industrial strength laser or else is using
large diameter astronomical optics to focus the pointer laser
and reduce the beam divergence. I will not go into detail
how this could be done, but if this is in fact what happened,
the irresponsible meathead who did it should be prosecuted
and have his equipment confiscated.
Clif Ashcraft

  #20  
Old December 31st 04, 05:42 PM
Jax
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wrote in message
oups.com...


I'm sorry to report that the accident referred to did occur, and
although it was an accident, I was responsible for it. It was not a
green pointer, but a collimator.


Thanks for your quick response, Howie. I have been accidently hit in my
dark adapted eye with a green laser pointer of yours from 20' away with no
impact other than it was annoying. Is the collimator more a risk than the
pointer?

Peace,
Jon


 




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