🚀 go-pugleaf

On Wed, 14 Aug 1996, Thorsten Franz wrote:

> Hello,
> 
> when I was sitting in my living room tonight, a spot of red light (at
> most one inch in diameter) appeared on the wall and wandered over it,
> coming to rest on the back of the head of my girlfriend. I wasn't able
> to determine the exact size because it was obviously steered by a
> shaking hand.
> 
> I thought it might have to do with a construction site across the
> street and went downstairs to check, but found noone. From down there
> it was clear that the angle wasn't right anyway and that the beam must
> have come from one of the dark windows in a nearby administration
> building, probably 5th or 6th floor.
> 
> A laser pointer, as used for presentations on blackboards, would have
> been too unprecise over the estimated distance of 100 meters. I don't
> know of lab lasers with in-built magnifying glasses, and when you play
> with measuring devices you don't aim them at people's head because you
> are probably professional enough to know about the danger of blinding.
> You would also use a stand.
> 
> So I figure someone might have been playing with the aiming device of
> a rifle, especially considering how restless the spot was. I will go
> to the police tomorrow and report the scary incident. If anyone can
> give me information that might be useful, confirm my suspicion (so I
> have something at hand when talking to a lazy officer), or calm me
> down, I will certainly appreciate it. :-)
> 
> Maybe a physicist can draw conclusions from the estimated distance and
> approximate diameter of the beam, or you know what else portable,
> aimable lasers without a stand/tripod are made for.
> 
> Thank you very much,
> kind regards
> 
> -- 
> uzsd78@uni-bonn.de
 
Dear Thorsten,

I sympathize with you, it does sound scarey.  But I am skeptical.

You cannot conclude that it was "obviously steered by a shaking hand". 
The change in position of any light beam over a distance, is very great
in realation to slight changes in angle.  Over large distances, a
shaking hand could not be steady enough to hold a spot steady enough to
be noticed.  If it was from a tripod mounted device, it would still
"shake", especially in a location with large buildings as you describe. 
I see no evidence that it was a laser, or that it was not a reflection
off something in your room from your own light.  So I will ask some more
questions-- I am interested in helping, but I need to know more: 

1.  Exactly what time of day was it?

2.  Was there direct sunlight outdoors anywhere in the vicinity of your
neighborhood at the time? (ie, daytime, and not overcast skys?)

3.  Were there any artificial light sources in your "abode" at the time?
And again, I mean ANY?

4.  Was there any traffic, or even a parked vehicle visible from your
window at the time?

5.  Were there any artificial sources of light outside, such as street
lamps, commercial lighting, etc?

6.  Were there any exposed reflective surfaces in your "abode" at the
time--
such as a mirror, tv screen, silverware, cd-rom disks, jewelry (even on
your girlfriend), brass knobs, furniture hardware, shiney book cover,
plastic buttons, anything?

And do me this favor:  recall the exact physical locations of where the
spot of light occurred.  Go to those locations and place your right
eyball as closely as possible in those locations.  Look at the world
around you from those locations and tell me if you see any reflective
surfaces (they don't have to be reflecting anything at you at the time).
Also note exactly what can be seen out of the window from those
locations.

Fulfill these needs for details, and I will try to be of more help!

Bill Bailer

\\\  William Bailer ("Bill")
\\\  Rochester, NY, USA;  Phone (voice): 716-473-9556
\\\  wbailer@concentric.net (same mailbox as wbailer@cris.com)
\\\  Some interests: acoustics, JS Bach, anthropology, & education.

In article <4urchf$m16@news.rhrz.uni-bonn.de>,
Thorsten Franz <UZSD78@Uni-Bonn.DE> wrote:
 >Hello,
 >
 >when I was sitting in my living room tonight, a spot of red light (at
 >most one inch in diameter) appeared on the wall and wandered over it,
 >coming to rest on the back of the head of my girlfriend. I wasn't able
 >to determine the exact size because it was obviously steered by a
 >shaking hand.
 >
 >I thought it might have to do with a construction site across the
 >street and went downstairs to check, but found noone. From down there
 >it was clear that the angle wasn't right anyway and that the beam must
 >have come from one of the dark windows in a nearby administration
 >building, probably 5th or 6th floor.
 >
 >A laser pointer, as used for presentations on blackboards, would have
 >been too unprecise over the estimated distance of 100 meters. I don't
 >know of lab lasers with in-built magnifying glasses, and when you play
 >with measuring devices you don't aim them at people's head because you
 >are probably professional enough to know about the danger of blinding.
 >You would also use a stand.
 >
 >So I figure someone might have been playing with the aiming device of
 >a rifle, especially considering how restless the spot was. I will go
 >to the police tomorrow and report the scary incident. If anyone can
 >give me information that might be useful, confirm my suspicion (so I
 >have something at hand when talking to a lazy officer), or calm me
 >down, I will certainly appreciate it. :-)
 >
 >Maybe a physicist can draw conclusions from the estimated distance and
 >approximate diameter of the beam, or you know what else portable,
 >aimable lasers without a stand/tripod are made for.
 >

I think the gun lasers are basically the same as the pointers
used. I basically use the pointer to do the same types of things,
shining through windows, activating shooting galleries
at amusment parks, and general fooling around.
Each device focus is variable and sometimes adjustable.
I would judge a 100 meter, spot the size of a quarter is not
unheard of using a solid state device.

greg

On Wed, 14 Aug 1996 02:03:58 GMT, UZSD78@IBM.RHRZ.Uni-Bonn.DE
(Thorsten Franz) wrote:

>Hello,
>
>when I was sitting in my living room tonight, a spot of red light (at
>most one inch in diameter) appeared on the wall and wandered over it,
>coming to rest on the back of the head of my girlfriend. I wasn't able
>to determine the exact size because it was obviously steered by a
>shaking hand.
>
>I thought it might have to do with a construction site across the
>street and went downstairs to check, but found noone. From down there
>it was clear that the angle wasn't right anyway and that the beam must
>have come from one of the dark windows in a nearby administration
>building, probably 5th or 6th floor.
>
>A laser pointer, as used for presentations on blackboards, would have
>been too unprecise over the estimated distance of 100 meters. I don't
>know of lab lasers with in-built magnifying glasses, and when you play
>with measuring devices you don't aim them at people's head because you
>are probably professional enough to know about the danger of blinding.
>You would also use a stand.
>
>So I figure someone might have been playing with the aiming device of
>a rifle, especially considering how restless the spot was. I will go
>to the police tomorrow and report the scary incident. If anyone can
>give me information that might be useful, confirm my suspicion (so I
>have something at hand when talking to a lazy officer), or calm me
>down, I will certainly appreciate it. :-)
>
>Maybe a physicist can draw conclusions from the estimated distance and
>approximate diameter of the beam, or you know what else portable,
>aimable lasers without a stand/tripod are made for.
>
>Thank you very much,
>kind regards
>
>-- 
>uzsd78@uni-bonn.de
>

If it is the size of 1 inch, you can look into it.
The energy which reaches the retina is small
enough. Then you will know from where it comes.

Do a short calculation:
Original Laser beam diameter = 1 mm
Power in the range 1 to 4 mW usually
Diameter at your window = 25 mm
Intensity per square mm is....
The light has to fill the whole area.

Diameter of eye pupil = 5 mm
how many mW reach the retina?

Red Lasers below 1mW and a diameter of 1mm are
not dangerous, because the eyelid will close
automatically before a damage will occur.
That's why infrared is much
more dangerous.

You can risk a short glimpse.

yours,
wabi


--
==================================================
  W E  A R E  T H E  M I S S I N G  L I N K   !
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Here are         Here               There will be
         ------>  we   ----------->  -possibly-
the apes         are!               Homo Sapiens
==================================================

In article <32121610.3129776@news.carinthia.co.at>,
wabi@mail.carinthia.co.at (Helmut Wabnig) wrote:

> On Wed, 14 Aug 1996 02:03:58 GMT, UZSD78@IBM.RHRZ.Uni-Bonn.DE
> (Thorsten Franz) wrote:
> >when I was sitting in my living room tonight, a spot of red light (at
> >most one inch in diameter) appeared on the wall and wandered over it,
> >coming to rest on the back of the head of my girlfriend.

> You can risk a short glimpse.
> 
> yours,
> wabi

  Or if it happens again, tell your GF to stay still and make a mark on
the window where the beam passes through it (find the place by seeing
where your body interrupts the beam if necessary).  After the beam is gone
you can sight along the GF-to-spot line and see whence it's coming.

Ron
-- 
Ron Larkin (r-larkin@uiuc.edu)
Illinois Natural History Survey, Champaign IL 61820

Your assumption that the device was hand held might be wrong.  If the beam 
were properly collimated it could have come from a great distance where even a 
tripod mount would have considerable jitter.  

More than likely, what you had was someone listening on your conversation 
through an amateur reflectance or interference device.  This would use a laser 
(professional devices would use an infra-red laser) to produce a reflection 
from your window which would be detected and amplified, or compared to a 
reference beam, to produce an audio output.  These devices are easily built, 
and often mounted to a small telescope or binoculars for an optical system for 
detection.  Since the glass in your windows will vibrate from any noise in the 
room, these devices can be quite sensitive.

Laser gun sites are usually only useful on side-arms which have a useful range 
that would be far smaller than the range required to produce a 1" beam 
divergence.  Long distance firearms would require so many adjustments for 
using a laser site at various distances that it would be impractical to use 
one.  A professional would just as soon use a standard telescopic site - an 
amateur would simply miss.


In article <4urchf$m16@news.rhrz.uni-bonn.de> UZSD78@IBM.RHRZ.Uni-Bonn.DE 
(Thorsten Franz) writes:>From: UZSD78@IBM.RHRZ.Uni-Bonn.DE (Thorsten Franz)
>Subject: Question: Curious Laser Beam
>Date: Wed, 14 Aug 1996 02:03:58 GMT

>Hello,

>when I was sitting in my living room tonight, a spot of red light (at
>most one inch in diameter) appeared on the wall and wandered over it,
>coming to rest on the back of the head of my girlfriend. I wasn't able
>to determine the exact size because it was obviously steered by a
>shaking hand.

>I thought it might have to do with a construction site across the
>street and went downstairs to check, but found noone. From down there
>it was clear that the angle wasn't right anyway and that the beam must
>have come from one of the dark windows in a nearby administration
>building, probably 5th or 6th floor.

>A laser pointer, as used for presentations on blackboards, would have
>been too unprecise over the estimated distance of 100 meters. I don't
>know of lab lasers with in-built magnifying glasses, and when you play
>with measuring devices you don't aim them at people's head because you
>are probably professional enough to know about the danger of blinding.
>You would also use a stand.

>So I figure someone might have been playing with the aiming device of
>a rifle, especially considering how restless the spot was. I will go
>to the police tomorrow and report the scary incident. If anyone can
>give me information that might be useful, confirm my suspicion (so I
>have something at hand when talking to a lazy officer), or calm me
>down, I will certainly appreciate it. :-)

>Maybe a physicist can draw conclusions from the estimated distance and
>approximate diameter of the beam, or you know what else portable,
>aimable lasers without a stand/tripod are made for.

>Thank you very much,
>kind regards

>-- 
>uzsd78@uni-bonn.de


Allen R. Sampson

Advanced Research Systems
317 North 4th. Street
St. Charles, IL 60174

PH (708) 513-7093  FAX (708) 513-7092
EMail: ars@mcs.net  WWW: http://www.mcs.net/~ars/home.html

repair and maintenance services for analytical instrumentation

>
>> On Wed, 14 Aug 1996 02:03:58 GMT, UZSD78@IBM.RHRZ.Uni-Bonn.DE
>> (Thorsten Franz) wrote:
>> >when I was sitting in my living room tonight, a spot of red light (at
>> >most one inch in diameter) appeared on the wall and wandered over it,
>> >coming to rest on the back of the head of my girlfriend.


"Ronald P. Larkin" <r-larkin@uiuc.edu> writes

>  Or if it happens again, tell your GF to stay still and make a mark on
>the window where the beam passes through it (find the place by seeing
>where your body interrupts the beam if necessary).  After the beam is gone
>you can sight along the GF-to-spot line and see whence it's coming.
>
>Ron



WARNING:
Anyone who tells his girl friend to stay still while he measures where
the laser gun sight on her head is coming from, is very likely going to
loose his GF, one way or another !
-- 
Keith Stein

>You cannot conclude that it was "obviously steered by a shaking hand". 
>The change in position of any light beam over a distance, is very great
>in realation to slight changes in angle.  Over large distances, a
>shaking hand could not be steady enough to hold a spot steady enough to
>be noticed.  If it was from a tripod mounted device, it would still
>"shake", especially in a location with large buildings as you describe. 
>I see no evidence that it was a laser, or that it was not a reflection
>off something in your room from your own light.  So I will ask some more
>questions-- I am interested in helping, but I need to know more: 
>

With regards to the statement that someone cannot hold a beam on a target at 
around 100 meters  steady enough for the beam to be noticed is not true.  I 
know from experience that it is possible that an experienced shooter could 
hold a rifle steady enough to hit a target 6" in diameter at up to 1000 yards. 
 100 meters is nothing.  When you use a laser sight with a rifle over long 
ranges (too far to see the dot) you have to use some sort of a magnifing sight 
to be able to tell where exactly you are aiming.  However if the window was 
closed then the light would have been defracted out of the shooters scopes' 
sight picture.  This would not have allowed them to get the dot to the persons 
head, since they couldn't see it themselves unless they had a wide-field scope 
which would let them see the dot even though that was not where they were 
aiming the gun itself!

On 17 Aug 1996, ironman wrote:

>William Bailer wrote to Thorsten:
>>The change in position of any light beam over a distance, is very great
>>in realation to slight changes in angle.  Over large distances, a
>>shaking hand could not be steady enough to hold a spot steady enough to
>>be noticed...

Ironman wrote:
>With regards to the statement that someone cannot hold a beam on a target at 
>around 100 meters  steady enough for the beam to be noticed is not true.  I 
>know from experience that it is possible that an experienced shooter could 
>hold a rifle steady enough to hit a target 6" in diameter at up to 1000 yards. 
> 100 meters is nothing.

To Ironman, Point #1:
I must agree with your point about the steadiness of a marksman's hands.
I was responding to the suggestion of Thorsten that it could be a
hand-held pointing device of the sort that is used to point at a map in
a class-room, etc.  The individual using such a device is not a
marksman, and is not aided by the shoulder support and the stability of
the mass of a heavy piece of steel (rifle).

>When you use a laser sight with a rifle over long 
>ranges (too far to see the dot) you have to use some sort of a magnifing sight 
>to be able to tell where exactly you are aiming.  However if the window was 
>closed then the light would have been defracted out of the shooters scopes' 
>sight picture.  This would not have allowed them to get the dot to the persons 
>head, since they couldn't see it themselves unless they had a wide-field scope 
>which would let them see the dot even though that was not where they were 
>aiming the gun itself!

To Ironman, Point #2
Sometimes even educated people forget what it is they are trying to
visualize.  I think you confused the path of a bullet with the paths of
light, and in this case, it is only the paths of light that concern us.
The path of the light from the laser would be exactly the same as that
to the scope.  Even if the window were a thick prism, a foot thicker
thicker on one edge than the other, it would make no difference, and the
laser spot would always be in the same place in the view-finder scope--
the refraction of the glass window is exactly the same for both light
paths, and you would have no way of knowing that the refraction had
occurred.  If you fired the gun, only THEN would you discover the visual
shift, for the bullet would not hit the spot--  but unfortunately, this
is irrelevant!  Now go ahead, slap your forehead, and yell at yourself!
:=)

Bill Bailer

\\\  William Bailer ("Bill")
\\\  Rochester, NY, USA;  Phone (voice): 716-473-9556
\\\  wbailer@concentric.net (same mailbox as wbailer@cris.com)
\\\  Some interests: acoustics, JS Bach, anthropology, & education.