peter173 wrote in post #11638007
To me he was trolling, wikipedia a crappy source? lol...
No Peter I wasnt Trolling, and yes Wikidpedia is a crappy source. Anyone can go in there a change a definition in Wikidpedia.
also your post would be much more valuable if you wouldn't use abbreviations that nobody understands. NOHD? MPE?
Kendon, The abreviations for those things you stated are spelled out in the post, as well some of those abbreviations are mentioned in earlier posts and are talked about in more detail. the first time an abbreviation is used it is spelled out right next to it. But since you called out those two abbreviations specifically ill be happy to define them.
NOHD is NOminal Occular Hazard Distance, this is the distance from the aperture of the system to your eye in which you are safe and no eye damage will be incured. Grunt terms eye safe distance.
MPE is Maximum permisable Exsposure Limit, this is the Maximum allowable energy within a set distance that an eye can be exsposed to Laser radiation before damage will incure.
a reflection carrying the same energy as the beam? 100% reflective surfaces? i take it you work with NASA then...
Yes a specular reflection will carry the same energy of the main beam due to the fact that the is merly redirected. Since this is a Hazard more comin in HIgh Powered systems, the amount of fall off from the redirection is so minimal it wouldnt make a differance. Here is an example.
If the NOHD if a system is 50 feet and you fire that LASER at lets say a Mirror and you are ten feet away. If that beam hits that mirror on the right plane and the right angle to reflect back toward your eye and hits you then there is a very high probability you will incure eye damage. The reason is NOHD is a cumulative measurment . The 10 Feet there and 10 Feet back dont equal to greater than 50feet and therefor you r still within the NOHD. Now if you shot the LASER from a distance of 26 Feet and it hit the Mirror then 99.9999999% of the time you will be fine, but there is always the fluke accident.
Every LASER in the US that is higher than a Class 1 must have a label on it. This LABEL must have the Power Output of the system and the NOHD on it.
how does a coherent, parallel beam lose power over distance? and we're not talking infinity here, you said 3ft vs 3.1ft?
Yes it is a coherant beam, but what you are not accounting for is beam divergance ( spread of the beam). Every LASER is built for a differant thing. A LASER pointer is designed to point things out , so the beam is very tight and has a very low divergance. But a LASER for a LASER light show or a LA-9P ( Military Hail and Warning LASER ) is specifically designed to spread over distance so it has a much larger divergance, in this case about an 18 inch spread every 100 Meters. So the NOHD is based upon the size of a Laser and how much energy it can place on the eye over distance as well as the type of Laser Wavelength, the Beam Path and the LASER beam profile ( Top Hat, Gausian etc...). So in my example the Maximum Permissable Exsposure Limit (MPE) set that Nominal Occular Hazard Distance (NOHD) at 3Feet because of that beams power output and divergance exceded that MPE at 3 Feet, beyond 3 Feet the amount of energy now being placed on the eye is less than the MPE and there for "SAFE"
you said you fired a laser for much longer than in the videos at your sensors. this information is pretty much useless without knowing at least the output power of the laser. i can take an el-cheapo laserpointer that maybe outputs 0.5mw, and shine that at my sensor until the batteries run out and nothing will happen, but that doesn't tell us anything about the several 100 mw that are used at laser shows...
Come on Kendon, do the pictures I posted look like a .5mw Laser to you, but hey ill be happy to share it with you. One of those Lasers is a 250MW system on pulse mood, on continuous it drops to about 175MW of power ( all Lasers do this but its to much to type to go into ) and the other is a 1W System.
Yes I wrote this at 11 pm last night and was trying to be as vague as possible for certain reasons, as well as to keep it as simple as possible so as to not have people think I work for NASA ( which I dont ).
then where does the damage come from? care to elaborate?
I have no clue, but based off of the conversations with Canon, Nikon, JVC, and Sony's technical personel a 532NM LASER System up to and slightly above 1W will not damage the sensor on any of the Cameras we were using, and we used everything from the 7D, 5DMKII, Nikon D300, Nikon D3, Sony Digital HD Records, JVC Digital HD Recorders and a slew of other recording systems, in all to gather more than 150 Hours of digital images.
More than 50% of this digital movie gathered has LASER's pointed directly into the lens of the system being used to record ( both Still and Video ) with no adverse effects. And at distances from far away to as close as 3 feet. In the case of the 7D, i use this camera just about every day and it has no deffects what so ever.