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problems with my NV goggles

— Posted by Hergor on 11:18 am on Feb. 18, 2002

does anyone know what exactly happens when an over-ammount of light enters the image intensifier tube of NV devices?

a friend of mine (that darn bastard, grrrr) aimed my NV goggles at a car’s top searchlights and now i got a little ‘star’ in the upper right corner…
it also flashes from time to time originating from that small mark.

do you know a way to undo this damage and restore a clear view or has the photo cathode or the microchannel plate taken irreversible damage?

— Posted by OzzY on 3:00 pm on Feb. 18, 2002

take a baseball bat and take a small “visit” to your friend.. feel fine?!
so go to an electronics store and ask for a reparature service 😀

— Posted by Hergor on 6:00 pm on Feb. 18, 2002

Quote: from OzzY on 3:00 pm on Feb. 18, 2002
so go to an electronics store and ask for a reparature service 😀

well, actually i was thinking if somebody might explain the process of ‘over-lighting’ to me 🙂

but looks as if i’ll have to go to the electronics store anyways

— Posted by Zambosan on 11:10 am on Feb. 19, 2002

You’ve probably got some permanent damage.  Photomultiplier tubes typically consist of a semiconductor layer that uses the photoelectric effect to eject an electron when hit by a photon of infrared and near-infrared light.  These electrons are then accelerated across a semiconductor diode junction, amplifying the signal by generating many more electrons (typical gain is 1000, or 60 dB), which then impinge upon a phosphor screen, generating a display similar to a CRT monitor.  If you have too high of an input signal, the current through the diode layer(s) can damage the crystalline nature of the silicon junction, destroying its semiconducting properties and turning it into a conductor.  This will murder your signal-to-noise, resulting in “false” images.  Newer NV devices have protection against over-input, turning off the photomultiplier until light levels fall below a safe level… but these devices cost more.  Sorry for the bad news, but I think your device is fried, hopefully not to the point that it’s useless. 🙁

— Posted by Hergor on 11:23 am on Feb. 19, 2002

thanks for the info.

no it’s still operational but it’s flashing from time to time like i said…

i’ve been looking for a head mounted device anyway…

— Posted by qube on 6:02 pm on Feb. 19, 2002

How much are night-vision goggles? I saw sum in Argos for 20 but they were just a pair on glasses with a torch attatched on them…..
OH and also it is most likely permanent damage, its like shining a laser pen in a webcam or your eye for too long.

— Posted by Hergor on 10:35 am on Feb. 20, 2002

mine are worn-out russian military NV goggles. i got them from an unofficial market in ‘stetin’ (near the border from germany to poland). they did cost me about 80 euros (at that time 160 german marks).

new head mounted NV goggles with ‘milspec’ rating cost from 400 euros to 2500 euros…

— Posted by balor on 3:14 pm on Feb. 20, 2002

No offence Qube but I would rather trust Zambosans diagnosis of the problem as he has a scientific background and knows what he is talking about.I mean really 20 at Argos.LOL

— Posted by qube on 6:36 pm on Feb. 20, 2002

Yes, i never doubted his diagnosis, just confirmed it. Haha, and that was a joke abotu the shitty Argos goggles….hehe what peice of shit!

Also, Hergor thanks for telling me, i may have to go to a market of such you went to, it seems kool, and i would love to get my hands on some nv goggles.

Also spell it qube, i dont like capital letters! lol!
AND one more thing, im only 15, dont expect me to be a war veteran or scientific genius 😀 lol!

— Posted by Zambosan on 10:15 am on Feb. 21, 2002

Hergor, given that it only flashes from time to time, it sounds as if the damage isn’t as extensive.  There’s obviously been some damage in the microchannel layer, but it’s only fused a small bit of the semiconductor.  The effect is a lowered threshold voltage, which is why that portion of the device “flickers” on even in the absence of any meaningful signal.  But if it had been completely melted, it would conduct all the time, resulting in a persistent patch of white on your display… which would probably also “burn” the phosphor like an old monochrome monitor.

— Posted by Hergor on 12:07 pm on Feb. 21, 2002

well, luckily the damage isn’t that hard.

but do you think if it was constantly conducting this would cause more electrons to flow thus making the spot grow bigger and as a result ‘blind’ the phosphorus layer?

— Posted by Zambosan on 12:20 pm on Feb. 21, 2002

Because of the structure of the microchannel layer, I don’t believe the damage can spread; the electrons will want to follow the path of least resistance to the positive terminal, so they shouldn’t affect neighboring areas.  However, the same principle *may* cause charge carriers from neighboring areas on the substrate to flow towards the damaged area, resulting in reduced sensitivity to images in the surrounding region… you may or may not notice this as increased darkness around the bright spot.  The layer of nerves that covers your retina actually produces this effect in your eye; if a rod or cone cell stimulates a retinal nerve to fire, the output of that nerve cell will feed a subtractive input to its immediate neigbors, effectively raising its firing threshold.  The result is a point spreading function (the 2-D equivalent of an impulse response in a one-dimensional filter) that looks like a peak with a shallower valley around it, kind of like a Daubechies wavelet.  The result in your vision is that edges are enhanced, allowing the pattern-recognition circuitry in your brain to identify separate objects more easily, even when the edges are rounded and gradual.  So you may not even notice this secondary effect of the damage to the photomultiplier, since your eye is already attenuating the signal in the area around the bright spot when you’re viewing it.

— Posted by Hergor on 1:45 pm on Feb. 21, 2002


i just wanted to make sure no additional damage may occur during further use if exposed to relatively ‘bright’ (still in usual levels) sources of light. 🙂

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