NVG - How do they work?

[Hueymeister]

Looking for some hints as to a document with diagrams that I can use for lesson. Have googled and only got ads for devices. AP 3456 has proved a fruitless search too. Thanks in advance.

HM

[[email protected]]

It's all a black art to me.

[adr]

You might find this resource (http://science.howstuffworks.com/nightvision1.htm) useful.

adr

[Lima Juliet]

Simply get two SMARTIES (TM) tubes, put some green cellophane over the ends and try doing close formation on a Ford Mondeo on the M1 whilst wearing them. You'll soon see how they work...

LJ:E

[Hueymeister]

Thank you ADR...can't seem to copy the all important pictures though..anyone out there got a cross-section diagram?

[MightyGem]

Of course, the important thing to remember is that they must have some light to work. They won't work on an overcast night out in the middle of the middle of nowhere without any cultural lighting.
http://img.photobucket.com/albums/v465/MightyGem/nightvision-tube.jpg

[Hueymeister]

Now I'm showing my non-adeptness with the box...but whenever I try to 'save as' I get an image I can't look at....HELP!!!!!!

[Rakshasa]

hmm Have you got software that can view Jpegs? maybe try flicking it ove to .Bmp and using paint?

[Hueymeister]

Tried that..still won't play......

[wg13_dummy]

Huey, if you are able to see 3456, you may be able to get hold of H21. There is quite a good bit of gen in the front ref 'how NVG works'. Very laymen and easy to digest too.

[petitfromage]

The most important thing to remember is that in perfect conditions the very best visual acuity you can get from a GEN 3 NVG is 20:200

What does that mean?

Well, you could claim a disability benefit for being "legally blind".....and you can never hold a drivers licence.

Of course its pefectly OK to fly around 'safely' at 25ft, 140kts at 0.2mLux, being shot at!

:confused:

[snafu]

Huey

Try typing "night vision goggles theory -game" into Google. This will bring up a few sites that give the theory and avoid the reviews for games that involve NVG.

This will bring up sites like:

ATN Corporation (http://www.atncorp.com/HowNightVisionWorks)
or
Physlink (http://www.physlink.com/Education/AskExperts/ae356.cfm)
:8

[Captain Kirk]

Huey,

PM me your email and I will send you a ppt presentation - it's a few years old but should suffice. What is your target audience?

[Stitchbitch]

[quote]petitfromage
The most important thing to remember is that in perfect conditions the very best visual acuity you can get from a GEN 3 NVG is 20:200

What does that mean?

Well, you could claim a disability benefit for being "legally blind".....and you can never hold a drivers licence.

Of course its pefectly OK to fly around 'safely' at 25ft, 140kts at 0.2mLux, being shot at! [end quote]

Just do me a favour and remember to take your daylight filters off first or you WILL think you're blind... :O

I remeber a guy on Gr.7's who actually tried to attach his goggles the wrong way round (ala binos).Nice one FAQ!

[Onan the Clumsy]

That's like the story someone told me of where he bought some Foggles and just couldn't wait to play with them...


...so he put them on while he was driving his car to the airport.

:} :}


(I'd believe it with him too)

[Bclass]

Try this:

http://www.photonis.com/en/pdf_download/Principles%20of%20IITs.PDF

The result of a search based on quite a few (un)happy days super gluing fingers to broken Anvis & Nite-Ops whilst waiting for the Swift to open…

[US Herk]

The most important thing to remember is that in perfect conditions the very best visual acuity you can get from a GEN 3 NVG is 20:200

Errr...OK, I'll bite - I'm not sure which GEN 3 goggles you're using, but GEN 3 are good to 20/40 or so. GEN 4 are good to 20/25 with a few sets hitting 20/20 on the Hoffman tester (mine do every time).

What does that mean?

Not sure if this is serious or not:confused: , but at the risk of egg sucking - visual acuity is measured on a relative scale against average vision. Traditionally this distance is 20' (6m now that Imperial is a bad word). So 20/20 (6/6 = 20/20) means you can see at 20 feet what the average person sees at 20 feet. 20/200 means you can see at 20 feet what the average person sees at 200 feet & yes, you are legally blind!.

Of course its pefectly OK to fly around 'safely' at 25ft, 140kts at 0.2mLux, being shot at!

Although not necessarily intuitive to the non-NVG experienced folks, when illumination is poor, flying lower makes it easier to see!:D

[16 blades]

My understanding (from CAM orientation cse) is that the best one could expect (on average) was 6/18, which whilst not quite 'legally' blind, would be illegal for driving in the UK! Still, good enough for what we need them for at night, as long as you stay well away from pylons! on nights with good mlux levels, I have been able to see right into some houses with poorly lit rooms when flying slowly (on appch and DZs) - now THATS spooky!

16B

[sikhorsey]

For Mighty Gem
'Of course, the important thing to remember is that they must have some light to work. They won't work on an overcast night out in the middle of the middle of nowhere without any cultural lighting.'
I would have to disagree old chum. Have had plenty of nights over the last 15 years with overcast in the middle of nowhere without any cultural lighting (whatever that is, must be something that occurs in old blighty that us colonials can only dream about), in formation at 50' landing in dusty pads when the gogs worked just fine. Then again most of the time I had my eyes closed and just hoped for the best.
Cheers Sikhorsey.:D

[adr]

Cultural lighting = light from towns, villages, farms, roads, refineries, car importers' compounds (Lincolnshire at night!), and so on, reflecting down from the cloudbase. I've heard it called 'cityglow' (not quite right for Lincolnshire at night).

adr

[L Peacock]

US Herk

You've educated me. But does that really mean 20/20 merely defines average vision, not perfect?
I had always assumed 20/20 was as good as it gets.

[MightyGem]

Sorry Sikhorsey, as shown in the diagram, gogs work by amplifying the light that comes in the front. If there's no light going in, there's nothing coming out. I've been there.

http://img.photobucket.com/albums/v465/MightyGem/nightvision-tube.jpg

[MadsDad]

L Peacock.

The 20/20 is the ability to read a certain size font at 20 feet (can't remember the size though) with each eye. Also these days referred to as 6/6 (same test, 6 metres).

20/20 is a good average but if you could read it further away you could, for instance, have 24/26 vision, or something like that. (As opposed to me with about 02/04 - out of 20).

[Hueymeister]

Thanx....worked a treat....so tvm.

HM

[US Herk]

You've educated me. But does that really mean 20/20 merely defines average vision, not perfect?

There is no such thing as perfect vision. You've nailed it - 20/20 is really just an average, but it is more than that, it is the accepted benchmark for "perfect" eyesight.

It is quite possible to obtain better vision. My near vision, for example is 20/15 & used to be 20/10 when a youngster - as did my distance vision (which is now marginally 20/20 on a good day:ugh: )

20/15 means that I can see at 20 feet what the average person has to move up to 15 feet to see.

I recall when my vision started to slowly degrade as I got older - when I got to 20/20 I thought "F*** me! This is what everyone else sees?!":ooh:

My understanding (from CAM orientation cse) is that the best one could expect (on average) was 6/18, which whilst not quite 'legally' blind

16B - if you're flying with Fen-2000 (which I think you are), you should do much, much better than 6/18. You should be closer to 6/8 in the Hoffman....

Realize that Hoffman & real-world are close, but not quite the same. Everything you put between your eyes & the goggles (like glasses or contacts) & the goggles & the object you're viewing (like windscreens, airborne dust, obscurants, etc.) & it degrades significantly.

Also, it is essential to be viewing through the exact centre of the goggles to obtain the best resolution. And the gogles need to be tilted to 0 in reference to your eyes. As your helmet sags a bit, your vision degrades as you look through a (potentially) less capable portion of the tube with a (potentially) less capable portion of your eye.

The key is the micro-channel plate. When I got my training as an NVG instructor several years ago, the early Gen III tubes were state-of-the-art. At that time, there were something like 3,000 tubes in the micro-channel plate, all lined internally with lead, & tilted at 8-degrees. All in something only slightly larger than a 10p piece. As the electrons are released by the photo-cathode, they will strike the edges of the tubes (why they're tilted) & as the electron bounces into the side of the tube, it releases two electrons, both of these will deflect off the tube at an angle equal to their impact angle & will likely strike the tube & each release two more electrons & so on & so on - so that the electrons end up multiplied something on the order of 3000-4000 times before they hit the phosphor screen.

So, yes, there must be SOME light entering. Sikhorsey, I have no doubt that you have flown on "zero illumination" nights, with no moon & <0.2 mlux w/cloud cover, but there's always SOME light about...if your goggles aren't scintillating, you've got adequate light. And the lower you fly on a dark night, the easier it is to see! So 50' is easier than 300' I'm at & I'm going twice as fast as you when I fly on those dark as ink nights!:ooh: