NVD FAQs

Discuss night vision equipment and technology

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NVD FAQs

Postby Kalua1969 » Mon Nov 06, 2006 3:09 pm

* Please note that this is just a simple outline of the most-frequently asked questions regarding NVD units and purchasing factors commonly found throughout the forum. Most general questions can often be found by using the "Search" option link provided at the top of this page.
You may also post your question(s) within the "General Night Vision Discussion" forum, to which we have dozens of very helpful and friendly members who are always willing to share their knowledge and expertise regarding NVD's with you.

THE BASICS:

Q: I'm new to night vision devices. Can you give me some information on how these things work?

A: This link will provide you with very good information about how NVD's operate, as well as the technological evolution of Generation 1, Generation 2, and Generation 3 devices...
http://www.nightvisionmall.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=ANV

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Q: I am planning to purchase my very first NVD. What should I look for in a good NVD unit?


A: There are many factors that could affect your decision. First, ask yourself what your primary usage of the unit will be for? NVD's come in a variety of shapes and sizes, as well as performance levels... from simple hand-held monocular's, head-mounted / hands-free units, long-range binoculars, and hunting / tactical rifle scopes. These can be used for scenarios such as home / work security observation, viewing nocturnal wildlife, or hunting. "Multi-purpose" units are often a favorite since they can be configured to fit a variety of such roles.

Next, consider the cost of investment. NVD's are very sophisticated devices, and "technology" does indeed come with a price tag...

$ - Lower-cost 1st Generation units can do the job just fine for those on a very limited budget. These units are a great bargain for basic recreational usage by entry level NVD enthusiasts.

$$ - 2nd Generation units have always been a favorite for those willing to invest a little more for a step up in clarity, gain, and extended tube life over Generation 1.

$$$ - 3rd Generation units are quite costly, but are the closest you will get to actual military quality, with very high resolution / clarity, gain, and very long tube life.

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Q: Are there risks in purchasing a used NVD unit?


A: In short, yes. Many people often browse online auction web sites to purchase used NVD devices being sold by private sellers. Unless you have the opportunity to handle and test the unit yourself prior to paying, you never really know what you will be getting. Basically, you will be taking the word of the seller in that the unit is 100% fully-functional.
Though many private sellers are indeed very honest people, we have also heard many horror stories in the forum of purchases gone horribly wrong with highly flawed units with dead power sources, burnt tubes, are overly-blemished, have switched tubes, high-hour count on used tubes, etc. The list can go on and on with the risks that you will take in purchasing a used NVD unit.

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Q: If purchasing a used NVD unit is a risk, who do I turn to?


A: Simple... a reputable NVD dealer. This is the absolute safest option you will have on your investment. Purchasing from a reputable dealer assures you of a brand new NVD unit which is covered by a full manufacturer's warranty. If your unit arrives in inoperable condition, it can often be quickly replaced for you with a fully-functional one within days. You also have the luxury of talking one-on-one with experts within the field of civilian, law enforcement, and military NVD devices in regards to any questions you may have with your purchase.

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Q: I do not live within the United States. May I still purchase night vision devices?


A: Yes and no ---
Yes... 1st Generation has no export restrictions, while 2nd Generation / Mil-spec. units can be exported, but must be accompanied with a proper data sheet indicating that its tube operates within specific parameters in accordance to export laws (you may also need an export license from Department of Commerce).

No... 3rd and "so-called" 4th Generation NVD's are not legal for export. The exception to this is the proper license(s) from the U.S. Department of State must first be obtained and approved. Also, it may be a good idea to check your own country's import laws regarding the purchase of such devices from the U.S.. Several countries have local regulations and/or restrictions regarding the use of NVD scopes for hunting.

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Q: Lately I've been seeing a lot of hype about "digital" night vision devices. Are these the same as regular NVD's, and, are they better?


A: No... "digital" night vision is NOT the same as standard NVD's. Despite all the hype by marketers, digital night vision devices (D-NVD) do not even come close to the performance of true NVD's.
First, D-NVD's utilize a CCD imager, rather than a photocathode tube. These special imagers require an external illumination source to be effective, usually in the form of several IR-LED bulbs (infrared light emitting diodes). This thereby makes the D-NVD a "non-passive" system... meaning, you would quickly and easily be spotted by others using standard NVD's. D-NVD's do not convert ambient light (moonlight, starlight, etc.) to be truly "passive".
Secondly, IR-LED's on many, if not all, of these D-NVD units are extremely limited in range... typically no more than 20 - 25 or so yards at best. For these reasons alone, D-NVD's are not better in any way when compared to truly "passive" NVD units (which obviously explains why the military DOES NOT use digital night vision whatsoever).
Again... do not fall for the fancy words and marketing hype by sellers insisting that "digital" night vision units outperform standard NVD's.
(*** NOTE: This site does not really discuss "digital" night vision devices since the forum is mainly geared towards "passive" commercial, law enforcement, and military-grade NVD's)

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Q: What is "geometric distortion"?


A: The term "geometric distortion", or commonly known as the "fisheye" effect, is a visual trait inherent of all 1st Generation NVDs due to early tube / lens design. When viewing objects through such tubes, the center appears quite sharp and focused, while the area within the mid to outer edges of your visual field will appear distorted and fuzzy.

To visually explain this effect, the object being viewed in the following pictures are that of horizontal window blinds. The first picture, as viewed through a 1st Gen. NVD, clearly shows the "fisheye" effect. The second picture, as viewed through a 2nd Gen. NVD, shows the technological improvements of tube / lens design to help limit or totally eliminate geometric distortion...

Image

Image

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THE TECHNICAL:



Q: How long can I expect my unit to last before naturally wearing itself out?

A: Tube lifespan depends on many factors, both internal and external in source. Generally, if you keep your unit properly protected from continuously extreme bright light exposure, these are the average lifespan of tubes by generations...

1st Generation = 1,500 hours
2nd Generation = 2,500 to 3,000 hours
2nd Generation SHP = 5,000+ hours
3rd Generation = 10,000+ hours

*** Please note that these are "continuous" hours of operation.

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Q: As I browse the forums, I see a lot of acronyms being used (lp/mm, EBI, SNR, etc.). What do these mean?

A: The basic rundown of the most frequently used night vision acronyms...

ABC (auto-brightness control) - A built-in feature which automatically reduces voltage to keep the image intensifier's brightness within optimal limits and protect the tube.

AN/PVS - An assigned military designation for fielded night vision devices. "AN" meaning "Army-Navy"... and... "PVS" meaning "Passive Vision System". Examples: AN/PVS-7, AN/PVS-14, etc.

"ANVIS" is typically designated for military aviation usage ("Aviator Night VISion", or, "Aviation Night Vision Imaging System"). Also used is "AN/AVS" (Army-Navy / Aviator Vision System). Examples: AN/AVS-6, ANVIS-9, etc.

BSP (bright source protection) - Somewhat similar to auto-brightness control in protecting the photocathode from moments of extreme and / or direct bright light exposure (such as automobile headlights, flashlights, room lights, etc.). BSP, while not incorporated into every NVD unit, will cut the voltage to protect a tube from damage.

EBI (equivalent background illumination) - The measured amount of lowest light at which an object can be detected. The lower the EBI value, the better.

FOM (figure of merit) - An image intensification tube designation often used for legal export classifications. Figure of merit can be determined by using the following calculation:
Lp/mm x SNR (signal to noise ratio) = FOM

FPN (fixed-pattern noise) - A characteristic most often seen through 2nd and 3rd Gen. devices under bright light conditions. A notable "honeycomb" or "chicken wire" pattern of the unit's micro channel plate can be seen within the field of view. This is normal and of no cause for concern.

Lp/mm (line pairs per millimeter) - A measurement used to determine a "resolution" rating of NVD tubes. A test pattern, which consists of a series of different sized patterns of three horizontal and three vertical lines is used. You must be able to clearly distinguish all the horizontal and vertical lines, including the spaces in-between, to qualify for a designated resolution pattern rating. Higher lp/mm numbers equate to higher resolution (sharpness in detail to the object being viewed).
SIDE NOTE: Though many 1st Gen. units advertise a 40lp/mm resolution (which may seem higher than 2nd Gen. resolution ratings of 28-38lp/mm) this is only measured from the absolute center of view, as opposed to the overall view.

If you have a tube data sheet and would like to determine your actual Lp/mm rating, you may use the following calculations:
FOM (figure of merit) divided by SNR (signal to noise ratio) = Lp/mm

MCP (micro channel plate) - First used in 2nd Generation NVD's, the MCP is a wafer-thin charged disc containing millions of holes which increases electron output as electrons pass through. This in turn allows the photocathode to produce a significant increase in gain, as well as nearly eliminating the geometric distortion inherent of earlier 1st Gen. units.

NVD / NOD (night vision device / night observation device) - Two of the most commonly used acronyms for night vision units. "NVD" seems to be the most widely used term by civilians, while "NOD" is often used by those within the military.
"NVG" (night vision goggles) is typically used for dual-eye / bi-ocular, hands free units such as the military's AN/PVS-7 goggles.

PR / PS (photoresponse / photosensitivity) - The ability of the photocathode material to produce an electrical response when subjected to light waves (photons). The higher the value, the better the ability to produce a visible image under darker conditions.

SNR (signal to noise ratio) - A measure of the light signal reaching the eye divided by the perceived noise as seen by the eye. A tube's SNR determines the low-light-resolution of the image tube; therefore, the higher the SNR, the better the ability of the tube to resolve objects with good contrast under low-light conditions. Because SNR is directly related to the photocathode's sensitivity and also accounts for phosphor efficiency and MCP operating voltage, it is the best single indicator of an image intensifiers performance.


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* Moderator's Note: This page is an ongoing work in progress. As more common questions are asked within the forum pages, they will be added to this thread.
Last edited by Kalua1969 on Mon Nov 19, 2007 7:57 pm, edited 8 times in total.
Kalua1969
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Postby vincep » Mon Nov 06, 2006 4:12 pm

$$$ - 3rd Generation units are quite costly, but are the closest you will get to actual military quality, with very high resolution / clarity, gain, and very long tube life.


I would like to add that with Michaels(Optics HQ) Gen 3 tubes you do get actual military quality and then some.
Don't buy ATN Nightvision! Ask me and i'll tell you why.
vincep
 
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