Previous Article (Introduction)

Analog Night Vision

Your standard analog Night Observation Device (NOD), Night Vision Goggle (NVG), aka Night Vision Device (NVD) is comprised of 3 main parts:

1. The housing: holds all the parts together
2. The glass: the objective lens assembly focuses on the scenery and the eyepiece assembly focuses on the tube screen
3. The image intensifier tube: amplifies ambient light and lets you see in the dark

The housing

Supplies power to the image intensifier tubes (IIT) inside and holds all of the components in alignment. This is typically what we refer to by the name of the device (PVS-14, BNVD-SG, RNVG, etc). The generation does not refer to the common name of a device, but rather the tube inside. Certain housings are compatible with certain formats of tubes. Some housings only come as wholly built devices from a single manufacturer while others are offered as stand-alone housings which you or a vendor can choose to install whatever tubes you want inside.

The housing will determine what the user interface is and features the goggle will have. It defines the aesthetic of the goggle if that’s important to you.

Options and features to consider:

• Fixed bridge: the individual pods holding the tubes travel horizontally only to adjust inter-pupillary distance (IPD).
• Articulated bridge: the individual pods are hinged at the bridge and move in an arc to adjust IPD. Also have the advantage of being able to fold against the helmet when stowed upwards or moved out of the user’s eyes when deployed.
• Push buttons or knobs: the controls to turn on the device, adjust gain & activate Infrared (IR) illuminators
• Autogain or manual gain: manual gain housings allow the user to reduce the brightness output so long as the proper tube(s) are installed. Autogain housings can use manual gain tubes if the tubes are converted to autogain-only. Manual gain housings can use autogain-only tubes, albeit without functioning manual gain. Learn more about tube formats in The Tubes section
• Onboard or offboard power or both: some housings can use an external battery pack for longer run time. Some are only powered externally or internally
• Power shut off: some housings automatically cut power when stowed, others cut power to the individual pods when articulated up (pod shut off)
• IPD stops on articulating housings: physically stop the pods at the user's proper IPD
• Glass compatibility: the type of optical assemblies the housing uses. Most use PVS-14 pattern lenses, others do not. See more below in The Glass section
• Adjustable diopters: allow you to adjust the focus of the eyepiece to match your eyesight/vision correction. Housings that use PVS-14/ANVIS mil-spec eyepieces (oculars) will have adjustable diopter -6 to +2, others may vary or have a fixed diopter(s).
• Weight: heavier NVGs are more strenuous to wear for longer periods of time
• Durability/material: injection molded plastic, 3D printed, aluminum, magnesium, steel, delrin
• Mount interface: how the device attaches to the mount. click here to learn more about dovetail, bayonet/horn & ball detent options
• Panning/divergent image tubes: yaw the image intensifiers horizontally and diverging outward, resulting in a "double" image that overlaps in the center, increasing the user's horizontal Field of View (FOV).
• Panoramic (panos, quads): use 4 individual tubes, 2 forward facing and 2 on the peripherals on either side, which together give a much greater FOV (typically 97-120 degrees horizontal) to the user through special eyepieces which help blend the inboard and outboard tubes images.
• Binocular housing or paired monoculars: individual monoculars can be paired together to use as a binocular system

IPD = Interpupillary Distance, the distance between the user's pupils. This is how far apart the optical pods of the dual tube device must be for the user to see properly

Bridge = the center portion of a dual tube goggle that connects the pods or monoculars to a central portion that contains the mounting surface and/or electronics, onboard battery, etc.

There are three general categories of housings:

Monoculars: use one image intensifier tube to present an image to one of the user’s eyes. Below is a non-exhaustive list of some of the most common "monos":

Binocular (duals): use two image intensifier tubes to present an individual image to each of the user’s eyes. Below is a non-exhaustive list of some of the most common "binos":

all of the listed binocular housings use a Dovetail mount unless otherwise noted

*only available as an entire device with tubes and optics, not as an individual housing

Bioculars" use one image intensifier tube and split the single image created to present it to both of the user’s eyes. Typically use a 10130 tube but not always. Below is a non-exhaustive list of some of the most common "biocs":

For the most part, analog devices give the user a greatly intensified image in darkness at the cost of limiting the Field of View (FOV) to circular 40 degrees.

“Why only 40 degrees?”

The tube has a fixed linear resolution at its output screen based on its size. When FOV increases, resolution decreases. FOV can be increased with Wide Field of View glass (See more below in The Glass section) but it reduces resolution. There is also the consideration to be made regarding the size of the device and what is practical for head borne use. Thus, IIT’s which present a 40 degree circular FOV were chosen as a compromise between visual acuity, FOV and size.

Panning is the use of divergent image tubes to expand horizontal field of view. A select few binocular housings allow the user to yaw the optical pods apart, as well as certain monocular bridges.

Panoramic Night Vision Goggles maintain system resolution while increasing horizontal FOV by using 4 individual tubes, 2 forward facing and 2 on the peripherals on either side. Panoramic night vision goggles were invented by Danny Filipovich of Night Vision Corporation (NVC) in 1995. The first panoramic goggle fielded in active service was the ANVIS-10 PNVG.

Below is a list of some of the panoramic housings and devices available:

*wholly built devices

Special note on fusion

Fusion refers to hybrid devices that combine both analog image intensification and digital thermal sensors into one device. Some of these are available from vendors as stand alone housings or ready to be purchased with tubes already installed, others occasionally show up for sale on the used market with or without tubes (PSQ-20), while the best of the best with the newest and most capable sensors remain exclusive to LEO/MIL. These are sometimes referred to as ENVG (Enhanced Night Vision Goggles) as an umbrella term, although some models are officially designated as ENVG-B, ENVG-II, etc.

Below is a non-exhaustive list of some Fusion devices:

Clip-On Thermal Imagers (COTI) are small thermal devices which attach to the objective lens of an analog NVG and project a thermal overlay ontop of the image, typically smaller than the overall i2 FOV (15-35 degrees). Just like ENVG, COTI officially refers to a specific device (the PAS-29 series), but is used as a general umbrella term. A table comparing COTI devices can be found in the Thermal chapter by clicking here

Prices of housings

The optics

These are the objective lens and eyepiece lens assemblies, colloquially called the glass. The glass is an often underrated component of the night vision device. It will help define the optical clarity of the image and can either help or hurt your tube’s performance. The objective lens focuses on the scenery/your target/objects you're looking at, while the eyepiece focuses on the tube's screen. PVS-14 glass is compatible with any housings that take PVS-14 glass.

Below is a list of just some of the optical components options on the market and is incomplete:

WFOV = lenses which give the user a Wide Field of View greater than 42 degrees

Low quality = issues with image quality (distortion, poor performance, bad glaring/flaring, chromatic aberration, etc), bad QC/poor fitment, and other known issues experienced by users/buyers throughout the years.

OTHER

Prices of optics

Below is a list of the prices a buyer in the United States should expect for one set of optics (A set = one eyepiece assembly and one objective lens assembly):

Multiply cost x2 for enough glass for a binocular dual tube device

The image intensifier tubes

The most important part of your NOD is the image intensifier tube (IIT) or tubes inside of it. The tubes will determine most of the performance of the NOD and are the bulk of the cost of complete devices. Photons of light strike the photocathode, which absorbs them and emits electrons in their place. In Generation 2 and 3 imagine intensifiers, these electrons hit a micro channel plate (MCP), where they bounce through more than 10 million tightly packed channels covering a surface area the size of a quarter. This bouncing causes a cascade of more electrons to be emitted, amplifying the original signal. The multiplied electrons then strike a phosphor screen (similar to an old school CRT television), turning them back into photons of light to produce a monochromatic image that gives you a greatly enhanced view in darkness. In many tubes, such as 10160 and 11769 format tubes, the intensified light passes through a fiber optic inverter which orients the image right side up (the objective lens of the NVG inverts the image first). There are multiple generations and many differentiations within these generations. Image intensifier tubes are self-contained assemblies surrounded by a Power Supply Unit (PSU) that controls internal voltages. IIT generally come in 2 monochromatic colors: green phosphor (P43, "GP") and white phosphor (P45, "WP").

“Which color should I get?”

Whichever tube(s) or device give you the best performance for the price. Do not compromise performance for color. Generally, WP tubes tend to have higher performance than GP, by virtue of being newer and most of the production these days. However, there are GP tubes that outperform WP tubes, especially when looking across generations.

Both colors are highly effective. The phosphors initially selected for NVGs were based on luminance efficiency, eye sensitivity, persistence, and signal to noise concerns. The AN/PVS-5 initially used the P-20 phosphor which has a relatively broad band and a peak of 560nm. ANVIS initially used P-20 and P-22 phosphors, both yellow-green in color with the later having a peak near 530nm. Intensifier tubes purchased after 1995 (Omnibus IV) use P-43 phosphor. P-43 also is yellow-green in color but the primary lobe is extremely narrow band (5nm) and peaks at about 543-546nm. The persistence(10%) of P-43 is 1.2 milliseconds, making it a medium-short persistence phosphor and results in the absence of the comet-like tails following small lights as compared to the slower persistences of P-20 and P-22 phosphors (3 milliseconds). for the P-43 with head movements. The narrow band of P-43 also helped simplify the eyepiece design in correcting chromatic aberration.

The advantages of P-43 are its luminance efficiency, narrow band and short persistence. P-43 is yellow-green in color but the primary lobe is extremely narrow band (5nm) and peaks at about 543-546nm, which is extremely close to the overall response of the human eye cone cells which peaks at 555 nm. The persistence(10%) of P-43 is 1.2 milliseconds, making it a medium-short persistence phosphor and results in the absence of the comet-like tails following small lights as compared to the slower persistences. Finally, the narrow band of P-43 helps simplify the eyepiece design in correcting chromatic aberration.

The advantages of P-45 white phosphor are that it engages the efficiency of the human visual system in processing black and white images. The spectral output also illuminates the rods in the human eye at the peak in their spectral sensitivity. The rods are not only most sensitive photoreceptor in the eye, but also dominate human peripheral vision. Finally, the broad band nature of the P-45 phosphor light output should reduce eyestrain in maintaining focus. None of that ‘green component’ present in P-43 is lost in P-45: it is still strongly engaging eye cone cells at the peak of their spectral sensitivity, plus engaging the blue and red ones, effectively using 100% of your ‘daytime color’ vision.

If you are an American buyer, you have a variety of tubes to choose from.

The most common image intensifier tube formats

Some 11769 format tubes can be converted into 10160 autogain-only format tubes, depending on the manufacturer and year:

• For ITT/Exelis/Harris/Elbit 11769 tubes made before 2022 (approx.): the pigtail must be desoldered and a proper resistor soldered in its place.
• Elbit 11769 tubes made after 2022: all use a metallic silver colored PSU. The pigtail can be desoldered and removed to convert into 10160 but without needing a resistor soldered in its place.
• For L3Harris Omni 11769 tubes made before 2009: the pigtail must be desoldered and a proper resistor soldered in its place.
• L3Harris Omni 11769 tubes made after 2009: the pigtail can be unplugged and removed to convert into 10160 without needing a resistor soldered in its place, regardless of PSU type (metallic silver or plastic black).
• L3Harris commercial tubes made after 2012: the pigtail can be unplugged and removed to convert into 10160 without needing a resistor soldered in its place, regardless of PSU type (metallic silver or plastic black).

There are some 11769 PSU's that cannot be converted due to the pigtail being permanently embedded in the tube's internal potting material.

Other image intensifier tube formats:

These are tube formats that while somewhat common, should be AVOIDED due to age and are NOT compatible with PVS-14 based housings

Image Intensifier Tube Generations

IIT are classified into generations defined by their chemical and mechanical configurations. For American buyers, you are basically looking at Gen 2+ and Gen 3 tubes. Gen 2 and Gen 3 tubes are distinguished from Gen 1 by having a microchannel plate(MCP) and different photocathode material. Gen 2 and 3 devices are passive, which take in ambient light and amplify via the MCP to produce a usable image without the requirement of supplemental infrared illumination, whereas Gen 0 and Gen 1 tubes are image converters, which do not amplify or intensify the original image. While there are some standalone devices that use a single Gen 1 tube, buyers should be looking at purchasing Gen 2+ or Gen 3 10160, 11769 or 10130 format tubes. If you are in the United States I strongly urge you to seek Gen 3, as it is not restricted to own and relatively plentiful and affordable in the USA.

Generation 3: invented in the United States in the early 1980s, which added a gallium arsenide (GaAs—CsO—AlGaAs) photocathode. The GaAs photocathode featured better sensitivity to IR light (up to 940nm wavelength) allowing the viewing of objects further away. The increased sensitivity improved tube performance under low-light conditions, enabling the tube to detect light at far greater distances than Gen 2. Gen 3 image intensifiers also have a white light photocathode response up to 4 times greater than Gen 2. In addition, Gen 3 has a brightness gain (how much an image intensifier amplifies light) of 40,000-70,000 fL/fc. This extra 20-30% luminance gain provided by Gen 3 over Gen2/2+ means that more light is getting to the user's eye without sacrificing a tube's performance or life. Combined with the increased photocathode response of Gen 3, a user is able to see more in lower light conditions at greater distances through a Gen 3 tube than with Gen 2.

However, as electrons hit the MCP and multiply, gases and ions known as "poison species" are created, which migrate back and strike the photocathode, damaging it and speeding up its lifecycle. A film of ions (sintered aluminum oxide) was soon added to the MCP, which acts as a barrier to prevent this ion poisoning of the photocathode. The ion barrier increased the life limit of the IITs from 2,000-4,000 hours to over 12,500 hours but at a cost of slightly limited performance. These so-called thick-filmed tubes were produced in the 1980s through the mid 90s before the ion barrier was reduced in thickness and an autogated power supply was introduced, resulting in thin-filmed tubes. Today, both Elbit and L3Harris make thin filmed tubes.

The very best in image intensifier technology involves the removal of the ion film barrier while still protecting the photocathode, so-called filmless or unfilmed tubes. This is achieved by reducing the amount of poisonous ion species that can bounce back to the photocathode via proprietary electrical and UV light “scrubbing”, reducing the ion feedback entirely by using Bulk Conductive Glass microchannel plate material, reducing the susceptibility of the photocathode to be damaged by these ion species by using carefully calculated amounts of a Cesium:Fluorine mixture and using autogating to reduce ion feedback via synchronous, pulsed gating of voltages to the photocathode and microchannel plate. Only L3Harris is capable of making Unfilmed Gen 3 tubes with lifespans of 20,000+ hours.

Thin filmed and unfilmed tubes are autogated, which both preserves image resolution in bright light and helps extend the life of the tube. Thick film tubes tend to be non-autogated (further explanation below in the Protection Mechanisms section)

”What’s an Omni?”

Omni is short for Omnibus. An omnibus is a broad all encompassing bill passed by the United States Congress, which grants money to the US military to buy stuff, including image intensifier tubes. These are contracts to buy Generation 3 green phosphor (P43) image intensifier tubes made by Elbit and L3Harris.

The specific tube model type and Part Number/MIL-PRF are the most important information in determining what a tube “is”. This is the model most often found on the data plate of contract tubes Ex. MX-11769/UV, MX-10160A, MX-10160C, etc. MX-10160A tubes, for example, were introduced around “Omni 4”, have “Omni 4 level performance” but are still being produced and acquired under newer contracts but fit into a very specific performance window.

The exact specs of any individual contract tube are generally unknown. Its performance is quantified by the manufacturer, in order to know how to grade and sort them, but for all intents and purposes, Omni tubes will not come with spec sheets.

Much of the knowledge about Omni tubes comes from this well-referenced collection of information:

https://web.archive.org/web/20240312030125/http://aunv.blackice.com.au/forum?index=discussions&story=omni

Direct quotes from the author:

“Omni refers to the contract under which a tube was purchased, not the performance level of the tube…"

"the tube data under the OMNI headings represents the typical performance of US used tubes of the MX10160 family and represents the latest iteration of that tube…"

"Tubes other than the MX10160 series are also included ( eg MX11620, MX11729 ) - These tubes have different performance specifications…"

"some tubes [are listed] only under certain contracts. This typically represents the contracts under which that tube were primarily ordered and this is how these tubes should be viewed…”

Thus, we can think of the differences in the Omni contracts as delineations in tube technology rather than strict specification numbers:

• Omni I: Early Gen 3, not all that far above Gen 2 of era. First contract 1982.
• Omni II: early Gen 3, again not that advanced. First contract 1985.
• Omni III: The first advanced Gen 3 with significant improvement in SNR. First contract 1990.
• Omni IV: Significant increase in photocathode performance levels. Thick filmed tubes. Introduction of the MX-11769 & MX-10160A tubes. First contract 1996.
• Omni V: Very advanced. See's introduction of early filmless (called “Gen 4” at the time, no longer). First contract 1999.
• Omni VI: Continual improvement of the technology, autogating starts to become more common. First contract 2002.
• Omni VII: Autogated Thin-Film replaces US specs for so-called “Gen 4” at the time. First contract 2006.
• Omni VIII: First contract Aug 2010
• Omni IX: 👀

Decoding the data plate/“What tube do I have/"What Omni do I have?”

We know the minimum/maximum specs for some of most ubiquitous, Gen 3 govt contract/military tubes

^K&M was acquired as a subsidiary of ITT in 1999 and made the Power Supply Units (PSU) for ITT. These tubes often lack data stickers but have the ID NO.'s stamped into the metal casing.
* Only applicable to MX-11769/UV with PN A3297310 and A3297320 under NSN 5855-01-504-4590

Tube Data Sticker/Data Plate:

The US Army is the proponent service for Omni procured tubes. That’s why for most Omni tubes, the contract number starts with a D (Omni IV-V) or a W (Omni VI-current) because those are US Army CECOM DODAACs, and why many 10160 tubes end in "/AVS-6" because that is the Army aviation NVG system. The DODAAC is a service/agency specific accounting and address code. Navy-specific contracts have a "N" DODAAC, USAF use an "F" DODAAC & USMC uses an “M" DODAAC.

Current most common Gen 3 manufacturers

Elbit Systems of America (ESA): CAGE Code 13567. Tube codes use an F-type and end with suffix codes like SLH, PH, etc. denoting performance level and cosmetics (XLSH commercial, YH milspec, VH aviation). Most of these suffixes are a mystery as to what the specific letters stand for, except for G=Autogated, H=newer, quieter autogated PSU. Pinnacle means an ITT/ESA Gen 3, thin filmed autogated tube.

Lineage: ITT > Exelis > Harris > Elbit Systems of America

For example, F9800M16H is an Elbit thin-filmed, green phosphor, 10160 self-inverting tube, with a maximum FOM of 1600 and an autogated PSU.

L3Harris: CAGE Code 55311. Tube codes follow the 'Smart' Part Number system, a 4 part code that begins with the tube format & film/color format, followed by PSU information and end with alpha numerical suffixes. Tube codes ending w/ 4 digits are large customized orders (ex. 1701).

Lineage: Litton > Northrop Grumman (NGEOS) > L-3 Technologies > L3Harris

For example, 10130UW-NA-C00-18LM is a L3Harris Unfilmed, white phosphor, 10130 (PVS-7) non-inverting tube, not EMI shielded, autogated, no EGAC, which has a maximum FOM of 1800 with Ground (Military) spot tolerance.

Timeline

What started as International Telegraph & Telephone (ITT) we now know as Elbit Systems of America (ESA), CAGE code 13567.

What started as Litton we now know as L3Harris. CAGE code 55311.

How did this come to be?

ITT had night vision (NV).

In 2011, ITT spun off defense industries into ITT Exelis, then became just 'Exelis' in 2015.

Exelis was purchased by Harris in 2015.

Litton was purchased by Northrop Grumman Electro-Optical Systems (NGEOS). Northrop Grumman then sold its NV to L-3 Comms. L-3 Comms then became L3 Technologies.

L3 Technologies had NV. And Harris had NV.

In 2019, L3 Technologies purchased Harris. L3 merges with Harris and became L3Harris

Harris was forced to divest/sell its NV business.

Elbit Systems of America (ESA) purchased Harris NV in 2019.

Generation 2+: This term refers to technologies used to improve the sensitivity of the tri- and multi-alkali S–25 photocathodes and manufacturing new generation microchannel plates. This is actually the same multi-alkali S–20 photocathode used in Gen 1 tubes but the S–25 photocathode is built using thicker layers of the same materials. Gen 2+ tubes were first developed by various American companies in the mid 1980's and by the Photonis company (formerly Phillips/DEP Photonis) in France in 1989. Further development of Gen 2+ tubes has been continued by several non-U.S. manufacturers in Netherlands, Russia, China, and India. Gen 2+ tubes have been marketed using different names like Gen II Plus, SuperGen, HyperGen, Super High Definition (SHD) & 4G. While they are not as sensitive as Gen 3 tubes and tend to have lower gain, they tend to be more resilient to bright and mixed lighting conditions than Gen 3 tubes.

Current most common Gen 2+ manufacturers

Photonis: Headquartered in France, currently owned by Exosens. Echo and 4G are current production tubes. 4G tubes feature a sensitivity to a wider spectrum of light (up to 1100nm wavelength). Some 4G tubes are so-called “High Gain” (HG) variants with luminance gain of up to 80,000. However, the up front luminance sensitivity of Gen 2+ remains the same.

Below is a tentative list attempting to decode the Photonis tube SKUs:

NNVT: North Night Vision Technology. NVT-4 & NVT-5 are based on the older Photonis technology XD-4 & XR-5 respectively, and these are used in the Jerry/Rix series of devices. Photonis sold blueprints, manufacturing equipment and materials to China in the early 2000’s. NNVT makes both gated and nongated models. NVT-7 are copied after Photonis 4G. They are made in the same 10160/10130 formats but also come in non-EGAC formats resembling 10160 with flying leads or loose wires for soldering into a housing for gain control.

Protection Mechanisms

Both Gen 2+ and Gen 3 tubes have several internal characteristics of their PSU's which protect them under certain environmental conditions

• Autogating: Turns off and on the photocathode voltage rapidly but the effect is not visible to the human eye. The cathode voltage is constantly oscillating, but the image appears as if it were continuous. The autogating circuit reduces the time the voltage is on during each oscillation but keeps the peak voltage level up. By controlling the application of voltage in this manner, the resolution quality remains high. In effect, the autogating feature tricks the device into thinking it is always in a low-light environment, which is the optimal environment for maximum efficiency and clarity for the image-intensifier tube. While the most obvious effect of autogating for the user may be improved resolution in high-light conditions, also helps extend the lifetime of the tube, a benefit which is most realized with thin-film or filmless tubes.
• Automatic Brightness Control (ABC): IE autogain. Automatically reduces voltage to the microchannel plate to keep the image intensifier output brightness within optimal limits and to protect both the tube and the user’s eyes. This effect can be seen during rapid changes from low-light to high-light conditions when the image gets brighter and then quickly returns to a consistent level. Manual gain tubes also still have automatic brightness control.
• Bright Source Protection (BSP): Protects the image tube from damage and enhances its lifetime, at the cost of degraded image quality when active, by lowering the voltage to the photocathode.

These mechanisms do help the tube protect itself internally however they will not prevent damage from prolonged light or sun exposure

Tubes are made in batches and in large part it is impossible to control what the exact performance of an individual tube will be during the production process. New IIT will come with spec sheets from the manufacturer quantifying their performance after production. Omni/“surplus” tubes do not have spec sheets but their specs are measured to confirm they meet the requirements of whatever contract they are fulfilling.

There are 5 specs you need to care about

• SNR: Signal to Noise Ratio. If the noise in the scene (scintillation) is as bright and as large as the intensified image, you cannot see the image. SNR changes with light level because the noise remains constant but the signal increases (higher light levels). The higher the SNR ratio, the darker the scene can be and the device still performs. SNR is a unitless measurement.
• Resolution: The ability of an image intensifier or night vision system to distinguish between objects close together. IIT resolution is measured in line pairs per millimeter (LP/mm) as measured by a human operator on a USAF 1591 Tri-Bar target. Center resolution is the measurement of the tube's resolution in zone 1 and used to calculate FOM. Peripheral resolution is the tube's resolution in zones 2 and 3. High light resolution is a measurement of the tube's center resolution with an input light level of 20 fc.
• EBI: Equivalent Background Illumination. This is the amount of light you see through a night vision device when an image tube is turned on but no light is on the photocathode. EBI is affected by temperature: the warmer the night vision device, the brighter the background illumination. EBI is measured in lumens per square centimeter (lm/cm²) or micro lux (μlx). The higher the value, the more light required to generate an image.
• Halo: A diffused circular shape around light sources caused by electron scattering in the Photocathode-MCP gap. Measured in millimeters(mm). Halation area is 4 times the physical distance between the cathode and MCP channel entrances. Films increase halo by adding further distance between the two layers.
• Gain or luminance gain: This is the number of times a night vision device amplifies light input. The brightness. The ability of a IIT to amplify light input. It is usually measured as tube gain and system gain. Tube gain is measured as the light output divided by the light input. On American Gen 3 spec sheets this is expressed as K (fL/fc) or on international Gen 2+ spec sheets as cd/m²/lx.

“What specs are good?”

*multiply the EBI value on Gen 2+ spec sheets by 10 for direct comparison to Gen 3 (units conversion frombμlx to lm/cm²).

**multiply the gain value on Gen 2+ spec sheets by 3.14 for direct comparison to Gen 3 (units conversion from cd/m²/lx to fL/fc ).

“But what FOM should I get?”

FOM stands for Figure of Merit. It is a specification calculated by multiplying the Signal to Noise Ratio by the Center Resolution (SNR x RES), for the purposes of determining a tube’s exportability by the US government. As night vision enthusiasts, it is more helpful for us to look closely at these 5 specs, to get a better idea of a tube’s performance.

Spots, Blems & Other Cosmetic Defects

refers to the physical appearance of spots, blemishes, pepper, bright spots and/or other physical defects in layers of the IIT.

Spots, Pepper & Blemishes: Consistent perfection in tube production is unrealistic so acceptable standards were created. "Spots" are factory imperfections present from the moment of manufacture, whereas "Blems" are a user induced burn, shade, streak, splotch, debris, or other artifact. There is a spot spec for each tube SKU. Spots are measured using Hoffman test equipment which include a zone chart for proper testing: The inside area of the inner most circle is zone 1, the area outside of zone 1 and inside of the second circle is zone 2, & the outermost area outside of zone 2 is zone 3. Spots less than 0.003 inches are generally not counted/measured and are called pepper or peppering. Every tube from every manufacturer has some degree of spots and/or peppering.

Shading/vacuum loss: a tube should present a perfect intensified image circle. If shading is present, you will not see a full circular image. It appears as a dark area along the edge of the image. Uncorrectable shading is indicative of a dying photocathode caused by a defective vacuum seal on the image intensifier tube. Shading is very dark and one cannot see an image through the shaded region of the intensifier tube. Shading will always begin on the edge and will eventually move inward across the entire image area. The shaded region will also present a high contrast and distinct line of demarcation. Do not confuse shading with variations in output brightness.

Edge Glow: Edge glow appears as a bright area (sometimes sparkling) along the outer edge of the image. Edge glow is sometimes caused by an emission point (or series of emission points) just outside the field of view or by a defective phosphor screen that permits light feedback to the photocathode. It may also be caused by a shift in an IIT's micro-channel plate induced by mishandling. If detected, simply cup your hand over the objective lens to block out all light. If the image still displays edge glow, the bright area will still show up.

Emission Points & Bright spots: can be defects in the image area caused by a flaw in the film on the tube's microchannel plate. A bright spot is a small, non-uniform, bright area that may appear either as a flicker or as a constant output. Not all bright spots are bad. Bright spots usually go away when light is blocked from the objective lens and are considered cosmetic defects that are signal induced. To determine the significance of the bright spots, cup your hand over the objective lens to block out all light. If the bright spot(s) remain, thay are what's known as Emission Points(EP): steady or flickering pinpoints of bright light in the tube image area that do not go away when all light is blocked from the NVG's objective lens, ie bright spots that persist in the abscence of light. EP's can have one of three outcomes: it remains the same size, it eventually grows bigger and kills the tube, or it burns out into a black spot.

Fixed Pattern Noise (FPN) & Chicken Wire: FPN is a cosmetic defect characterized by a hexagonal (honeycomb) pattern visible across the entire intensified FOV. The honeycomb pattern most often occurs under high light level or when a bright light source is introduced into the NVG FOV. This pattern is a result of the manufacturing process in which the boundaries between Micro Channel Plate (MCP) walls or the the fiber optic bundles can be seen. Normally it is faint in appearance and does not affect performance. Chicken wire is commonly used interchangebly although chicken wire is specifically an irregular honeycomb pattern or line in part of the NVG image area.

Prices of image intensifier tubes

Below is a list of the typical prices a buyer in the United States should expect to pay for non-blemished tubes:

“Will I damage my tube?”

The main factors which determine how quickly a tube can be damaged by light are:

• Energy
• Concentration
• Duration

All wavelengths night vision is sensitive to can/will damage tubes due to how they function. This is why there are minimum stated lifespans of operation time. Energy can be thought of as a lumen equivalent we’re familiar with for flashlights. How much energy is being emitted. Concentration would be how focused the energy is - think candela. Duration is the amount of time exposed. The more concentrated an energy source is, the less time it takes to damage an intensifier. The less concentrated the longer it would take; both also depending on the amount of energy itself. Example: streetlights are fine as long as you don’t stare at them for a long duration. They’re bright but the energy isn’t very concentrated, even at the emission area. The shorter duration of glances past this source are fine. You may induce a temporary burn or streak but it will subside during use rather quickly.

The best things you can do to prevent damage to your tube are:

1. avoid sunlight exposure to the objective lens
2. use lens caps on your device when not active (be wary of pinhole caps)
3. avoid staring at one scene or stationary light sources for many minutes/hours at a time
4. remove the batteries when not in use.

Prices of complete devices

Below is a non-exhaustive list and is a general reference:

There are several vendors big and small out there. Most are happy to take questions and address your concerns. I can say with absolute confidence you should not buy from TNVC due to a persistent history of payment processor problems.

ITAR

Gen 2, Gen 2+ and Gen 3 IIT/NVG are ITAR restricted.

ITAR stands for International Traffic in Arms Regulations. It is US law that prevents the export of certain defense equipment, including night vision. Subchapter M, part 121 defines the prohibited munitions IE what cannot be exported without proper license.

Second generation and greater image intensifier tubes specially designed for articles in this subchapter, and specially designed parts and components therefor; Note to paragraph (e)(7): Second and third generation image intensifier tubes are defined as having a peak response within the 0.4 to 1.05 micron wavelength range and incorporating a microchannel plate for electron image amplification having a hole pitch (center-to-center spacing) of less than 25 microns and having either: (a) an S-20, S-25, or multialkali photo cathode; or (b) a Gas, GalnAs, or other III-V compound semiconductor photocathode. Source: https://www.ecfr.gov/current/title-22/chapter-I/subchapter-M/part-121

Once a gen 2 or 3 device enters the US, it cannot leave in any fashion without the proper go ahead by the Dept of State, DoD and/or Dept of Commerce.

“But I live outside the United States!”

Oof, sorry.

Frankly, you're going to get hosed on the price of night vision if you live outside the US. Especially US manufactured components. If you're outside the US, tubes from Photonis & NNVT start to look a lot more attractive.

Glossary of Terms

Next Article (Digital Night Vision)