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Generations of Night Vision explained.

• What is a Generation?

A night vision "Generation" is a military defined transition between two different technologies. Generations are officially recognized in the United States, Canada and Australia by treaty to ensure interoperability between equipment and standardization of terminology. Later, this extended to all AUSCANZUKUS countries. 

You will find that others will use the same technology, however the lack of standards in the rest of the world leads to many marketing claims of devices being of a generation that they are not. Also, even within AUSCANZUKUS countries, some colloquial terms are not defined yet are still used. 

To this extent. I'll provide information on each term.

Generation 0.

This covers the period from WW2 to the 1950's and defines Infra-Red Image Converter tubes. These tubes only convert infra-red into visible through the use of a converter tube. This is a colloquial term as it was never defined. These devices require a powerful source of NEAR INFRA-RED light, between 800 and 1300nm to operate. Of note, Lights of over 1000nm are not readily visible to most modern night vision equipment and are still considered covert by many.  Although most Generation 0 tubes were electrostatic inversion and suffered distortion as a result of this, some were proximity focussed and should have provided an image similar to second or third generation wafer tubes. Illumination was most commonly provided by a spotlight with an IR filter. With a good illumination source, a Generation 0 device can see out as far as a normal spotlight will carry.

Generation 1 - Typical Lifespan: 1000 hours.

Although this was defined by it's exclusion, it is still a colloquial term as no definition for this standard exists, despite it's widespread use militarily. In the 1950's, photocathode technology developed to the point where significant gain could be achieved, making passive "moonlight" capable devices. These devices usually exhibit high levels of distortion and do not have sufficient gain to work by starlight, however can be used in "active" mode like a Generation 0 device with the addition of an IR illuminator. Generation 1 is often able to be discerned by it's very quiet high-pitched whine, due to the power supply and voltages involved. A typical Gen1 stage will have as much as 15,000 volts to power it. Also, the screen will stay "on" for some time after it's turned off.

Typical usability includes bright moonlight nights and short-range with illumination.. Also very useful for spotting fires and corona discharge.

Generation1+

This is purely a marketting term, though is recognized by some as having characteristics. Those agreed characteristics are a Fiber Optic faceplace, to allow a more curved photocathode that reduces distortion significantly. Many manufacturers claim Gen1+ to make their devices sound better, but if there is no Fiber Optic faceplate, then it's just Generation 1.  Generation 1 and Generation 2 use the same photocathodes. Be wary of claims, no matter how reputable the supplier, though if you can see the photocathode and confirm there's a fiber optic screen in front of it, that's sufficient.

Cascade or Multi-Stage Generation 1.

This is still known as Generation 1, however is usually referred to as two stage or three stage, or more commonly, cascade. This was developed with fiber plate technology that allowed distortion to be reduced and for one tube's output to be connected to another tube's input. This allowed multiplication of gain.

Cascade tubes can provide gain levels well over 100,00 times ( fl/fc) and can provide images comparable to modern military tubes, including third generation devices. They are very long compared to other tubes, which is due to multiple stages, and usually very heavy. The multiple stages also magnifies distortion, so the outputs are usually somewhat distorted, though more advanced or modern tubes can produce a flat image with no visible distortion. These resemble second generation tubes in both image quality and gain. 

Very usable in starlight, with many showing less noise and more gain than second generation tubes.

Generation 2 - Typical Lifespan 2000 hours.

Second generation tubes use a Micro-Channel plate to achieve additional amplification and can be made as an electrostatic inversion tube ( like Gen1) or a Proximity Focussed tube ( Like Gen0 ). The MicroChannel Plate was developed after the Vietnam war and allowed sufficient gain to produce an useable image with only starlight and an excellent image with just a thin sliver of moon available.  Most tubes are much smaller than First Generation tubes and are usually silent in operation.

Second generation tubes have little to no visible distortion and are very useful militarily. The specification for Second Generation tubes is definitive with the differentiator being the inclusion of a MicroChannel Plate ( MCP ) for additional gain.

Most Second Generation tubes are proximity focussed, with inverted image tubes using a Fiber Optic inverter rather than electrostatic inversion.

Photocathode sensitivity is typically above 230 uA/lm and these tubes are quite useable in starlight and should be considered as entry level for any serious night vision work.

Generation 2+  - Typical Lifespan 2500 to 5000 hours

Although not officially recognized, this is generally accepted to have an Extended Red photocathode to increase the infra-red sensitivity of the screen, improving use under starlight. Most have either an extended-red S20 photocathode or an extended-red S25 photocathode. Lifespan may be improved using an Ion Barrier film. More useable in starlight than Gen2 alone, however be very wary of claims to be Gen2+ unless you have a datasheet and it shows something like "Extended Red S20" or "Extended Red S25" or has sensitivity in excess of 300uA/lm and S/N of greater than 10:1.

Super Second Generation - Typical Lifespan 10,000 to 15,000 hours.

Super Second Generation ( also known by the marketing terms Supergen, SHP and Hypergen ) is an extension of Generation 2 that, while not official, is fully defined. Super Second Generation tubes have a photocathode sensitivity of more than 500 uA/lm ( Typically more than 650 uA/lm) with a S/N ration of >15:1 and lifespan > 10,000 hours.  These tubes have improved with third generation technology and while leading edge third generation tubes still outperform Super Second Generation, modern Super Second Generation tubes already significantly outperform early Third Generation tubes.

These tubes are high-end tubes and compete directly with Generation three devices. I believe they are the tube of choice for the Australian Army. 

Generation 3 - Typical Lifespan 10,000 to 15,000 hours.

Third generation tubes are functionally the same as second generation tubes, however they use a Gallium Arsenide (GaAs) based photocathode, which is more sensitive to Infra Red light than second generation. These tubes are primarily only available in the US, although Russia, China and Japan also make these tubes. Presently, recent examples of these tubes are considered the best available. 

The GaAs photocathode however is very sensitive to positive ions, caused when electrons with sufficient energy string the surface of the microchannel plate. For this reason, they have a thin film of Aluminium Oxide to stop these positive ions travelling to the photocathode where they can cause damage. Generation three comes in both filmed and thin film versions. It's worth noting that the GaAs tubes do not function well in extremely bright environments were the more easily damaged photocathode will be affected more than that of second generation.

Unfortunately, Generation 3 doesn't say anything about the quality. Some older, lower end Generation 3 tubes perform rather badly, almost at Generation 2 levels. FOM ( Figure Of Merit ) is a useful tool for comparing these. FOM1300 is considered low, while above FOM1600 is restricted. High end generation three should be above FOM2000.

Generation 3 Omnibus VII.

After the specification for Generation 4 ( Filmless ) came out, Thin-Film Autogated tubes were proposed as an alternative standard. Although some referred to this as Generation 4, it is officially known in the US Military as Generation 3 Omnibus VII ( or Gen3 Omni VII )

These are exceptional tubes and currently considered the world's best. They may be available in Australia. 

Generation 4.

Generation 4, like 2 and 3, is a defined generation. It is functionally the same as Generation 3, however there is no positive ion barrier film. ( Filmless ). They are also Autogated, which is a means of turning the tubes on and off to allow use in high light environments. You may be able to buy these and they should outperform Generation 3 Omnibus VII tubes, however there is some question as to whether many tubes have sufficient lifespans to meet the specification. These tubes are not available in Australia.

Fusion

Fusion systems mix the image from an Image Intensifier with the output from a thermal sensor - typically an uncooled bolometer.  The result is that thermal information is mixed in over the image from the image intensifier as a different colour.

Autogated.

Autogating is available in Second and Third generation tubes and a requirement of Fourth generation tubes. While it's theoretically possible to do in first generation tubes, no known tubes have been manufactured to do this. Autogating is designed to allow use in high light environments such as twilight to allow a greater transition period between day and night for the use of Night Vision Devices, as well as coping with sudden unexpected light, such as when clearing buildings. 

Hybrid

Hybrid tubes area a cascade tube ( multi-stage tube ) that incorporates a 1st Gen tube and a 2nd Gen or 3rd Gen tube. Generation 3 hybrid tubes are presently the most sensitive tubes available and exhibit excellent contrast. The choice of photocathode is denoted by alternate descriptions, eg, Gen2+1 and Gen3+1. These are exceptional tubes, but not currently known to be in production. They are highly sought after and often go for considerable amounts. They are almost never available in Australia.

Digital

Digital devices use a camera and screen to produce an image. Current technology usually provide first-generation levels of gain, with second-generation levels of S/N ratio and resolution. However they are comparable only to very small tubes ( less than 10mm ) at this present time. These make good general purpose spotting scopes and are good for people who may inadvertently leave them on, since they are not affected by daylight and work quite well during the day. They are good for spotting and shooting out to around 100m.

Digital Fusion

A recently developed technology, Digital Fusion is an advanced military version of Digital and uses multiple sensors in both SWIR and LWIR to produce a high resolution ( Roughly equivalent to HDTV ) monocular or goggles. This recently reached TRL6 ( Technology Readiness Level 6 ) which is a functioning prototype for evaluation in the field.  These are presently required to meet the performance of the mx10160C tube as a base level for light amplification and mix both thermal and photonic images.

SWIR - Short Wave Infra Red.

Thought to be one of the next advances in Night Vision, these tubes see well up into the Infra Red spectrum where skyglow and starlight are similarly bright to moonlight. As such, they can usually provide a high quality image regardless of whether a moon is available or not. Their ability to penetrate fog and smoke also allows use in overcast conditions and conditions of severe smoke and haze or heavy fog. Presently SWIR only exists as digital and is likely to see use in vehicle operations. These are not available in Australia that I've been able to determine.

LWIR - Long Wave Infra Red.

LWIR is also known as "Thermal" night vision. This sees long-wave infra-red radiation emitted by warm bodies such as people. It is most effective when there's a temperature difference between the target and the background. These are available in Australia, but are very expensive. If you have to ask how much they are, you can't afford one.

Image Inversion Systems common to ALL generations.

In a normal optical system using tubes, there is an objective lens, a tube and an ocular lens. This leads to a problem where the image, if viewed, would be inverted due to the objective lens. To make the scopes useful, an additional "inversion" point must exist within a night vision device.

• Inverter Tubes - These tubes use an electron lens within the tube itself which inverts the image.
• Fiber Plate inverter - A fiber plate is twisted through 180 degrees and used to invert the image.
• Eyepiece inversion - A special eyepiece inverts the image.
• Second Focal Plane tube - This tube is located at the second focal plane of the objective lens system and includes day scopes with interchangeable ocular lenses and night vision tubes.
• Roof prism - Includes using mirrors to invert the image, either before or after the tube.
• Intensified CCD - Using a camera, the camera can simply be installed upside down.