The basics
Night vision devices are often divided into different classifications, such as FOM brackets, Military or Commercial Grade, and most commonly, generation.The goal of today’s blog is to better understand what defines Night Vision Generations and how relevant type of classification is in today’s world, diving deep on their inner workings, pros and cons.
Understanding Modern Generations
A common misconception among inexperienced Night Vision enthusiasts is to think generations refer to technical specs or features such as auto-gating, while in reality modern image intensifiers are only classified as Gen 2+ or Gen 3, depending on technical differences found in the Photocathode.
To better understand this article, we highly recommend you read our previous entry about IIT’s.
Generation 3 Breakdown
Third Generation IIT’s employ the use of a Gallium Arsenide (GaAs) Photocathode, to convert photons (visible light particles) into electrons thanks to the photoelectric effect.Incoming light will hit the GaAs molecules, triggering the release of electrons, which will then be multiplied (intensification) by the Micro Channel plate.
This forces manufacturers to place an ionic barrier between the PC and MCP, to catch incoming ions preventing MCP decay, at the cost of worse contrast, lower resolution, SNR and higher EBI values.
Generation 2+ Breakdown
Generation 2+ IIT use a different type of photocathode, composed of various alkaline metals (Multi-Alkali), to transform light into electrons, and thanks to the nature of these metals, no negative ions are produced, thus resulting in a system that doesn’t require an ionic barrier to protect the MCP.
This however results in lowered photocathode sensitivity due to the less reactive nature of multi-alkali compounds, which generate less electrons per each photon.
While this, at first glance might seem like a total loss, the use of an ionic-barrier-less system, generally allows for a much sharper image, and thanks to the use of a Light Diffraction Coating, which can be applied to the input window (typically found in Photonis and NVT-7 tubes), the operational bandwidth of the tube can be increased by a considerable margin (i.e. Photonis tubes are sensitive up to 1064nm as opposed to the typical 950nm found in Gen 3 tubes).
This happens because Gallium Arsenide, found in Gen 3 tubes is not sensitive past 950nm, while Multi-Alkali compounds allow manufacturers to extend the margin with said coating, and for this reason Photonis markets their tubes as OOB (out of band).
What does it all come down to?
Ultimately, the decision between Gen 2+ and Gen 3, comes down to a number of case specific factors, such as operational environment, budget constraints, restrictions and most importantly specifications.
Modern Autogated Gen 2+ tubes, of the likes of Photonis excel in mixed lights conditions, giving operators an edge thanks to their added ruggedness against blunt force trauma (rated up to 500g’s as opposed to the typical 75g’s found on Gen 3 tubes) and higher resistance to light damage thanks to lower PC sensitivity and their fast auto-gating, which facilitates identification and scanning.
This comes with the downside of having significantly less Luminance Gain than most modern Gen 3 tubes due to their less sensitive photocathode, although this doesn’t hold true for High Gain Gen 2+ tubes that have recently hit the market.
Generation 3 tubes, will usually provide a much better performance in remote areas characterized by ultra-low light levels, where you would need as much gain as possible to be able to visually process what’s around you. This kind of environment is where most Gen 2+ devices will tend to struggle as opposed to Gen 3.
In short, you should not choose your device based on Generation, rather you should choose it based on what you plan on doing with it as well as, going based off minimum specifications and budget.