One of the hardest parts for prospective, or new, night vision consumers to make sense of is the unit specifications (or ‘specs’). These tell everything about the individual unit (typically documented on a paper accompanying the device called a ‘spec sheet’), but are extremely complex and all relate to another, and can be difficult to compare against other devices. As numbers in some specs go up, there is often a corresponding decline in others. Some spec differences can only be measured using a Hoffman testing device, and may not be discernable to the naked eye. These specs include:
- Resolution: The ability of the device to resolve an image, given the environment, and distinguish detail/differences in objects otherwise closely together
- Measured in “line pair per millimeter” (lp/mm)
- Higher resolution is betterMilspec minimum standard is 64 lp/mm (industry established in late 1990s)Commercial Gen II units around 50s
- Newer Gen IIIs around 80s
- SNR (Signal to Noise Ratio): The ability of the device to present a “clean” image in darker environments by taking the ‘signal’ (level of light absorbed and converted to an image) in contrast to the ‘noise’ (the scintillation) produced
- Higher is better
- Avoids “noise” in image
- 30+ is good, 35+ is great
- FOM (Figure of Merit): A mathematical formula used to present the best (and summarized) performance in a tube
- Resolution * SNR = FOM
- Arguably the best metric for determining a tube’s “quality” (sans spots)
- A desirable tube FOM is 2000 or greater
- EBI (Equivalent Background Illumination): The base illumination number that represents the “floor” in performance for that device to generate any image
- Lower is better
- Effected by ambient temperature factors
- 2.5 or less is good
- Halo: A tube statistic that reflects the ability of the image intensifier to generate a “bloom” around any given light source
- Lower is better
- 1.0 or less is good
- Gain: Gain is an expression of photocathode sensitivity (i.e. how bright the controls can enhance an image) and sometimes referred to as ‘luminance gain’.
- Lower gain numbers produce a darker image
- Higher gain numbers are more ideal, but too high can create image scintillation (noise)
- Gain numbers directly correlate to SNR
- Fixed Gain: A fixed level as part of the image intensifier’s hardware that limits the level of gain the device can take in before it shuts the unit off to protect the device. Often paired with the Autogaining function
- Manual Gain: A physical knob that gives the user the ability to increase/decrease the image brightness. However, increasing the gain too much may cause scintillation
An example of good-average stats for a GEN III AN/PVS-14 would look like:
- Resolution: 64 lp/mm or greater
- SNR: 30 or higher
- FOM: 1900 or higher
- EBI: Less than 1.0
- Halo: Less than 1.0
Ultimately, each individual NVG is as unique as a fingerprint, and most will give good performance provided you know what specs to keep an eye out for. When in doubt, ask questions because any good manufacturer and retailer should be able to provide you clear responses and guide you in which NVGs have better specs and performance.
In the final segment, we will cover some of the more common accessories one can consider with their NVGs. These often can augment your device’s performance, but are not necessary for regular use. However, if you would like to return to the Beginner’s Guide main post you can do so here.
Disclaimer: The purpose of this series is strictly informational, much like our COVID Chronicles, body armor, or gear guide, this series is not intended by High Ground to sway or convince the reader that one specific brand of night vision manufacturer is superior to all the others. In the end, this series is intended to provide the reader with a condensed and focused resource—nothing more. It is not to be considered definitive advice nor instruction.
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