In South Africa, with its vast landscapes, both bush, rural and urban, and diverse wildlife, not to mention the crime rate, the demand for clear vision in the dark is more pronounced than ever, be it for security, wildlife monitoring, or simply navigating the bushveld at night.
Night vision technology has seen incredible advancements over the years, with devices now spanning several generations, each marked by distinct characteristics.
Generations
While Gen 1 devices, with their limited range and resolution, have become largely obsolete, they serve as a starting point in understanding the evolution of this tech.
Gen 2 and Gen 2+ devices, with their improved image clarity and battery longevity, present a significant upgrade and offer great value, especially for the South African market where quality and affordability often go hand-in-hand.
Meanwhile, Gen 3, the pinnacle of night vision technology, offers unmatched performance, but its availability and cost can be a barrier for many.
More than just Gen this and Gen that…
It’s essential to understand that the generational label isn’t the sole determinant of performance. In some instances, a high-end Gen 2+ device might rival a Gen 3’s performance.
As we delve deeper, we’ll compare these generations, emphasizing the importance of evaluating individual device specs. Using the PVS-31 Dual Tube NVG’s (Gen 2+) by Terratac as a case study, we’ll illustrate how one device’s specifications can straddle different generational benchmarks.
What are the differences in each generation of night vision?
In the following section, you’ll find a comprehensive table delineating the key specifications of each night vision generation. To provide a clearer context, I’ve highlighted the metrics for a locally available and highly competitive device, the PVS-31 Dual Tube NVG’s (Gen 2+) by Terratac in blue.
This serves to underscore the intriguing reality: that a well-engineered Gen 2+ unit, like Terratac’s offering, can indeed rival the performance of a Gen 3 device, blurring the strict delineations we might expect between generations.
| Parameter | Gen 1 | Gen 2 | Gen 2+ | Gen 3 |
|---|---|---|---|---|
| FOM (Figure of Merit) | 100 – 200 | 500-800 | 1000-1250 | 1500-2200 |
| Resolution Ratio (lp/mm) | 20-35 | 40-45 | 45-60 | 60-72 |
| Signal to Noise Ratio (SNR) | Low | 12-15 | 15-20 | 20-30 |
| Photocathode Sensitivity (μA/lm) | 120-180 | 350-400 | 500-600 | 600-700 |
| Luminance Gain | 300-900 | 10,000-30,000 | 30,000-50,000 | 40,000-70,000 |
| Equivalent Background Illumination | 1.0-2.5 | 0.5-1.0 | 0.2-0.5 | 0.1 – 0.3 |
| Auto-Gating | No | Rarely | Some models | Commonly |
| Life Expectancy (hours) | 1,000-2,000 | 2,500-3,000 | 4,000-5,000 | 10,000-15,000 |
| MTF @ 25lp/mm (%) | Low (~20-30) | 30-55 | 55-65 | 65-75 |
| Typical price | R5,000 – R30,000 | R30,000 – R70,000 | R70,000 – R200,000 | R200,000 |
Clearly, a high-quality Gen 2+ device can outperform a subpar Gen 3 unit. Hence, understanding these specifications is essential to make informed comparisons, ensuring you’re evaluating products on a level playing field.
Let’s unpack these features further.
What exactly is the Signal to Noise Ratio?
The Signal to Noise Ratio (SNR) is a crucial metric that measures the quality of the image under low-light conditions. Essentially, SNR quantifies the contrast and clarity of the displayed image by comparing the level of the desired signal (the actual image you want to see) to the level of background noise (undesired fluctuations and artifacts).
- Signal: This represents the desired information in the image. In the context of night vision, it refers to the actual light information captured from the scene you’re viewing.
- Noise: This pertains to random electronic static or “graininess” in the image, which can obscure the desired information. Noise is inevitable in electronic systems, especially when amplifying low-level signals, as is the case in night vision devices.
A higher SNR value indicates a clearer, more defined image. This means that the device can provide a clearer picture with less graininess in low light conditions, making it easier for users to discern details and differentiate objects.
What is a good signal-to-noise ratio for a night vision device?
An SNR of 20 or more is considered very good and generally be found in Gen 3 devices, as it provides a clear image in most conditions. So if you are able to find a Gen 2 or Gen 2+ device with an SNR of 20 or more, you’re on the right track in terms of performance and budget.
What is the “resolution ratio” in a night vision device?
The Resolution Ratio in night vision devices quantifies the level of detail they can reproduce, given in terms of line pairs per millimeter (lp/mm).
The resolution ratio denotes the smallest set of parallel lines (a black line adjacent to a white one) that the device can distinctly display. A higher value indicates a finer level of detail, allowing for better identification and recognition of objects.
What is a good resolution ratio for a night vision device?
A resolution of 50 is usually enough for most applications, however, a resolution of 60+ lp/mm is exceptional. Such a specification not only surpasses many other Gen 2+ models but also rivals the clarity and precision of many Gen 3 devices.
The PVS-31 Dual Tube NVG’s (Gen 2+) by Terratac is a perfect example with a resolution ratio of 64lp/mm!
What is the “Figure of Merit” of a night vision device?
In night vision technology, the Figure of Merit (FOM) is a metric used to evaluate the overall performance of an image intensifier tube.
Figure of Merit is calculated by multiplying the resolution (measured in line pairs per millimeter or lp/mm) by the Signal-to-Noise Ratio (SNR), FOM provides a composite score that considers both image clarity and the contrast between light and dark areas in the visual scene.
A good Figure of Merit (FOM) can vary depending on the generation and the intended use of the device. However, as a general guideline:
- Gen 2: FOM values around 1000-1250 are considered good.
- Gen 2+: Anything above 1250 is notably impressive. (High end Gen 2+ devices can have FOM’s of up to 1600)
- Gen 3: FOM values of 1600 or higher are typical for high-end commercial devices, with some reaching over 2000.
These values offer a good balance of resolution and signal-to-noise ratio, ensuring clear and detailed imagery, especially under varied light conditions.
What is a good “Figure of merit” in a night vision device?
Anything higher than 1500 can be considered a good figure of Merit in a night vision device. Such a device would have an SNR of about 25 and a Resolution Ratio of about 64lp/mm. (FOM is calculated by multiplying the SNR and the Resolution Ratio)
What is photocathode sensitivity in night vision?
In night vision devices, the Photocathode Sensitivity refers to how efficiently the photocathode inside the image intensifier tube converts ambient photons (light) into electrons. A higher photocathode sensitivity indicates that the device is more effective at capturing and converting available light, which can result in a clearer and brighter image in darker environments.
In the context of night vision devices, especially when looking at Gen 2 and Gen 3 image intensifier tubes, a sensitivity value in the range of 400 to 600 µA/lm is typically considered decent.
What is a good “photocathode sensitivity” for a night vision device?
A photocathode sensitivity of 850μA/lm is quite good, especially for a Gen 2+ device, and is comparable to high-end Gen 3 devices. It suggests the device would offer strong performance in low light conditions, converting a significant proportion of incoming light into the electron signals that form the visible image.
What exactly is “Luminance Gain” in night vision?
Luminance Gain refers to the amplification factor of the device. It’s a measure of how much the available light (typically from sources like the moon or stars) is amplified to produce a clear and bright image in low-light conditions. Luminance Gain quantifies how many times the light is intensified as it passes through the night vision device.
Typically, the luminance gain is represented as a ratio. For example, if a night vision device has a luminance gain of 1,000, it means that the light entering the device is amplified 1,000 times by the time it reaches the viewer’s eyes.
What is a good “Luminance Gain” in a night vision device?
An extremely high gain isn’t always better, as excessive amplification in certain situations can wash out an image. It’s essential to balance gain with other factors like signal-to-noise ratio and resolution for optimal image clarity.
A Gen 2+ device with a luminance gain of 10,000 is really good as long as it has an SNR of 20 (or more) and a Resolution Ratio of 60+lp/mm (or more).
As a comparison:
- Gen 1: Often have gains between 300 to 900.
- Gen 2: Can have gains ranging from 10,000 to 30,000.
- Gen 3: Typically exhibit gains from 30,000 to 50,000 or even higher.
Equivalent Background Illumination (EBI)
Equivalent Background Illumination (EBI) in the context of night vision devices refers to the amount of light within the device that isn’t attributable to the external environment. In simpler terms, it’s the “noise” level in the image when there is absolutely no light entering the device. This internal noise is usually a result of thermal emissions from the photocathode and other electronic components. EBI is usually measured in lumens per square centimeter (lm/cm²).
A lower EBI value is desirable as it indicates less internal noise, leading to a clearer image. High EBI values can cause a grainy or “snowy” appearance in the image, especially in very low light conditions.
The acceptable or good value for EBI largely depends on the generation and quality of the night vision device:
- Gen 1: Typically have EBI values ranging from 0.1 to 2 lm/cm².
- Gen 2: Common EBI values are in the range of 0.01 to 1 lm/cm².
- Gen 3: These devices have even lower EBI, often below 0.025 lm/cm².
For a Gen 2 or Gen 2+ device, an EBI of 0.2 or lower is considered good.
As always, the actual performance of a night vision device depends on the combination of all its specs, so EBI should be considered alongside other factors like resolution, signal-to-noise ratio, and photocathode sensitivity.
What is Auto-Gating in a night vision device?
Auto-Gating in a night vision device refers to a technology that rapidly switches the power to the image intensifier tube on and off, effectively “gating” the supply of electrical power. This function has several benefits:
- Protection from Bright Lights: The rapid on/off cycle helps protect the image intensifier tube from being damaged by sudden bright light sources, like car headlights or street lamps, which could otherwise reduce the device’s lifespan.
- Improved Image: By continuously adapting to varying light conditions, auto-gating can deliver a clearer image in dynamic lighting environments. For example, if you were using the night vision device in an area where there were intermittent flashes of light (like muzzle flashes), auto-gating would help maintain image clarity and contrast.
- Reduced Halo Effect: The halo effect is a phenomenon where bright light sources in the field of view can create distracting circular halos. Auto-gating reduces the prominence of these halos.
- Enhanced Tube Life: By preventing potential overexposure to bright light sources, auto-gating can prolong the operational life of the image intensifier tube.
In essence, auto-gating ensures that the night vision device remains functional and delivers a clear image in varying lighting conditions, making it especially valuable for military and law enforcement applications where users might encounter unpredictable lighting.
Do you need Auto-Gating in a night vision device?
Auto-gating is not strictly necessary for all users, its benefits in protecting the device and providing a clearer image in varied lighting conditions make it a valuable feature for many. When deciding on a night vision device, consider your intended use and weigh the advantages of auto-gating against the added cost.
Life Expectancy of night vision devices
The life expectancy of a night vision device hinges on the durability of its image intensifier tube, essential for enhancing low-light vision. Gen 1 devices last around 1,000-1,500 hours due to older technology. Gen 2 and Gen 2+ devices, improved by the micro-channel plate, last between 2,500-5,000 hours. Advanced Gen 3 devices have a lifespan of 10,000-15,000 hours.
The device’s longevity can be influenced by factors like auto-gating, usage conditions, and build quality. Although the tube has a limited life, other parts of the device can outlast it, and in some cases, the tube can be replaced to extend the device’s utility.
Modulation Transfer Function (MTF)
Modulation Transfer Function. It’s a metric used to describe the ability of an optical system to transfer contrast from the subject to the image, essentially a measure of image sharpness and clarity.
When you see “MTF @ 25lp/mm (%),” this refers to the system’s contrast performance at a specific spatial frequency. Specifically, “25lp/mm” refers to 25 line pairs per millimeter. This is a measure of fine detail, and the percentage indicates how well the system preserves the contrast of these fine details.
For example, if an optical system has an MTF of 60% at 25lp/mm, it means that fine details (at that frequency) are represented in the image with 60% of the contrast they have in the subject. A higher MTF percentage indicates better contrast and clarity for those fine details, resulting in a sharper image.
In night vision systems, higher MTF values typically indicate better optics and/or image intensifier tubes that can reproduce finer details more clearly.
Why Gen 2+ Night Vision Strikes the Right Balance
For individuals, like farmers, who are in search of an ideal blend between performance and affordability, Gen 2+ NVGs firmly plant their flag. They offer dependable night vision without necessitating the steep investment associated with military-standard equipment. Here’s the breakdown:
- A Leap in Performance: In comparison to Gen 1 and several digital options, Gen 2+ catapults forward. It promises sharper imagery, superior sensitivity, and enhanced resolution—raising the bar for visual excellence.
- Value Meets Efficacy: Gen 3 may be the pinnacle of night vision, but its lofty price point is a barrier for many. On the other hand, Gen 2+ presents a compelling alternative, delivering a significant portion of Gen 3’s capabilities at a fraction of the cost.
- Durability Defined: Tailored for continuous outdoor activities, Gen 2+ devices exude reliability and durability. They’re steadfast allies in the ever-changing world of farming.
- Multi-faceted Utility: Their adaptability is noteworthy. Whether it’s overseeing livestock, identifying potential hazards (from wild animals to unwelcome guests), or navigating nocturnal farm terrains, Gen 2+ shines.
- Reliable Battery Duration: Overpowering its Gen 1 counterpart, Gen 2+ boasts impressive battery longevity.
The Dual Tube Advantage
Dual tube night vision, such as the Terratac PVS-31 Dual Tube NVG (Gen 2+), utilizes two separate optics—one for each eye. This configuration ensures reduced eye fatigue, a broader view, and superior depth perception, crucial for tasks like walking, running, and assessing distances. As a simple experiment, try catching a tennis ball first with one eye closed, then with both eyes open. The difference is evident.
Meet South Africa’s perfect balance between cost and performance in Night Vision
Given all these factors, we spotlight Terratac’s PVS-31 Dual Tube NVG (Gen 2+). With standout specifications, including FOM: 1600, Resolution: 26lp/mm, SNR 25, EBI: 0.2, and Luminance gain: 10,000, its dual optics further improve depth discernment. At a price of R139000, it exemplifies the perfect blend of performance and cost-effectiveness.