Frequently asked questions
light-amplifying tube works by capturing and amplifying available light, even in very small quantities, to enable vision in the dark. The process begins with the collection of photons via a lens. These photons strike a photocathode, which converts them into electrons. The electrons are then accelerated and multiplied by a microchannel plate (MCP), thereby amplifying their number. Finally, these electrons strike a phosphorescent screen, producing a luminous image visible to the user, which is an amplified version of the original scene.
As a small drawing is worth a thousand words:
Collimation is essential for night vision (NVG) because it ensures that the images seen through the goggles are correctly aligned with the user's line of sight. Proper collimation ensures that the two images perceived by the eyes are merged into a single coherent image, reducing eye strain and improving accuracy when observing or shooting. Without proper collimation, the user may experience difficulty judging distances and maintaining focus, which can compromise performance in low-light conditions.
To evaluate the performance of an image intensifier tube in night vision, several key characteristics are used:
SNR (Signal-to-Noise Ratio): Measures the ratio between the useful signal (captured light) and electronic noise. A high SNR indicates a clearer and more detailed image, even in low light conditions.
FOM (Figure of Merit): Calculated by multiplying the SNR by the resolution (usually in line pairs per millimeter, lp/mm). The FOM gives an overall indication of the tube's performance; the higher the FOM, the better the image quality.
Resolution: Expressed in lp/mm, it determines the tube's ability to distinguish fine details. Higher resolution means a sharper image.
Light gain: Indicates how many times the light is amplified by the tube. High gain improves visibility in the dark, but too much gain can introduce noise. In summary, SNR, FOM, resolution, and light gain are essential parameters for evaluating the clarity, sharpness, and overall quality of a light intensifier tube.
Autogate and manual gain are two technologies used in night vision systems to manage light intensity.
Autogate: Automatically regulates the amount of light entering the image intensifier tube, quickly adapting to sudden changes in brightness, such as lightning or artificial lights. This protects the tube and improves image quality in variable conditions, while preventing overexposure.
Manual gain: Allows the user to manually control light amplification, adjusting the image according to specific needs. This provides more control, but requires active intervention to adapt to changes in brightness.
In summary, autogate provides automatic and responsive protection against light variations, while manual gain gives the user direct control over image intensity.
Values such as SNR, FOM, resolution, and light gain are variable and sometimes random during the manufacture of image intensifier tubes due to the complexity of the production processes and materials used.
Complex manufacturing process: Tubes are made from sensitive materials and advanced technologies such as photocathodes, microchannels, and phosphor screens. Small variations in material purity, assembly precision, or manufacturing conditions (such as temperature and pressure) can affect final performance.
Component sensitivity: Photocathodes, which convert light into electrons, are particularly sensitive. Variations in their chemical composition or processing can lead to differences in the conversion of photons into electrons, impacting the SNR and light gain.
Microchannel uniformity: The Microchannel Plate (MCP) amplifies electrons, and any variation in the size or shape of the microchannels can affect electron multiplication, influencing resolution and FOM.
Electronic interactions: Tubes are subject to complex electronic interactions, and even slight variations in internal circuits can generate noise or affect gain stability.
In summary, the complexity of the materials and manufacturing processes, as well as the sensitivity of the components, lead to inevitable variations in SNR, FOM, resolution, and light gain values from one tube to another. This is why each tube must be tested individually to evaluate its specific performance.
Image intensifier tubes (IIT) in night vision systems are classified into different generations, each offering improvements in performance and technology. Here is an overview of the different generations of tubes:
Generation 1 (Gen 1)
Technology: Generation 1 tubes use a photocathode and a basic image intensifier. They offer limited light amplification.
Performance: Resolution is generally low, with a limited field of view and poor performance in very low light conditions.
Use: Although less powerful than later generations, it is often used in basic civilian applications and is more affordable.
Generation 2 (Gen 2)
Technology: Introduces the Microchannel Plate (MCP), which allows for more efficient electron amplification, improving image quality.
Performance: Better resolution, wider field of view, and significantly improved performance in low-light conditions compared to Gen 1. Black spots and noise are also reduced.
Use: Used in military, security, and professional applications due to its better value for money.
Generation 3 (Gen 3)
Technology: Evolves with the use of a GaAs (Gallium Arsenide) photocathode, offering better light sensitivity and longer life. The protective filter helps reduce the effects of excessive light.
Performance: Excellent resolution, low noise, high performance in very low light conditions. The image is much sharper and clearer, with fewer visual defects such as black spots.
Use: Mainly used by the military and professionals due to its superior performance.
Purging night vision goggles (NVG) involves removing moisture and internal contaminants from the image intensifier tube (IIT) and replacing the air inside with a neutral gas. This operation is crucial for the following reasons:
Prevention of Condensation Buildup: Removing moisture prevents condensation from forming inside the tube, which can impair image quality and cause malfunctions.
Maintaining Optical Performance: Purging helps maintain image clarity and brightness by removing contaminants that could cause spots or distortions.
Extended Lifespan: By keeping the inside of the tube clean and dry, purging contributes to the longevity of the device by reducing wear and potential damage.
In summary, purging an NVG is essential to ensure optimal performance, consistent image quality, and increased equipment durability.
Our partners
PRS Technologies is a French company specializing in the design, assembly, and modernization of night vision goggles (NVGs). We meet the needs of armed forces, security services, and industrial companies seeking reliable, high-performance, and sovereign optronic solutions.