Night Vision Generations
Night Vision Generations
Night Vision Image Intensifiers exist in several shapes and sizes and four main generations.
Gen 0 and Gen 1 systems use electrostatic inversion and electron acceleration to produce gain.
Both are characterised by geometric distortion, but Gen 0 requires active infrared illumination, whereas Gen 1 has higher photosensitivity and was the first truly passive image intensifier.
Gen 1/Super Gen 1+ offers the optimum in performance/cost-effectiveness for the non-professional user.
One of the unique characteristics is that it can potentially stay ‘on’ for some time after it is physically switched off due to it holding a residual charge.
Gen 2 and Gen 3 systems do not suffer this ‘afterglow’ - the image disappears as soon as they are switched off.
They are generally smaller in size and weight and use noticeably less current.
They both use a microchannel plate (MCP) to improve gain and image resolution, but on Gen 3 the tube is also coated with an ion barrier film to increase tube life.
However, they are very similar internally with the main difference being their photocathodes.
Whereas Gen 1 and Gen 2 photocathodes may be the same (Tri-Alkali), Gen 3 technology is based on a completely different substance, Gallium Arsenide, that is up to three times more light sensitive.
Be wary of systems claiming to use US Gen 2+ image intensifier tubes.
The US has manufactured only Gen 3 tubes for most of the last 10 years. The likely source for any US Gen 2+ tube is therefore military warehouse clearance stock.
Whilst you may be lucky to get a tube that has been sitting as a spare, it is still many years old and unlikely to offer the performance of current production.
Worst case scenario is that you get a well-used, lifetime limited tube with much reduced sensitivity due to usage and age.
Although Gen 3 intensifiers are the most sensitive, they are not necessarily the best for all applications.
They are more highly sensitive to the invisible, near infrared part of the spectrum.
In many urban and suburban areas lit by street lights, there are insignificant amounts of near infrared.
Gen 3 performance then appears to be no different to that of the earlier generations. In fact, Gen 3 systems tend to ‘white-out’ when exposed to high light levels losing a lot of image detail and contrast.
They are really only seen at their best in the very darkest rural locations.
Latest development is auto-gating image intensifier tubes.
These are designed to give optimum performance and minimal halo when scanning from very dark to light areas or vice versa.
This makes them the most effective solution for urban operations and offers the best protection where there is likely to be bright light sources such as street lights, car headlights etc.
It is more true of night vision than almost any other product, you really do get what you pay for.
There is a noticeable performance advantage as you work up the intensifier tube scale.
However, as with many products, the percentage of performance gain reduces compared to the noticeably increased outlay in cost for the highest capability units.
Typically uses an S-1 photocathode with peak response in the blue-green region (with a photosensitivity of 60 uA/lm) using electrostatic inversion and electron acceleration to achieve gain.
Gen 0 tubes are characterised by the presence of geometric distortion and the necessity for active infrared illumination.
Typically uses an S-10 or S-20 photocathode (with photosensitivity of 120-200 uA/lm), electrostatic inversion, and electron acceleration to achieve gain. Because of higher photosensitivity, Gen 1 was the first truly passive image intensifier.
Characteristics of Gen 1 include high voltage power supplies, geometric distortion toward the periphery, reasonable performance in low light and ‘blooming’.
The tube can potentially hold a charge for some time even if no power is being supplied, the image just gradually fading.
Tube gain varies between 100-500x - beware of claims for much higher values.
Resolution in the centre varies between 25-30 lp/mm.
Gen 1 tubes generally have a high power requirement which can mean that they emit a high pitched tone when driven hard - especially true of twin tube designs (binoculars/goggles).
Due to the manufacturing process it is usual to find cosmetic blemishes (spots/patches) in the tube - these are considered normal and are not a defect.
Most budget Gen 1 night vision tubes are manufactured in Russia/Belarus - they account for approximately 95% of the world market. Typical MTTF: 1000 hrs.
CF Super/Super Generation 1+
True CF Super/Super Gen 1+ tubes are only available from one source - Pulsar/Yukon Advanced Optics.
They feature the addition of a fibre optic plate (not an MCP) on the front of the tube.
There is less geometric distortion which gives much better edge-to-edge definition than standard Gen 1 tubes.
Resolution in the centre can be as good as 42 lp/mm (a 30% increase over the best Gen 1) and there is much reduced geometric distortion around the periphery with a resolution here of about 32lp/mm.
These are the first systems that allow the possibility of reasonable still photography and video imagery through the scope.
Beware of some companies claiming to offer ‘Gen 1+’ models - many are really only Gen 1, not Super Gen 1+.
Typical MTTF: 1000 hrs.
Usually an S-25 (extended red) photocathode (with photosensitivity of 240-350 uA/lm) with a microchannel plate (MCP) to achieve gain.
Normally uses fibre-optic inversion.
Gen 2 tubes provide good performance in low light levels and exhibit very low distortion making them reasonable for use with video or still cameras.
They are equipped with automatic gain control, flash protection and feature edge-to-edge definition.
Resolution in the centre varies between 28-32 lp/mm. They are more tolerant of urban lighting than Gen 3 systems.
Typical SNR: 11. Typical MTTF: 2000 hrs.
Based on Gen 2 tube technology, but has enhanced photocathode sensitivity (typical photosensitivity of 350-450+ uA/lm).
Resolution in the centre varies between 32-40 lp/mm.
Typical SNR: 13. Typical MTTF: 2000 hrs.
Based on Gen 2 tube technology, but with further enhanced photocathode sensitivity (photosensitivity of 500-600 uA/lm).
Resolution in the centre varies between 45-54 lp/mm.
Typical SNR: 18-21. Typical MTTF: 10000 hrs.
The highest development in Gen 2 tube technology, with further enhanced photocathode sensitivity (photosensitivity of 600-800+ uA/lm).
Now available with the option of auto-gating, improving capability in scenarios where lighting changes from dark to bright very rapidly.
Resolution in the centre varies between 55-72 lp/mm.
Typical SNR: 20-28. Typical MTTF: 15000 hrs.
Uses gallium-arsenide for the photocathode and a microchannel plate for gain.
Can produce more than 800 uA/lm in the 450 to 950 nanometer region of the spectrum.
Gen 3 provides very good to excellent low-light-level performance and long tube life. Gen 3 tubes show virtually no distortion.
Resolution in the centre varies between 45-64 lp/mm.
All countries producing Gen 3 image intensifier tubes strictly control the availability and export of these systems - in many, they are limited to strictly military/government agency use.
Typical SNR: 18-28. Typical MTTF: 10-15000 hrs.
Utilises a CCD sensitive in the IR spectrum and an LCD screen.
Primarily for consumer/commercial use since it relies heavily on an active IR light source for optimum performance.
A major advantage over image intensifier tube systems is that the CCD cannot be damaged by normal bright light exposure.
Resolution equates to approx 40 lp/mm.