Night Vision Generations
What Is The Difference

Image Intensifiers exist in four main types, referred to as Night Vision Generations.

Generation 0 and Generation 1 systems use electrostatic inversion and electron acceleration to produce gain. Both are characterised by geometric distortion but where Generation 0 requires active infrared illumination, Generation 1 has higher photosensitivity and was the first truly passive image intensifier.

Generation 1 and Generation 1+ offers the optimum in performance/cost-effectiveness for the non-professional user. One of the unique characteristics is that a unit can potentially stay 'on' for some time after it is physically switched off due to it holding a residual charge.

Generation 2 and Generation 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 Generation 3 the tube is also coated with an ion barrier film to increase tube life.

However, Generations 1, 2 and 3 are very similar internally with the main difference being their photocathodes. Whereas Generation 1 and Generation 2 photocathodes may be the same (Tri-Alkali), Generation 3 technology is based on a completely different substance (Gallium Arsenide) that is three times more light sensitive.

Although Generation 3 intensifiers are the latest and most sensitive, they are not necessarily the best for all applications.

Because of an inherent liability to internal electrical damage, much of their gain advantage is lost by built-in protection systems. They are also most highly sensitive to the invisible, near infrared part of the spectrum.

In many urban and suburban areas lit by streetlights, there are insignificant amounts of near infrared. Generation 3 performance then appears to be no different to that of the earlier generations. In fact, Generation 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.

Generation 0:

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. Generation 0 tubes are characterised by the presence of geometric distortion and the necessity for active infrared illumination.

Generation 1:

Typically uses an S-10 or S-20 photocathode (with photosensitivity of 120-20Q uA/Im), electrostatic inversion, and electron acceleration to achieve gain. Because of higher photosensitivity Generation 1 was the first truly passive image intensifier.

Characteristics of Generation 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.

Generation 1 tubes generally have a high power requirement which can mean that they emit a high pitched tone when driven hard - this is especially true of twin tube designs (binoculars or 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.

They are not well suited to still photography due to limited light amplification (plus limitations of film speed/aperture/shutter speed combinations) and noticeable drop-off of image sharpness towards the periphery. Video filming is possible (thanks to the additional light gain of the video camera's CCD), in those units offering the best quality/highest sensitivity tubes.

Most budget-priced Generation 1 night vision tubes are manufactured in Russia - they account for approximately 95% of the world market.

Generation 1+:

An adaptation of high quality Generation 1 tubes with the addition of a fibre optic plate on the front of the tube. There is less geometric distortion, noticeably fewer cosmetic blemishes and both higher photosensitivity ( 240 uA/lm) and IR sensitivity than standard Generation 1 tubes.

Tube gain is generally 1000x. Resolution in the centre can be as good as 45 lp/mm.

They also have a lower power requirement than Generation 1 systems, tending not to suffer power supply noise and offering noticeably better battery life.

These are the first systems that allow the possibility of reasonable still photography and good video imagery through the scope.

Generation 2:

Usually an S-25 (extended red) photocathode (with photosensitivity of 240 - 400 uA/lm) with a microchannel plate (MCP) to achieve gain. Normally uses fibre-optic inversion.

Generation 2 tubes provide good performance in low light levels and exhibit very low distortion making them well suited 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 30 - 35 lp/mm. They are more tolerant of urban lighting than Generation 3 systems.

Generation 2+:

Based on Generation 2 tube technology, but has enhanced photocathode sensitivity (typical photosensitivity of 500 - 600+ uA/lm). Resolution in the centre varies between 35 - 45 lp/mm.

SuperGen:

Based on Generation 2 tube technology, but with further enhanced photocathode sensitivity (photosensitivity of 600 - 700+ uA/lm). Resolution in the centre varies between 45 - 60 lp/mm.

Generation 3:

Uses gallium-arsenide for the photocathode and a microchannel plate for gain. The microchannel plate is also coated with a protective ion barrier film to increase tube life. Can produce more than 800 uA/lm in the 450 to 950 nanometer (near-infrared) region of the spectrum.

Generation 3 provides very good to excellent low-light-level performance and long tube life.

Military specification Generation 3 tubes show virtually no distortion. Resolution in the centre varies between 32 - 64 Ip/mm. Current US specification is Omnibus 4.

In almost all countries where they can be sold, Generation 3 systems are limited to strictly military use.

Generation 4:

It now appears that the US may be classifying Omnibus 5 tubes as Generation 4 because they have been able to do away with the protective ion barrier inherent in Generation 3 systems.