The first practical Night Vision devices were developed, more or less simultaneously, by both sides in the Second World War.Now known as 'Generation O', these early examples suffered the major drawback that they required powerful infra red illumination, which is invisible to the naked eye, but stood out like a bright light to an enemy who was also using infra red night vision equipmentBy the time of the Vietnam war, however, "Active Infra Red' night vision devices were being phased out of military use, in favour of so called 'Starlight' systems, which are now known as 'Generation 1' and which could produce a visible image in very dim natural light.'Generation 2' image intensifiers, incorporating multichannel plates, were first produced back in the early eighties, offering better low light performance and less distortion, but they were quickly overtaken by'Generation 3' versions with improved photocathodes giving them even better low light response. Various later improvements - aimed in particular at allowing the tube to handle rapidly changing light levels, such as in urban situations - are sometimes known as 'Generation 4'.
 

All sorts of makers of all sorts of products like to give us the impression that they are using military technology or that they supply the armed forces with vital equipment. But in the case of Night Vision equipment, that really could be true. Image intensifiers that include a multichannel plate are officially classed as 'dual use* products, because they could be of use for military purposes. As such, they are subject to export controls.Within the EU, this shouldn't be a problem, but if you take a Gen 2 night vision device outside the EU it reqires an export licence, even if you keep it on board and bring it home again.Officials at the Department for Business, Enterprise & Regulatory Reform tell me that a licence shouldn't be too hard to obtain and that applications are usually dealt with in about three weeks, but that a separate licence is required for each trip.For further information about licences and applying for them, log on to www.berr.gov.uk/europeandtrade/strategic-export-control/index.html
 

A built-in infra red torch seems to be pretty standard: all nine of our group included it. But whilst it may be of use to naturalists or paintballers who are likely to be dealing with targets at close quarters in dark woodland, we could see no practical use for it on a boat. The effect is almost exactly the same as using a conventional torch: it lights up a relatively small area, at short range, but at anything more than a few metres it achieves next to nothing.
 

Most of the less expensive night vision devices are in the form of monoculars: they have one objective lens and one eyepiece.Bi-ocular devices have one objective lens and one image intensifier tube, but the image is viewed through two eyepieces.You are seeing the same image with both eyes, so there is no real impression of 'depth', but this configuration is supposed to reduce eyestrain. Binocular devices, which have two objective lenses, two tubes and two eyepieces, are available, but, we weren't offered any for this particular test. Inevitably, they are significantly more expensive than monocular versions, but they offer a '3D' image, in much the same way that conventional daylight binoculars do.Goggle or hand-held?Any of the three types are potentially capable of being turned into goggles, by bolting them to a headmount that supports them in front of your eyes to leave your hands free.Which configuration is best is a moot point bi-ocular goggles are more common than monoculars, but monoculars have the important advantage of preserving your natural, unaided night vision in the other eye.The main problem with goggles, we found (apart from the fact that they make you look like something out of a sci-fi movie and may frighten the horses), is that they can be quite disorientating, and that it is only too easy to bump into things when you have a dalek-tike protrusion sticking out of your head.