http://www.night-optics.com/ Night Vision Scopes, Goggles, Binoculars and Monoculars by ATN en-us Copyright (c) 2002 - 2008 night-optics.com general@night-optics.com webmaster@night-optics.com Fri, 25 Jul 2008 03:36:36 GMT Night Vision news http://www.night-optics.com/night-vision-news/8 The ghostly green-hewed image produced by night vision gear has become familiar to all of us in recent years. For boaters though, these images need not come from some distant battlefield. In fact, image intensifying night vision devices are no longer the exclusive domain of the military. Commercial models have been available for over a decade now, a number of them tailored to the needs of boaters. Night vision technology continues to improve while prices have fallen well within the means of any boater. Driving these trends are the slow but relentless research of the Defense Department and the proliferation of low cost producers from Europe, Russia and China. Image intensifiers are not the only kind of night vision device; thermal imagers (also know as infrared) are the other major category. While image intensifiers produce an image by amplifying the miniscule amount of light present at night many thousand-of-times to create an image, thermal imagers detect the heat from objects in the form of infrared energy. Seeing Red...Infrared that is While a few thermal imaging devices are available to consumers, their costs tend to be prohibitively high in comparison to image intensifiers. Even though thermal imagers are capable of detecting objects at greater ranges and with no ambient light at all, the level of detail that can be discerned by commercial models pales in comparison to image intensifiers. Additionally, thermal imagers have great difficulty discerning objects that are the same temperature as their background and are often severely impaired by rain and fog. While the military can afford to use both of these technologies together in a complimentary fashion, all but the most demanding technophile with money to burn should stick to mid-range image intensifiers. Intensify Your Image Most of todays image intensifiers work by taking the small amount of light produced by starlight, moonlight or ambient light from manmade sources and converting it from photons to electrons visible light to electrical energy. Electrons then pass through a microchannel plate. These plates contain millions of channels that propagate even more electrons as the first electrons pass through. Finally, this avalanche of electrons strikes a phosphor screen that converts them back into photons visible to the human eye. The major advances in night vision technology are roughly categorized by generation. Youll hear most modern image intensifiers being described as Gen 2 or Gen 3 . In fact these technological generations go from Gen 0 to Gen 4. The divisions are not ironclad but, broadly speaking, Gen 0 refers to the earliest devices that were developed at the end of World War II while Gen 4 is used by some manufacturers in describing their most advanced products today with 2 and 3 falling in between. Generations... Gen 0 devices werent really image intensifiers at all. They were more like glorified flashlights. By using infrared light along with optics that made the otherwise invisible light apparent to the viewer, Gen 0 devices really were somewhat-covert flashlights. As with normal flashlights, their limitations were range and field of view along with the fact that the user could be revealed if another party possessed similar optics. Gen 1 devices refer to the first generation of real image intensifiers developed in the 1960s. Being made of three image intensifier tubes connected in a series these units were heavy and bulky. They were called starlight scopes, a title that reflects their limited abilities in very low light situations. Gen 2 devices were the first to use the microchannel plate. This innovation eliminated the need for multiple tubes, reducing size and weight while improving performance. The Gen 2 technologies rolled out in the 1970s allowed for the development of the first real night vision goggles for soldiers and pilots. Gen 3 devices developed during the 1980s and 1990s introduced advanced gallium arsenide photocathodes and ion-barrier-film on the microchannel plate. The new photocathode technology enabled increased range and sensitivity in very dark conditions. Improvements to the microchannel plate increased the operational lifespan of the tube from about 2000 hours in Gen 2 devices to about 10000 hours in this newest generation. Gen 4 devices use gated filmless tube technology. Calling this kind of night vision device fourth generation is not universally accepted though. Gen 4 NVDs are also sometimes known as Gen 3+, Gen 3 Ultra, or advanced third generation units. These are the most advanced systems available and are primarily intended for military and law enforcement users. There are export restrictions placed on these high performance night vision systems by the US Government, so taking them to your favorite international cruising spot is something of a no-no. How Much Green for Green? Gen 3 systems tend to cost 2000 and up and are best for boaters that demand detailed situational awareness while operating in areas with very little ambient light. This kind of capability is very helpful close to shore or in uninhabited and constricted waterways and anchorages. Gen 2 systems cost around 1000 usually and are very useful with slightly more ambient light, whether that be moonlight or lights from shore. The kind of NVDs you find for 500 and under should be considered toys more than anything. These are almost always Gen 1 and require not only significant ambient light (full moon plus) to be of any use, but also suffer serious glare from light sources in their field of view. These units almost always have an infrared illuminator to provide some marginal capability in darker conditions and for observing details up close (map reading, etc.). This is not to say that IR illuminators are a sign of a poor product. They can be quite useful and are included on many advanced models as well. It should be a supplementary feature though, and not (as in down-market models) the primary means of detection. The performance characteristics that anyone considering purchasing a night vision device should be familiar with are sensitivity, signal and resolution. Sensitivity also called photoresponse is the image intensifiers ability to detect available light. This is measured in microamperes per lumen. Signal defines the strength of the transmission through the microchannel plate. Resolution is the ability to discern detail in an image and is measured in line pairs per millimeter. Tunnel Vision: Don amp;#8217;t Believe Everything you See What you see when you use an image intensifying night vision device is quite different from what can be seen with the naked eye. Obviously, everything is green hewed but that is not the only difference. Regardless of an objects color to the naked eye, it is its reflectivity that has the greatest impact on how light or dark it appears when viewed through an NVD. A shiny black surface may appear brighter than a dull white surface under some circumstances. When it comes to depth perception, night vision devices have serious limitations. Most units have only one tube and a limited field of view while some also have some level of magnification or use fish-eye lenses to increase their field of view at the cost of distortion. With the exception of a few binocular and goggle style units, stereoscopic vision is eliminated. Even with two-tube units, the narrow field of view produces a tunnel vision effect that has proved dangerous even to highly trained soldiers and airmen. Precipitation of any kind reflects ambient light and can degrade performance if it is severe enough. A sort of faint honeycomb pattern and a few black spots in the field of view are totally normal and are, in fact, inherent in NVDs. When a Binocular is not a Binocular - NVD Form Factors A few NVD form factors were mentioned earlier but, to be comprehensive we will go through all of them. The most basic difference in form factors are the number of tubes; one or two (though advanced systems for military pilots can have up to four). One tube models come in both monocular and binocular styles. How, you say, can a binocular have only one tube? Of course, technically, they cant; but a one tube unit can have a binocular-style output that projects one image into both eyes. One and two tube units can be handheld or use a head mount (goggle style) and some one tube units can be mounted on tripods or cameras. How to find your inner Navy SEAL Generally speaking, an unmagnified handheld monocular device is quite sufficient for most boaters as a supplemental navigational and boat handling aid. A detachable lens with some level of magnification as well as a magnetic compass attachment for taking bearings may also be of use. If you want to play Navy SEAL many of these same units can also be head mounted (just be careful not to turn near anything that might knock the unit off your head and ,perhaps, into your drink). http://www.night-optics.com/night-vision-news/8 general@night-optics.com Night Vision news 2005-04-01