Using binoculars to examine a deer to confirm its legality is fine, but often by the time it's identified, there is little or no time to lower the binocs, raise the rifle, and take the shot. With a scope, it's fast and easy to make the shot once the game has been identified. These days I very rarely head to the woods to hunt without a scoped rifle.

For almost all hunting applications, 3x is plenty low. Even at a close ten-yard shot, you will be able to see plenty of your critter in the scope lens. I wouldn't want the low end of a hunting scope's adjustment to be any higher than 4x, because for close shots and/or shots at moving game, anything higher than that will narrow your view too much. And 9x is usually plenty high for zooming in on far game at reasonable ranges.

In some cases a higher magnification is desirable, but of course that depends on the type of terrain you hunt and how far the longest shot may be, and only you can determine your needs when choosing a scope. Anything above 12x is really overkill for most realistic hunting scenarios, and the higher you go with magnification, the more your every shake and tremble shows up in the movement of the crosshairs on your target.

Another caveat is that eye relief often changes with the power setting, too. Eye relief is the optimum distance between your eye and the scope's eyepiece to get the proper view of your target. With a variable scope, that distance will often change somewhat depending on where the magnification is set, meaning that the position of the cheek on the buttstock will have to change as well.

Again, this problem is almost always present in cheap scopes, but it also finds its way farther up the ladder of scope values than does the point-of-impact problem. In comparison, this is a less important malady than a shifting point of impact.

That said, the larger (44mm and up) objectives are nothing to get excited about, in my opinion. The largest objective on any of my deer-hunting scopes is 40mm, and that's plenty big. At dusk or daybreak, any of my good scopes will gather enough light to alllow me to peer into dark brushy areas and see much more detail than I can see with my naked eye.

Also, larger objectives invariably mean that the scope must be mounted higher on the gun - and the higher the line of sight, the more awkward the sighting process becomes, and the more awkward the gun is to handle, as it becomes increasingly top-heavy.

Another feature found on some scopes is the adjustable objective. This allows better focus at varied ranges, and requires adjustment depending on how far your target is from your scope. I believe this feature does help make some lower-priced variable scopes more dependable as far as point-of-impact goes, but again it usually means that a higher mount is required.

How To Get the Most Out of Your Mil Dot Reticle.

Over the last couple of years the mil dot reticle has become less of an option and more the standard in tactical rifle scopes. Since its inception with the Unertl USMC sniper scope and later in various versions of the Leupold Mark IV scope, military snipers have come to know the mil dot reticle as a reliable means of determining distances to targets, establishing leads for moving targets, and for alternate aiming points for windage and elevation holds. Military snipers who are graduates of formal programs of instruction have spent numerous hours honing their ability to use the mil dot reticle and are comfortable and competent with it. Military snipers are easy to train on the mil dot reticle, as the military has been using the mil relation formula in one form or another for many years. As the WERM rule (width of correction = Range x mils observed), it has been the mainstay for determining adjustments when calling and adjusting indirect fire weapons such as mortars and artillery. On the other hand, some Law Enforcement and civilian tactical and practical long-range precision shooters are a little hesitant sometimes of the mil dot reticle because of a lack of proper training. I hope this article will help remedy this problem.

The mil dot reticle is a post and wire reticle with 10 mils (milliradians) between opposing posts and dots spaced 1 mil apart on the wires, minus the reticle intersection so

as not to obscure the aiming point. A milliradian is an angular unit of measure that just happens to equal one yard at 1000 yards and 1 meter at 1000 meters. Knowing this fact we can, through the wonders of elementary mathematics, use this little critter to determine distance to an object when the size of the object is known. The sniper simply measures his target using the dots, then works a simple formula to obtain the target’s distance or the distance to an item near the target.

How the milliradian became the unit of measure of choice is fairly interesting as sniper trivia. Back when the military was determining how to graduate their artillery pieces the techno-geeks settled on the milliradian as the unit of measure for their sights. Since there were 6,283 milliradians (2 PI for all you math whizzes) in 360 degrees they rounded up to 6400. The Soviets on the other hand rounded down and ended up with 6200 mils in a circle for their artillery sights, compasses, etc.

As the Marine Corps sniper program grew and matured during the late 70’s, the snipers desired more accurate range estimation abilities than what the issue 6x30 and 7x50 binoculars and the 3x9 Redfield scope were allowing. The binoculars had hatch marks that were graduated in 10 mil increments with the actual hatch mark lines being 5 mils long (Steiner M22), which were all too coarse for obtaining much precision. Add to this that the Accu-trac system in the Redfield, using an 18-inch stadia line intended for deer hunting, left much to be desired for tactical shooting. We at the Scout/Sniper Instructor School used a "barber pole" to teach students to mentally break the reticles of the binoculars into finer subtensions than for what the binoculars were originally designed. This barber pole had 4" bands painted on it and we set it out at 111 yards where each band equaled 1 mil. This allowed the student to see what the graphics on the reticle subtended including hatch marks, numbers etc. For example, the base of the number 2 equaled a certain fraction of a mil and the tips of the number 3 equaled another number of mils. All of this was fine and dandy but a better way was needed.

Although the mil dot system is both simple and accurate, as with anything else it does have limitations, especially if you haven’t received formal training on them. The owner’s manuals that usually come with the civilian scopes are very basic when they explain the use of the reticle. I’ve been teaching the use of the things for over 18

years and have seen most of the problems that students run into when first encountering mil dot reticles. Even high-tech devices such as laser range finders have limitations and disadvantages and low-tech mil dots are no exception. In this article I will cover some facets of mildot usage that will enhance your ability to use them.

The Mil relation formula. There are a couple of permutations of the mil relation formula floating around. At first look most of them strike fear in the hearts of most of us Neanderthal, knuckle dragger types, but they are really quite user friendly. Granted the formulas require you to use more than your fingers and toes, but we Marines can handle it! Well, here we go. The basic one is:

Height of item in yards (meters) x 1000/Mils read = Distance to item in yards (meters)

This formula is good when the sniper knows an item’s size in yards. My only problem with this version is that cops often have to deal with small items such as vehicle wheels, small stickers on windows, headlights etc. This requires the officer to convert a 7" headlight into a decimal equivalent in yards before they can work the formula. And since most cops are fellow Neanderthals and are usually under a fair amount of stress to begin with, I prefer to teach the formula:

Size of item in inches x 27.8 (25.4)/Distance in yards (meters) = Mils

Knowing the sizes of items being measured is a matter of knowing your prospective area of operation and making a list of the sizes of standard items. Make sure you get both height and width of objects as you can mil both dimensions but the largest dimension mathematically will usually give the most accurate answer. Military snipers should have sizes of enemy vehicles, enemy weapons, average heights of soldiers, etc. An LE sniper should have sizes of traffic signs, bricks, license plates, etc. So carry a tape measure and a notebook with you and prepare to have people look at you funny as you measure curbs, traffic lights, mailboxes and other commonly found objects in your area of operation.

So as you can see the mil relation formula shouldn’t scare anyone off. As a matter of fact there are ways to make the use of the formula even easier. Many databooks such as the TRGT data book and others have charts developed using computer spreadsheets that allow the shooter to find the target size and the mil reading on the chart and it gives the shooter the distance without any hate or discontent. You can even make your own using the above formulas if you know how to use a spreadsheet such as MS Excel.

The EASIEST way to deal with this formula is to get yourself a Mil Dot. This handy slide-rule type device does the calculations for the mil relation formula, corrects for target size when viewed at angles, corrects for slope, gives MOA/mil/in equivalence and even predicts the future. (You have to bury some chicken bones and some other stuff to get the last feature).

Reticle Focus. The first thing we will talk about is reticle focus. In order for the sniper to obtain precise mil readings the reticle must be properly focused. If the reticle is out of focus, the reticle will appear fuzzy and go in and out of focus as the eye attempts to zero in on it. Not only will mil readings be difficult to obtain but the sniper will also suffer eye fatigue over long periods behind the scope as the muscles of the eye attempt to maintain focus. Steps for focusing a scope’s reticle are:

• Look at a distant object (about 300 yards) and allow your eyes to become focused on it.

• Quickly look through the scope at the sky or a blank wall and check to see if the reticle is immediately sharp and crisp. If it is, then no further adjustment is needed.

• If your eye has to re-focus AT ALL on the reticle then proceed.

• Grasp the eyepiece and back it away from the lock-ring. Turn the eyepiece several turns so as to move at least 1/8". It will take this much change to achieve any measurable effect on the focus. Then repeat step one.

• If the image is better, continue to turn the eyepiece in the same direction. If it is worse, turn the eyepiece the other way and repeat the previous steps until the image of the reticle is sharp and crisp immediately upon looking into the scope.

• Do this several times. Taking the focus past the point of best focus and back again will help to ensure you have the clearest setting. Then lock up the eyepiece by screwing the lock-ring back to the eyepiece.

• Some scopes feature a quick-adjust eyepiece and therefore simplify this operation.

There have been many occasions while working as an instructor where I have found students do worse on ranging with mil dots than with binoculars or even the naked eye. Most of the time this ceases to be a problem after they begin ensuring that both the objective and the reticle are sharply focused.

Ambient Light Conditions. As with all other methods of range estimation that uses the sniper’s eyes, the nature of the ambient light conditions can affect the sniper’s ability to obtain an accurate mil reading. Effects such as glare, mirage, haze/fog can obscure the target or alter how the sniper sees the edges of the target which will all cause inaccurate readings. In order to deal with this, a sniper must practice obtaining mil readings in all weather conditions and take notes as to corrections that he must make in those conditions. For example a sniper knows that in foggy conditions he needs to add .1 mil to his mil readings or in bright sunny conditions he has to subtract .1 mil on light colored targets due to glare. So practice obtaining distances with your scope in all conditions and confirm distances with a laser range finder. Keep notes as to how different light conditions alter your mil readings.

Hang on a minute!! Use a laser range finder to confirm distances? You are probably asking, "Then why the hell worry about mil dots if I have a laser range finder?" Well, have you ever had batteries die on you or have a piece of electronics go belly up? Also, have you heard of laser detectors? Besides, mildot reticles have other uses besides ranging. Okay, now that we’ve cleared that up I’ll continue.

Okay, let’s look at what we have up to this point. We’ve learned that we have to make sure our reticle and target are in focus. No problem here as we should have these items under control anyway. We’ve had to either learn a simple formula or buy a Mildot Master. No big deal here either. All we are left with now is to figure out how to measure objects with the reticle. Let’s see if there are any major obstacles here.

Reading the Dots. The precision tactical shooter must be able to obtain accurate mil readings to the tenth of a mil. This is where it is important to know the subtensions on your reticle. For example, I know in my Leupold 3.5 x 10 M3LR with the USMC stamped wire reticle pattern, the dots themselves are .25 mils and the posts are 1 mil wide when the scope is at maximum magnification (more on this in a minute). In Leupold scopes with round, dot-etched glass reticles the dots are .22 mils in diameter and the posts are .5 mils wide. This enables me to break the reticle down as in the illustrations above right.

The importance of being precise on your readings becomes evident when working at long range. For example, if a 40-inch target (the size of a kneeling man) is incorrectly

measured at 1.5 mils it would range out to 740 yards where if the correct reading were 1.6 mils it would actually be at 693 yards. Assuming there is 5 MOA drop with a .308 between 700 and 800 yards you could be dialing on around 2 MOA too much elevation. At 700 yards that is 14 inches and may put you over the target depending on your aiming area. So here are some helpful tips when measuring a target.

• Have a steady rest for your rifle. Just as steady as when you are firing. Lay the rifle on its side if you have to.

• Use a post for one end of the measuring scale if possible. This will give you a clear point for one end of your measurement.

• Make sure the target/reticle are focused.

• Practice obtaining mil readings on targets at known distance. Using the formula given above determine how many mils a target should read then work on it until you can see that measurement in the scope.

Variable Power Scopes. My last tip there brings up an interesting point in regards to variable power scopes with mil dot reticles. Most American variable power scopes do not magnify the reticle along with the target. In other words the reticle remains the same size as the target image zooms. This can wreak havoc if you try to measure a target at the wrong magnification, as the dots will only equal 1 milliradian at one magnification setting. Knowing what magnification setting your scope is set up to use the dots on is CRITICAL to getting accurate readings. Most scopes are set up to use their highest power setting and some have an index mark on the power ring. One problem I’ve noted with the variable power scopes is that the setting that the factory tells you to use can often be off a bit. I’ve had students be constantly off on readings by 1 or 2 tenths and get flustered as hell. Some of this can be due to out of focus reticles but many of them figure out that the index mark is off a hair. By using the barber pole I mentioned earlier, you can find the EXACT point where the mil dots subtend precisely 1 mil. As a side note you can also find the point where the dots equal 2 mils and other readings.

Leads for Moving Targets. When a shooter is training on moving targets he should be taught to calculate leads for moving targets knowing the targets speed, time of flight of the bullet and the targets direction of movement. The formula is:

Since it is easiest to establish a lead from a target’s leading edge and we want a lead in mils we will then use the formula:

(Lead in feet x 12) – 6

(Range x .01) x 3.4

(Range x .01) x 3.4

(Range x .01) x 3.4

We can now use our mil dot reticle to hold off instead of having to guess at target widths and other not-so accurate methods. This formula is a bit ungainly to use in tactical situations, and it doesn’t take into account different shooters’ reaction times, but it should be used in training to determine starting leads when engaging live fire moving targets. The shooter then fine tunes his leads and writes them in his databook.

Elevation/Windage Hold-Offs. Mil dot reticles can also be used for alternate aiming points for elevation and windage holds, as there are often situations where a sniper may not have time to dial on his elevation and sight settings. Snipers often have to deal with targets that appear unexpectedly, multiple targets at different distances, gusting winds of varying direction and the thing we all don’t want to think about, a miss or an insufficient hit. In these situations the shooter often doesn’t have time to deal with turret caps, 1/ 4 MOA target turrets, or in the case of the miss or insufficient hit, changing the sights. In these occasions, WHEN EXTREME PRECISION IS NOT A REQUIREMENT, it is better to establish an alternate aiming point with the mil dot reticle and hit the target.

Windage Hold-Offs. When the USMC Unertl scope first came out in 1981-82, it only had 4 MOA of windage in each direction. As anyone who has shot past 300 yards knows, that isn’t enough windage to handle windrift caused by your buddy’s heavy breathing from the next firing point. So we had to use the mil dots for windage. This is a simple feat if you just remember that 1 mil is 3.5 MOA. So if I need 3.5 minutes of right windage I leave "0" windage on the windage knob and hold 1 mil dot right of center mass. If I need 4 MOA then I hold a tad more than 1 mil dot. 2 mils? Hey, remember when we broke the mil dot reticle down for precise measurements when determining distances? It’s the same deal with wind hold-offs. Break the mils into thirds and you have 1 MOA hold points; okay, so it’s 1.13 MOA hold-offs, big deal.

Elevation Hold-Offs. Now let’s talk about elevation hold-offs. In order for us to use a mil dot reticle for elevation holds we have to determine from what sight setting we will be holding off from. In most situations this will mean that we will leave a certain sight setting on the rifle when not set for a specific target. This is very similar to the military battle-sight zero concept where an M16A2 is zeroed for 300 meters, which allows the rifleman to engage targets from 0-325 meters by just aiming center mass. In US Army doctrine with the M24 sniper weapon system and M118LR ammunition (175 gr. Sierra BTHP @ 2600 fps) the sniper leaves his 500m zero on the scope with zero windage. Then by using the elevation holds in the chart below, he can get rounds on target without taking the time to change his elevation setting. Another use for mil dots is when we have to engage multiple targets at different distances and we have time to set it up. We know that if we have to engage a target at 600 yards then drop down to 300 yards and drop another one all we have to do is calculate the elevation difference between 300 and 600 yards then dial on the elevation for 600 and hold low for the 300 yard shot. In this case I know that there is 7.5 MOA difference between the 600 and 300 yard shot. So after engaging the 600 yard target with my 600 yard sight setting, since it is the more difficult shot, I will then hold 2 mils under the 300 yard target and engage it. The .5 MOA error (1.5 inches at 300 yards) in hold is nothing to worry about in MOST situations.

Follow-up Shots. The last thing I will talk about in regards to the mil dot reticle is its usefulness when firing rapid follow-up shots when a quick correction in elevation or windage is required. In these situations a follow-up shot is needed quickly! If the first shot was a miss, it won’t take the target long to figure out what is going on. If he is trained or just real smart, as soon as he hears the crack of the round or some result of its impact he is gonna move. But in many situations the target won’t move due to ambient noise masking the shot or just plain stupidity as in the case of the FBI field SWAT snipers that got off 3 shots at a hostage taker without the perp figuring out what was going on. (In this case the snipers’ shots were hitting a low wall in front of the rifle that the sniper didn’t know was in the way. The third shot hit home after the sniper raised his position.)

In the case of a well fired shot that missed or was off-center, the observer can give the sniper an alternate aiming point using the mil dots as with windage holds. If the shot was at 200 yards and it was 4 inches (2 MOA) low, the observer tells the sniper to hold 2/3 mil high and fire again. This is all assuming of course that the sniper calls the first shot a good shot. If he called the shot low, then the sniper should fire center again and pay attention to the fundamentals this time.

And you thought that all mil dots were for was range estimation, didn’t you?

I hope this information has shown you that mil dots are a valuable aid for the precision tactical shooter/sniper. It may seem like a lot of information at first but as you absorb this stuff remember that much of it can be simplified with aids like cheat sheets, crib notes and through the use of devices like the Mil Dot even us Neanderthals can handle mil dots. Those that can’t or refuse to use them are missing out on a valuable tool. But that’s okay. Those batteries in that laser are probably okay.

Infrared Light

In order to understand night vision, it is important to understand something about light.The amount of energy in a light wave is related to its wavelength: Shorter wavelengths have higher energy. Of visible light, violet has the most energy, and red has the least. Just next to the visible light spectrum is the infrared spectrum.

 

 

Infrared light is a small part of the light spectrum.

 

Infrared light can be split into three categories:

• Near-infrared (near-IR) - Closest to visible light, near-IR has wavelengths that range from 0.7 to 1.3 microns, or 700 billionths to 1,300 billionths of a meter.
• Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1.3 to 3 microns. Both near-IR and mid-IR are used by a variety of electronic devices, including remote controls.
• Thermal-infrared (thermal-IR) - Occupying the largest part of the infrared spectrum, thermal-IR has wavelengths ranging from 3 microns to over 30 microns.

The key difference between thermal-IR and the other two is that thermal-IR is emitted by an object instead of  reflected off it. Infrared light is emitted by an object because of what is happening at the atomic level.

Atoms
Atoms are constantly in motion. They continuously vibrate, move and rotate. Even the atoms that make up the chairs that we sit in are moving around. Solids are actually in motion! Atoms can be in different states of excitation. In other words, they can have different energies. If we apply a lot of energy to an atom, it can leave what is called the ground-state energy level and move to an excited level. The level of excitation depends on the amount of energy applied to the atom via heat, light or electricity.

An atom consists of a nucleus (containing the protons and neutrons) and an electron cloud. Think of the electrons in this cloud as circling the nucleus in many different orbits. Although more modern views of the atom do not depict discrete orbits for the electrons, it can be useful to think of these orbits as the different energy levels of the atom. In other words, if we apply some heat to an atom, we might expect that some of the electrons in the lower energy orbitals would transition to higher energy orbitals, moving farther from the nucleus.

 

An atom has a nucleus and an electron cloud.

 

Once an electron moves to a higher-energy orbit, it eventually wants to return to the ground state. When it does, it releases its energy as a photon -- a particle of light. You see atoms releasing energy as photons all the time. For example, when the heating element in a  toaster turns bright red, the red color is caused by atoms excited by heat, releasing red photons. An excited electron has more energy than a relaxed electron, and just as the electron absorbed some amount of energy to reach this excited level, it can release this energy to return to the ground state. This emitted energy is in the form of photons (light energy). The photon emitted has a very specific wavelength (color) that depends on the state of the electron's energy when the photon is released.

Anything that is alive uses energy, and so do many inanimate items such as  engines and rockets. Energy consumption generates heat. In turn, heat causes the atoms in an object to fire off photons in the thermal-infrared spectrum. The hotter the object, the shorter the wavelength of the infrared photon it releases. An object that is very hot will even begin to emit photons in the visible spectrum, glowing red and then moving up through orange, yellow, blue and eventually white. 

In night vision, thermal imaging takes advantage of this infrared emission. In the next section, we'll see just how it does this.

 

Thermal Imaging

undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined Here's how thermal imaging works:

1. A special lens focuses the infrared light emitted by all of the objects in view.

    

2. The focused light is scanned by a  phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermogram. It only takes about one-thirtieth of a second for the detector array to obtain the temperature information to make the thermogram. This information is obtained from several thousand points in the field of view of the detector array.

    

3. The thermogram created by the detector elements is translated into electric impulses.

    

4. The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display.

    

5. The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the impulses from all of the elements creates the image.

 

Types of Thermal Imaging Devices
Most thermal-imaging devices scan at a rate of 30 times per second. They can sense temperatures ranging from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000 C), and can normally detect changes in temperature of about 0.4 F (0.2 C).

 

It is quite easy to see everything during the day...

...but at night, you can see very little.

Thermal imaging lets you see again.

There are two common types of thermal-imaging devices:

• Un-cooled - This is the most common type of thermal-imaging device. The infrared-detector elements are contained in a unit that operates at room temperature. This type of system is completely quiet, activates immediately and has the  battery built right in.

   

• Cryogenically cooled - More expensive and more susceptible to damage from rugged use, these systems have the elements sealed inside a container that cools them to below 32 F (zero C). The advantage of such a system is the incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can "see" a difference as small as 0.2 F (0.1 C) from more than 1,000 ft (300 m) away, which is enough to tell if a person is holding a gun at that distance!

While thermal imaging is great for detecting people or working in near-absolute darkness, most night-vision equipment uses image-enhancement technology.

1. A conventional lens, called the objective lens, captures ambient light and some near-infrared light.

    

2. The gathered light is sent to the image-intensifier tube. In most NVDs, the power supply for the image-intensifier tube receives power from two N-Cell or two "AA" batteries. The tube outputs a high voltage, about 5,000 volts, to the image-tube components.

    

3. The image-intensifier tube has a photocathode, which is used to convert the photons of light energy into electrons.

    

4. As the electrons pass through the tube, similar electrons are released from atoms in the tube, multiplying the original number of electrons by a factor of thousands through the use of a microchannel plate (MCP) in the tube. An MCP is a tiny glass disc that has millions of microscopic holes (microchannels) in it, made using  fiber-optic technology. The MCP is contained in a vacuum and has metal electrodes on either side of the disc. Each channel is about 45 times longer than it is wide, and it works as an electron multiplier.

   When the electrons from the photo cathode hit the first electrode of the MCP, they are accelerated into the glass microchannels by the 5,000-V bursts being sent between the electrode pair. As electrons pass through the microchannels, they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. Basically, the original electrons collide with the side of the channel, exciting atoms and causing other electrons to be released. These new electrons also collide with other atoms, creating a chain reaction that results in thousands of electrons leaving the channel where only a few entered. An interesting fact is that the microchannels in the MCP are created at a slight angle (about a 5-degree to 8-degree bias) to encourage electron collisions and reduce both ion and direct-light feedback from the phosphors on the output side.

5. At the end of the image-intensifier tube, the electrons hit a screen coated with phosphors. These electrons maintain their position in relation to the channel they passed through, which provides a perfect image since the electrons stay in the same alignment as the original photons. The energy of the electrons causes the phosphors to reach an excited state and release photons. These phosphors create the green image on the screen that has come to characterize night vision.

    

6. The green phosphor image is viewed through another lens, called the ocular lens, which allows you to magnify and focus the image. The NVD may be connected to an electronic display, such as a monitor, or the image may be viewed directly through the ocular lens.

Generations

undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined NVDs have been around for more than 40 years. They are categorized by generation. Each substantial change in NVD technology establishes a new generation.

• Generation 0 - The original night-vision system created by the United States Army and used in World War II and the Korean War, these NVDs use active infrared. This means that a projection unit, called an IR Illuminator, is attached to the NVD. The unit projects a beam of near-infrared light, similar to the beam of a normal flashlight. Invisible to the naked eye, this beam reflects off objects and bounces back to the lens of the NVD. These systems use an anode in conjunction with the cathode to accelerate the electrons. The problem with that approach is that the acceleration of the electrons distorts the image and greatly decreases the life of the tube. Another major problem with this technology in its original military use was that it was quickly duplicated by hostile nations, which allowed enemy soldiers to use their own NVDs to see the infrared beam projected by the device.

   

• Generation 1 - The next generation of NVDs moved away from active infrared, using passive infrared instead. Once dubbed Starlight by the U.S. Army, these NVDs use ambient light provided by the moon and  stars to augment the normal amounts of reflected infrared in the environment. This means that they did not require a source of projected infrared light. This also means that they do not work very well on cloudy or moonless nights. Generation-1 NVDs use the same image-intensifier tube technology as Generation 0, with both cathode and anode, so image distortion and short tube life are still a problem.

   

• Generation 2 - Major improvements in image-intensifier tubes resulted in Generation-2 NVDs. They offer improved resolution and performance over Generation-1 devices, and are considerably more reliable. The biggest gain in Generation 2 is the ability to see in extremely low light conditions, such as a moonless night. This increased sensitivity is due to the addition of the microchannel plate to the image-intensifier tube. Since the MCP actually increases the number of electrons instead of just accelerating the original ones, the images are significantly less distorted and brighter than earlier-generation NVDs.

   

• Generation 3 - Generation 3 is currently used by the U.S. military. While there are no substantial changes in the underlying technology from Generation 2, these NVDs have even better resolution and sensitivity. This is because the photo cathode is made using gallium arsenide, which is very efficient at converting photons to electrons. Additionally, the MCP is coated with an ion barrier, which dramatically increases the life of the tube.

   

• Generation 4 - What is generally known as Generation 4 or "filmless and gated" technology shows significant overall improvement in both low- and high-level light environments.

  The removal of the ion barrier from the MCP that was added in Generation 3 technology reduces the background noise and thereby enhances the signal to noise ratio. Removing the ion film actually allows more electrons to reach the amplification stage so that the images are significantly less distorted and brighter.

  The addition of an automatic gated power supply system allows the photocathode voltage to switch on and off rapidly, thereby enabling the NVD to respond to a fluctuation in lighting conditions in an instant. This capability is a critical advance in NVD systems, in that it allows the NVD user to quickly move from high-light to low-light (or from low-light to high-light) environments without any halting effects. For example, consider the ubiquitous movie scene where an agent using night vision goggles is “sightless” when someone turns on a light nearby. With the new, gated power feature, the change in lighting wouldn’t have the same impact; the improved NVD would respond immediately to the lighting change.

Many of the so-called "bargain" night-vision scopes use Generation-0 or Generation-1 technology, and may be disappointing if you expect the sensitivity of the devices used by professionals. Generation-2, Generation-3 and Generation 4 NVDs are typically expensive to purchase, but they will last if properly cared for. Also, any NVD can benefit from the use of an IR Illuminator in very dark areas where there is almost no ambient light to collect.

 

Night Vision Equipment and Applications

undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined Night-vision equipment can be split into three broad categories:

• Scopes - Normally handheld or mounted on a weapon, scopes are monocular (one eye-piece). Since scopes are handheld, not worn like goggles, they are good for when you want to get a better look at a specific object and then return to normal viewing conditions.
• Goggles - While goggles can be handheld, they are most often worn on the head. Goggles are binocular (two eye-pieces) and may have a single lens or stereo lens, depending on the model. Goggles are excellent for constant viewing, such as moving around in a dark building.
• Cameras -  Cameras with night-vision technology can send the image to a  monitor for display or to a  VCR for recording. When night-vision capability is desired in a permanent location, such as on a building or as part of the equipment in a helicopter, cameras are used. Many of the newer  camcorders have night vision built right in.

Whether for fishing, camping, or nature watching, night vision has made significant advances and has become affordable to the general consumer. Their uses stretch far beyond the confines of this article. The major intended application for consumers will determine what type of device is best and what quality is needed.

Many consumers are learning about this technology as the devices become more affordable. Night vision devices are becoming very popular because they open the nighttime world to see what has always been hidden in a cloak of darkness. They are very different from daytime optics and take some time to learn how to use effectively. It is a bit like using a pair of binoculars for the first time. There is a period of time needed to learn how to find things in the view and focus on them quickly. Night vision devices take practice to master all the advantages they offer.

In the case of nature observation, which is our main consideration with these devices, there are many animals and birds that only become active at night and a good night vision device can be an invaluable tool. Not only are there many critters and birds that are primarily nocturnal (active at night), many of the diurnal (primarily active in the daytime) animals and birds will allow much closer approaches from observers in the dark.

Getting a new device these days usually involves a period of learning to use the controls and becoming proficient with them. If you are accustomed to using daytime optics, there are also some things you have to unlearn. In general, night vision devices have three controls: the on/off switch (or switches), the eyepiece focus, and the front lens focus.

Some night vision devices have separate switches for the main power and the IR illuminator, while others have one switch that cycles from off to main power on, then both main power and IR illuminator on, and finally back to off. These switches also control two indicator lights: a green LED for main power and a red LED for the IR illuminator. It is important to be aware of these LEDs, as the IR illuminator beam is not visible to the unaided eye, and leaving it on could drain the batteries unnecessarily. Some models also have IR illuminator controls for adjusting from wide field illumination to narrow beam.

Focusing night vision devices is a two-step process. First, focus the eyepiece. The easiest way is to set the eyepiece in lit environment without removing the Protective Lens Cap. It does not matter if the objective lens is in perfect focus to be able to tell when you have the best focus for the eyepiece - just find where the image is the sharpest. Once set, this focus should not change for a given individual as the distance from the eyepiece to the phosphorescent screen is fixed. Some units, however, have very loose focus rings. For these, a small piece of electrical tape will keep the focus ring in place.

Once the eyepiece is set only the objective lens will need to be adjusted to focus on different areas or objects being observed.

A fourth control available on some night vision devices is an aperture ring. Similar to the f-stop of a camera lens, this ring controls the amount of light entering the device. This is a very useful adjustment for dimming or brightening the display to get a comfortably lighted view.  

Night vision devices are electronic instruments and will not stand careless or exceptionally rough use. Contrary to this many models are waterproof and have durable designs to withstand typical outdoor use. Those that are not specifically rated for damp conditions (waterproof or weather-resistant) may be damaged by exposure to water or even high humidity.

Night vision devices are not susceptible to, nor negatively affected by airport x-ray machines, and it is absolutely safe to pass a night-vision device through baggage security checks. First Generation (or Generation 1) devices may be taken in and out of the country freely. Second and third generation night vision devices are regulated by the State Department and their movements are restricted around the world. Consult proper authorities if planning to travel out of the country with a Generation 2 or higher device.