The Image Intensifier 

Night Vision scopes are electro-optical devices that intensify (amplify) available light. The main component of such a device is the Image Intensifier - basically a vacuum tube. At the input end, the objective lens collects the particles of light (photons) arriving from the subject and focuses them on the image intensifier tube. Inside the image intensifier tube a photocathode absorbs these photons and converts them into electrons which are amplified and projected on to a green phosphor screen at the rear. When this highly intensified electron image strikes the phosphor screen, it causes the screen to emit light that you can see. Since the phosphor screen emits this light in exactly the same pattern and degrees of intensity as the light that is collected by the objective lens, the bright night-time image you see in the eyepiece corresponds closely to the outside scene you are viewing. The phosphor screen is coloured green because the human eye can differentiate more shades of green than any other phosphor colour.
The number of times the screen image is brighter than the one arriving at the photocathode is called the gain of the Intensifier.However, gain is a function of two factors, the ability of the photocathode to convert the weaker photons into electrons, and the amount of amplification which accelerates these electrons onto the screen. If the type of photocathode is fixed, more gain means more screen brightness, not the ability to see better in the dark. There are two ways to measure gain - tube gain and system gain.Tube gain is usually seen in values of tens of thousands and is more a laboratory figure that is not necessarily indicative of a devices performance. If tube gain is too high, the tube will be "noisier" and the signal-to-noise ratio may go down. System gain is based on the total system ie. tube, optics, power supply etc. System gain is usually seen in the low hundreds for Gen 1, mid-hundreds for Gen 1+ and 1000-3000 for Gen 2/2+/SuperGen,Gen 3 (Omni I/II/III/IV/V/VI) ,HyperGen (SHD-3/XD-4/XR-5 ) and Gen 4. System gain is the figure that potential night vision purchasers should compare. Beware of claims, especially for Gen 1 units, in the tens of thousands - this can only be tube gain and not system gain.

The Generation Game
 

Image Intensifiers exist in many different shapes and sizes and four main types. Gen 0 and Gen 1 systems use electrostatic inversion and electron acceleration to produce gain. Both are characterised by geometric distortion but where Gen 0 requires active infrared illumination, 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. Beware of systems claiming to use US Gen 2+ image intensifier tubes. The US has manufactired only Gen 3 tubes for at least the last 5 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 probably not up to the specification 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 HyperGen 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 light, 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 increased outlay in cost for the highest capability units.

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

Generation I 

Typically uses an S-10 or S-20 photocathode (with photosensitivity of 120-250 uA/lm), electrostatic inversion, and electron acceleration to achieve gain. Because of higher photosensitivity, Gen I 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 100-900x - beware of claims for much higher values. Resolution in the centre varies between 25-35 lp/mm. Gen 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. 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 Gen 1 night vision tubes are manufactured in Russia - they account for approximately 95% of the world market. Typical MTTF: 1000 hrs

Generation I+ (Super I+) 

This is the next modification of the Gen. I NV tube with a fiber optics plate being installed at the front or at the back of a tube. This modification allows for an improvement of the image resolution and prevents distortion from other light sources in a field of view. Tubes of Gen. I+ have light amplification of approx. 1 000 times, while the photocathode sensitivity increases to min. 280 mA/lm. Resolution in the center is 45–50 lp/mm,typical MTTF 1000 hours. 

NV units built with the Gen I+ tubes differ from the Gen. I units by increased image quality, lower distortions and better viewing distance in passive or active mode (with an IR illuminator). These scopes work well in an urban environment. In the open space, the units are effective with the ambient light levels down to ¼ of a moon. When light conditions are lower, an IR illuminator is needed. The cost of the Gen. I+ tubes is in 4–9 times higher than the cost of the regular Gen. I.

Note. The Buyer should take into consideration that some producers use the designation Gen. I+ for their devices Gen I. It often misleads buyers because in fact tubes Gen. I have a resolution not higher than 38–40 pl/mm. We use the designation Super Gen I+ in our English advertising to make clear for the buyers peculiarities of the tubes Gen I+ with high resolution. 

Generation II 

The construction of the Gen. II tubes differs from the Gen. I+ by using a special electron amplifier — the micro channel plate (MCP). 

The performance characteristics of such NV tubes are: a higher photo cathode sensitivity of 240-350 mA/lm, with the resolution of 28–38 lp/mm. The lifetime of these tubes is designed to be not less than 1 000–3 000 hours of operation (Typical MTTF 2000 hours ),typical SNR 11. Two types of NV tubes with micro channel plates (MCP) are currently available: the 25mm and 18mm ones. From the users prospective the larger diameter is more efficient but also requires larger NV unit. In this category,  manufactures a multifunctional NV Scope — series of rifle scopes . All of the above mentioned units are equipped with an additional manual brightness control that allows the viewer to adjust the scope for the optimal gain/noise ratio. 

Generation II+ 

With a light gain of 25 000–35 000 the Gen II+ tubes have photo cathode sensitivity of 300–450+ mA/lm and are sensitive to light in the infrared spectrum. Resolution is 32–45 lp/mm. Work capasity of the tube is estimated to be 1 000–3 000 hours (Typical MTTF 2000 hours ),typical SNR 13 . Since the Gen. II+ tubes are smaller (they do not have a speed up chamber) they have a slightly lower light amplification than the Gen. II. Yet due to the especially high sensitivity in the IR spectrum the Gen. II+ units have better viewing distance in the open space. If the main task for the unit is photo or video recording, the Gen II NV unit should be chosen due to its higher light gain. NV units with the Gen. II+ tubes are equipped with automatic gain control, flash protection, protection from the side light distortions and feature a high quality image throughout the entire field of view. Units equipped with Gen. II+ tubes are used by the armed forces of many countries and considered to be of professional quality by the experts. 

Generation III 

Gen. III differs from the Gen. II+ in use of a photo cathode based on Gallium Arsenate with even deeper sensitivity in the IR spectrum. The photo cathode sensitivity is 800+ mA/lm,typical SNR 18-28 (min 16), resolution is 32–72 lp/mm and capacity for work is 10,000 hours. This is 3 times longer than with the Gen. II tube. The NV units using the Gen. III tubes work very well in the low light environment. The image comes out clean and with excellent contrast. The only drawback of Gen. III units is their vulnerability to the side light distortions due to lack of the fiber optical plate on the front of the tube. Until recently Gen. II+ and III units where used mostly by the military, these units became more widely available not long ago.

Dep Technology Image Intensifier

  DEP produces a range of in-house developed compact Image Intensifiers for use in Night Vision applications. This product line runs from standard Image Intensifiers to SHD-3™ and XD-4™ up to the top quality of XR5™ Image Intensifiers. All these tube types are available both in 18 mm inverting and non-inverting format and for SMALL as well as FAT ANVIS configurations. Further, they can also be coupled via tapered fibre-optics to a number of commercially available CCD’s for Intensified CCD (ICCD) cameras. DEP Image Intensifiers perform extremely well in every environment and under all circumstances. With its wide spectral range and specific design, they are ideal for use under dynamic light conditions and in green environments, deserts, coastal areas and on water and snow. DEP makes the difference and is your best choice, if you go for high performance and high quality. Image Intensifier performance is mainly determined by three major parameters: Signal-to-Noise Ratio, Resolution and MTF. Night Vision Imaging at low light-levels is a fight against noise and the determining factor with respect to picture quality is the Signalto-Noise Ratio of the tube. In the High Light-Level Range the Resolution and MTF determine the image quality. Especially the MTF at low spatial frequencies is very important for the sharpness and contrast of the image.

• SUPERGEN® Technology Image Intensifier

In the SUPERGEN Image Intensifier we combined the improved sensitivity of GEN II with a best-of-class resolution, signal-to-noise and MTF.
The Supergen® tube’s improved sensitivity under wider spectral conditions provides enhanced contrast under all low light level conditions.
Special technology reduces the vulnerability for burn-in effects caused by higher light levels.
The SUPERGEN® Image Intensifier has a guaranteed minimal Signal-to-Noise Ratio (SNR) of 18 (typical 21 +) at 108 μlx , a minimum limiting resolution of 45 lp/mm in the centre,a minimum photocathode sensitivity 500mA/lm at 2850k and a Typical MTTF 10000 hours.

• SHD-3™ Technology Image Intensifier

The introduction of the SHD-3™ technology set the new European standard for low-light-level imaging. This technology combines the very good sensitivity of the Super Generation Image Intensifiers with superior resolution and MTF. These improvements produce a much higher contrast in the image. You can see much more image details.
SHD-3™ Image Intensifiers perform extremely well in all low light level conditions.
Its broad spectral sensitivity range results in a perfect picture.
New production technology resulted in improved performance of the Signal-to-Noise Ratio (SNR), the Modulation Transfer Function (MTF) and Resolution.

• XD-4™ Technology Image Intensifier

The introduction of the XD-4™ technology set the new European standard for low-light-level imaging.

XD-4™ Image Intensifiers perform extremely well in all environmental conditions.

Its broad spectral sensitivity range results in a perfect picture.

New production technology resulted in improved performance of the Signal-to-Noise Ratio (SNR), the Modulation Transfer Function (MTF) and Resolution.

Add to this features like the small halo and the extended lifetime and you will be convinced of its unique performance.

The XD-4™ is also available with an autogating power supply unit.

The XD-4™ Image Intensifier has a guaranteed minimal Signal-to-Noise Ratio (SNR) of 20 (typical 23 +) at 108 μlx , a minimum limiting resolution of 57-72 lp/mm in the centre,a minimum photocathode sensitivity 600mA/lm at 2850k and a minimum MTTF 15000 hours.

The XR5™ Image Intensifier has a guaranteed minimal Signal-to-Noise Ratio (SNR) of 25 (typical 28 +) at 108 μlx , a minimum limiting resolution of 64 --82 lp/mm in the centre,a minimum photocathode sensitivity 700mA/lm at 2850k and a minimum MTTF 15000 hours.

Generation IIII

 4th generation / Gated Filmless technology represents the biggest technological breakthrough in image intensification of the past 10 years. By removing the ion barrier film and "Gating" the system Gen 4 demonstrates substantial increases in target detection range and resolution, particularly at extremely low light levels.

The use of filmless technology and auto-gated power supply in 4th generation image intensifiers result in:

• Up to 100% improvement in photoresponse.
• Superb performance in extremely low light level (better S/N and EBI)
• At least triple high light level resolution (a minimum of 36 lp/mm compared to 12 lp/mm)

With significant improvement in contrast level and in performance under all light conditions, 4th generation represents the top of the line performance in the night vision market. Note: The term 4th generation is used/accepted among Night Vision manufactures to describe gated filmless tubes. However, this designation is widely debated and is currently referred to as Filmless & Gated image intensifiers by the US Military.

Gen 4 technology improves night operational effectiveness for military users of night vision goggles and other night vision devices. The filmless MCP provides a higher signal-to-noise ratio than Gen 3, resulting in better image quality (less scintillation) under low-light conditions. The gated power supply further improves image resolution under high light conditions, and the reduced halo minimizes interference from bright light sources. These improvements also substantially increase the detection range of the systems.

	Gen 3 Omni IV	Gen 4	% Improvement
Photoresponse (µA/Im)	1800	1800	-
Signal-to-Noise Ratio	21.0	25.0(ground)	20% Higher
		26.0(air)	24% Higher
Resolution(lp/mm)	64	64	-
Halo(mm)	1.25	0.75	40% smaller
Reliability(hours)	10,000	10,000

RANGE IMPROVEMENT

Relative direction ranges

Overcast Starlight Conditions (-1x10E-5 tc)

Vehicle Size Target, 30% Contrast

	Gen 2	SuperGen 2	Gen 3 OMNI I and II	Gen 3 OMNI III	Gen 3 OMNI IV	Gen IV
Detection Range (m)	170	270	240	290	360	430
% Improvement over Gen II	0%	60%	40%	70%	110%	153%

Optics

Optical part of a night vision device consists of an objective and an ocular. The main demand on the objective is a high light transmittance in visible and near IR diapason. It is expressed with geometric light power from the line (F-number) 1; 1,4; 2,0; 2,8; 4,0 and so on. The objective with increased number (in a step) makes light transmission twice less. High light power is very important for night vision devices especially for devices Gen. I, I+. By light power degradation till 2,4–2,8 a naked eye can see better than with night vision devices Gen I in passive regime. Elaboration and producing of high light power optic with focal ratio less than 1,5 is a difficult task. Not every manufacturer is able to produce it. Of course cost of light power optic of high quality has an influence on the final cost of night vision devices. A lot of manufacturers equip their night vision devices with objectives of larger focus distance and low light power to get a bigger magnification (3,5–5,0). If you prefer to choose between two devices (of the same Generation and dimension but with greater magnification) the distance and the image you get is going to be worser than in items with lesser magnification and greater light power. It is very important especially for night vision riflescopes for hunting. 

All devices series are completed with objectives of a lightweight design and good light power F/1.2 or F/1.5. Sometimes night vision devices are completed with mirror lens objectives. They guarantee smaller overall pivotal dimension but have a decamouflage effect and have by the same conditions the worse light power. That is why they refuse to produce night vision devices with mirror lens objectives in Russia and abroad. 

1. Front Lens	4. High Voltage Power Supply
2. Photocathode	5. Phosphorus Screen
3. Microchannel plate	6. Eyepiece

Infra Red Illuminator 

When an Image Intensifier is used in really dark conditions the quality of the picture on the phosphor screen drops dramatically. Its overall brightness level falls and individual scintillations, tiny flashes of light, become more clearly visible. Such a picture is said to have become 'noisy' and we describe this situation as being 'information-limited'. The only way to improve any image that shows signs of information-limiting is to increase the number of photons used to create it.
A few of the basic problems of seeing at very low light levels are so fundamental to the physical state of darkness that they can only ever be overcome by the use of active illumination, be it visible or covert. All generations of Image Intensifiers need light to work - they cannot provide a useful image in complete darkness.
They are, however, sensitive to infrared light. At night, some 70% of light is in the infrared spectrum. The introduction of semicovert/ covert illumination overcomes this problem and users should consider having some sort of IR illuminator available to assist the Intensifier when climatic or lighting conditions restrict its performance.
Semi-covert/covert illumination can be produced in three ways. Infrared lamps offer the greatest range and they are more eye safe, although they are bulky and can consume a lot of power. Laser illuminators are not eye safe - they stay cool and use very little power, but are generally expensive. The only illuminators that are truly discreet and safe use LED's. Unfortunately, with many of these the useful range is restricted to 30 metres, although there are exceptions. Only SuperGen/HyperGen or Gen 3 systems are sensitive enough to be used with truly covert (900+ nm) IR illuminators. Due to the tube sensitivity, IR illuminators produced for Gen 1/Super Gen 1+ and standard Gen 2 systems produce a dull red glow from the LED and are described as semi-covert.
The use of IR illuminators is the most cost effective way of getting big increases in Intensifier performance. The downside would be if someone else was using a night scope - they would potentially see your IR illuminator very clearly.

Construction 

The physical characteristics of NV units are usually designed with three factors in mind, compactness, weight and observation distance. Unfortunately sometimes these characteristics are in conflict with one another. For example, greater observation distances can be provided by a unit with a larger lens with the inherent disadvantage that the device will be bigger in size and weight. The customer has to decide which characteristic is a priority and buy accordingly. 

One factor, which is especially important, is the construction of NV rifle scope — it must be extremely rugged to withstand the shock of up to 500 Gs along the optical axis due to recoil. In this harsh environment the cross hairs, sighting posts and targeting adjustments must remain unmoved and be visible in all types of viewing conditions. Many NV rifles copes currently offered on the market are not designed to compensate for these stresses (cal. .365H&H, .416Rirby) and may have weak mounting and zeroing-in systems. This will require repeated readjustments to maintain accuracy. This is a complicated subject that cannot be discussed properly in a short article. We encourage you to contact our company for a special consultation on the subject. 

BLACK SPOTS ON THE SCREEN

As you look through a night vision device you may notice black spots on the screen. A NVD is similar to a television screen and attracts dust and dirt. Typically these spots can be cleaned. However, this may also be a spot in the tube itself. This is normal. Most tubes will have some spots in them. These black spots will not affect the performance or reliability of the night vision device.

Distance of observation and identification 

The buyer should take into account that the distance of observation and identification, which night vision devices provide, depends on the level of night illumination, clarity of atmosphere and contrast between an object of observation and background. When illumination increases the distance of identification becomes higher. When illumination reduces it becomes lower. 

The table of average distance of night observation and identification of an object is given below (based on the domestic and foreign data).

 

International Identification range (human)	Full moon 0.1lux ( meters)	Half moon 0.05lux (meters)	Quartermoon 0.01lux ( meters)	Starlight 0.001lux ( meters)	Overcast 0.0001lux ( meters)
Without nightvision device	230	130	45	_________	________
Generation I	300	200	150	100	50
Generation II	630	630	590	390	145
Generation III	810	810	770	530	200

Congratulations on your successful purchase! 

  

USA ATN Identification range	Full moon 0.1lux(meters)	Quarter moon 0.05lux (meters)	Starlight 0.001lux(meters)	Overcast 0.0001lux (meters)
Generation I Deer Human Ship	182 228 685	137 182 457	91 137 274	68 91 137
Generation II Deer Human Ship	274 457 914	205 411 731	160 274 502	91 137 274
Generation III Deer Human Ship	365 594 1142	274 457 914	205 342 731	137 182 502
Generation.IIII Deer Human Ship	457 685 1280	365 548 1051	251 365 868	182 228 594

Evaluating The Performance Of A Night Vision Scope

The very need for a night vision capability necessarily focuses on performance as the most important factor. What subjects do you need to see ? At what distance ? And in what lighting conditions ? The darker the conditions and the smaller or more distant the subject, the tougher the job gets for a night vision system. If you need to see fine details, such as car number plates/recognising an
individual, especially at fairly long range, then you need to ensure that the system you are considering is capable of this.
Most Gen 1 night vision equipment available today will provide an adequate image for most non-professional requirements under higher night light conditions, such as full moon. But, if you need to see under truly dark conditions, such as starlight, need longer range or need to see finer details then you will have to consider Super Gen 1+ or Gen 2/SuperGen/HyperGen systems.
It is difficult to choose a night vision system by simply reading technical specifications. Not only are the performance specifications tough for most people to understand but they are even tougher to relate to real-world use. Comparison of specifications is also only valid if test instrumentation and methodology are consistent and reliable - unfortunately, this is unlikely. The best way to evaluate a night scope is to test it in real-world conditions. Ideally, you should conduct your evaluation under the same conditions in which you intend to use the scope.

.

Factors to consider include:
• Photosensitivity - The ability of a night vision system to detect light energy and convert it to an electron image is reflected in the image intensifier's photosensitivity. Usually, the higher the value, the better the ability to "see" under darker and darker conditions. However, be aware that at night there is more light energy available in the near-infrared region than in the visible region. Therefore, if a device claims a high photosensitivity, make sure to find out where in the spectrum this is measured. A high photosensitivity in the blue or visible region may not perform as well as another system with a lower overall photosensitivity, but a higher value in the near-infrared region.
• Gain - This tends to be a confusing parameter when evaluating night vision devices. The darker the conditions, the harder it is for the system to render a clear image with reasonable contrast. Additional gain is required as conditions grow darker and for longer range. The most important gain measurement is the system gain. Very high gain values for an image tube are not especially significant - military devices can have tube gains ranging anywhere from 20,000 to 80,000. Look for the system gain. Military systems operate at gains in the region of 2,000 to 3,000. The higher the value the better the ability of the device to amplify the light it detects. However, if a system does not possess a good photosensitivity and SNR, a very high gain value simply means that you will make a poor image brighter, not better. Populated areas always have an atmospheric glow from artificial lighting. A high-gain device might be required in remote areas on overcast nights, but it would not be necessary for use in urban or suburban conditions. Even in isolated locations without man-made light, a high-quality, affordable Gen 1 monocular/binocular will provide good imaging with a half-moon and clear skies - this can be further enhanced with the use of an IR illuminator. The very best test is field
evaluation in real-time conditions.
• Range - Can you see your subject 75m away? Effective range is a balanced function of the system’s gain, resolution, image magnification and the amount of ambient light available. While a powerful lens will provide more image magnification, it will also reduce the amount of available light captured. The best effective range with most intensifiers is achieved with a high-speed lens that has minimal magnification (<3x). Higher levels of ambient light dramatically increase any device’s range capability. Just as more gain is required for longer range in darker conditions, less gain is required as conditions grow brighter. Most applications are satisfied with systems offering image magnification of 1x to 3x. Goggles, for instance, are specifically designed for near-field viewing and use 1x image magnification to keep the wearer from becoming disoriented. For marine use, a good quality 1x magnification monocular is ideal because it gives a wide field of view - if you also need higher magnification, buy a model with interchangeable lenses. High image magnifications mean a narrow field of view and the possibility of missing a subject you are searching for.
• Image Quality - High resolution, high contrast and a lack of distortion and noise contribute to a premium Night Vision image. With higher resolution you might identify someone you know at 60m as opposed to simply recognizing a human figure. Superior contrast allows you to see dark subjects against darker backgrounds. Lower distortion renders a flatter, less rounded image with crisper details. Always try and choose a model that offers glass optics - these will give you the sharpest, clearest optical quality. Units that use plastic optics tend to offer lower optical quality and higher distortion.
• Resolution - Usually this is measured as tube resolution (lp/mm) or system resolution (cy/mr). The higher the value, the better the ability to present a sharp picture. Gen 1 devices may produce a reasonably clear image in the centre of the viewing area, but sharpness drops off noticeably toward the periphery. 

• Target Characteristics - System performance is not only limited by intensifier/system parameters and light level, but also by the target characteristics and atmospheric conditions. To the right is a graph showing the spectral reflectance of various elements - a man in drab clothing, for instance, would stand out dark against green foliage, which is more reflective, especially in the nearinfrared
spectrum. The degree of contrast between the various elements visible has a lot of influence on the
detectability of a subject.
• Magnification and Field Of View (FOV) -Consider the size of your target, the distance you wish to see over and the overall area you are observing or searching. For most surveillance or search applications, the higher the magnification , the narrower the FOV & the greater the number of times you need to scan an area to avoid missing important objects or events. Usually a 1:1 lens with a wide FOV provides optimal performance. For longer range observation or weaponsight applications, the amount of magnification needed will vary; take into account that, as the magnification increases so does the lens ƒ-number while the FOV decreases - this reduces the amount of light captured. How versatile is the device you are considering ? Do you need, and does
it offer, interchangeable lenses ?
• Ergonomics - Size, weight and ease of use are important considerations. If you plan to carry your scope in your pocket or briefcase, then smaller systems will suit you better. Lightweight devices are more comfortable during extended viewing. Since you will be using the device in the dark, the switches and controls should be positioned logically and be easy to use.
• Distortion - Gen O, Gen 1, and 25-mm Gen 2 electrostatically inverted image tubes produce a certain amount of geometric distortion in the image. In Gen 2 and Gen 3 systems, geometric distortion is normally eliminated through the use of an MCP,although it is possible to encounter some perceptible S and shear distortion. Especially when the application involves photography, video work, or weaponsights, the distortion and peripheral resolution can be critical.
• Extended Viewing - If you intend to look through a device for extended periods of time (20+ minutes) you may find that a binocular or biocular better suits your requirements. Using a monocular continuously for this period of time will mean that your eyes will adjust individually to their lighting conditions - one to the scene through the night scope and the other to the ambient lighting. This could lead to eye strain. If you use the device for extended periods, a tripod socket may be a useful feature.
• Weather Resistance - The ability of a night vision system to operate under adverse environmental conditions. Most devices will withstand a light shower, but if you expect to regularly use the device in inclement weather or a marine environment, choose a model that has protection against such conditions. If you want full waterproofing, ie can be fully submersed, choose a system built
to mil specs or that is guaranteed as such..
• Practicality - Is the battery a size and model that is commonly available? This is important, especially if you use your system in the field. All Tianying Optics/Yukon scopes use batteries that are readily available from camera shops or electrical retailers.
• Reliability - With proper care, modern Night Vision designs are relatively trouble-free. However, please be aware that intensifier tubes have a finite duty cycle (they will eventually wear out). Thomas Jackss test every single device that it sells. Every unit has to pass stringent quality checks before it is boxed for resale. Thomas Jacks Ltd sells only new Night Vision systems that incorporate
protection circuitry which turns the intensifier down or off when exposed to bright light. Our intensifier tubes are conservatively rated at 1,000 hours of use under normal conditions. It should be noted, however, that any tube will degrade and eventually fail under repeated, prolonged or excessive exposure to bright light. We recommend you always cover the objective lens and store
the scope properly when not using it. The image intensifier is a vacuum sealed glass tube - it can be easily damaged if the device is knocked or dropped. Ensure that you protect your scope well from such possibilities. The intensifier tube is by far the most expensive component to replace in a night scope, on average accounting for some 60-70% of the total cost.
* Secondhand or Reconditioned Devices - As stated above, intensifier tubes have a finite duty cycle (they will eventually wear out). Knocks, abuse or exposure to bright light will further compromise a tube’s performance and life. Thomas Jacks Ltd does not supply "second hand" or "reconditioned" equipment and would not recommend the purchase of such devices unless you can be absolutely certain of their usage/performance. While the price may be attractive, be aware that the intensifier tube cannot be restored to ‘new’ condition. "Reconditioned" usually means the system has a new or repaired power supply, but the tube photosensitivity, SNR and the remaining life cannot be improved and will be noticeably lower than from an equivalent new device. Some second hand or reconditioned units may be operating at below acceptable minimums and few companies possess the necessary test equipment to evaluate the tube's level of performance.
• Service - Is the product supplied by a reputable, branded supplier, protected by a warranty that will be honoured and is technical service available ?
• Warranty - We offer a 1 Year Exchange Warranty on all Tianying Optics branded devices and 3 Years on Yukon Advanced Optics models (unless otherwise stated). If the unit proves to have failed due to parts or labour, we will exchange it with a new device