Night Vision: Image Intensifier VS Thermal Imaging VS Digital Night Vision, Which is Best?

Night vision technology has revolutionized the way we see in the dark. There are three main types of night vision: image intensifier, thermal imaging, and digital night vision. Each type has its own unique features and benefits.

A. Three main types of night vision

B. Specifications of image intensifier, thermal imaging, digital night vision

C. Comparison of three types

A. Three main types of night vision

1. Image Intensifier(IIT): This type of night vision works by amplifying the available light in the environment. It uses a photocathode to convert photons into electrons, which are then accelerated and focused onto a phosphor screen. The screen emits a greenish image that is visible to the human eye. Image intensifiers are commonly used in night vision goggles and scopes.
2. Thermal Imaging: Thermal imaging night vision operates by detecting the heat emitted by objects and converting it into a visible image. It uses a special sensor called a microbolometer to detect the infrared radiation emitted by objects. The sensor creates a thermogram, which is then processed to generate a visual representation of the temperature differences in the scene. Thermal imaging is effective in complete darkness and can detect objects based on their heat signatures.
3. Digital Night Vision: Digital night vision technology uses an image sensor to capture the available light and then processes it digitally to enhance the image. It can work in low-light conditions and even in complete darkness with the help of infrared illuminators. Digital night vision devices often have the ability to record images and videos, and some models offer additional features such as zoom and image enhancement.

B. Specifications of image intensifier, thermal imaging, digital night vision

1. Image Intensifier(IIT):

  Military procurement tubes are judged by an "Omnibus" (OMNI) contract for their minimum specifications. The current OMNI contract calls for the following specs:

FOM: 1600+

SNR: 25+

LP/MM: 64+

Photocathode Sensitivity: 2000+

Luminance Gain: 25,000-110,000

HALO: <1.0

EBI: <2.5

• FOM (Figure Of Merit): Figure of Merit is simply the tubes Resolution (or LP/MM) multiplied by it's SNR (Signal to Noise Ratio). LP/MM * SNR=FOM
• SNR (Signal To Noise Ratio): Signal to Noise Ratio is the relation between how much information the tube is giving you is "true" vs "false". Think of an image intensifier tube like a camera sensor. A tube with a SNR of 30 will give you 30 pixels that accurately represent the image, with one inaccurate one. A vague guideline of SNR specs would be something like:

25+ SNR: Average

30+ SNR: Good

35+ SNR: Great

• Resolution or LP/MM (line pairs per millimeter): To keep using the camera analogy, think of this like megapixels. In our experience, everything above 64lp/mm looks the same to the eye in a headborne unit, especially 72+. 81+ lp/mm tubes are really desired in magnified rifle clip-on scopes where the extra resolution will be noticeable when using magnification.
• EBI (Equivalent Background Illumination): This can be simplified as how good the tube is at forming an image in low light conditions. The lower score the better. EBI is the amount of light a tube is putting out as default, and so in order for an image to be shown to the user, the incoming light must be greater than what the tube "sees" by default. Realistically, anything below 2.0 is good, and anything below 1.0 is great.
• HALO: It's going to be the glow you see when you look at a light source, or an IR laser. In general, under 1.0 is ideal, and considered good. However, for clip-on units that will be used on a rifle, you would typically want a tube with a Halo above 1.0, as the lower numbers are also more sensitive to recoil.
• Luminance Gain (or Brightness Gain): This is the ratio of brightness of the output of the phosphor screen (what you look at), to the input to the photocathode (what receives the light). Out put vs input. In easier terms, it's how many times the light was multiplies before it got to your eyes. The higher the number, the better. A general guide would be something like:

<50,000 Gain: Bummer

50-60,000 Gain: Usable/Acceptable

60,000+ Gain: Good

• Photocathode Sensitivity: This is how well the tube converts photons (incoming light) into electrons (what the tube amplifies). We generally see tubes in the 2000-2700 range. Anything under 2,000 would be a lower performing tube, and 2,700 would be great. We most commonly see tubes around the 2,200 mark.

Confused by lots of data and numbers? Then the following points chart can help.

• Generation: We concentrate on the performance of each generation.

  Gen1 Limitations:

  -maximum useful range is about 75 yards depending on the night. A good Gen 3 device is capable of several hundred yards even in lower light conditions.

  -lower resolution images, more static/noise in the images, not as bright.

  -inability to operate "passively" - Gen 1 relies on built-in IR illuminators that are always on, making the user very visible to anyone using another night vision device.

  -smaller field of view due to distorted image on outer one third of the field of view.

  -shorter battery life.

  -more susceptible to "blooming" - which is image distortion caused by excessive light.

  -Gen 1 monoculars don't have the versatility that higher generations do. Examples: adapting to rifle scopes, spotting scopes and weapon mounting capability.

  -shorter life expectancy. Gen 1: about 1500 hours, Gen 2: about 5000 hours, Gen 3 over 10,000 hours.

  Gen2:

   The major improvements over Gen 1 are as follows:

  -much longer useful range, in the 200 yard area depending on model.

  -better resolution, cleaner images, brighter.

  -the ability to operate "passively" without the necessity of IR illumination.

  -full field of view- no distorted image on outer one third of viewing area.

  -longer battery life

  -less susceptible to "blooming" or image distortion caused by light when compared to Gen 1.

  -Gen 2 monoculars have greater versatility due to increased durability and adaptability.

  -3 times longer life expectancy than Gen 1 and better reliability.

  Gen3:

  -longest ranges, in the 300 yard plus range depending on model and conditions.

  -best resolution, cleanest and brightest images.

  -best low-light performance.

  -even greater ability for completely "passive" operation - operating without the use of IR illumination/covert operation.

  -autogated Gen 3 image tubes allow for operation in ALL light conditions. Significant reduction to "blooming".

  -best versatility due to better performance when using with magnification lenses, scopes, camera adapters, and other night vision accessories.

  -longest life expectancy of 10,000+ hours and best reliability/durability.

  Gen4:

  This is a tricky one as technically there is not really a Gen 4 classification, according to the US Army. When it was initially introduced the US Army recognized the Gen 4 technology classification. However, after testing reliability and life span of the Gen 4 the Army determined that this technology did not meet their strict requirements and thus recanted the Gen 4 definition. Now some companies use the 'Gen 4' Term as a marketing ploy to say its the best image.  So what does this mean for someone looking for the best equipment they can get?  There is new technology that is similar to the Gen 4, it is called 'Unfilmed' or 'Filmless Gen 3'.  This is what the military is using alot of now, and is still classified as a Gen 3, but it has the same Filmless feature and better performance of the Gen 4, with the reliability of a Gen 3.

  

2. Thermal Imaging:

• Pixel pitch

Pixel pitch is the distance between the centres of two pixels of a microbolometer. In thermal imaging sensors, it is measured in microns (µm).

• Fill Factor

Fill factor is the ratio of sensitive surface of all pixels to the total area of pixels. Sensors with a higher fill factor can absorb a larger amount of energy.

• Magnification

The magnification value shows how many times the observed image (with the help of the optic device) is larger compared to the object observed with a naked eye.

Magnification Dependencies:
The higher the focal length of the objective lens, display size, the higher magnification.
The higher the focal length of the eyepiece, sensor size, the smaller magnification.

• Field of View(FOV)

The field of view defines the size of space that can be viewed through the optical device at a defined distance. Field of view is usually given in degrees (angular field of view is shown below in the image as 2Ѡ) or in metres for a specific distance (M) (usually 100M) to the observed object (linear field of view is shown as A in the image).

The field of view of a digital night vision device is defined by the focal length of the objective lens (f objective lens) and the physical size of the sensor (B). For calculation purposes, they usually use the width (horizontal size) as the physical size of the sensor and in the result, they get the horizontal field of view:

If vertical sensor size or diagonal sensor size are known it is possible to calculate the vertical or diagonal field of view similarly.

The wider the field of view, the more comfortable observation as there is no need to move the device constantly to view the necessary part or space.

It is important to understand that field of view is inversely proportional to magnification – meaning that when magnification increases field of view shrinks. This is one of the reasons why infrared systems (thermal imagers in particular) with high magnification are not manufactured. At the same time, it is important to understand that an increase in the field of view leads to a decrease in detection and recognition range.

Field of View Dependency:

The larger sensor size or smaller focal length of the objective lens, the wider angular field of view.

• Frame Rate

The frame rate is one of the main characteristics of a thermal imaging device. From the user’s point of view, it is the number of frames displayed on the screen in one second. This is usually measured in Hertz (Hz) where 1Hz is equal to 1 frame per second. The higher the frame rate value, the less visible the effect of lagging of image produced by thermal imager in respect to the real scene. Observation of dynamic scenes with a thermal imager that has 9 fps rate shows a blurry image and object movements may seem laggy and “jerky”. On the contrary, the higher the frame rate, the smoother will be the rendering of dynamic scenes.

3. Digital Night Vision:

Magnification, Resolution, Sensitivity, Field of view are the same from the above.

• Sensitivity

In order to characterise the sensitivity of digital video cameras, they often use the parameter of minimal illuminance level on the observed object when the device is still able to produce an image.

This definition is the most suitable for digital devices operating in the visible range of the spectrum. For visible ranges a unit of sensitivity measurement is a light unit – “lux”.

The sensitivity of a device depends on the following parameters:

-Light-gathering power and quality of objective lens

-Sensor parameters – physical size, its type and sensitivity

-Display parameters – brightness and contrast, resolution

-Algorithms for signal processing

-Quality of electric circuitry solutions implemented in the device

Relations:

The higher the light-gathering power of the objective lens (increases when the entrance pupil is increased and the focal distance is decreased), the higher the overall sensitivity of the device.

The more lenses that are used in the objective, the smaller the light-gathering power and the sensitivity of the device.

The higher the optical transmission coefficients of lenses constituting the objective, the higher the sensitivity.

• Eye Relief

Eye relief is the distance from the external surface of the last lens of the eye piece to the plane in which the observer’s eye is located when the observed image is optimal (the largest possible field of view, minimal distortions). This parameter is very important for weapon sights, where eye relief should be at least 50 mm (optimal 80-100 mm).  Such big values of eye relief are necessary to avoid injury to the observer because of the recoil during the shot. In night vision devices eye relief as a rule equals the length of eye shade which is necessary to mask illumination of the image intensifier tube or screen.  

• Detection And Recognition Distance

Detection distance – the maximal distance from the observation device to some object (usually man) which may be detected with the help of the device.

Recognition distance – the maximal distance at which the observer can recognise the type of observed object (human, animal, building, etc.).

C. Comparison of three types

 Knowing that you’re already exhausted in studying the parameters various, we list a clear sheet to help you distinguish these three types. Which best? It depends on the circumstance. Usually image intensifier is for military use for its complete function. Thermal is for hunting. And digital is for police evidence collection for its video supportable.

See dark in the night, night vision is also in our catalogue. Hurry to inquire us, even customizable parameter is supported. We Partner service you as the night vision brighten your vision.