The buying guide for night vision devices

The market for night vision technology is fascinating, but often confusing for beginners and even for experienced users. Abbreviations like Gen 2, Gen 3, FOM, white phosphor and countless housing options make the decision difficult. On top of that, this usually means investing a considerable sum of money.

To avoid bad purchases, it is not enough to look only at the generation of the device. You have to understand the technical measurements on the tube’s data sheet and also be able to assess the housing quality. This guide breaks down all the relevant data for you.

Step 1: Which design concept suits you?

Before you get into the measurements on the inside, you have to decide how you want to use and wear the device.

Monocular (single eye)

A monocular such as the PVS 14 uses a single image intensifier tube for one eye. The other eye stays free and keeps its natural, dark-adapted night vision.

• Advantages: Cheaper entry, extremely versatile, light and compact.
• Disadvantages: No spatial depth perception; the brain has to process two completely different images, which can be tiring.

Binocular (both eyes)

A true binocular such as the DTNVS or BNVD has two separate tubes and two lens systems, one for each eye.

• Advantages: True spatial vision, significantly higher movement speed possible in the field, more relaxed for the eyes on long operations thanks to stereo vision.
• Disadvantages: Very expensive, since two tubes are needed, and heavier than a monocular.

Step 2: The device generation

The generation describes the technological level of the installed image intensifier tube.

Step 3: Decoding the data sheet

Every high-quality analog night vision device has an individual image intensifier tube, for which a data sheet with exact measurements exists. Be sure to ask to see this sheet when buying!

1. SNR (Signal to Noise Ratio)

The signal-to-noise ratio is the most important single value for performance in extremely poor light. It describes the ratio between the usable image signal and the electronic noise.

• In practice: The less light is available, the more the image starts to get grainy. A high SNR means the image stays extremely clear, calm and detailed even on dark nights.
• Reference values: A value below 20 is obsolete. Good modern Gen 2+ tubes reach values of 24 to 28. Gen 3 tubes deliver values of 30 to over 35.

2. Resolution

Resolution indicates how many line pairs per millimeter the eye can still perceive as separate through the tube.

• Reference values: Standard resolutions are usually around 64 lp/mm. Top tubes reach 72 lp/mm or even 81 lp/mm.

3. FOM (Figure of Merit)

The FOM value is calculated by multiplying resolution by signal-to-noise ratio: $FOM=\text{SNR}\times \text{Resolution}$. It serves as a quick guide to the performance class.

• Reference values: A value of 1400 to 1600 offers solid performance. Values of 1800 to 2200 are considered upper-class level. Anything above that is top military level.

4. Halo

When you look at a point light source in the dark, a bright ring forms around that source, the so-called halo.

• Reference values: A value of 0.7 mm to 1.0 mm is the standard. Values below 0.7 mm are excellent and noticeably minimize the dazzling effect in urban use.

5. EBI (Equivalent Background Illumination)

The EBI measures the light that the tube generates on its own. If the incoming residual light is weaker than the EBI, the image is swallowed up by noise.

• Reference values: The value should ideally be below 2.5. Top values for use in the deepest darkness are below 1.0.

6. Spots and zones

No tube is perfect. Microscopic black dots often form during production. The field of view is divided into three zones:

• Zone 1 (center): This is where you look the most. No large spots at all should be present in this zone.
• Zone 2 (middle ring): Small spots are tolerable here, but should not be distracting.
• Zone 3 (outer edge): Spots are completely normal here and hardly interfere in use.

Step 4: Optics and housing

A tube with top values is useless if the housing or the glass in front of it is of inferior quality.

Lens quality

The glass determines how much light reaches the tube at all. Look for military-spec optics. Cheap commercial lenses swallow light, create optical distortions and ruin the performance of an expensive tube.

Field of view

The standard field of view for night vision devices is 40 degrees. There are now special lenses that offer a field of view of 50 degrees. This greatly increases peripheral perception, but often creates slight blurring at the edge.

Protection and control functions

• Autogating: Protects the tube from sudden bright light by switching the tube on and off thousands of times in milliseconds. This prevents the tube from burning out.
• Nitrogen filling: Make sure the housing has been professionally filled with nitrogen. This prevents the lenses from fogging up from the inside during rapid temperature changes.
• Power supply: Does the device use conventional AA batteries or CR123A cells? Some binocular models have a connection for an external battery pack at the back of the head, which also serves as a counterweight.

Step 5: The great debate over phosphor colors

The phosphor layer on the screen determines the image color. There are green phosphor and white phosphor.

• Important to know: The color is not a quality feature. A green tube with excellent SNR values beats an inferior white tube any time.
• There is no statistical evidence proving that one color is factually superior. White phosphor often looks more natural, like a black-and-white photo, and the eye tires less quickly. Green phosphor is often perceived as higher in contrast in deep forest. Choose purely according to your personal preference.

Step 6: Accessories and mounting

A night vision device only unfolds its full potential through the right mount.

• The helmet: A sturdy tactical helmet with a robust front plate.
• The helmet mount: The mechanical hinge for flipping up and down. For example, go for wobble-free systems like the UDAPT F25 NVG Mount, which uses an adjustable dovetail clamping system and eliminates any play.
• The J-Arm: Connects a monocular to the helmet mount.
• Counterweights: Indispensable at the back of the head to relieve the neck muscles when the device is mounted at the front.

Conclusion

A night vision device should never be bought in haste. Always ask the dealer to show you the exact data sheet of the installed tube, and check the values for SNR, EBI and the zone distribution of the spots. If the optics and the housing are right, nothing stands in the way of your successful operations in the dark.