In short: A binocular (BNVD) has two tubes – each eye gets its own channel, so the image has real depth and moving over terrain feels more confident. The price is more weight and a higher cost. To stay comfortable over long wear, a binocular must be set up correctly (especially interpupillary distance – IPD) and balanced on the helmet with a counterweight.
What a BNVD is and what “PVS-31 style” means
BNVD (binocular night vision device) is the general term for a night vision device with two tubes, two objective lenses and two eyepieces. The PVS-31 is a specific model that gives its name to a whole style of binoculars: two separate channels (pods) on a common bridge that can rotate and fold.
The L3Harris sell sheet for the AN/PVS-31A describes the features that define “PVS-31 style” today: rotating pods that let you use the device as a single monocular, low-profile stowage against the helmet, automatic shut-off when stowed, and compatibility with standard dovetail helmet mounts. It lists the weight as under 450 g with an AA battery, excluding accessories.
Advantages of a binocular
Depth and confidence on the move
Each tube looks from a slightly different position, so your brain receives two slightly different images and combines them into a stereoscopic (3D) picture. In a US Army study where participants walked over rough terrain, the binocular performed better than the monocular and the biocular, and participants preferred it.
To be fair: even with a binocular, you don’t judge depth as well as with the naked eye in daylight. A review of earlier measurements showed that depth perception with night vision remains worse than without it. A binocular is a big step forward, but not a miracle.
Comfort over long wear
With a monocular, one eye sees an intensified image and the other sees darkness – your brain constantly has to reconcile two very different inputs. With a binocular, both eyes get a similar image. That is why binoculars are chosen where a device is worn for hours.
One important condition: both channels must be properly aligned with each other and the device set up for your eyes. Research by Australia’s Defence Science and Technology Group names misalignment between the eyes as one of the expected sources of visual fatigue in binocular devices, and a 2019 study measured worse performance and signs of greater fatigue under induced misalignment. A badly adjusted binocular can tire you more, not less.
Using just one channel
On articulating (PVS-31 style) units you can flip up one pod and use that eye unaided – for a map, a screen or when stepping into a lit area.
Drawbacks to know about
- Weight. Two tubes and two optical channels weigh more than a monocular. On a helmet, that weight sits at the front, far from your head’s centre of gravity.
- Cost. Two tubes mean roughly twice the most expensive component.
- More adjustment. IPD, height, tilt, eye relief and diopter for each eye separately.
- Tube matching. Both tubes should produce a similar image (brightness, phosphor colour, specs), otherwise the difference between eyes is distracting.
Weight and counterweight
An example from a spec sheet: the AN/PVS-31A weighs under 450 g without accessories. Add the helmet mount and possibly a battery pack. Everything at the front of the helmet pulls your head forward and strains your neck over time.
The answer is a counterweight at the back of the helmet. For example, Gentex describes its Ops-Core counterweight as “designed to enhance comfort and reduce neck strain particularly when wearing NVGs”, supplied with five removable 70 g weights so you can fine-tune it. An external battery pack can partly do the same job – L3Harris offers an optional four-AA battery pack for the PVS-31A. We describe the full setup in Helmet night vision setup.
Setting IPD and other adjustments step by step
IPD (interpupillary distance) is the distance between the centres of your pupils. If the binocular’s channels don’t match your IPD, you’ll see two overlapping circles or dark edges, or your eyes will soon feel tired. The setup is simple, but take your time:
- Put on the helmet and tighten it so it doesn’t move on your head. Without a stable helmet, nothing else is worth adjusting.
- Set the mount height so the eyepieces are level with your eyes.
- Set eye relief by moving the device forward or back until you see the full circular image without dark edges.
- Set IPD: move the pods closer together or further apart until the two circles merge into one sharp circle.
- Adjust tilt so you look through the centre of the optics, not the edge.
- Focus the eyepieces (diopter) for each eye separately – cover the other eye while you do it.
- Focus the objective lenses at the distance you will look at most often.
- Remember or mark your settings – next time it will be quicker.
If the two images still won’t merge after careful adjustment, or your eyes start hurting quickly, the channels may be misaligned. That is a job for a service centre, not for home repair.
Types of binoculars
| Type | Characteristics | Best for |
|---|---|---|
| PVS-31 style (articulating) | two independently rotating pods, folds against the helmet, one pod can be used alone | helmet wear, moving over terrain, when you want the option of a free eye |
| Fixed-bridge BNVD | channels fixed together, mainly IPD is adjustable | when you don’t need to flip pods independently |
Several manufacturers now make binocular housings – for example Low Light Innovations (MH-1 and UH-1 models – also in our shop). As with monoculars, the image depends mainly on the tubes, so ask for a datasheet with a serial number for each one. See How to read a tube datasheet.
NGS binoculars
We offer two binocular setups: NGS 3114 and NGS 31H. Both are hand-built and tested before shipping. If you’re not sure whether you need a binocular or a monocular is enough, see the comparison in Night vision device types.
Sources
- L3Harris – AN/PVS-31A BNVD sell sheet (under 450 g with AA battery, excluding accessories; rotating pods, single-monocular use, low-profile stowage, auto-off when stowed, compatible with dovetail helmet mounts, optional 4 × AA battery pack) – L3Harris (PDF) (checked 9 Nov 2026)
- DTIC ADA294018 – A Comparison of Monocular, Biocular, and Binocular Night Vision Goggles for Traversing Off-Road Terrain on Foot – DTIC (checked 9 Nov 2026)
- Armentrout, J. J. (1993): An Investigation of Stereopsis with AN/AVS-6 Night Vision Goggles…, Virginia Tech (DTIC ADA275332) – DTIC (PDF) (checked 9 Nov 2026)
- Changes in physiological parameters induced by optical misalignment in night vision binocular devices, SPIE – Situation Awareness in Degraded Environments 2019 – DOI 10.1117/12.2517297 (checked 9 Nov 2026)
- Defence Science and Technology Group (Australia) – Improving visual performance of the warfighter (2017) – dst.defence.gov.au (checked 9 Nov 2026)
- Gentex Ops-Core – Counterweight product sheet (“designed to enhance comfort and reduce neck strain particularly when wearing NVGs”; 5 × 70 g weights) – Gentex (PDF) (checked 9 Nov 2026)