In short: A handheld thermal monocular is the most versatile option for scanning and observation. A clip-on mounts in front of optics you already own – a day scope or a night vision device – and clip-on manufacturers state that you zero the day scope, not the clip-on. Fusion combines thermal with tube-based night vision: thermal finds the warm object, night vision shows the surroundings. Which one makes sense depends on what you already have and what you need it for.
Three ways to use thermal
- Handheld monocular – a stand-alone device with its own eyepiece and display, used for scanning terrain and observation.
- Clip-on (front attachment) – a thermal module without its own viewing eyepiece that mounts in front of another optic’s objective lens. You see the image through the optic behind it.
- Fusion – thermal and image-intensified night vision (I²) combined in one view. In civilian use most often as a thermal clip-on in front of a night vision monocular.
Handheld monocular: when it makes sense
A handheld monocular makes a good first thermal: it doesn’t depend on any other optic, it’s easy to scan with, and it suits wildlife observation, property protection, outdoor use or tracking. Think about field of view – a wider view is more practical for scanning, a longer lens for detail at distance. We explain how to read these specs in How thermal imaging works and how to read the specs.
- Pro: self-contained, quick to use, nothing to mount.
- Pro: can serve as a handheld observation device alongside other gear.
- Con: one more device to carry and charge.
Clip-on in front of a day scope
A clip-on mounts on the objective of an existing day scope via an adapter (for example a ring adapter with an insert matched to the objective diameter). The thermal image is projected into the day scope and you aim through its reticle.
What about zero? This is how clip-on manufacturers describe it: Pulsar, for example, states that its Krypton attachment does not need zeroing – only the day sight is zeroed – provided it is installed correctly according to the manual. If the point of impact shifts with the clip-on fitted, Pulsar recommends checking the clip-on installation, the adapter and insert ring, the rifle’s zero with the day scope, and using the display calibration function. Other manufacturers may have their own procedures – always follow the manual for your device.
- Pro: you keep the day scope and reticle you’re used to.
- Pro: quick to fit and remove as needed.
- Con: adds weight and length in front of the scope.
- Con: you need an adapter that fits your scope’s objective diameter.
Clip-on in front of night vision and fusion
The other option is to fit a thermal clip-on in front of a tube-based night vision device, such as a PVS-14-style monocular. The thermal image is projected into the night vision objective and you see both at once – that’s fusion. Thermal shows warm objects regardless of lighting, while night vision shows the surroundings, terrain and details that may not stand out on thermal.
Because the thermal image passes through the night vision tube, the result takes on the tube’s phosphor colour – you won’t see thermal colour palettes. Another approach is to run a thermal and a night vision monocular side by side (one in front of each eye), but The Firearm Blog notes that this reduces depth perception.
- Pro: quickly find a warm object while staying oriented in your surroundings.
- Pro: adds a new capability to night vision you already own.
- Con: more weight on the helmet or monocular – on a helmet, consider a counterweight (see Helmet NVG setup).
- Con: more batteries and one more device to set up.
If fusion with night vision interests you, see Jerry C-5 in the shop (usable on its own or mounted on a night vision device) and JerryC PRO in the shop (a clip-on with a 640×512, 12 µm sensor and a clamp for PVS-14-style optics). Both are tested and supported by our lab.
Comparison at a glance
| Handheld monocular | Clip-on on a day scope | Clip-on on NV (fusion) | |
|---|---|---|---|
| Main use | scanning, observation | using a day scope at night | find a warm object + see surroundings |
| You also need | nothing else | a day scope and adapter | a night vision device |
| Zero | not relevant | per manufacturers, the day scope is zeroed | not relevant for observation |
| Colour palettes | yes | depends on the device | no (tube phosphor colour) |
What to watch for with every type
- Glass: thermal can’t see through ordinary glass – not through a car window, not through a glass protective cap. A clip-on always goes in front of the optic, never behind it.
- Calibration: the image freezes briefly during calibration. On Pulsar Krypton clip-ons the shutter is internal in automatic and semi-automatic modes; in manual (silent) mode you close the lens cover.
- Intense energy sources: manufacturers warn not to point the lens at the sun or at lasers – this can damage the device’s electronics. More in Care and troubleshooting.
How to decide – checklist
- What do you already own? A day scope, night vision, or nothing?
- Do you mainly need to scan and observe (monocular), or to work with an existing optic (clip-on)?
- For a clip-on, check adapter compatibility with your scope’s objective diameter.
- For fusion, check whether the clip-on can be attached to your night vision device (e.g. a clamp for PVS-14-style optics).
- Consider weight and balance, especially on a helmet.
- Check the rules for your intended use in your country.
Legal aspects
Rules for using thermal devices and clip-ons differ from country to country – see our overview at Night vision and thermal laws in Europe.
The information on this page is general, is not legal advice, and laws change. We cite the source and the date we checked it. Before buying or using a device, verify the rules with the relevant authority or hunting association. Last checked: 9 Nov 2026.
Sources
- Pulsar FAQ: Do I need to zero the Krypton attachment? – the attachment needs no zeroing, only the day sight does – pulsarvision.com (checked 9 Nov 2026)
- Pulsar FAQ: What should I do if I’m experiencing issues with the point of impact? – pulsarvision.com (checked 9 Nov 2026)
- Pulsar Krypton 2 FXG50 – mounting on the day scope objective with a ring adapter – Official manufacturer manual (external link, third party – NGS is not responsible for its content) (checked 9 Nov 2026)
- The Firearm Blog: Friday Night Lights – Thermal Fusion (2019) – fusion principle and clip-on thermal in front of a PVS-14 – thefirearmblog.com (checked 9 Nov 2026)
- Axis Communications: Thermal cameras – thermal principle, independence from ambient light – axis.com (PDF) (checked 9 Nov 2026)
- Pulsar FAQ: Can I use a thermal imager to see through glass? – pulsarvision.com (checked 9 Nov 2026)
- Night Gear Solutions: Jerry C-5 and JerryC PRO product pages (mounting description and specs) – nightgearsolutions.eu (checked 9 Nov 2026)