THERMAL CLIP-ON UNITS

Fit and what's supplied

A clip-on is designed to be used with a separate, compatible host optic rather than replacing it. Attachment designs vary. Pulsar describes its Krypton 2 FXG50 as a front attachment, for example, but that is not a rule for every model here.

Fit depends on the exact clip-on variant and the exact optic. Compare these before you choose:

• The clip-on manufacturer's compatibility information, including the type of host optic the unit is intended for.
• Your optic's make, model and external dimensions. These are the measurements the clip-on manufacturer asks you to match, such as diameter.
• The adapter specified for that particular combination.

Supplied parts can differ between models, even within one series. Before ordering, confirm on the product page whether the adapter and any other parts you need are included.

Comparing models: what each specification means in use

A series name such as Krypton 2, HUNT Pro or MATE covers several variants with different sensors, lenses and features. Compare exact models rather than series.

• Sensor (detector) resolution. A higher detector resolution can provide more potential detail. How much of it you actually see depends on the whole system, including the lens, image processing, distance and conditions, so it does not guarantee that you will recognise a subject. It matters most when you need to make out what a subject is, not just notice that something is there.
• Lens, field of view and magnification. A wider field of view shows more of the scene at once, which helps when scanning or working at closer range. A narrower field of view covers less of the scene. How large a distant subject appears also depends on the model's magnification and optical design, so compare each exact model's field of view and magnification together. Choose based on whether you mainly scan or observe, and on the distances and terrain you usually deal with.
• Sensor and lens together. These two points work as a pair. Between them they influence how much detail is available on any one subject at a given distance.
• Power arrangement. Two things affect how long a session can run and what spares you carry: how the unit is powered, and whether its batteries can be swapped.
• Handheld option. Do you want one device for both observing and use with your optic? If so, check whether the manufacturer lists a handheld configuration for that exact model, and what it needs.

What the thermal image can and cannot tell you

A thermal imager builds its picture from infrared radiation reaching its sensor. Some of that radiation is emitted by the surfaces in view. Some may be reflected by those surfaces from their surroundings.

The balance between the two is not fixed. It depends on each surface's emissivity, which varies with material and finish, and on what surrounds it. That is why water, wet ground or shiny surfaces can sometimes show patterns that are not the object's own heat.

The display therefore shows differences in signal, or contrast. It is not necessarily a temperature reading. A subject can stand out whether it is warmer or cooler than its background, provided there is enough contrast at the time.

Detecting that something is there is not the same as recognising what kind of thing it is, or identifying it. Sensor detail, lens, distance and conditions all affect how far you can get from detection to identification. This is why the sensor and lens choices above matter.

Related categories

• Thermal rifle scopes: our thermal riflescope range. Some devices can serve more than one role.
• Night vision add-ons: our range of night vision add-ons.
• Thermal monoculars: handheld thermal devices for observation.

FAQs

How is a thermal clip-on different from a thermal riflescope or monocular?

A clip-on is designed to work alongside a separate compatible optic and add thermal viewing to it. A thermal riflescope or thermal monocular is designed to be used as a viewing device in its own right. The lines are not absolute. Some clip-ons can be set up for handheld viewing, and some devices serve more than one role, so treat the category as a starting point rather than a rule.

Will a thermal clip-on fit any optic?

No. Fit is specific to each pairing of clip-on and optic, and the clip-on manufacturer's compatibility information is the reference point. If you have not chosen an optic yet, you can compare compatible combinations of clip-on and optic before you buy either.

Are adapters included?

Do not assume so. For example, Pulsar's manual for the Krypton 2 FXG50 lists the suitable ring adapter as separately available. Arrangements differ between brands and models. When comparing prices, allow for the cost of an adapter unless one is listed as supplied.

Can a thermal clip-on also be used handheld?

Some can. Pulsar's manual for the Krypton 2 FXG50, for instance, lists a 3×20 B monocular as a separately available accessory for handheld viewing. Not every clip-on offers this, and an accessory made for one model will not necessarily suit another. If handheld observation is your main use, compare our thermal monoculars as well.

Should I prioritise image quality or extra features?

Start with the things you cannot change later. The first is fit with your optic. The second is a sensor and lens combination that suits your usual distances. Extra functions are worth paying for only if you will use them, because they will not make up for an image or field of view that does not suit how you work. The newest or highest-numbered model is not automatically the right choice.

Why can the same clip-on show a different image on another evening?

Thermal contrast depends on conditions. Humidity, rain, mist, fog and changes in air temperature can all reduce how clearly differences show. The air between you and the scene can also absorb and emit infrared radiation. The same unit can therefore give a noticeably different image from one session to the next. No thermal device can guarantee what it will show.