Understanding Thermal Optics 






It has long been known that Pulsar is ‘the brand’ when it comes to general consumer thermal optics. Whether you bought a brand new Axion or a second-hand Trail, you knew you were getting a good product. But while Pulsar have been riding the wave of their notoriety, many other brands have been quietly developing their products in the background, each iteration growing stronger and stronger, to a level where they can offer equal (or better) spec, at a far more reasonable price point.

So, what are the key details you should know about thermal imagers and why should you be taking these competitor brands far more seriously than you may have in the past? Before we go into that, a key point to consider when looking for a thermal optic, is what is your use case for the device? Much like traditional optics, there are very much ‘horses for courses’ – you aren’t going to put a Leupold Pig-Plex 1.5-4x scope on your 2,000m PRS rifle, are you? The same can be applied to thermal imagers.

Scope or Handheld (or both?)

My stepping off point is always, which device do you need? In an ideal world, you’d have both, but even though these other brands are releasing magnificent units at reasonable prices, you can still spend north of $6000-7000 to have a reasonably basic scope and handheld setup, which is not a price point everyone can accommodate. So, make sure (if the budget allows for one unit only) you choose the right piece first. In a general sense, a handheld is the simpler one-unit option – it is easy to use and handle (given you don’t have to raise your rifle every time you want to survey the lands) and generally they are cheaper in regard to ‘bang for buck’ (since they don’t also have to deal with the rigors of recoil). The modus operandi here being that you would scan your hunting region with the handheld, identify what you are looking for and then get yourself close enough that you can take the shot under spotlight or torch.

With a scope, it can be slightly more complex given you will need to consider what kind of shooting you’re primarily doing – some devices exist for a more point and shoot, short distance style operation (i.e. units more akin to a short range 1-4x optical scope) and some devices are designed to operate more like your longer range scopes, where you might set yourself up on a hill or berm and wait for that perfect longer distance shot. Once this decision has been made, then you can move into the slightly murky waters of technical specs of the device. Of course, if you can buy both, then this is ideal!


Focal Length (often mistaken or represented as lens size):

Much like photography camera lenses, lens focal length will dictate your use case, to some degree.

 • 19mm: These are generally entry level devices and are good for close range, bush hunting.
 • 25mm: Slightly stronger magnification with a decent field-of-view thus, more general use.
 • 35mm: Now we’re pushing into medium/longer range. Useful at distances to around 500m.
 • 50mm: Long range


Sensor size:

Nearly all thermals use 384x288, 640x480 or 640x512 sensors – there are other variations too, but these three make up most of the market right now. 640x480/512 doesn’t necessarily mean higher resolution and better image quality, but more resolution/imaging, meaning a wider field of view (FOV). This isn’t a hard and fast rule, as other factors also contribute to FOV but in general, just know 640x480 doesn’t mean sharper image quality, necessarily. A good way to visualise this is, if you cover half your cell phone screen and then uncover it - you haven’t gotten higher resolution, you’ve gotten more resolution.


Pixel Pitch:

This is where a lot of development has happened recently and where these aforementioned ‘other brands’ are catching or exceeding the established brands.  Currently, 12μm (micron) is the standard. The smaller the pixel, the higher resolution the device can capture data HOWEVER, smaller pixel pitch also means less sensitivity to temperature information. It is quite tricky to get your head around but put plainly, a 12μm sensor will give you exceptional clarity but may suffer a small drop-off in temperature detection performance in worse weather conditions like fog or heavy rain (because it is less sensitive to temperature, even though it is capturing more detail).

It can get a little granular and pixel pitch isn’t the only thing that contributes to the quality of your thermal optic, it is a combination of sensor size, pixel pitch, lens size/focal length (and aperture) and software processing. A figure very much worth paying attention to is the NETD value which is basically the sum of all the parts (sensor size, pixel pitch, lens size etc) represented as a value.


NETD Value (Noise Equivalent Temperature Differences)

This is a bit simpler to convey: the smaller the number, the higher the sensitivity. <35mk (millikelvins) is about the standard, at present. You will notice temperate gradients with a smaller NETD i.e. the chest, head and flank of an animal will be much brighter (because they are warmer) than the ears, hooves, tail of the animal (because they are colder). A high NETD value will represent this animal as a bit more of a solid blob of thermal information. Basically, low NETD means the device can distinguish between smaller differences of temperature. This can be very important in identification, especially at longer distances.


Other factors to consider:

Mounting options – this primarily concerns scopes; some devices mount with their own once piece mount designed for picatinny rails and some devices mount with standard 30mm ring mounts. Most handhelds also have the standard thread mount underside to attach to a tripod/bipod mount for if you do want to have the handheld mounted.

Batteries – internal vs removable. Both have pros and cons. Internal batteries are good because it is one less place for water ingress, with the con being if it runs flat you must charge it again before use, rather than just dropping in a fresh battery. Given the fact most people have USB spots/chargers in their vehicles or power bricks on hand, internal batteries aren’t something to be concerned with. Most units will give you 10-12 hours of runtime on internal battery too, which generally is ample time.

Rangefinders – many devices offer laser rangefinding capabilities. While not a vital feature, it is an extremely useful feature. Thermal optics have a tendency to mask distance more than regular optics, so sometimes it can be hard to distinguish just how far away that deer is. Plenty of devices that don’t have laser rangefinders have computer controlled stadiametric rangefinders which, while not perfect, do a solid ballpark ranging for you.

Thermal optics have become an intensely competitive market segment and like always, this competition brings technological advancement, specification novelty (like the Thermtec Dual Lens system) and more favourable pricing. It is time to very much consider a Thermtec, Guide or Infiray before some of the other brands because these devices offer incredible results at more reasonable prices – they have industry leading specification at a considerable discount over the ‘big brands’. Overall and most importantly, get one in your hands – look through it, play with the features and get a feel for how you like the unit. Thermal optics are hunting with cheat codes, they save vast amounts of time and effort and will yield you higher returns per hunting trip.