A Visual Guide to Thermal Sensors

A Visual Guide to Thermal Sensors

Choosing which thermal imager to buy can be a very confusing process. There is plenty of information online but that becomes quickly outdated as newer models come out. We aim to try and demystify thermal technology and help people understand their needs and which unit would suit them best.

I am often asked what does X unit look like compared to Y, and it's hard to explain over the phone (or email!) so I thought this would be the best way to show the differences

I've taken photos from some current units that we sell to show you what image different sensors give. I have started with the minimum sensor size we would recommend for anyone wanting to look for birds, and work up. I took the pictures from the same position, and have the same tree on the bank in each shot (I had to pan either side to chase the mallard and moorhen)

I have stuck to two brands, Zeiss and Pulsar. There are plenty of other brands on the market but in our 10years experience in selling thermal, these two brands offer the best quality image, unit build and the best back up if anything were to go wrong. We proudly offer great customer service and this is only possible when we have good relationships with great companies who help us to help you.

Lets have a look at some images! 


384 x 288 Sensor

As mentioned before, this is where we recommend birders and ringers start when venturing into thermal. These units will allow for quick location of individuals with enough background information to help locate with a lamp, or binoculars.


Zeiss DTI 3/35 V2 384x288 17 μm ≤ 35 mK NETD  £2150



 Axion XQ35 Pro 384x288, 17µm, <25 mK NETD  £1639



640 x Sensor

 The two units here have similar sized sensors and are the two most popular units that we sell for birding. They are bigger units, with bigger lenses and give much more information on the heat source and the background. The are the go-to units for professional ecologists and surveyors.


Zeiss DTI 4/50 640x512 12 μm <25 mK NETD sensor £3100 

(The mallard had been spooked by this point sadly)

ZEISS 4/50


Pulsar Telos XP50 640x480, 17 µm <18 mK NETD sensor £3099



1024 x 768 Sensor

This sensor truly offers a huge amount of detail to the user. This particular unit is a set of binoculars which provide a very immersive experience and are built for viewing areas for longer periods of time. The size of the files are huge too - I was able to print images onto banners for Global Birdfair and could stitch together footage to display on the TV without losing detail. It also means that you can use the digital magnification and not loose lots of detail - important when surveying at further distances. These are a serious consideration for people wanting to record and share important footage.


Pulsar Merger XL50 1024x768, 12µm, <40mK NETD sensor £5,889.95



NETD Rating

There is more to a sensor than the size. I have explained more about the other specifications on the About Thermal page but one to note is the NETD rating. The lower this number is, the better image will be in foggy and rainy weather. Thermals do not like moisture and cannot see through it. Those of you who have used older thermal units will know that the image can quickly go grainy and cloudy when the weather turns. Newer units have lower NETD rating which deal with moisture much better. 

The Pulsar Telos has the lowest (an astonishing <18mK) so if you are in a coastal area or monitoring around water then this would be an important factor. The Pulsar Merger XL50 though, with the huge 1024x768 sensor have a rating of <40mK which wouldn't be as good in rain. 

The day that I took these pictures there was some fog in the air. Due to this the images on both the Zeiss DTI units are slightly grainer than they are in dry conditions. The Pulsar units with similar sensors have better NETD ratings so do give clearer images. The Zeiss images still show great amounts of detail and depth though -you can actually see the hollow part of the tree trunk better with the Zeiss DTI 4/50 than the Pulsar Telos. 

All of the units shown above would be perfectly usable for birders and ringers. The main decider is your budget and what species size, and distance you would be using it at. If smaller and further then you would want to jump up to a 640x480 sensor if possible. If you are a professional and need to record and share footage then the 1024x760 would be the best bet.


Thanks for reading




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