Thread: Thermal advice

There are three things you look for in a thermal rifle scope:

* Noise Equivalent Temperature Difference (NETD) - it dictates how well your thermal detects something.
* pixel size, it directly affects the resolution of the target that you want to see. Currently there are only the 17µm and 12µm. The smaller the more resolution.
* aperture, it affects your scope's reach. this is because almost all thermal scopes have a fixed aperture ratio of F1.0~F1.2. Basically a 25mm scope will have half the reach as a 50m scope.

Thermal rifles scopes have no optical zoom. The absolute optical reach is always limited by focal length (which is limited by aperture) and pixel size.

This means you must choose between reach and FOV. it is one or the other for the same price. if you want both, you need to pay more for a scope with larger sensor (of the same pixel size).

Currently the smallest sensor size is about 320 x 240, while the largest is 1280x1024.

So for example, if you have compare two scopes both having 50mm aperture and and 12µm sensors , one has a sensor of 320x240 and the other 1280x1024. They should give you the same clarity on the same target from the same distance, but the 1280 one should have over 4 times the field of view, you see far more at once. It helps a lot with target acquisition. But it will probably cost 4 times the price.

Also for example, if you have compare two scopes both having 50mm aperture and 640x480 sensors, one has a 12µm sensorand the other 17µm. From the same distance, the 12µm one should have about 40% higher resolution on the target, while 17µm will give you about 40% more FOV.

I have a 50mm 320x240 12µm ATN Mars LT. Using it to scan fields is fine, but scanning trees is a pain. Once you find a target, the clarity is excellent.