The Size of the Thermal Core or Detector is one of the key elements of any thermal cameras performance.
Simply put the more pixels you have for the same field of view the better the image is going to be.
A 320×240 Detector has 76,800 Pixels.
A 384×288 has 110,592 Pixels (44% more)
A 640×480 has 307,200 Pixels (400% more)
As you can see even the increase from 320 to 384 has resulted in a large number of extra pixels, of course a 640 is nearly 3 times as much again.
The overall magnification and Field of View also comes down to what Lens is installed as well – that’s another topic in itself