384 or 640: what does sensor resolution actually buy you?
Updated 2026-09-20
Resolution buys you range and field of view at the same time, and nothing else. A 640-wide sensor puts 2.8 times as many pixels on the scene as a 384, so behind the same lens it either sees a wider slice of the field at the same detail, or the same slice at 1.67 times the range. It does not make the image sharper per pixel, it does not improve sensitivity, and inside 150 yards on hogs or coyotes a 384 with a good lens is not the thing holding you back.
Pixels are pixels; the lens decides what they see
A thermal sensor is a grid of tiny thermometers — 384 by 288 of them, or 640 by 512, or 1280 by 1024. Each one reports the temperature of whatever part of the scene the lens paints onto it. How big a slice of the world one pixel covers is fixed entirely by the pixel's physical size and the lens's focal length: a 12 µm pixel behind a 35 mm lens sees 0.34 milliradians whether there are 384 of them across or 640. What resolution changes is how many of those slices you get. More slices, wider view — or, put a longer lens on and trade the width back for range.
The 1.67 rule
640 divided by 384 is 1.67. That is the whole comparison. Behind identical lenses, a 640 shows 1.67 times the horizontal field of view. Put a 1.67 times longer lens on the 640 and it shows the same field of view as the 384 with 1.67 times the range at every Johnson level — detect, recognize, identify. Every unit in this catalog has those three ranges computed on its page, so the comparison is a matter of reading two numbers rather than believing a box.
What resolution does not do
It does not lower the noise. Sensitivity — the NETD figure — is a property of the pixel design and the electronics, and a cheap 640 can be noisier than a good 384. It does not make the image crisper: an image with more pixels on a small display is still limited by the display, and by the eyepiece, and by your eye. And it does not change how hot the animal has to be against its background to show up at all; that is contrast, and contrast is weather.
When 384 is the right answer
Inside about 150 yards, on hog-sized or coyote-sized animals, from a fixed position. A 384 with a 35 mm lens recognizes a coyote-sized target at roughly the distance most people actually shoot one, costs a third to half what a 640 does, and the money saved buys a rangefinder or a second battery. Where the 640 earns its keep is scanning big open ground, where its wider view means fewer passes and its extra reach means you see the animal before it sees you.
And 1280?
A 1280 core doubles the pixels again, and the same arithmetic applies — twice the reach of a 640 behind the same lens, or twice the field. The cost is a large sensor die, which needs a large germanium lens to cover it, which is heavy and expensive. It is the right tool for open-country scanning from a truck and the wrong tool to carry up a ridge.