The frame (refresh) impacts things moving, and to be able to pan around, with any sort of speed.
If it is slow, it takes a moment for the thermal signal to show, and if the movement is fleeting (a rat crosses a small gap) may not even show what is there.
Resolution has a 'usable' range, so going above a set number of pixels does not guarantee better airgun use.
There is no point being able to count whiskers at 100m, when you just want to know what the animal is at 30m.
The main advantage of higher resolution is where something is partially visible, but it's orientation, or even identification is in question, but there are drawbacks to going higher resolution beyond the initial purchase cost.
For each generation of sensor, the higher the number of sensor pixels, the greater the required processing and, as a result the battery drain.
As electronics moves on, it tends to move towards lower power consumption, so the third generation of a scope normally has less power drain than the first, OR they have increased the resolution to the point where the battery drain is the same.
My take (which will be laughable in months) is that 384 is currently a good resolution for airgun ranges.
Lower resolution will still work, but often the lower resolutions are associated with lower refresh rates, so not only is it less distinct, it is slower to appear.
640 shows greater detail, and that detail may be of benefit for FAC airgun, or shooting at greater distances, but a 640 over a 384 at up to say 30m is not going to make much difference (IMHO).
The newer combined scopes like the DNT Thermnite have gone over to 21700 batteries, with their higher capacity, due to the processing required for both NV and thermal in one scope.
The generation of 640 spotter I have (Hikmicro Gryphon Pro LRF GQ50L) still uses 18650, I have wondered if the cartridge bands in my jacket would double as spare battery holders.
As it is I would not like to go for a stalk with only one spare battery.
As technology moves on (assuming we are not thrown into the dark ages again) the consumption goes down, but for those who go out for long sessions may benefit from a 'realistic' thermal resolution, over the awkward 'Battery low, range finding disabled' message that seems to arrive at just the wrong time.
The newer 1280 and beyond sensors look amazing, and if you have the money why not, but don't spend more on the part of the hobby that devalues quickest, if that extra grand or two would be better spend on something that will still have decent residual value, a couple of years from now.
Thanks for reading if you got this far.
This is mainly me, trying to talk myself out of, an obsession with the latest thermal kit.
I still walk around at night with any thermal, amazed at the technology.
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