NETD (thermal sensitivity)
How small a temperature difference the sensor can show. Lower is better, but brands measure it differently, so numbers from two makers are not a fair comparison.
What it means
NETD stands for noise equivalent temperature difference. It is the smallest temperature difference the sensor can tell apart from its own electronic noise, given in millikelvin (mK, a thousandth of a degree Celsius). Spec sheets list it as a ceiling, for example “<25 mK”. Hunting thermals commonly claim somewhere from under 15 to under 50 mK.
What it changes in the field
A more sensitive sensor gives a cleaner, more detailed picture when contrast is low: fog, drizzle, high humidity, or summer evenings when the ground and the animal are close to the same temperature. On a cold, dry night most units show a coyote clearly regardless of NETD. Sensitivity matters most in exactly the weather that makes thermal hard.
Why the numbers don’t compare
There is no single test everyone follows. Makers choose the lens f-number, the scene temperature and other test conditions, and those choices move the result. Some publish the bare sensor figure; others publish a system figure after image processing, which usually looks better. At least one maker now lists both side by side, and on one of its models the system figure is half the sensor figure. A “<15 mK” from one brand and a “<25 mK” from another may describe sensors that perform about the same.
Hunters on forums rarely rank NETD high. Reviewers and marketing push it harder than buyers do.
What to look for
- Compare NETD only within one brand, where the test method is likely the same.
- If you hunt humid country, brush or summer nights, give it more weight.
- Read a published sample video in conditions like yours over a spec line.
How we use it on this site
We show the maker’s claim and do not score it. A wrong comparison is worse than none.