If you’re looking for a high-end thermal monocular or scope, you’ll have seen the acronym NETD followed by a number (e.g. < 25mK). This is not just another technical specification: it is the most important factor in defining image quality in difficult conditions.
What is NETD?
NETD (Noise Equivalent Temperature Difference) measures the thermal sensitivity of the sensor. It is expressed in millikelvins (mK).
Simply put: NETD indicates the smallest temperature difference the camera is able to distinguish.
- High NETD (e.g. 50mK): The sensor needs a lot of thermal contrast to ""see"".
- Low NETD (e.g. 20mK): The sensor is extremely sensitive and captures tiny details.
Why is a lower number better?
The lower the NETD value, the better the image. Imagine a day with rain, fog, or high humidity. In these conditions, the thermal contrast of the landscape is very low (everything is at a similar temperature), and water droplets act like a mirror, preventing the detection of thermal variations.
A device with a high NETD will show a ""gray blotch"" with no definition. A device with a low NETD (<25mK) will be able to capture the slightest temperature differences between the fur of a wild boar, the branches of a shrub, and the cold background, delivering a sharp image even without ambient contrast.
Device classification by NETD
- < 25mK (Current trend): Maximum definition. Able to see details such as antlers or fur in heavy rain. (e.g. Pulsar Telos / Helion range).
- < 35mK (Advanced models): The current quality standard. Excellent performance in most situations. (e.g. Hikmicro Falcon).
- < 50mK (Older models): Enough for detection in good weather conditions.
Our Recommendation
If you’re looking for maximum detail, visit our collection of High-Sensitivity Thermal Monoculars.