Detection range
The maker's figure for how far away a warm object shows up as a dot or two. It is far longer than the distance you can tell what the animal is.
What it means
Detection range is the distance at which the device can show that something is there, usually as a pixel or two brighter than the background. It does not mean you can see what it is. Hunting thermals commonly claim anywhere from about 1,300 to over 3,000 yards.
How makers get the number
Detection range is almost always calculated, not measured on animals. The usual method uses Johnson’s criteria: a target about the size of a standing person, roughly 6 feet tall, covering about 1.5 pixels, with a 50 percent chance an observer notices it. A coyote is a much smaller target.
Methods differ. Published research comparing calculation methods found at least nine in use, with results differing by up to about 30 percent. Makers rarely say which they used or what target size they assumed, so two detection figures from different brands are hard to compare.
For digital night vision, the condition matters even more. Some makers measure with the infrared illuminator on, some in daylight, and some don’t say. A daylight figure says little about what you will see at midnight.
What it changes in the field
Detection is useful in one way: a long-detecting unit will show you more warm dots across a big field. But the decision to shoot rests on identification, which comes in at a fraction of the box figure. On this site the gap is easy to see: a common 50 mm, 384-pixel scope is rated to detect at close to 2,000 yards, and our identification estimate for it is about 150.
How we use it on this site
We show the maker’s claim, labeled as theirs, and do not score it. For night vision we show the condition it was measured in when the maker states it. Our own identification distance is the number to compare across models.