FOV, IFOV, and IFOVmeasurement.
FOV, or Field of View, is the largest area that your imager can see at a set distance. It is typically described in horizontal degrees by vertical degrees—for example, 23º X 17º. (These “degrees” are units of angular measurement, not to be confused with the degrees of temperature measurement.) Essentially, it is like a rectangle extending out from the center of your camera’s lens extending outward. The farther away you look, the larger the rectangle becomes.
Think of Field of View as the windshield that you are looking out as you drive your automobile down the road. You can see everything from the top of the windshield to the bottom, and from the left to the right.
IFOV, or Instantaneous Field of View (otherwise known as Spatial Resolution), is the smallest detail within the FOV that can be detected or seen at a set distance. This means that at a certain distance, you may not be able to see certain small details if your Spatial Resolution is not good enough.
Think of IFOV as the ability to see a roadside sign in the distance (through your windshield). You can see that it is a sign, but you may not be able to read it when it first becomes recognizable. IFOV is typically measured in units called milliradians (mRad). Milliradians are small fractions of an angular degree.
IFOVmeasurement, or Instantaneous Field of View Measurement (otherwise known as Measurement Resolution), is the smallest detail that you can get an accurate temperature measurement upon at a set distance.
Assuming that you do not have the power to make the object itself bigger, in order to “read” the temperature measurement more accurately, you usually need to be closer to the object… either physically or optically. IFOVmeasurement, or Measurement Resolution, is also typically specified in milliradians, and it is often two to three times more than the specified Spatial Resolution.
Infrared imagers, like photographic cameras, can often have different kinds of optional optics and lenses that will allow you to change your Field of View, Spatial Resolution, and Measurement Resolution. Telephoto lenses magnify the scene and bring you “optically closer”, but generally make the Field of view narrower. Wide-angle lenses, on the other hand, give you a much wider Field of View, but you may not be able to see the same level of detail.