F#: Acronym for F-number, which is the ratio of the focal length of the lens to its optical diameter. Smaller F-number lenses allow more light through; the phrase “stopping down the lens” refers to increasing the F-number, thereby allowing less light in and allowing the thermal imager to image objects at higher temperatures.
Fahrenheit: The unit of temperature in the English measuring system. 32° F is the freezing point of water at sea level, while 212° F is the boiling point. An increment of 1° F is equal to an increment of 1.8° C.
Fill Factor: The ratio of active detector area to total detector area.
FLIR: A military-derived acronym meaning “Forward Looking Infrared”. All thermal infrared cameras can be described as “FLIR” cameras (not brandname).
FOV: Acronym for Field of View, it is the total angular extent that a camera or imaging system can view.
FPA: Acronym for Focal Plane Array. Most modern imaging systems use an array of individual imaging elements (pixels). Collectively, this array of pixels is referred to as a focal plane array.
Frame: One of many still images which, when played rapidly, appear to display smooth motion (video). See Frame Rate.
Frame Rate: The rate at which frames are required, usually expressed in Hz. Standard NTSC frame rate is 29.97 Hz.
