What is F-Stop and Why is the F-Number of the Lens So Important

An f‑number (ƒ/#) or f‑stop refers to the ratio of a lens’s focal length to its aperture’s diameter (lens opening vs focal length) and indicates the amount of IR energy (heat) coming through the lens to the infrared sensor. The lower the f-number the larger the aperture diameter, meaning more thermal IR energy is reaching the infrared sensor.

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