Camera Max Distance for a Pixel Density (DORI)
The inverse of the camera-lens-fov tile: the farthest distance a camera still meets a target pixel density (a DORI task), distance = px x focal / (target ppf x sensor). A 1920 px camera with a 4 mm lens on a 5.37 mm sensor holds 76 ppf (Identify) out to about 18.8 ft; drop to 38 ppf (Recognize) and it doubles to 37.6 ft. Answers 'how far can it Identify' instead of the density at a set distance. FOV is fixed by the lens. A design aid; verify against the lens chart, low light, and a live view.
Formula and source
max_distance = h_pixels x focal_length / (target_ppf x sensor_width), the inverse of ppf = h_pixels / (distance x sensor_width / focal_length); fov = 2 x atan(sensor_width / (2 x focal_length)); DORI band by ppf (8 Detect / 19 Observe / 38 Recognize / 76 Identify).
IEC 62676-4 (Video surveillance systems - Application guidelines) DORI criteria, by name, solved for the distance; first-principles thin-lens field-of-view geometry.
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