CCTV lens calculator
Pick the right lens before the ladder comes out: field of view, scene width and pixels-per-metre at your distance, verdicted against the DORI identification thresholds.
Field of view
85°
horizontal angle
Scene width at 10m
18.2 m
what the frame covers
Detail level
141 ppm
Recognise: can recognise someone you know; read a plate
| DORI level | Needs | This setup |
|---|---|---|
| Identify | ≥ 250 ppm | up to ~5.6 m |
| Recognise | ≥ 125 ppm | Yes |
| Observe | ≥ 62 ppm | Yes |
| Detect | ≥ 25 ppm | Yes |
Reading the result
A wide lens (2.8mm) sees a lot and identifies little; a telephoto (12mm) identifies at distance through a keyhole. The DORI thresholds (IEC 62676-4) turn that trade-off into numbers: 250 pixels per metre to identify a stranger, 125 to recognise someone you know or read a plate, 62 to observe what happened, 25 to detect movement.
The practical pattern: a wide lens at the door for context, and a tighter lens (or a higher-resolution camera) on the approach path where identification matters. Where one camera must do both jobs, a varifocal model lets you set the compromise on site.