2.8 vs 3.6 vs 6 mm lens and the DORI standard
The lens sets the balance between area and detail. On a 1080p camera, a 2.8 mm lens covers 103° and identifies a person up to 2.8 m; a 3.6 mm covers 87° and identifies up to 3.9 m; a 6 mm covers only 54° and identifies up to 7.4 m.
What DORI is
DORI is four levels of detail defined by the IEC 62676-4 standard, measured in pixels per meter of scene: detect (25 px/m), observe (62), recognize (125) and identify (250). Manufacturers publish the DORI distances of each model; the planner computes the same distances from the lens and the resolution.
Distances by lens and resolution
Camera 2.8 m high, face at 1.6 m:
| Lens | Resolution | Identify | Recognize | Observe | Detect |
|---|---|---|---|---|---|
| 2.8 mm (103°) | 1080p (2 MP) | 2.8 m | 6 m | 12 m | 31 m |
| 2.8 mm (103°) | 4 MP | 3.9 m | 8.1 m | 16 m | 41 m |
| 2.8 mm (103°) | 4K (8 MP) | 6 m | 12 m | 25 m | 60 m |
| 3.6 mm (87°) | 1080p (2 MP) | 3.9 m | 8 m | 16 m | 40 m |
| 3.6 mm (87°) | 4 MP | 5.3 m | 11 m | 22 m | 54 m |
| 3.6 mm (87°) | 4K (8 MP) | 8 m | 16 m | 33 m | 60 m |
| 4 mm (84°) | 1080p (2 MP) | 4.1 m | 8.4 m | 17 m | 43 m |
| 4 mm (84°) | 4 MP | 5.6 m | 11 m | 23 m | 57 m |
| 4 mm (84°) | 4K (8 MP) | 8.4 m | 17 m | 34 m | 60 m |
| 6 mm (54°) | 1080p (2 MP) | 7.4 m | 15 m | 30 m | 60 m |
| 6 mm (54°) | 4 MP | 10 m | 20 m | 41 m | 60 m |
| 6 mm (54°) | 4K (8 MP) | 15 m | 30 m | 60 m | 60 m |
How it is calculated
scene width = 2 × distance × tan(angle ÷ 2)
pixels per meter = horizontal pixels ÷ scene width
The distance used is the slant one, from the camera down to face height. A 1080p camera has 1,920 horizontal pixels; a 4K one, 3,840.
Which to choose
Use 2.8 mm in garages, yards and passages, where people walk close by. Use 3.6 or 4 mm on the facade. Use 6 mm to watch a gate from a distance. More resolution helps too: a 4 MP camera with a 2.8 mm lens identifies up to 3.9 m, against 2.8 m for 1080p.
The numbers in this guide come from the planner's model: pixel density per the DORI standard, each lens's typical field of view and average bit rates. Real cameras vary; check your model's data sheet.
Frequently asked questions
The data sheet's angle differs from the planner's. Which one counts?
Your model's data sheet. Select the camera and type the horizontal angle in the Field of view field.