Is a wider lens always better for security cameras?

No. A wide lens covers more area but spreads pixels thinner, reducing the distance at which you can recognize or identify anyone. Good designs mix wide overview cameras with narrower detail cameras at choke points like doors.

Lens & Field of View Calculator

Q: What focal length do I need to identify a face?

It depends on sensor, resolution and distance. As a rule of thumb, a 4MP camera with a 2.8mm lens can only identify within about 4–5 metres. For longer identification distances you need a narrower lens (6mm, 12mm) or higher resolution.

Convert focal length and sensor size into field of view, scene width at a target distance, and pixel density (px/m or px/ft) — then check the result against the DORI standard to see what the camera can actually do at that distance.

Camera details

Sensor size

1/2.8″ is the most common sensor in 2–4 MP cameras.

Horizontal resolution (px)

Focal length (mm)

Fixed lenses: 2.8 / 3.6 / 4 / 6 / 8 / 12 mm are common.

Target distance

Units

Results

—

pixel density at — → —

Horizontal field of view—

Scene width at distance—

Max distance — Identify (250 px/m)—

Max distance — Recognize (125 px/m)—

Max distance — Observe (62.5 px/m)—

Max distance — Detect (25 px/m)—

DORI levels per EN 62676-4. “Identify” means enough detail to identify an unknown person beyond reasonable doubt.

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Understanding DORI

The EN 62676-4 standard defines four levels of image usefulness based on horizontal pixel density on the target:

Level	Pixel density	What it means
Detect	25 px/m (~8 px/ft)	You can tell a person or vehicle is present.
Observe	62.5 px/m (~19 px/ft)	You can see characteristic details — clothing colour, general behaviour.
Recognize	125 px/m (~38 px/ft)	You can recognize someone you already know.
Identify	250 px/m (~76 px/ft)	Enough facial detail to identify an unknown person for evidence.

The single most common CCTV design mistake is mounting one wide-angle camera and expecting it to both cover a whole parking lot and identify faces. Pixel density falls off linearly with distance — a camera that identifies at 5 m only observes at 20 m. Professional designs use wide lenses for overview and narrow lenses (or higher resolution) at choke points: doors, gates, tills and corridors where every subject must pass.

Frequently asked questions

What is DORI in CCTV?

DORI (Detect, Observe, Recognize, Identify) is the EN 62676-4 standard for image usefulness, defined by minimum pixel densities on target: 25, 62.5, 125 and 250 px/m respectively.

What focal length do I need to identify a face?

It depends on sensor, resolution and distance — that's exactly what this calculator solves. As a rule of thumb, a 4 MP camera with a 2.8 mm lens identifies only within ~4–5 m; use 6–12 mm lenses or higher resolution for longer reach.

Is a wider lens always better?

No — wider coverage spreads pixels thinner. Mix wide overview cameras with narrower detail cameras at the points people must pass through.

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AMT SYSTEMS LTD. does free on-site assessments across Toronto & the GTA and designs camera layouts to meet identification requirements at the points that matter.

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