Lens & Coverage Geometry Calculator

Lens and Coverage Geometry Calculator

Lens & Coverage Geometry Calculator

Pick the right focal length for Detect / Observe / Recognize / Identify per IEC 62676-4.

Inputs

Results

Required pixel density-
Maximum scene width-
Required horizontal FoV-
Recommended focal length-
Adjust inputs to see a lens recommendation.

How this works

  • IEC 62676-4 defines pixel density targets for surveillance tasks. Detect = a person is present. Observe = action visible. Recognize = match to a known person. Identify = positive ID of a stranger from the footage.
  • Given resolution and the required pixel density, we compute the maximum scene width the camera can cover while still meeting the task.
  • Given the distance and the maximum scene width, the required horizontal field-of-view (FoV) and focal length are calculated from sensor width using focal = (sensor_width × distance) / scene_width.
TaskPixel density (px/m)Pixel density (px/ft)Typical use
Detect25~8Motion alarm, fenceline awareness
Observe62~19Crowd flow, package presence
Recognize125~38Known person matching
Identify250~76Court-admissible positive ID
Sensor width (mm) drives focal length: 1/2.8" = 5.0mm, 1/2.5" = 5.7mm, 1/2" = 6.4mm, 1/1.8" = 7.2mm. Larger sensors capture more light and require longer focal lengths for the same FoV — a key trade-off for low-light coverage.

Worked example

Goal: recognize a face at 40 ft using a 4MP camera with a 1/2" sensor:

  • Recognize target = 38 px/ft
  • Camera horizontal resolution = 2560 px
  • Maximum scene width = 2560 px ÷ 38 px/ft = ~67 ft
  • Required horizontal FoV = 2 × arctan((67 / 2) / 40) = ~80°
  • Focal length = (6.4mm sensor × 40 ft) / 67 ft = ~3.8mm

A 3.6mm fixed lens delivers ~85° FoV on a 1/2" sensor — close enough. For tighter framing pick a 4mm or 6mm lens. Any 2.7-13.5mm motorized varifocal in the IPSD catalog covers this case with room to spare.

Recommended IPSD products

Fixed Lens Cameras
Fixed 2.8mm, 3.6mm, 4mm, 6mm options for known scenes
Motorized Varifocal
2.7-13.5mm or 4.3-129mm zoom for flexible commissioning
PTZ Cameras
Optical zoom 20x-44x for long-distance identification tasks
Multi-Sensor Cameras
Four sensors per dome — combined >180° with identification-grade density

FAQ

Why use IEC 62676-4 over the old DORI standard?

DORI (Detect / Observe / Recognize / Identify) is the original informal standard. IEC 62676-4 formalizes it with measurable pixel density targets that map to legal-evidence usability. Both use the same terminology; IEC adds numbers.

Does this account for lens distortion?

No. Wide-angle lenses (under 3mm) introduce barrel distortion that warps the edges of the frame. Pixel density in the corners is lower than the center. For identification tasks, design with the center 70% of the frame. Fisheye and panoramic cameras have specialized dewarping and their own coverage models.

What about angle and height?

The calculator assumes the subject is roughly perpendicular to the lens axis. Cameras mounted high and aimed steeply downward foreshorten subjects; effective pixel density on a vertical face decreases. Rule of thumb: keep tilt angle under 30° for identification work, under 15° for license plate capture.

How do I cover a 200-foot parking lot?

Detect-only at 200 ft with a 4K camera works with about a 12mm lens. Recognize-grade at 200 ft requires a long-focal-length camera (30mm+) which gives you a narrow scene — you cover one lane, not the whole lot. Use multiple cameras or a multi-sensor panoramic.

Does the calculator handle vertical scenes (corridors)?

The math is the same — just use the corridor mode FoV figure from the camera datasheet, which rotates 90°. Hanwha and Axis call this "corridor format" or "hallway view."

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