Free tool · IT & Security
CCTV lens & DORI calculator
Choose the right lens: see how wide a camera sees at a given distance and whether it can detect, observe, recognise or identify a person.
How it’s calculated
The method, in plain terms.
Horizontal field of view = 2 × arctan(sensor width ÷ (2 × focal length)). The scene width at a distance is distance × sensor width ÷ focal length, and pixels per metre = horizontal pixels ÷ scene width.
The DORI levels from IEC 62676-4 are: Detection 25 px/m (is someone there?), Observation 62 px/m (what are they doing?), Recognition 125 px/m (is this someone we know?) and Identification 250 px/m (who is this, beyond doubt?).
- Entrances and billing counters usually need identification.
- Corridors and floors usually need observation.
- Perimeters usually need detection, with alarms or analytics.
What does DORI mean in CCTV?
DORI stands for Detection, Observation, Recognition and Identification — pixel-density levels defined in IEC 62676-4 that describe what a camera can usefully show at a given distance.
Is a 2.8 mm or 4 mm lens better?
A 2.8 mm lens sees wider but with fewer pixels on each person; a 4 mm lens sees narrower but further. Choose by what each camera must achieve.
Do I need a varifocal camera?
Varifocal lenses let the installer set the exact field of view on site — useful for gates, car parks and long corridors.
Does a higher-resolution camera always see further?
More pixels raise pixel density at the same field of view, but lighting, lens quality and compression matter just as much.
Get in touch
Want us to design the full system?
Send us your calculator result and site details — we’ll survey, specify the right equipment and send an itemised quote.
- Call+91 98913 73456
- Emailinfo@goldensolutions.in
- Visit5/1, New Rohtak Road, Anand Parbat Industrial Area, New Delhi 110005