Practice

How far does a CCTV camera really see?

5 September 20263 min readcctvfinder

You are standing at the gate looking up at the camera on the wall of the shed. Thirty metres, at a rough guess. The question going through your head is always the same: would you make out a face on that? The salesman said “up to 50 metres” at the time. What he did not say was: up to 50 metres for what.

Why “range” in metres means nothing

Every camera sees infinitely far. A mountain on the horizon is in the picture, so is an aeroplane. The question is never whether something is in the picture, but how many pixels of it are left.

Which is why a camera does not have a range as a single number. It only has one together with a task. Out to twenty metres you may be able to see that someone is walking across the yard. Whether it was your own employee, you can no longer tell at twelve. And whether you could put a name to him in court is decided somewhere around six.

Three different tasks, three different ranges, one single camera.

DIN EN 62676-4 is what makes exactly that measurable. It translates every task into a pixel density, measured in pixels per metre where the action happens. Recognise demands 125 px/m, Identify 250 px/m. As soon as you know the task, range becomes arithmetic.

Range in metres, split by task

The table shows how far out a camera still manages each level. Calculated with a mounting height of 3 metres and at the head height of a standing person. The angle of view is on the left, because it makes the biggest difference.

Lens and resolution	Recognise (125 px/m)	Identify (250 px/m)
90° wide angle, Full HD	7.6 m	3.6 m
90° wide angle, 4K	15.3 m	7.6 m
60° standard, Full HD	13.2 m	6.5 m
60° standard, 4K	26.6 m	13.2 m
30° telephoto, Full HD	28.6 m	14.3 m
30° telephoto, 4K	57.3 m	28.6 m

Read the table across once and you see the essential thing. A 4K camera with a wide angle gets to 15 metres. The same resolution with a telephoto lens gets to 57. The camera is the same in both rows. What changes is the area it spreads its pixels over.

To double the range, halve the angle of view. It costs nothing extra and works immediately.

What shifts the numbers in practice

Three things come on top, and all three work against you.

Mounting height. The camera looks down at an angle, and the real line of sight is longer than the walk across the site plan. At six metres of height and ten metres of distance it is around eleven metres of sight line.
Viewing angle. Look down steeply at a person and you see the top of a head and a pair of shoulders. The pixels are there, the face is not.
Light. Pixels that disappear into the noise of a dark scene are not pixels. The table above holds for daylight.

Which is why the honest answer to “how far does the camera see” is always a question back: what do you want to see there, how high is it mounted, and how bright is it?

How to work it out for your own spot

You need three figures, and two of them you measure with a tape: the distance to the spot you care about and the planned mounting height. The third is the question of what you want to make out there.

The cctvfinder turns that into a pixel density and shows you in 3D the picture that arrives at that spot. If a face turns to mush there, it will turn to mush on the real recording too.