Can you explain how to work out the range of a CCTV camera ?

The first thing to say is that it has very little to do with the Infra-red illumination fitted. This may seem strange because most companies refer to cameras based on their infra-red range. You can more or less put any number you like on the I/R range. The way I/R works is that it hits a surface and illuminates it. If it illuminates an object at 10 metres it will still provide some illumination at 15 metres or even 20 metres. At what point you say there isn't enough I/R light to work properly is pretty much up to you. It also depends on how sensitive the electronics are within the camera. Our 0.01lux CCD / DSP combinations are 50 times more sensitive than a 0.5lux CCD / DSP for instance. So you can see why we don't put too much importance on quoted I/R range figures.

Actually the most important thing which determines a camera's effective range is the lens fitted to it. The actual numbers depend on which size of CCD image sensor is fitted but the smaller the focal length of the lens the wider the angle of view. As a guide a 3.6mm lens on a 1/3 inch CCD image sensor will give around an 80 degree angle of view, on a 1/4 inch CCD this figure drops to around 60 degrees.

Why does the angle of view determine a camera's effective range? Well elsewhere on the site we explain how there are a given number of available pixels per recorded picture frame. In D1 resolution this equates to around 400,000 pixels, (in CIF it falls to 100,000). If you have a wide angle lens you spread the pixels very thin especially if you move away from the camera. With a wide angle lens you don't have to move far away from the camera before you become unrecognisable because not enough pixels are being used to represent your head on the screen.

Of course different applications require different levels of detail to be recorded, a home cctv system may have different requirements to a system fitted in an airport but in both cases there is simply no way a wide angle camera lens is going to give useful information a long way from the camera. Let's imagine we want to read a vehicle number plate. Many people sell cameras which claim to be able to do this but the problem is their product information is misleading. They may have a 4-9mm lens camera which has an I/R "range" of 20-30 metres and the camera claims to be able to capture a number plate. The problem is that at the most zoomed in a 9mm lens is never going to be able to read a number plate at anything like 20 or 30 metres. To give you an idea our 9-22mm equipped cameras are able to capture registration numbers up to a maximum distance of 15 metres when recording in D1 resolution. Beyond that distance you need to be using our 6-60mm lens cameras.

So ultimately the lens on the camera is going to determine it's maximum effective range. The actual distance will depend on the amount of detail you want to capture so it is impossible to say a particular camera has a range measured as an absolute number but in general terms the larger the focal length of the lens, the further away it will be able to record.