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Guide to Closed Circuit TV (CCTV)

So would you like to play "Spot the CCTV Camera?". Eagle eyed visitors may recognise the profusion of street furniture, surrounding a single heritage dome camera keeping watch over part  of Londons' prestigious Oxford Street shopping area.

All you need to know about lenses,
for all types of video surveillance.

Most manual zoom lenses have three seperate control rings, one each for Iris, Zoom & Focus; however there are a limited number of Auto Iris manual zooms, which only provide manual control of the zoom and focus settings.


Unlike manual zooms, the motorised versions have small electric motors fitted to each of the control rings, so that the lens can be operated remotely either by direct drive or telemetry control.

Almost all modern lens motors now operate on 12v DC, although there are the occasional units that work on differing voltages.

In practice, most motorised lenses only require remote control over the zoom and focus settings, as ‘Auto Iris’ is now accepted as standard in almost all situations.

Incidentally it’s worth mentioning at this point that despite recent developments in camera technology, particularly domestic 'camcorders' ‘Auto Focus’ zoom lenses are still not a ready option to bolt on to an average CCTV camera, although some camera / lens modules are available with this option, and mostly used in Dome housings.

For an experienced CCTV operator, remote manual overide control of the iris can provide significant benefits during daylight hours, especially if fitted to a very high performance, high sensitivity colour camera; but in practice, this rarely if ever happens.

One particular option which is available on some motorised zoom lenses, is ‘preset positioning’. This relatively simple idea allows a system operator to program his control system (if compatible) to memorise key positional set ups. The idea is actually quite straightforward to use; if you want to turn a camera round to zoom in and focus on a preset point, having done it once, any subsequent repeat can be activated by the press of a button, and the system will inititiate the instructions automatically.

As advanced as this technology is, most control systems cannot achieve absolute total repeat accuracy time and time again, but having said that, modern control systems are far more accurate and usable, than those of even just a few years ago.

Information on covert 'pinhole' lenses>

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