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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.

VARIFOCAL LENSES for Industrial CCTV Cameras (continued)

So far we’ve looked specifically at the options for controlling the amount of light passing directly through the lens; manual iris, Direct Drive and Auto Iris all control the eventual exposure at the cameras imager. If we now consider the basic difference between the various lens groups, there are essentially three main types available (Fixed focal length, varifocal and zoom).

Fixed focal length lenses, can only produce the degree of coverage which is dictated by their optical design.

So for example, on their respective format imagers:-
6mm (1/4”) 8mm (1/3”) 12mm (1/2”) 16mm (2/3”) and 25mm (1") will all produce a coverage (or view) very similar to that of the human eye, and this is what is termed a
'standard' lens. Any lens with a shorter (smaller) focal length is a 'Wide Angle', and longer (greater) is a 'Telephoto'.

For most static camera applications, these fixed ‘focal length’ lenses should still be the preferred choice for CCTV professionals, equipped with the knowledge and experience to get the best out of them.

However, in recent years Doktor Jon has noticed an increasing shift towards the CCTV industry’s reliance on ‘varifocal’ lenses for a wide range of applications.

Varifocal lenses are best considered as a very basic type of ‘zoom’ lens, although to be strictly accurate there is a significant difference in the way they function. For an inexperienced, or possibly even lazy installer, varifocals can provide a simple method for framing the image, without having to fiddle around trying different lenses.

Unfortunately, there is no such thing as a free lunch, and Doktor Jon would have to say that with few exceptions, a varifocal will not produce the level of optical quality possible using fixed focal length optics. You might consider that most varifocals carry a premium cost over a single (correctly chosen) fixed lens, but then the normal argument put forward is that they’re a lot cheaper than the two or three fixed lenses needed to provide an equivalent degree of coverage.


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