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Guide to Closed Circuit TV (CCTV)

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


VARIFOCAL LENSES for Industrial CCTV Cameras (continued)


The bottom line of course, is that if the camera is looking at a fixed view, there is nearly always going to be a quality fixed optic available that can fulfil the requirements, without necessarily having to resort to a varifocal.

For the inexperienced, they are undoubtedly extremely useful, but for the serious end of the industry, they’ll rarely be the first choice of lens. In general, most varifocals only have a relatively short ‘range’, for example the 3.5 - 8mm, generally with a ratio from shortest to longest focal length, of perhaps 2 or 3 :1.

There are a limited number of extreme varifocals that go up to about 10:1 or more (for example a 5 - 50mm lens), but to be honest, in some situations you may be better off using a proper zoom lens.

It should perhaps be mentioned at this point, that whilst varifocals are increasingly being fitted to cameras "off the shelf" as a complete package, the fact remains that the latest varifocal designs, are significantly better quality than some of the rather poor offerings available in the not so distant past..

So what exactly is the differance between a ‘short’ zoom and a ‘long’ varifocal; well it’s all to do with elements.

Any complex lens is actually made up of individual pieces of glass called ‘elements’, which are themselves arranged in ‘groups’.

With a varifocal, one or more fixed groups are moved in relation to another; whereas with a zoom lens, individual elements (lenses) and groups can move to create complex relationships to each other.

This latter more sophisticated degree of optical design, does generally produce a much better quality, and more highly corrected approach to achieving top quality images.

 

Manual Zoom Lenses>

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