Welcome to the
"Technical Section"
of
Doktor Jons
Guide to Closed Circuit TV (CCTV)

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

If you thought CCTV cameras were complicated, Doktor Jon has some interesting news for you ... lenses are even worse! The thing about lenses is that whereas some people spend an absolute eternity deciding which CCTV camera best suits their needs, they then stick any old piece of glass on the front, simply to get a picture.

And yet the correct choice of optics is perhaps the key to good images. If you plonk a top quality lens on a crappy camera, the picture will probably look ok, but if you try it the other way around, apart from at best having seriously horrible pictures, it will almost certainly be a complete waste of money.

So what are the secrets for selecting the most appropriate lenses?
Well there are actually three main considerations:- a) camera location, b) lighting levels and c) imager format.
Now in practice there could be loads of other points worthy of consideration, but at the end of the day, remember these three and you're well on the way to achieving quality results.

Before we look at the "key three" , one very important point to consider is the lens mount.
All industrial CCTV lenses have a standardised screw thread mount which allows any lens to be fitted onto any interchangeable lens camera (the exception being normally PCB cameras, which accept a unique 'barrel' range of lenses. These basic optics are not high performance, and are therefore considered in more detail, elsewhere on this site).

Sounds nice and easy so far, but, and you just knew there had to be a but somewhere, the same threaded lenses are actually engineered as two different types; which are known in the industry as 'C' and 'CS' mount versions.

Both types of lens can be made to work on any CS mount camera, but the CS mount lenses will not work on C mount cameras. The explanation is actually quite simple (if you believe that, you'll believe anything!).

Decades ago when CCTV cameras were fitted with large format 'tubes', the lens mount (type C) was borrowed from the world of cinematography, that's film cameras to you and me.
So existing lens designs which were actually widely available for 16mm Cine cameras, could easily be adapted for use on CCTV cameras (2/3" = 16.9mm).

Continued>

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