Are Cheap CCTV Lenses Ever Acceptable?
SEN Help Desk has made some interesting points about lensing lately but wouldn’t you agree that even with relatively low cost lenses attached to compact cameras there’s a sweet spot in the centre which offers universally high performance? Given this, is lens selection as important as you suggest?
Answer: We’d reiterate that low cost lenses with good, simple designs without too much internal tolerance (in the case of varifocal) and with suitable coatings against internal reflections can offer unexpectedly high performance. So we may well agree with you. But if you mean that poor performing lenses with excessive barrel distortion, vignetting, chromatic aberration and flaring from lens elements and/or housing windows or dome bubbles, can be excused their deficiencies thanks to a portion of admissible image that comprises say, 50 per cent of the camera view, we think not.
Yes, flaws can be accommodated by adjustments to viewing angle to ensure redundant parts of the scene are those worst affected by poor lens design but there are going to be open-ended compromises in your image streams which might deny face recognition at short ranges, at night, at wider angles of view, out at the edges, or during digital zooms. Cramp bit rate and/or frame rate over an under-resourced network or storage solution, and reduce levels of light, and the performance of poorly designed lenses will be weaker still.
As security managers know, many incidents take place at the edges of scenes. Assaults in particular unfold at unusual angles to the traffic flow expectations that governed camera view selection during system design and commissioning. And attackers often wait in areas of low light on the edges of public space for victims. End users may have to tolerate poor lenses – especially in compact domes or bullet cameras bought in bulk on the basis of price – but they’ll pay an operational price during investigations – that’s not an opinion, it comes down to the laws of physics.
The fact quality PTZs from practically all manufacturers offer excellent performance suggests it’s not that quality lens technology doesn’t exist but that low price and low performance are directly related. Of course, that’s not always the case. There are some excellent lenses in compact cameras. Objective testing tells you which is which. ♦