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Power zoom lenses used to be prohibitively expensive; now, thanks to developments in consumer video equipment, theyíre becoming a viable option in cost-sensitive surveillance installations



CCTV lenses have changed little in the past thirty or so years but a quiet revolution is underway. Itís being fuelled by on-going developments in domestic camcorder design, where manufacturers are spending considerable amounts of time and money developing ever smaller and more flexible optics. Power zoom lenses used to be heavy, bulky devices, suitable only for the most critical, cost-no-object installations using heavy-duty cameras and mounts, but thatís changing.


The latest generation of CCTV power zooms are not much larger or heavier than conventional fixed lenses. Power requirements are usually quite modest, so there are few, if any problems with longer cable runs. Generally speaking these reductions in size and weight have not been at the expense of performance, quite the opposite in a lot of cases.


The Rainbow EX-H6X8.5 MGE 6x power zoom is a fairly typical example. Itís small, just 80 x 65 x 65mm, and it weighs just 180 grams. Itís fitted with a standard CS mounting collar, and has a pre-wired zoom/focus connections, terminated in a lockable 4-pin socket; an unwired female connector is supplied, along with a lead and plug for the auto-iris connection to the camera. The case is made from a tough ABS plastic, as are most of the rest of the internal components.


There are just three adjustments, accessed through a slot in the side of the case, protected by a rubber bung. These are for automatic level control (ALC), sensitivity or level, and gain or response speed. These are all factory-set for optimal performance under a wide range of conditions; the instruction sheet contains brief details for fine-tuning and the requirements for the control unit.  


The standard of construction is generally very high; the built-in control electronics are mounted on a single glass-fibre PCB next to the auto-iris socket. The motors, gear trains and iris actuator operate smoothly and almost noiselessly. Installation is very straightforward and our sample functioned perfectly well on the factory defaults.



The quality of the optics is excellent. The image is bright and clean, with no significant internal reflections. Linearity is also good with negligible barrelling at the edges at the Ďwide angleí setting. The zoom is smooth and fairly sedate, taking just under 10 seconds, to move from the wide-angle setting to maximum zoom. The focusing action is very well damped, for precise manual adjustment.



Zoom lenses used to be an expensive option, used sparingly on critical installations. The compact optics of the Rainbow MGE range are well suited to smaller cameras on lightweight motorised mount, bringing the considerable benefits of a power zoom to a much wider market.





Magnification            6x

Focal range                   8.6 - 51mm

Aperture                        f1.8

Fitting                           CS

Iris                                DC controlled

Controls                        gain, ALC, level



Zoom/focus                   4-wire control

Iris                                standard 4-pin connector                     


Dimensions                   80 x 65 x 65mm

Weight              180 grams, excluding cable

Mount                           standard 1/4-in BNC threaded collar





Product design            8

Build quality                  9

Ruggedness                  8



Instructions                   7

Manuf. support                          



R. Maybury 1996 1509




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