RAINBOW MGE ZOOM LENS
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.
Focal range 8.6 - 51mm
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
” R. Maybury 1996 1509