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VIDEO SURVEILLANCE > Lenses
Choosing NSH lenses
There are two main
features related to camera lenses: Focal distance and Iris.
Focal distance
It determines the angle of view of the lens
and it's measured in millimeters. Lower the lens focal (e.g. 3 mm), higher
its wide-angle; higher the lens focal (e.g. 12 mm), higher its capability
to provide a focused picture. There are lenses with fixed focal, lenses
with predefined angle of view, and lenses with variable focal (named
VARIFOCAL), in which the angle of view can be adjusted within a predefined
range.
Iris
It's the aperture that allows the light to reach the lens.
Its dimension is related to a number named F-Stop. If the F-Stop is low
(e.g. F:1,2) the Iris is wide and more light will pass through the
lens, if the F-Stop is high (e.g. F:2) the Iris is narrower and less
light will pass through the lens. A lens with low F-Stop is suitable for
use with normal or low light, a lens with high F-Stop is not suitable for
use with low light, but it will be suitable for outdoor usage under
sunlight conditions. There are lenses with fixed Iris, with a precise
value of F-Stop, lenses with manually adjustable Iris, and lenses
with automatic Iris (named AUTOIRIS) able to automatically adjust to
light exposure.
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FIXED LENSES - Fixed focal and Iris
They are the most common used in the CCTV systems.
They have an excellent image quality and brightness. The focal,
that determines the angle of view, is fixed; many different focal
lengths are available in order to allow wide-angle or focused
shots. The Iris aperture is fixed and it's adjusted on an
average value to shot under conditions of average brightness (offices,
shops).
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VARIFOCAL LENSES - Focal and Iris manually adjustable
With these lenses, the focal (angle of view) and Iris aperture (exposure) are
manually adjustable using two metal rings. One metal ring is used
to adjust the angle of view, from wide-angle to zoom. The other
metal ring opens and closes the Iris to adapt the ambient exposure.
The main advantage is related to its versatility that allows the
same results of using different lenses for indoor shots in full
light and penumbra conditions.
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AUTOIRIS LENSES - Fixed Focal and automatic Iris
These lenses have a fixed focal, as for standard lenses; the Iris is automatically adjusted by
means of an internal motor that opens and closes depending to the
ambient light exposure. This allows the camera to shot under low
and full light conditions, avoiding shots too dark or clear. Auto-Iris lenses are essential for outdoor shots.
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VARIFOCAL AUTOIRIS LENSES - Focal adjustable and automatic Iris
These lenses inherit the advantages of auto-Iris and VARIFOCAL lenses.
The automatic Iris adapts to the light and shots well under full light and
penumbra conditions, allowing outdoor usage or under variable
light conditions. The variable focal allows perfect adjustment of
the area to be viewed. Certainly, they are the most complete
lenses, but also the most expensive.
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THREE MOTORS ZOOM - Remote control of Focal, Iris and Focus
These lenses have 3 built-in motors used to adjust the focal, Iris and focus. The
focal range is very wide, and with the highest zoom can reach a
value of 60 mm for use at long distances. These lenses are
controlled by means of 6 wires to be connected to a console, where
the user can operate in real-time looking at the monitor screen.
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MINILENSES - Lowest volume, fixed Focal and Iris
These are very small lenses, originally developed for mini-cameras,
predefined for a small socket named "type S".
The main advantages of mini-lenses are their small dimensions that allow the
use in very small volumes for hidden cameras applications. Mini-lenses are
generally mounted on small cameras, but may also be installed on standard
cameras (C or CS socket) using an adapter (always included in the package).
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PIN-HOLE MINI-LENSES - Miniaturized for hidden cameras
These lenses have to be used with totally hidden cameras, being able to shot through an aperture of 1
mm diameter. PIN-HOLE lenses have a fixed focal of 3.6 mm that
offers a wide-angle view. They are included by default in the
special hidden cameras with refined electronic Iris. We suggest
you to avoid their installation on standard cameras, even if
technically feasible, due to their lower brightness.
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IR LENSES - To be used with infrared illuminators
Using infrared illuminators with
standard lenses might encounter the FOCUS-SHIFT phenomenon (i.e. a
perfectly focused image in daylight will become slightly unfocused
at infrared light. IR lenses are specifically made to concentrate
both infrared light and natural light on the same focal plan, thus
allowing a precise focusing under daylight and darkness conditions. NSH
range of lenses includes varifocal IR lenses both manual iris and
auto-iris.
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