Some
information to help you choose from the DSE range of lenses
DSE
offers a vast range of different lenses. There are two factors which
differentiate the different types are focal length and size of
diaphragm.
Focal length
This is measured in millimeters and determines the viewing angle of the
lens. The shorter the focal length (eg 3 mm), the wider the viewing
angle is, while longer it is (eg 12 mm), the greater the zoom. There are
lenses with a set focal length, which therefore offer a single viewing
angle, and lenses with a variable focal length, where the viewing range
can be adjusted, known as VARIFOCAL lenses.
The iris
This is the hole in the lens that the light passes through. The size of
the iris is expressed as a number known as F-Stop. If the F-stop is low
(eg F:1.2), this means that the iris is large and lets in more light,
while with a high F-stop (eg F:2), the iris is small and lets in less
light. There are lenses with a fixed iris, with a set F-stop, lenses
with a manual iris, and lenses with an automatic iris known as AUTOIRIS,
which adjust automatically to the amount of light present.
The various types of lens
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FIXED LENSES - Fixed focal length
and fixed iris
These are the lenses most commonly used in CCTV systems offering good value for money.
The focal length, which determines the viewing angle, is fixed, but
there are different focal lengths available, offering wide angle
views or more zoom. The aperture of the iris is also fixed,
with a medium setting suitable for filming in average light
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VARIFOCAL LENSES
- Adjustable focal length and manual
iris
In these lenses the focal length (which
determines the viewing angle), and the aperture of the iris
(which determines luminosity) can be adjusted by means of two
setting rings. One is used to adjust the viewing angle, from wide
angle to zoom, while the other opens and closes the iris to
adapt it to the amount of light.
These lenses cost more than those with a fixed focal length, but
they enable you to film any setting in the best possible way,
whether in full light or dim light, and a large or small area, using
only one lens.
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AUTOIRIS
LENSES
-
Fixed focal length and automatic
iris
These lenses have a fixed focal length, like
standard lenses, and there are versions offering a variety of
viewing angles, from wide angle to zoom.
The iris is automatically controlled by an internal motor
which opens and closes it according to the conditions of light.
The camera itself control the autoiris motor through a connection cable on the base of the amount of light that reach the CCD.
This enables the camera to film in an optimum way, whether in
semi-darkness or full sunlight, avoiding excessive darkening or
lightening of the image. Therefore Auto-iris lenses are recommended for
outdoor use.
It's good to remember that nowadays cameras come with advanced electronic shutter that enables you to film outdoor with pretty good result with fixed iris lens.
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VARIFOCAL AUTOIRIS
LENSES
- Adjustable focal length and
automatic diaphragm
As the name suggests, these lenses combine the
advantages of an auto-iris lens with the advantages of a VARIFOCAL
lens. The automatic diaphragm adapts to the light and films well
both in full sunlight and in dim light, ensuring image quality in an
outdoor setting. The adjustable focal length means that you can set
the viewing area as you wish. Varifocal/Autoiris lenses are the top
of the range in terms of performance, but also in terms of price. |
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3 MOTORS ZOOM – Remote control focal
length, diaphragm and focus
These lenses have 3 internal mechanisms which control focal
length, diaphragm and focus. There is a great range of focal length,
and at full zoom these can film over a long distance. This lens is
controlled by 6 wires connected to a control panel which enables the
operate to change the settings in real time, while viewing the
images on screen.
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MINI
LENSES
-
Compact size, fixed focal length and fixed diaphragm
These tiny lenses were originally
developed for mini cams, and feature an S mount. The main advantage
is the compact size, which makes them ideal for use in limited space
and for concealed use.
Mini lenses are usually mounted onto compact cameras but can also be
mounted onto normal sized cameras (with a C or CS mount), using a
reducer.
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PIN-HOLE
LENSES
-
Miniature lenses for hidden cameras
These lenses were specially designed for use in
totally concealed applications, and can film through a hole of 1 mm.
DSE PIN-HOLE lenses have a fixed focal length of 3.6 or 6.2 mm and
are available in flat or conical versions.
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IR
LENSES
- For use with infrared illuminators
If you use a normal lens with an infrared
illuminator you will encounter a phenomenon known as FOCUS-SHIFT,
which is when an image which is perfectly in focus by day goes
slightly out of focus in infrared light.
IR lenses are specifically designed to concentrate both infrared
light and natural light on the same focal plane and enable precise
focus both day and night. The DSE range includes varifocal IR lenses
in manual iris and autoiris versions.
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MEGAPIXEL LENSES - To be used on Megapixel IP cameras iris
These lense have been developed for use with megapixel IP cameras in order to suit the high resolution of the camera.
All kind of lenses can be available in Megapixel version which can be used for standard resolution as well.
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ASPHERICAL LENSES
A few lenses in the DSE range have aspherical lens. This technology reduces the optical aberration due to the curved surface of standard lenses.
Aspherical lenses gives accurate focus both in the center and the border of the image. The overall size of the lens is also smaller compared with standard lenses. . |
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