Specifications
The lens is connected via a short cable. Manufacturers have not been
able to agree on uniform plugs or plug configurations for these types
of lenses. Therefore, these lenses are supplied with bare wires. The re-
quired plug is supplied with the respective camera and must be
soldered
to the cable prior to mounting.
This type is generally marked with a letter "A" at the end of the item
number.
Lenses with DC-controlled iris
This is the latest kind of iris control. These lenses contain the setting
mechanism only rather than control electronics, because this is already
installed in current cameras and thus ensures a perfect adjustment with
the control mechanisms of the camera like AGC, ES, BLC, etc.
3 reasons for DC-controlled lenses
– Electronic. Perfect adjustment to the camera controls
– Practical. Due to uniform plugs and plug configurations already fit-
ted with plug connector, thus quicker assembly
– Economical. A more favourable price due to removal of the elec-
tronics
This type is generally marked with a letter "D" at the end of item num-
ber.
The trend clearly goes towards DC-controlled lenses at new video sur-
veillance systems. When selecting iris-controlled lenses, attention has
to be paid to the provision of corresponding outputs at the camera.
The lenses with the letters "A" and "D" are incompatible with one an-
other.
Zoom lenses
The second trend which can be noticed is the increased application of
lenses with adjustable focal length. These lenses offer a high degree of
flexibility because the exact focal length can be determined directly at
the position of installation.
Zoom lenses are available in different zoom ranges. The main
ranges are:
– Range 3.5-8mm for wide angle range and close range. Applica-
tions in a shop area or outside area are typical of these lenses. Main
application is the close range of 1-3m or the surveillance of complete
areas. The aim is to display a picture detail as large as possible.
– Range 5-50mm (up to 80mm) for the tele range. This is the typical
lens for petrol stations. Focal lengths of 30-50mm or more are re-
quired if number plates or persons standing at a gate are to be iden-
tified at a distance of 10-20m. With these lenses, the visual range is
reduced to such an extent that details are displayed as large as pos-
sible on the monitor.
Zoom lenses have become very interesting concerning the price, not
least due to accepting the fact that each adjustment of the focal length
means a readjustment of the focus each time. This adjustment has to be
carried out once at the time of installation, which is not in the least bit
annoying.
Zoom lenses with controlled iris are also available, of course.
Aspherical lenses
Lenses with a special cut. A higher luminous beam concentration is
possible due to the superior manufacturing. As a result, a higher lu-
minous efficiency and a clearer picture can be obtained.
This lens is suitable for high-quality video surveillance applications.
IR-corrected lenses
The application of infrared light is becoming more and more popular.
Unfortunately, the infrared light has other optical characteristics than
visible light. The concentration is different in the lenses. This results in
a clear picture at daylight, but the picture is blurred at infrared light.
This fact could be accepted or as a compromise, an adjustment could
be found in between. This is no longer necessary with infrared-
corrected
lenses. These lenses are extensively coated in order to have
an identical response afterwards at both visible and infrared light.
KNOW-HOW: Lenses
S56
KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW
image plane
spherical element
image plane
aspherical element
infrared light
visible light
Lack of focus due to different planes of sharp focus.
This dif
ference is rectified at the IR lens.
IR light and visible light are focussed in the same plane.
plane of sharp
focus at visible
light
plane of sharp
focus at IR
light
Lens for visible light
infrared light
visible light
plane of sharp focus
IR lens
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