Axis Network video - Matching Lens and Sensor

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> Varifocal lens: This type of lens oers a range of focal lengths, and hence, dierent elds of
view. The eld of view can be manually adjusted. Whenever the eld of view is changed, the
user has to manually refocus the lens. Varifocal lenses for network cameras often provide
focal lengths that range from 3 mm to 8 mm.
> Zoom lens: Zoom lenses are like varifocal lenses in that they enable the user to select
dierent elds of view. However, with zoom lenses, there is no need to refocus the lens if the
eld of view is changed. Focus can be maintained within a range of focal lengths, for
example, 6 mm to 48 mm. Lens adjustments can be either manual or motorized for remote
control. When a lens states, for example, 3x-zoom capability, it is referring to the ratio
between the lens’ longest and shortest focal length.
3.2.2 Matching lens and sensor
If a network camera oers an exchangeable lens, it is important to select a lens suitable for the
camera. A lens made for a 1/2-inch image sensor will work with 1/2-inch, 1/3-inch and 1/4-inch
image sensors, but not with a 2/3-inch image sensor.
If a lens is made for a smaller image sensor than the one that is actually tted inside the camera,
the image will have black corners (see left-hand illustration in Figure 3.2c below). If a lens is
made for a larger image sensor than the one that is actually tted inside the camera, the eld
of view will be smaller than the lens’ capability since part of the information will be “lost” out-
side the image sensor (see right-hand illustration in Figure 3.2c). This situation creates a tele-
photo eect as it makes everything look zoomed in.
Figure 3.2c Examples of dierent lenses mounted onto a 1/3-inch image sensor.
When replacing a lens on a megapixel camera, a high quality lens is required since megapixel sen-
sors have pixels that are much smaller than those on a VGA sensor (640x480 pixels). It is best to
match the lens resolution to the camera resolution in order to fully use the camera’s capability.
CHAPTER 3 - CAMERA ELEMENTS