Specifications
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Limits to the exposure time and gain can be set in some Axis cameras. The longer the exposure
time, the more light an image sensor receives. Bright environments require shorter exposure
time, while low-light conditions require longer exposure time. It is important to be aware that
increasing the exposure time also increases motion blur, while increasing the iris opening has
the downside of reducing the depth of eld, which is explained in section 3.2.6 below.
When deciding upon the exposure, a shorter exposure time is recommended when rapid movement
or when a high frame rate is required. A longer exposure time will improve image quality in poor
lighting conditions, but it may increase motion blur and lower the total frame rate since a longer
time is required to expose each frame. In some network cameras, an automatic exposure setting
means the frame rate will increase or decrease with the amount of available light. It is only as the
light level decreases that articial light or prioritized frame rate or image quality is important to
consider.
Figure 3.2d A camera user interface with options for setting, among other things, exposure in low-light
conditions.
3.2.5 Manual or automatic iris
In indoor environments where light levels may be constant, a manual iris lens can be used. This
type of lens either provides a ring to adjust the iris, or the iris is xed at a certain f-number. The
latter is what Axis uses on its indoor network cameras.
A lens with automatically adjustable iris is recommended for outdoor applications and where the
scene illumination is constantly changing. The iris aperture is controlled by the camera and is used
to maintain the optimum light level to the image sensor if exposure and gain settings are not
available or used in the network camera. The iris can also be used to control the depth of eld
(explained in the section below) and to obtain sharper images. Most automatic iris lenses are
controlled by the camera’s processor via a direct current (DC) and are, therefore, called “DC-iris”
lenses. All Axis outdoor cameras, whether xed, xed dome, PTZ or PTZ dome, use DC-iris or auto-
iris lenses.
CHAPTER 3 - CAMERA ELEMENTS