Chap.2 Lens and Image Sensor Technology
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Figure 2.2 shows image distortion caused by a shorter focal length and the telephoto effect resulting from a longer
focal length.
2.1.2 Iris
Iris can control the amount of light entering the lens during exposure. Iris is one of the most important elements for
light sensitivity, along with aperture, shutter time, sensor, and gain.
Lenses include the following types:
• Fixed lens:
the focal length cannot be changed.
• Vari-focal lens:
the focal length (field of view) can be manually adjusted;. The most common vari-focal
lens is 3.5 - 8 mm.
• Zoom lens:
a kind of vari-focal lens with motorized mechanism to adjust its focal length. Generally, AF
(Auto Focus) algorithm is used to focus automatically.
Tele/Wide
Focus
Fixed lens
Vari-focal lens
Figure 2.2 Comparison of images with (a) wide (b) normal (c) tele focal length
Figure 2.3 Fixed and vari-focal lenses
Iris
(a)
(b)
(c)
Figure 2.4 Iris in contrast to eye pupil
Summary of Contents for IP Surveillance
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