Lens
The generation of a high quality image is decided by many factors including light source of the environment, lens,sensor, compression engine, etc. However, for camera itself, a lens is the most fundamental component that firstly decides if the output of the quality is good or not. In the security industry, because the use of camera differs, especially fixed type with C/CS mount, system installers themselves have to select and purchase a lens fitting their specific needs.
Focal length is the distance between the sensor and secondary principal point of the lens.
Figure 2.2 shows image distortion caused by a shorter focal length and the telephoto effect resulting from a longer focal length.
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.
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