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
Focal length is the distance between the sensor and secondary principal point of the lens.
The shorter the focal length, the wider field of view it offers and higher level of distortion it may cause. In contrast, the longer the focal length, the smaller viewing angle and field of object it has.
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
Lens Mount Types
C- and CS-mount are two major lens mount standards developed for the purpose of changing lens. The main difference between C/CS-mount lenses lies in the flange focal distance. The flange focal distance for a CS-mount
lens is 12.5mm while 17.526mm for a C-mount lens. A CS-mount lens has higher cost efficiency and smaller size because fewer glass components are used.
