When the ambient illumination is constant, such as elevator car, closed corridor and room without direct sunlight, manual aperture lens can be selected. In this way, the aperture size of the lens can be set at one time according to the actual illumination of the environment during the initial installation and commissioning of the system to obtain a satisfactory brightness picture.
For the situation that the environmental illuminance changes frequently, such as the lobby, window and lobby where the illuminance changes greatly with the sunshine time, it is necessary to select the automatic aperture lens (the camera with the automatic aperture lens socket must be equipped), so as to realize the automatic adjustment of the picture brightness and obtain a good monitoring picture with relatively constant brightness.
The control signals of automatic aperture lens can be divided into DC and video control, namely DC voltage control and video signal control. In terms of the type selection of automatic aperture lens, the connection mode of camera automatic aperture lens socket and the driving mode switch of automatic aperture lens, the three should be well coordinated.
The selection of fixed focus and zoom lens depends on the size of the monitored project scene and the required clarity of the monitored scene.
Lens specifications (lens specifications are generally divided into 1 / 3 ", 1 / 2" and 2 / 3 ") under certain circumstances, the relationship between lens focal length and lens field angle is as follows: the longer the lens focal length, the smaller the lens field angle (see Fig. 1); When the focal length of the lens is fixed, the relationship between the lens specification and the lens field angle is as follows: the larger the lens specification, the larger the field angle of the lens. Therefore, it can be seen from the above relationship: when the lens object distance is certain, with the increase of the lens focal length, the picture range of the monitored scene seen on the monitor at the end of the system is smaller, but the picture details are clearer and clearer; With the increase of lens specification, the picture range of the monitored scene seen on the monitor at the end of the system increases, but the picture details become more and more blurred. On the premise of certain lens specification and focal length, the field angle of CS interface lens will be greater than that of C interface lens.
The field of view angle of monitoring engineering lens can be divided into image horizontal field of view angle and image vertical field of view angle, and the image horizontal field of view angle is greater than the image vertical field of view angle. Generally, the field of view angle we talk about generally refers to the image horizontal field of view angle of lens.
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