In recent years, the security surveillance camera intelligent industry has emerged as a new force, and the camera module has naturally become a basic industry, and the supporting surveillance camera lens is also the key to the monitoring project system. The quality (indicator) of the lens directly affects the overall indicator of the camera and the system quality of the entire project, as well as the project cost. Xiao Jin will take you to learn some basic knowledge about lens.
At present, the proportion of domestic lens demand for large lens (C/CS interface) and small lens (M12 interface) is 1:3. The lens accounts for about 20% of the camera cost, which is an important part of the camera. Corresponding to the complete product chain of cameras from high-end to low-end, CCTV lenses (surveillance lenses) have also formed a complete product chain from high-end to mid-level to low-end, with prices ranging from tens of yuan, hundreds of yuan to thousands of yuan.
Classification of camera lens:
● From the focal length, it can be divided into short focus lens, medium focus lens, long focus lens and zoom lens;
● According to the size of the field of view, it can be divided into wide angle, standard and long shot;
● Structurally, it can be divided into: fixed aperture fixed focus lens, manual aperture fixed focus lens, automatic aperture fixed focus lens, manual zoom lens, automatic zoom lens, automatic aperture electric zoom lens, electric triple zoom lens, etc.
- Classification by lens installation: all camera lenses are threaded. There are two industrial standards for camera lens installation, namely, C mounting base and CS mounting base. The screw parts of both are the same, but their distances from the lens to the sensitive surface are different.
C Mounting base: the distance from the lens mounting datum plane to the focus is 17.526mm.
CS mounting base: For special C installation, remove the gasket at the front of the camera and then install the lens. The distance from the lens mounting datum plane to the focus is 12.5mm.
CS lens can be used for the camera installed in C type, but the camera installed in CS cannot use C lens. If a lens installed in C mounting base is to be installed on a camera installed in CS mounting base, a lens converter is required.
- Classification by camera lens specification: the camera lens specification shall be determined according to the sensor size of the camera, and the two shall correspond. When the sensor target size of the camera is 1/2 inch, the lens should be 1/2 inch.
When the sensor target size of the camera is 1/3 inch, the lens should be 1/3 inch.
When the sensor target size of the camera is 1/4 inch, the lens should be 1/4 inch.
If the lens size is inconsistent with the camera sensor target size, the viewing angle will not meet the design requirements, or the picture will be out of focus.
- Classification by lens aperture: fixed aperture lens, manual iris and auto iris.
Manual aperture lens is suitable for applications with constant brightness when used with cameras; The aperture of automatic aperture lens is also automatically adjusted when the brightness changes, so it is suitable for the occasion of brightness change; The luminous flux of a fixed aperture lens is fixed. It is mainly used when the light source is constant or the camera has its own electronic shutter.
- Classification based on field size of lens
Standard lens: the viewing angle is about 30 degrees. In the 1/2 inch sensor camera, the standard lens focal length is set as 12mm, and in the 1/3 inch sensor camera, the standard lens focal length is set as 8mm.
Wide angle lens: the angle of view is more than 90 degrees, which can provide a wide view. The observation range is large, and the near image is deformed
Standard lens: the viewing angle is about 30 degrees, and the use range is wide
Long focus lens: the angle of view is within 20 degrees, and the focal length can reach tens of millimeters or hundreds of millimeters. This lens can magnify the impact of the photographed object at a long distance, but make the observation range smaller
Zoom lens: also known as telescopic lens, there are two types of zoom lens: manual zoom lens and electric zoom lens.
Variable focus lens: It is between the standard lens and wide-angle lens, and the focal length is continuously variable, which can magnify distant objects, and at the same time provide a wide view to increase the monitoring range. The zoom lens can automatically focus on the minimum focal length and maximum focal length by setting, but the focus from the minimum focal length to the maximum focal length needs to be achieved by manual focusing.
Pinhole lens: The lens diameter is several millimeters, which can be concealed.
Note:
Three variable lenses: adjustable focus, adjustable focus, and adjustable aperture.
Two variable lenses: adjustable focus, adjustable focus, automatic aperture.