Surveillance lens refers to the lens of the surveillance camera. Because the surveillance camera is only a single video capture device, the pixel and resolution of the lens are higher than the video head of the computer, but can not catch up with the professional digital camera or DV. In the closed-circuit monitoring system, the camera is also called camera or CCD (charge coupled device), that is, charge coupled device. Strictly speaking, the camera is the general name of the camera and lens. The primary sensing component of the camera is CCD, which has the characteristics of high speed, small distortion, long service life, anti vibration, anti magnetic field, small volume and no residual shadow. CCD is the short name of charge couple device. It can change the luster into charge, store and transfer the charge, or take out the stored charge to change the voltage, Therefore, it is an ideal imaging element. It is a new device to replace the camera tube sensor.

Lens debugging:

Adjust lens aperture and focus

Close the electronic shutter and backlight compensation switches on the HD digital camera, aim the camera at the scene to be monitored, and adjust the aperture and focusing ring of the lens to optimize the image on the monitor. If the camera is used in the occasion with large illumination change, it is best to connect the automatic aperture lens and turn the electronic shutter switch (ELC) of the camera off. If manual aperture is selected, the electronic shutter switch (ELC) of the camera shall be turned on, and when the application site is the brightest (the ambient illumination is the largest), the lens aperture shall be opened as large as possible and the image shall be the best (the image shall not be too white and overloaded), and the lens adjustment shall be completed. Install the protective cover and the bracket. Due to the large aperture and relatively small depth of field range, the clarity of the whole monitoring site should be taken into account when focusing the focal length. When the on-site illumination decreases, the electronic shutter will automatically adjust to slow speed. With a large aperture, the image can still be satisfied.

In the above adjustment process, if you do not pay attention to opening the aperture of the lens as large as possible when the light is bright, but close it relatively small, the electronic shutter of the security monitoring camera will be automatically adjusted at low speed, so a better image can still be formed on the monitor; However, when the light becomes dark, the imaging may be dim due to the small aperture of the lens and the slowest electronic shutter (1 / 50s).

Adjustment of rear focal length rear focal length is also called back focal length

It means that when the standard lens (standard C / CS interface lens) is installed, the imaging of the subject can be just on the target surface of the CCD image sensor. Generally, the rear focal length of the camera is properly adjusted when the camera leaves the factory. Therefore, in the application of fixed focal lens, it is generally not necessary to adjust the rear focal length of the camera.

In some applications, when the lens focusing ring is adjusted to the limit position, it may still not make the image clear. At this time, we must first confirm whether the interface of the lens is correct. If it is confirmed to be correct, the rear focal length of the camera needs to be adjusted. According to experience, in most applications where surveillance cameras are equipped with electric zoom lenses, it is often necessary to adjust the rear focal length of Digital HD cameras.

The steps of rear focus adjustment are as follows:

a. Install the lens correctly on the camera.

b. Open the lens aperture as far as possible (the purpose is to narrow the depth of field to accurately find the imaging focus).

c. Push the lens to the tele state through zoom in, shoot a close-up of an object 10m away, and then adjust the focus to make the close-up image clear.

d. Perform the zoom out opposite to the previous step, and pull the lens back to the wide-angle state. At this time, the picture becomes a panoramic image containing the above close-up object, but the focus adjustment cannot be made at this time (Note: if the image becomes blurred at this time, the focus cannot be adjusted), but prepare for the back focus adjustment in the next step.

e. Loosen the Allen screw used to fix the rear focus adjusting ring at the front end of the HD camera, and rotate the rear focus adjusting ring (for the camera without the rear focus adjusting ring, directly rotate the lens to drive the built-in rear focus ring) until the picture is the clearest, and then tighten the Allen screw temporarily.

f. Push the lens back to the telescopic state to see if the close-up object just taken is still clear. If not, repeat steps a, B and C above.

g. In the telescopic state, if the close-up object is clear, tighten the Allen screw and adjust the aperture to the appropriate position.

The CCTV camera has many sensors of different sizes and specifications, and the height width ratio of the screen is usually 4:3 (horizontal width: vertical height). The size of the sensor has an impact on the field of view angle. Using the same lens, the field of view angle is narrower on smaller sensors. The size of the lens has nothing to do with the field angle. It only needs to make the image cover the whole sensor, that is, a camera of the same size or larger. This also means that a 1 / 3 "camera can use all lenses of 1 / 3" - 1 / ", for example, 1 / 3 × 12mm lens and 2 / 3 × The field angle of view of 12mm lens is the same. The latter improves the image pixel and imaging quality, because only the image of the central part of the lens is obtained, and the image in this part is usually sharper.