Security surveillance camera lens and its debugging method
The surveillance camera is a semiconductor imaging device, which has the advantages of high sensitivity, strong light resistance, small distortion, small size, long life and anti-vibration. In the surveillance camera security system, image generation is mainly from the CCD camera, and the stored charge can be taken out to change the voltage. It has the characteristics of anti-vibration and impact and is widely used.
Lens debugging method of surveillance camera
Install Lens
Monitoring cameras must be equipped with lenses before they can be used. Generally, suitable monitoring lenses should be selected according to the actual situation of the application site, such as fixed-focus lens or zoom lens, manual aperture lens or automatic aperture lens, standard lens or wide-angle lens or long-focus lens. In addition, attention should also be paid to the interface between lens and digital camera, which is C-type interface or CS-type interface. The threads of C-type interface and CS-type interface lenses are both 1 inch 32 teeth and 1 inch in diameter. The difference is that the distance between lens and CCD target surface is different. The distance between C-type mounting base and focus is 17.562 mm, which is more than that of CS-type interface lenses. The length of a special ring, CS type distance from the focus is 12.5 mm. Don't underestimate this collar. Without it, the lens and the network surveillance camera can't focus properly and the image becomes blurred. So before installing the lens, first look at whether the camera and the lens are the same interface mode, if not, you need to add or subtract the contact ring according to the specific situation. Some cameras do not need to engage the ring, but use the rear image adjusting ring. When adjusting, the screw on the adjusting ring is loosened with a screwdriver, and the adjusting ring is rotated. At this time, the CCD target surface will move backward (forward) relative to the mounting base, which also plays the role of engagement ring. When installing the lens, first remove the protective cover of the monitoring camera and the lens, and then gently screw the lens into the camera lens interface and put it in place. For the automatic aperture lens, the control line of the lens should also be connected to the automatic aperture interface of the digital surveillance camera. For the electric two-variable lens or three-variable lens, as long as the rotating lens is in place, the balance state of the lens will not need to be corrected for the time being (only after the adjustment of rear focus is completed, the balance state of the lens needs to be corrected finally).
Adjust lens aperture and focus
Close the electronic shutter and backlight compensation switches on the HD digital camera, align the camera to the scene to be monitored, adjust the lens aperture and focus ring, and make the best image on the monitor. If the camera is used in situations where the illumination changes greatly, it is better to match the automatic aperture lens and place the electronic shutter switch (ELC) of the camera in OFF. If the manual aperture is selected, the electronic shutter switch (ELC) of the camera should be placed on ON, and the lens light should be placed when the application field is brightest (the ambient illumination is the largest). The lens is adjusted when the circle is as large as possible and the image is still the best (the image cannot be too white and overloaded). Just install protective shield and bracket. Because the aperture is large and the depth of field is relatively small, the clarity of the whole monitoring site should be taken into account when focusing. When the field illumination decreases, the electronic shutter will automatically adjust to a slow speed, with a larger aperture, the image can still be satisfied.
In the process of adjusting, if we do not pay attention to opening the lens aperture as large as possible when the light is bright, but close it as small as possible, then the electronic shutter of the security surveillance camera will automatically adjust to a low speed, so it can still form a better image on the monitor; but when the light is dimmed, because the lens aperture is smaller, but the electricity The sub-shutter is already at its slowest speed (1/50s), at which time the image may be dim.
Adjusted rear focal length is also called back focal length.
When the standard lens (standard C/CS interface lens) is installed, it can make the image of the subject exactly on the target surface of the CCD image sensor. When the camera is out of the factory, the rear focal length of the camera is adjusted properly. Therefore, in the application of the fixed focal lens, it is generally not necessary to adjust the rear focus of the camera.
In some applications, it may occur that when the focus ring of the lens is adjusted to the limit position, the image is still not clear. At this time, we must first confirm whether the lens interface is correct. If the confirmation is 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 high definition cameras.
The steps for adjusting the rear focal length are as follows:
A. Install the lens correctly on the camera.
B. Keep the lens aperture as wide as possible (the aim is to narrow the depth of field in order to find the imaging focus accurately).
C. Push the lens to Tele state by zoom in, shoot a close-up of an object 10 meters away, and then sharpen the close-up image by adjusting Focus.
D. Zoom Out, which is the opposite of the previous step, pulls the lens back to Wide state, where the picture becomes a panoramic image containing the above close-up object, but the focus adjustment can no longer be made at this time (note: if the image becomes blurred at this time, the focus can not be adjusted), but prepare for the next post-focus adjustment.
E. The front end of the HD camera is used to fix the inner hexagonal screw of the rear focus adjusting ring and rotate the rear focus adjusting ring (for the camera without the rear focus adjusting ring, the camera rotates the lens directly and drives the built-in rear focus ring), until the picture is clearest, then temporarily.