A practical guide to C-mount and CS-mount lens installation, automatic gain control, white balance, iris control, backlight compensation, synchronization, flickerless mode, and night monitoring considerations for CCTV cameras.
1. CCTV Camera Lens Mounting Methods: C-Mount and CS-Mount
There are two common lens mounting methods for CCTV cameras: C-mount and CS-mount.
Both types use a 1-inch thread with 32 threads per inch, and the diameter is also 1 inch. The main difference between them is the distance from the lens to the CCD image sensor target surface.
For a C-mount lens, the distance from the reference plane to the focal point is 17.562 mm.
For a CS-mount lens, the distance from the reference plane to the focal point is 12.5 mm.
The difference between the two is the length of a special adapter ring. Do not underestimate this small adapter ring. Without it, the lens and camera may not focus properly, and the image will become blurred.
Therefore, before installing a lens, it is important to check whether the camera and lens use the same mounting type.
If they do not match, an adapter ring must be added or removed according to the actual situation.
Some cameras do not use an adapter ring. Instead, they use a back focus adjustment ring. For example, some Panasonic products use this method. During adjustment, loosen the screw on the adjustment ring with a screwdriver and rotate the ring. The CCD target surface will move backward or forward relative to the mounting base, achieving the same effect as adding or removing an adapter ring.
Some cameras, such as Sony and JVC models, use a similar back focus adjustment method. The fixing screw is usually located on the side of the camera. After loosening the screw, adjusting a gear at the top can make the image clear without adding or removing an adapter ring.
2. AGC ON/OFF: Automatic Gain Control
AGC stands for Automatic Gain Control.
Inside a camera, there is a video amplifier that amplifies the signal from the CCD to a usable level. The amount of amplification is called gain. Higher gain is equivalent to higher sensitivity.
However, in a bright environment, the amplifier may become overloaded, causing video signal distortion.
When the AGC switch is set to ON, the camera will fully open the lens aperture under low-light conditions and automatically increase the gain to obtain a clearer image.
When the switch is set to OFF, the image in low-light conditions will appear more natural and have lower noise.
3. ATW ON/OFF: Automatic White Balance
ATW stands for Automatic Tracking White Balance.
When the ATW switch is set to ON, the camera detects the characteristics and color temperature of the light source through the lens. It then automatically and continuously adjusts the white level.
Even when the light source characteristics or color temperature change, the camera can control the gain of the red and blue signals to maintain a more accurate color balance.
4. ALC/ELC: Automatic Light Control and Electronic Light Control
ALC stands for Automatic Light Control.
ELC stands for Electronic Light Control.
When ELC is selected, the electronic shutter automatically and continuously changes the exposure time of the CCD image sensor according to the brightness of the incoming light.
The adjustment range is usually from 1/50 second to 1/10000 second.
When using ELC mode, a fixed iris lens or manual iris lens can be used instead of an ALC auto iris lens.
However, there are several important points to note.
In outdoor or bright environments, because the control range of ELC is limited, an ALC lens should still be selected.
Under certain special lighting conditions, the following problems may occur:
- Strong smearing or blurring around spotlights, windows, or other high-brightness objects
- Significant image flickering and unstable color reproduction
- Periodic changes in white balance
If these problems occur, an ALC lens should be used.
When using a fixed iris lens in ELC mode, the depth of field may be smaller than that obtained with an ALC lens.
Therefore, if the camera fully opens a fixed iris lens and uses ELC mode, the depth of field will be smaller than with an ALC lens. Distant objects in the image may not be in focus.
When the lens is an auto iris lens, the switch should be set to ALC.
5. BLC ON/OFF: Backlight Compensation
BLC stands for Backlight Compensation.
When strong and unnecessary background lighting affects the clarity of the important object in the center of the image, the BLC switch should be set to ON.
However, there are two points to note:
- When the camera is used with a pan-tilt unit, or when the lighting changes rapidly, it is recommended to set BLC to OFF. This is because the lens iris response may become slower when BLC is turned on.
- If the target object is not located in the center of the image, backlight compensation may not work effectively.
6. LL/INT: Synchronization Selection Switch
The LL/INT switch is used to select the camera synchronization mode.
INT means internal synchronization, usually using 2:1 interlaced synchronization.
LL means line lock synchronization, also known as power synchronization.
Some cameras also have an LL PHASE control. When the camera is operating in line lock mode, this control can adjust the phase of the video output signal.
The adjustment range is approximately one frame.
This type of adjustment should be performed by professional technicians.
7. VIDEO/DC: Auto Iris Lens Control Signal Selection
ALC auto iris lenses use two types of control signals:
- DC control signal
- Video control signal
- When installing a DC-driven auto iris lens on the camera, the switch should be set to DC.
- When installing a video-driven auto iris lens, the switch should be set to VIDEO.
- When an ALC video-driven auto iris lens is selected, there may also be a VIDEO LEVEL L/H control that needs adjustment.
- This control adjusts the signal level output to the auto iris lens, which controls how much the lens iris opens or closes. In other words, it controls the amount of light entering the camera.
- Among the camera accessories, there is usually a small black plug with four pins. This plug connects to the black socket on the camera.
- If a DC-driven auto iris lens is used, the lens usually already has a plug. Simply connect it to the socket and set the switch to DC.
- If a video-driven auto iris lens is used, the user may need to solder the wiring according to the instructions in the manual.
- Because different manufacturers may define the wiring differently, the soldering method may also vary. Please pay close attention during installation.
8. SOFT/SHARP: Detail Level Selection
The SOFT/SHARP switch is used to adjust whether the output image appears sharper or smoother.
SHARP provides a clearer image with stronger detail.
SOFT provides a smoother image.
In most cases, the factory default setting is SHARP.
9. FLICKERLESS Mode
In areas where the power frequency is 50 Hz, the CCD accumulation time is usually 1/50 second.
If an NTSC camera is used, its vertical synchronization frequency is 60 Hz. This can cause visual image synchronization issues and flickering on the monitor.
Similarly, if a PAL camera is used in a 60 Hz power frequency area, the same problem may occur.
To solve this issue, cameras provide a flickerless mode in the electronic shutter settings.
For NTSC cameras, flickerless mode provides a fixed shutter speed of 1/100 second.
For PAL cameras, flickerless mode provides a fixed shutter speed of 1/120 second.
This helps prevent image flickering on the monitor.
10. Manual Electronic Shutter
Some users need to capture fast-moving objects with CCD cameras.
If the camera uses a shutter speed of 1/50 second, fast-moving objects may produce motion trails, seriously affecting image quality.
Some cameras provide a manual electronic shutter function. This allows the CCD charge coupling speed to be fixed at a certain value, such as:
- 1/500 second
- 1/1000 second
- 1/2000 second
- When the CCD charge coupling speed is increased, the captured image will have less motion blur.
- This setting is especially useful for observing high-speed moving objects or electric sparks.
- Therefore, some special-purpose cameras provide manual electronic shutter settings for users with special requirements.
- The adjustment method for manual electronic shutter should be checked in the camera manual.
11. Additional Note: Night Monitoring and Low-Light Environments
Many users want to monitor areas at night where there is no light.
It is important to understand that CCD cameras also rely on reflected light to form images.
If there is no light at all, the image will only appear completely dark with a large amount of noise.
There are two common ways to obtain usable images at night.
The first method is to add visible lighting, such as streetlights or searchlights.
The second method is to add infrared lighting. This is especially useful in locations where visible light sources cannot be installed.
For color CCD cameras, the response to infrared light is usually not strong enough.
Some day/night color cameras can automatically switch to black-and-white mode at night.
Therefore, if your surveillance system must be used at night, a black-and-white CCD camera or a day/night camera with good low-light and infrared performance should be selected.
12. Conclusion
Correct lens installation and camera switch settings are essential for obtaining clear and stable CCTV images.
Before installation, users should check whether the camera and lens use the same C-mount or CS-mount interface. If necessary, an adapter ring or back focus adjustment should be used.
In addition, camera function switches such as AGC, ATW, ALC/ELC, BLC, LL/INT, VIDEO/DC, SOFT/SHARP, flickerless mode, and manual electronic shutter should be configured according to the actual monitoring environment.
For night monitoring, additional lighting or infrared illumination is often required. In low-light or no-light applications, choosing the right camera type is just as important as adjusting the camera settings.
A properly installed and configured CCTV camera system can provide clearer images, more stable performance, and better surveillance results in different lighting and application environments.
