Installer Support: Tech Tips
We know our installing dealers are as committed to excellence as we are. That’s why we work to be a resource for you, with important updates and other information to assist you in understanding how to get the most out of our CCTV products.
Lens Focus Procedure
When cameras come with standard fixed focus manual iris lens installed the focus procedure is usually simply turning the focus ring of the lens by hand while watching the picture from the camera displayed on a video monitor until a clear picture is achieved.
If the installed lens is a varifocal lens the focal length adjustment of the lens (how wide or narrow the field of view) must be set first and then the focus ring of the lens can be adjusted for best picture.
When the camera does not come with the lens installed and it must be installed in the field then a back-focus procedure must be performed to match the lens to the camera. First install the lens on the camera body. Refer to the camera’s installation manual to find the “back focus” adjustment arrangement. It could be a lever on the side of the camera body, a large ring on the front of the camera around the lens mount or a screw driver adjustment. In most all cases the back focus adjustment will have a locking screw that must be released before making any back focus adjustments. To begin set the lens aperture (iris) to the wide open position (lowest f/number) and the focus ring to mid position. Find a target in the field of view that is approximately in the middle of the distance from the camera to the end of view and adjust the back focus up or down for best sharpness and clarity of the target. Lock the back focus adjustment and fine tune the focus using the focus ring of the lens. Close the lens aperture (iris) to a position where the picture has good contrast but is not too dark and the setting is complete.
If an auto-iris lens is to be installed on the camera the same procedure is followed but a filter will be required to open the aperture (iris) of the camera while making the adjustments. A #9 or 10 neutral density filter or a welder’s glass shade #8 or 9 can be used to artificially open the iris of an auto-iris lens while back focusing the camera. The welder’s glass (used in a protective hood) is a less expensive option and can be purchased at a welder’s supply or many hardware stores. A proper back focus can not be achieved if the auto-iris lens is not fully open during the procedure.
Horizontal Bars and Other Display Problems
The visual tell tail of ground loop problems is the dark horizontal bar or shadow rolling through the picture from a CCTV camera. Even though this is the main visual tell tail of ground loops it is not the only problem presented by ground potential differentials. Some focus problems and instabilities can also be the result of ground loops. In audio circuits a ground loop can be heard as a 60Hz hum.
So what is a ground loop or ground potential differences and how can they be eliminated? In CCTV a ground loop presents itself when a camera’s supplied power is provided from a power supply plugged into a different line source from the power provided to the termination device (DVR, monitor or other active electrical device in the video signal path). Even though ground is supposed to be ground as a reference value, earth ground can be at different potentials or values in relation to electronic devices powered from the utility grid. When power enters a building from the utility grid there is typically a ground rod attached to the service panel to provide an earth reference ground; but earth ground will be different from one building to another depending on many factors such as type of soil and its moisture content, the construction material of the building and the balance of electrical current usage in the building. This reference ground may even change from time to time depending on changes in moisture content of the soil where the ground rod is installed.
When a CCTV camera is installed at a distance from the head-end equipment there is a chance of a ground loop if the camera is powered from a different outlet from the head-end equipment or if the camera’s electrical ground is touching a grounded metal building or junction box. The BNC connector attached to coaxial cable is at the same potential as the electrical ground of the camera so if there are any BNC/BNC splices in the coaxial cable run there is a chance that the splice may come into contact with a different ground potential. Any BNC connector not connected directly to the camera or the termination equipment should be isolated by a boot or covered with electrical tape.
A ground loop problem can easily be confirmed by using a volt meter. At the termination device remove the BNC connection coming from the camera. Using the volt meter on the lowest AC scale measure the voltage between the BNC connector shield and the ground or BNC shield of the termination device and if there is a measureable voltage a ground loop exists. Remember the video signal is only one volt peak to peak so any measureable AC voltage will have an adverse effect on it.
Sometime mounting the camera can be a challenge especially if it requires mounting the camera to a metal building or structure like a light standard. A majority of the time indoor/outdoor mounts are constructed from metal and even dome bodies can be metal. If these mechanical/metal devices are not isolated from the metal structure there will most likely be some sort of ground loop issue.
If it is impossible to physically remove the ground potential difference between a camera and the termination device then the use of a “ground loop corrector” sometimes called “ground loop transformer” or for the older group “hum buck coil” is recommended. Some caution is advised when purchasing one of these devices because the inexpensive ones may not totally correct the ground loop problem if the ground potential difference is above 5 volts. The better devices may cost from $75 to $100.
What is White Balance?
“White balance is a camera setting that adjusts for lighting in order to make white objects appear white in photos. This is more difficult than it might seem due to the fact that light cast from different sources is different in color (technically called temperature). That is to say, light is rarely truly white in nature. The light emitted from an incandescent or halogen bulb, for example, is red/orange in color, while that from the sun is relatively blue. A proper white balance setting in a camera will prevent, for example, a white bed sheet in a photo from appearing orange in color when it is being illuminated by a candle.”
~Sourced from the Internet
The above definition is a general definition of white balance (WB). Basically WB is a camera adjustment that needs to be set properly so the image is reproduced correctly for recording or viewing. One of the factors that affect correct image reproduction is the light source which illuminates the camera scene. The light sources can vary and the variations on the scene or objects in a camera’s field of view can be subtle or obvious. Often one of the immediate indications for an improper WB setting is dark colors which appear faded, shifted, or a completely different color altogether is reproduced. Ideally a camera should be able to automatically adjust for these changes in light and lighting sources, unfortunately that is not always the case – at least not without the help of the proper WB setting. The process of proper WB starts at the camera imager or imaging chip also referred to as a charge-coupled-device or simply CCD, which collects light from these various sources as reflected off the scene or an object in the scene and converts that information into an electronic signal. The subsequent electronic signal is then amplified and several adjustments or corrections are performed to create a video signal – and one of those adjustments is white balance.
Since light sources vary across installation environments, it is necessary to look at what source is actually illuminating the scene – Infra-red (IR), Halogen, Metal Halide, High Pressure Sodium, LED or ultraviolet (UV) light sources. Just remember, not all light sources are visible – such as the case of the IR light. The human eye cannot see the IR light, yet in terms of a CCD camera this is an essential light source that turns low-light or completely dark scene to the human eye into a viewable scene for security purposes.
Many cameras have preset white balance settings which have been defined at the factory. In addition, Auto White Balance (AWB) and Auto Tracing White Balance (ATW) are not the same, but perform similar functions. The difference is the signal (temperature setting) processing, and the best advice is try both AWB and ATW and see which process best fits the installation environment. Sometimes it just comes down to which setting looks best.
Two additional common camera white balance options are INDOOR and OUTDOOR. The indoor setting should be selected for a fluorescent lighting environment, and the outdoor setting should of course be set for sunlight (outdoor or when sunlight is most prevalent in indoor scenes).
In many installations the factory presets will be suitable; however, sometimes the definition of what is truly WHITE needs to be defined to the camera. This is usually a function referred to as PUSH and is available in many of the higher-functioning Tyco IS cameras. To perform a PUSH function, simply place a white object (typically white paper) in the field of view, filling at least 50% of the image, and select the PUSH function in the camera menu. The camera will make the necessary corrections and the image recorded or viewed should be representative of the real image, if not, if may be necessary to reposition the white object slightly and simply try again until the desired image (with white defined) is obtained.
Note of caution, attention does need to be paid to specific camera models and how to properly save changed settings and exit the programming menu. Not doing so may result in the camera defaulting back to factory settings which may provide an opportunity for an unwanted service call to reprogram what was a perfectly fine looking camera yesterday. We always recommend reading the manufacturer’s product specifications and user’s manuals to make sure the camera you choose is the best fit for the application. Sometimes the environment may not require all a camera’s available features, leaving an option open for a lower cost camera selection and more money to be spent elsewhere.