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FAQ about CCTV security System

CCTV (Closed-circuit Television) surveillance systems and related equipment, application and terminology are the field that most people are not familiar with, so we get lots of questions. Below are some of the most commonly asked, Should you have additional questions, please don’t hesitate to Contact us.

@  What is the Difference Between C & CS Mount lenses?

The physical difference is that the back of a CS mount lens is 5mm closer to the chip than a C mount lens. You can always use a C mount lens on a CS mount camera by using a 5mm spacer ring (many cameras now have C/CS selectable adjustment screws or rings). You can never use a CS mount lens on an older style C mount camera. Cost wise the CS mount lens is much less expensive since it uses fewer glass elements. Quality of image is the same. C mounts are becoming less and less popular and are generally only used on the more telephoto focal lengths such as 25, 50 and 75mm, and bigger zooms.              

@  What is relationship of the angle of view and lens size of the CCTV camera lens?

This lens calculator displays the angle of view of common CCTV lenses. The calculator is compatible with all the standard CCD sizes, such as 1/4 inch, 1/3inch etc. These are the standard CCD sizes used in CCTV and security applications.

CCD Size (Inch)








Lens Size (mm)








Angle of View(degrees)










@  Can I use any type of CCTV security camera outside?

Not really. Some bullet cameras, Vandal proof Dome camera and most Infrared cameras are designed for outside use with waterproof cases, but if you need lenses of different focal lengths and especially if you need auto-iris lenses (which are best for outside because of varying light conditions) then mini-cams won't be satisfactory. Normally, box cameras are used outside but need to be mounted inside a special outside housing. These housings are rainproof and can also contain a heater unit for really cold climates and/or a fan for hot climates. Mini-dome CCTV security cameras, most Dome camera and some hidden camera meant for inside use only, should not be used outside.                    

What does an auto-iris lens do for me?

Outdoor security cameras or cameras indoors facing a window or an outside door will have varying light conditions. CCTV display and recording systems are set to a certain level of image brightness and contrast. When light levels change in the images produced by the cameras, the displayed and recorded images will either be too bright and washed out or too dark and non-resolvable. The only way to solve this is to use an auto-iris lens. These lenses have an electric motor-driven iris which is opened or closed according to signals fed to it from the camera. Once set, a camera equipped with auto-iris drive will attempt to produce a video signal of constant brightness by opening or closing the auto-iris of the lens, as light levels change.            

What is the vari-focal lens or zoom lens?

A Vari-focal is a lens that is designed to meet the most challenging jobs by giving the installer the flexibility to adjust between different focal lengths using only one lens. When the situation calls for an odd focal length lens or you are not sure of the correct focal length required for the installation, using a Vari-focal lens is the perfect choice. How many times have you or your installer set-up a job just to be called back because the customer was not satisfied with the field of view of the picture? More than once, most likely. A simple adjustment to the zoom and focus on a Vari-focal lens is all that is needed to rectify the situation on the spot: a less costly and time-consuming prospect than having to order and install a different monofocal lens altogether.Surveillance effects are maximized since any desired angle of view can be obtained.                  

Why use a vari-focal lens?

Surveillance effects are maximized since any desired angle of view can be obtained.
There is no need to carry several different focal length lenses to an installation job.
Once installed, even if the field of view requirements change, the system can be quickly adjusted by simply changing the focal length setting of the lens.        


If I purchase fixed focal length lens or security cameras with fixed lens, can I exchange those if I don't like the field of view that I see?

Yes you can, provided they are shipped back in the original packaging and are in "as new" condition. However, you will be liable for the shipping charges, both ways and this, combined with the hassle involved, usually makes it an unsatisfactory thing to do. Better, in the first instance, if you are unsure about the lens focal length required, to purchase cameras with vari-focal lenses. These are manually adjustable over a range of focal lengths, most commonly from 3.5 to 10.5mm, to give a wide range of field of view.        

How far from the DVR can I place security cameras?

Using RG59 Coaxial Cable, each CCTV security camera can be placed up to 600 feet from the computer and up to 1,000 feet with RG6 Coax. Even longer distances (>2,000’ )can be achieved using Baluns and CAT5 cable          

Can I use my old security cameras mixed with new ones?

Yes, providing certain conditions are met. Even with the same color type, some older cameras and some newer cameras mixed together can cause problems because of very different image synchronizing systems. In this event, you can get interference between one camera image and another. Color cameras are more prone to this type of problem.        

@  How many days/weeks of recording can I store?

 This depends on how big is your hard drive, how many cameras are you using and under what conditions are you recording (on motion, on alarm, continuously, etc.) and what type of compression you are using. Assuming that you are recording only when motion is present (the most common recording method today) using a 30fps board and assuming that you have 4 CCTV security cameras and that there is movement in the surveilled area for 16 hours a day, 5 days a week, and you are recording at 320x240 pixel resolution with MPEG4 compression, you could expect to use up about 20 to 25GB of disk space per week. So, a 40GB drive would hold about 2 weeks of recordings under those conditions.
Of course, if you record at 640x480 pixel resolution, and/or you are using a 120fps or faster board, the disk space used will increase. Because of the way that MPEG4 compresses video, there is not a definite mathematical formula that can be applied to say exactly by how much the recordings would grow.
Since hard drives are now relatively inexpensive, it pays to use as big a capacity drive as possible (and/or multiple drives) if you are concerned with storing many weeks of recordings before overwriting.                 

What happens when my hard disk is full?

Normally the system will begin to overwrite the recorded image files, oldest first. You can choose for recording to cascade from one drive to another (i.e if the "C" drive is full, the system can begin to write on the "D" drive), if you have more than one hard drive.     


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