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On the CCD camera

What is the Difference Between C & CS Mount lens?
The physical difference is the CS mount lens is designed to be mounted ~5mm closer to the image sensor than a C mount lens. (C-mount lenses are designed to be mounted 17.526mm in front of the image sensor vs. 12.5mm for CS-mount.) 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 unless you are willing to physically modify the 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.

Both the C and CS mount are 1 inch wide (25.4mm) with 32 threads per inch (0.03125 inches or 0.79375mm). This dimension comes in handy if you need to insert a spacer to obtain proper focus. Unscrew the lens (or unscrew the camera from the mount in the case of telescope use and count the turns until proper focus is obtained. Multiply the above dimension by the number of turns to obtain the needed spacer or washer. (Washers are sometimes used as spacers if there are enough threads available.) Example: 1.25 turns x 0.79 mm = 0.9875 or ~1 mm. Many cameras (especially newer ones) have set screws to allow small adjustments in the distance between the lens and the image sensor.

If you are using a zoom lens and notice that the system goes out of focus as the zoom is changed the distance between the lens and the image sensor needs to be changed. Set the lens for infinity focus. Zoom to wide angle and point the camera at a distant object or star. Adjust the distance between the lens and the image sensor for proper focus. Go to maximum zoom. Slightly adjust the focus ring on the lens to refocus the image if needed. The system should now maintain focus from minimum to maximum zoom. You may need to repeat this process more than once to refine the focus

How about the Type and Quality of the Imaging Chip in the camera.

CCTV security cameras produce images using CMOS or CCD ( Charge Couple Device ) chips. Tiny, very low price cctv cameras usually use CMOS technology, produce poor quality images and have very poor light sensitivity. Decent quality cctv cameras use CCD technology. The size of the CCD chip is normally 1/4", 1/3" or 1/2". As a rule of thumb, the larger the size, the higher the quality of the image produced and the higher the price. However, higher density 1/4" and 1/3" CCD chips can now produce as good an image as many 1/3" or 1/2" chips.

What is the Make of the CCD chip in the camera.

Not all CCD chips are equal, even with the same specifications. Quality varies by manufacturer.

The Type of DSP (Digital Signal Processing) Chip in the camera.

Digital cctv cameras use a DSP chip to digitize the video stream from the CCD chip, in order to improve certain picture quality elements and to add additional functionality. The DSP chip in the camera can have a very large effect on the quality of the video images produced by the camera.

What does the Number of TV Lines stands for?

The number of TV lines in the camera image is a measure of picture resolution (sharpness). The larger the number of TV lines, the better the resolution and hence, overall picture quality. Over 400 TV Lines is generally considered good resolution while over 500 TV lines is considered high resolution.

What is Light Sensitivity?

Sensitivity ratings are generally given in "lux" (a light level measurement). The lower the lux number, the lower the light levels at which the CCTV camera will produce an acceptable image. In other words, the lower the lux level rating, the more light sensitive the camera. B/W cameras generally have lower lux level ratings than color cameras ( i.e. B/W cameras will produce acceptable images in lower light conditions than color cameras).

How to understand the Signal to Noise (S/N) Ratio?

The higher the Signal to Noise ratio, the clearer the video image produced by the camera. Good cctv cameras will have a S/N ratio of at least 48dB.

Which two main types does the Fixed CCTV Cameras come in?

The first type has a camera body, to which lenses of different focal lengths and/or fixed or variable irises, may be attached. Features such as BLC ( Back Light Compensation), Auto Iris Drive and AES ( Auto Electronic Shutter) on/off are provided, as is availability in several power inputs (e.g. 12V DC or 24V AC). New technology cameras now provide an "On Screen Display" for choosing and setting functions. Because of it's flexibility of configuration, this type of camera is normally used in most commercial video surveillance systems.

The second type is basically a fixed lens mounted on a circuit board (board cameras). These cameras may be packaged in a small case (Mini Cameras) or dome (Mini Dome) or simply sold unpackaged, for mounting by the purchaser. Lenses in these cameras are either of a normal industry aperture or a "pinhole" lens of very small aperture. Pinhole lens cameras are often called "spy" cameras and may be mounted in a concealed way for covert surveillance purposes. Since the lenses in board cameras are pre-mounted, have a fixed iris and are usually of a short focal length (i.e. wide angle), their flexibility of usefulness is limited. However, this type of camera can provide a low cost solution in the right situation, particularly in a home environment.

How to define the Pan, Tilt, Zoom Cameras?

Once used almost exclusively by large Corporations, Government and Casinos, Pan, Tilt, Zoom (PTZ) cctv cameras have now become much more affordable and offer better performance than just a few years ago.

PTZ cameras are able to rotate horizontally through 3600, vertically through 900 and have electrically powered zoom lenses capable of giving better than fifteen times optical zoom. Movement can be very fast and is controlled through a connected controller and/or through an appropriate DVR.

PTZ cameras are normally mounted in domes and when used outside, the domes are weatherproof and cooled and heated

What is Focal Length?

Lenses either have a fixed or variable focal length. Manually variable focal length lenses are called

What is Vari-Focal Lenses?

Electrically powered variable focal length lenses are called Zoom Lenses and while they are often used in high-end video surveillance systems, they are generally too expensive for use in most systems. The focal length of a lens is usually given in Millimeters (mm). Focal lengths of most CCTV camera lenses vary from 3.6mm to 16mm for fixed focal length lenses, to well over 70mm for zoom lenses. So what does that mean? In general short focal length lenses (e.g. 4mm) have wide fields of view. This is good for close-ups or for seeing a large area. Objects appear smaller, rapidly, as distance from the camera increases. As lens focal length increases, the field of view narrows and more distant objects are easier to define.

What is The Lens Iris?

CCTV Cameras that are used in good and constant light conditions (e.g. indoors with electric lighting) will perform satisfactorily with a "Fixed Iris Lens". Fixed Iris lenses with fixed focal length are the least expensive and the most widely used.

In varying light conditions (e.g. outside or inside facing a window ) the iris on the camera will need to open and close to accommodate changes in light intensity, otherwise the camera images will be too bright or too dark. Lenses with electrically powered irises which automatically adjust as light conditions change are called "Auto Iris Lenses". They are more expensive but do a much better job in varying light conditions.

In constant light conditions that are either dim or very bright, a "Manual Iris Lens" may be the answer. As it's name implies, this type of lens can have the Iris aperture adjusted by hand to give the optimum camera image quality. Pricing for "Manual Iris" lenses is higher than Fixed Iris and lower than Auto Iris lenses.

The "F Stop" value of the lens.

While "F Stop" is actually a ratio between focal length and lens aperture, in practice, when comparing lenses of the same focal length, it is an indication of the lens aperture. The smaller the "F Stop" the wider the lens aperture and the more light that lens will let into the camera. This is of particular importance in lenses with adjustable irises ( both manual and auto ).

What is H.264 Compression Method?

International study groups, VCEG (Video Coding Experts Group) of ITU-T (International Telecommunication Union - Telecommunication sector) and MPEG (Moving Picture Experts Group) of ISO/IEC, have researched the video coding techniques for various applications of moving pictures since the early 1990s. Since then, ITU-T developed H.261 as the first video coding standard for videoconferencing application. MPEG-1 video coding standard was accomplished for storage in compact disk and MPEG-2 (ITU-T adopted it as H.262) standard for digital TV and HDTV as extension of MPEG-1. Also, for covering the very wide range of applications such as shaped regions of video objects as well as rectangular pictures, MPEG-4 part 2 standard was developed. This includes also natural and synthetic video / audio combinations with interactivity built in. On the other hand, ITU-T developed H.263 in order to improve the compression performance of H.261, and the base coding model of H.263 was adopted as the core of some parts in MPEG-4 part 2. MPEG 1,2 and 4 also cover audio coding.

In order to provide better compression of video compared to previous standards, H.264 / MPEG-4 part 10 video coding standard was recently developed by the JVT (Joint Video Team) consisting of experts from VCEG and MPEG. H.264 fulfills significant coding efficiency, simple syntax specifications, and seamless integration of video coding into all current protocols and multiplex architectures. Thus H.264 can support various applications like video broadcasting, video streaming, video conferencing over fixed and wireless networks and over different transport protocols.

H.264 video coding standard has the same basic functional elements as previous standards (MPEG-1,MPEG-2, MPEG-4 part 2, H.261, H.263) , i.e., transform for reduction of spatial correlation, quantization for bitrate control, motion compensated prediction for reduction of temporal correlation, entropy encoding for reduction of statistical correlation. However, in order to fulfill better coding performance, the important changes in H.264 occur in the details of each functional element by including intra-picture prediction, a new 4x4 integer transform, multiple reference pictures, variable block sizes and a quarter pel precision for motion compensation, a deblocking filter, and improved entropy coding.

Improved coding efficiency comes at the expense of added complexity to the coder/decoder. H.264 utilizes some methods to reduce the implementation complexity. Multiplier-free integer transform is introduced. Multiplication operation for the exact transform is combined with the multiplication of quantization.

The noisy channel conditions like the wireless networks obstruct the perfect reception of coded video bitstream in the decoder. Incorrect decoding by the lost data degrades the subjective picture quality and propagates to the subsequent blocks or pictures. So, H.264 utilizes some methods to exploit error resilience to network noise. The parameter setting, flexible macroblock ordering, switched slice, redundant slice methods are added to the data partitioning, used in previous standards.

For the particular applications, H.264 defines the Profiles and Levels specifying restrictions on bitstreams like some of the previous video standards.

Seven Profiles are defined to cover the various applications from the wireless networks to digital cinema. Besides H.264, other video coding techniques using the same functional block diagram with some modifications have been developed. These are Mocrosoft Windows Media Video 9 (WMV-9) by the Society of Motion Picture and Television Engineers (SMPTE) and AVS (Audio Video Coding Standard) by China.