Question 1. How does Cam Focal Length affect view

 
Focal length is measured in mm. A short focal length (e.g. 3.6mm) represents a wide angle of
view while a long focal length (16mm) represents a narrower angle of view and a very long focal length (50mm) would be considered long range. For the most common chip size of one third inch used in Domestic CCTV the table below is an excellent guide. Many of the cameras that we supply have adjustment of focal length between 2.8mm and 12mm although the offer camera systems are fixed focus 3.6mm.

Question 2. What features should I look for in a CCTV DVR?

All DVRs are different. There are various factors to consider when purchasing a DVR besides price comparison. The basic and most important factors to consider are
i) Number of cameras supported, i.e. number of video inputs
ii) Recording at how many frames per second (fps)
iii) Compression technology used
iv) Hard disk space, number of hard disk it can support
v) Network connection / remote viewing capability
vi) Motion detection or scheduling recording functions
vii) Video backup means, by USB, CD, DVD or other means.
viii) Easy and comprehensive search capabilities

Question 3. Do I need 30 frames per second (fps) recording ?

CCTV surveillance systems are generally intended to capture images and not to make movie quality videos. Recording rates of as low as 1 or 2 frames will be sufficient to capture critical moments for example, a criminal act in progress and this will greatly extend the recording time of your Hard Drive.

Even at low frame rates, recording on motion, the compressed video files produced per day are huge in size. Therefore, it is not advisable to set all cameras to be recording at a high frames per second rate.

Question 4. How much video will my DVR store?

 
This is a very complicated question because not only does it depend on many different factors, such as resolution, frame rate of each camera, etc. but it also depends on the compression technology used by the manufacturer to store the video.
In general storage time can be calculated using the following formula:
T = [(12000 * S) / (H * V * F * C)]  for a single camera ( If there are 4 cameras then divide time by 4)
T => storage time in days
S => storage capacity in Gigabytes
H => horizontal resolution in pixels
V => vertical resolution in pixels
F => frame rate in frames per second
C => average video compression rate as a decimal  ( Let us assume 4% = 0.04 )
 
EXAMPLE: S= 500 Gb,  H = 1000,   V= 600,  F= 10,  C= 0.04
then T = (12000 x 500 )/(1000 x 600 x 10 x 0.04 )  =  25 Days
Therefore for four cameras under these conditions the record time would be just over 6 days.
 
The difficult part of this calculation (aside from the fact that different cameras may be recording at different frame rates) is determining the average compression rate (C). This is because video is not compressed at a constant rate. The amount of compression achievable depends heavily on how much one frame changes from the next as compression technology relies on the ability to reco
rd only the (hopefully) small amount of information that changes from one scene to the next. If very little changes, compression rates will be high. If everything in the scene changes, there will be little to no compression.