Here is a very common question. How many TVL should the camera have to best use the resolution of my DVR? This is one of the most misunderstood relationships in CCTV. The resolution that the DVR records in refers to the SIZE of the image being recorded. So CIF resolution (360×240) and 4CIF resolution (704×480) refer to how large the image actually is. 4CIF is an image that is 4 times larger than CIF.
TVL refers to the Horizontal lines of resolution the camera can display in. This will determine the amount of detail you may see within a certain size image (CIF, 2CIF, 4CIF). When selecting the right camera, keep in mind that the resolution being recorded and the resolution being displayed are usually different. In most cases a DVR will display live video at 4CIF (704×480) or D1 (720×480) resolution, but be recording in a lower resolution like CIF (360×240). Though a live 4CIF display of video will benefit from a 520TVL camera, the recorded image in CIF will not see the difference between a 520TVL camera and a 420TVL camera. So in essence you will only benefit from the live view, not the recorded image.
You will notice that the maximum benefit for a cameras horizontal resolution when recording in 4CIF is actually around 520TVL. Also, notice when recording in CIF resolution a 420TVL camera and a 520TVL camera will look exactly the same in the recorded image if recorded in CIF, but the 520TVL camera will display an enhanced image when recording at 4CIF. This also applies to the live video since it is usually displayed at 4 CIF.