2.8mm is wider than 4mm is wider than 6mm is wider than 12mm. If you need to cover a large area to go wide. If want to zoom from a distance then buy a 50mm or 100mm lens.
Most common lens people buy 2.8mm to 12mm if you want to cover a wide view. If you want to read a license plate or entrance from a distance, 5mm to 50mm or 5mm to100mm will work for you. LPR camera already designed read license plates
Below is a link for lens calculator, you can use this calculator to determine what type of lens will work the best for you. After you have figured out what lens you need, you can purchase from us. If you are are still unable to decide what you need, please drop us a line, one of our experienced installers will suggest you the correct product.
Our technical support has nothing to do with sales; they will always suggest the correct part. http://www.ltsecurityinc.com/tools