Most of the people are confused to choose which lens is right for their application of the security camera, due to variety of lenses.the picture gives you a barrest idea about lens. Generally normal dome cameras having 3.6mm lens which covers 72-90 degree angle.if you go ahead with 6mm lens camera the angle of coverage will be 50-60 degree,which means lower mm lens covers wide angle.whereas higher mm lens camera used for zooming purpose.