There are many different types of security video camera lenses. The first division between lenses are the wide angle and the zoom lenses; the next division is between the fixed iris, manual iris, and auto iris.
It is important to use the right lens for the light conditions and desired field of view; otherwise the images seen and recorded will not be satisfactory.
The lens of a security video camera is like the cornea of your eye. Without it you cannot see, and same as the security camera. There are many factors involved in choosing a suitable lens; these choices and others depend on the intended use of your security camera system.