What lens do you have?
If you have a "zoom" lens, there should be two (or more) rings on it. The "zoom" function will typically be marked "T ~ W" (Telephoto/Wide). If you have a fixed lens, then there may not be any rings or one ring for focus only.
That must be the problem. The lens is a Computar "auto iris tv lenses dc drive series". There is no marking for T ~ W on it that I can see.