What does single focal length mean?
This means that they have a fixed focal length, they are also called prime lenses. They remain at one focal length, they don’t have a zoom ring, the ring on the Lens is a large manual focus ring. Prime lenses make the best Macro lenses, because they usually have large maximum apertures, here’s an example a great Macro prime lens: http://www.amazon.com/Canon-100mm-Macro-… The obvious disadvantage is that you can’t zoom in/out.
