All,

This seems like such a dumb question, but I was looking through lenses and it occurred to me: why are lenses sold with relatively small focal length ranges? For example, in the 18-55mm range provided by my D3100's kit lens, I could buy the following from Nikon:


  • 17-35 f/2.8
  • 16-35 f/4
  • 18-35 f/3.5-4.5
  • 16-85 f/3.5-4.5


I'm certainly not asking for the pluses and minuses of each lens, but I don't understand why there are so many focal length choices in the same range. Yes, I realize that the apertures are different, but why would I want an 18-35 f/3.5-4.5 to supplement my 18-55 f/3.5-5.6, or why would I want two lenses when I could just use one?